9th Class Notes

Biology Notes

Introduction to Biology


Our universe operates under certain principles. For understanding of these principles, the experiments are done and observations are made; on the basis of which logical conclusions are drawn. Such a study is called “Science”. In brief science is the knowledge based on experiments and observations.


The Scientific study of living organisms is called Biology. The word biology is derived from two Greek words “bios” meaning life and “logos” meaning thought, discourse, reasoning or study. It means that all aspects of life and every type of living organism are discussed in biology.

Branches of Biology

Biology is divided into following branches:


The study of form and structure of living organisms is called morphology. It can be further divided into following two parts:
1. The study of external parts of living organism is called external morphology.
2. The study of internal parts of living organism is called internal morphology or anatomy.


The study of cells and tissues with the aid of the microscope is called Histology.

Cell Biology

The study of structure and functions of cells and their organelles is called Cell Biology.


The study of different functions performed by different parts of living organism is called Physiology.


The study of organisms in relation to each other and their environment is called Ecology or Environmental Biology.


Living organisms are classified into groups and subgroups on the basis of similarities and differences. This is called classification Taxanomy is that branch of biology in which organisms are classified and given scientific names.


The study of development of an organism from fertilized egg (zygote) is called embryology. The stage between zygote and newly hatched or born baby is called embryo.


The study of methods and principles of biological inheritance of characters from parents to their offspring is called genetics.


The body parts of ancient organisms or their impressions preserved in rocks are called fossils. The study of fossils is called paleontology. It also includes the study of origin and evolution of organisms.
It can be divided into two parts:
1. The study of fossils of plants is called Palaeobotany.
2. The study of fossils of animals is called Palaeozoology.


The study of metabolic reactions taking place in living organisms is called biochemistry. These reactions may be constructive or destructive. The assimilation of food is a constructive process and respiration is a destructive process.


It is the branch of biology which deals with the practical application of organisms and their components for the welfare of human beings e.g. disinfections and preservations of food, preservations of insulin and biogas from bacteria etc.

Relationship of Biology with other Sciences

In ancient times, there was no distinction of biology and other sciences. Different fields of sciences like biology, chemistry, physics and mathematics are met together in the writings of ancient scientists. In ancient times, these subjects were studied under one head “science”, but with the passage of time, the science developed very much and the huge scientific knowledge was then divided into different branches.
However even today the interrelationship of these branches cannot be denied.


The study of various biological phenomena according to principles of physics is called biophysics. For example, movement of muscles and bones based on principles of physics.


The study of different biochemical like carbohydrates, proteins and nucleic acids etc found in cells of living organisms and hundreds of the underlying chemical reactions in cells of organisms is called biochemistry.


The data obtained from observations and experiments on living organism is analyzed by various statistical methods. This is called Biometry.


The study of plants and animals and the basis of geographical distribution is called Biogeography.


The study of living organisms from economic point of view is called Bio-Economics. It includes the study of cost effectiveness and viability of biological projects from commercial point of view.

Biological Method of Study or Method Used to Solve the Problem of Malaria


Most of the biological investigations start with an observation. After selecting, specific biological problem, observations are made to collect relevant information. For example; take the case of Malaria. Malaria is the greatest killer disease of man for centuries. Malaria was one among many other diseases for which a cure was needed.
In 1878, A French physician, Laveran, studied the blood sample of Malaria patient under microscope and observed tiny creatures in it. These creatures were later called Plasmodium.


To solve a scientific problem, one or more possible propositions are made on the basis of the observations. Such a proposition is called a Hypothesis. The hypothesis is tested by scientific method.


A good hypothesis has the following merits:
1. It is close to the observed fact.
2. One or more deductions can be made from this.
3. These deductions should be confirmed doing experiments.
4. Results whether positive or negative should be reproducible.
To know the cause of malaria, following hypothesis was made:
Plasmodium is the cause of Malaria.”
Note: One or more than one possible deductions can be made from the hypothesis.


The logical conclusion drawn from a hypothesis is called deduction. Testing one deduction and finding it correct does not necessarily mean the hypothesis is correct and scientific problem is solved. Actually, if more deductions are found to be correct; the hypothesis will be close to solution of the problem.


Following groups are designed to perform experiments:

Experimental Group

It is the group of those people who are affected in some way and we do not know the real cause e.g. a group of malarial patients.

Control Group

It is the group of unaffected people e.g. persons group of healthy persons.
By keeping both of these groups under similar conditions, the difference between them is determined. To know the real cause of malaria, the experts examined the blood of about 100 malarial patients (experimental group). On the other hand, the experts examined the blood of about 100 healthy persons (control group).


During the experiments mentioned above; the plasmodium was found in blood of most of malarial patients. The plasmodim was absent in the blood of healthy persons. These results verified the deductions and thus the hypothesis i.e. the plasmodium is the cause of Malaria, was proved to a considerable extent.


If hypothesis is proved to be correct from repeated experiments and uniform results, then this hypothesis becomes a theory.

Scientific Principle

When a theory is again and again proved to be correct, then it is called a scientific principle.

Contributions of Muslims Scientists in the Field of Biology

Many Muslim scientists contributed a lot in the field of biology but the following names are more respectable:


Period: 722-817 A.D
Books: Alnabatat and Alhaywan
Contribution: He studied the life of plants and animals and wrote many books about them.


Period:741 A.D
Books: Al-Kheil, Al-Ibil, As-Sha, Al-Wahoosh, Khalaqul Insan.
Contributions: He described the body structure and functions of horses, camels, sheep, wild animals and human beings in detail.

Abu-Usman-Umer Al-Jahiz

Books: Al-Haywan
Contribution: He explained the characteristics of about 350 species of animals. He wrote on the life of aunts especially.

Al-Farabi and Abu-ul-Qusim Al-Zahravi

Period: 870-950 A.D
Books: Al-Nabatat, Al-Haywanat
Contribution: The above mentioned books were written by Al-Farabi. On the other hand, Al-Zahravi was famous for removal of stone from urinary bladder.


Period: 965-1039 A.D
Books: Al-Manazir, Mizan-ul-Hikma
Contributions: Both of these books were famous and well known at that time. These books were translated into Latin, Hebrew, Greek and other western languages. He explained the structure and functions of eyes and suggested the cornea as a site of vision.

Bu-Ali Sina

Period: 980 A.D
Book: Al-Qanoon Fil Tib Al-Shifa
Contribution: He wrote about plants, animals and non-living things in one book. He was expert in mathematics, astronomy, physics and paleontology.


Contribution: he described the blood circulation in the human body.

Ali Ibne Isa

Contribution: He worked on structure, functions of eye and about 130 diseases of eyes and their treatment.

Non-Muslim Scientists

There is long list of non-Muslim scientists who contributed a lot in the field of biology. But, the following scientists are very well known.


Period: 382-322 A.D
Book: Historia Animalia
Contribution: He classified the animals and called as founder of biological classifications. He classified animals into two units, genus and species which was called Oedos.


Contribution: He accepted sex in plants and desired about 500 plants. He is known as father of botany.


Period: 1514-1564 A.D

Contribution: He wrote a book on human body structure in which he described bones, muscles and orans in detail.

William Harvey

Period: 1578-1657 A.D
Contribution: He described the blood circulation in human body.

Carolous Linnaeus

Period: 1507-1778 A.D
Contribution: He described the blood circulation in human body.

Carolous Linnaeus

Period: 1578-1657 A.D.
Contribution: He gave a system of binomial nomenclature. He is known as father of taxonomy.

Schlelden and Schwann

Contribution: Scheiden (1838) studied the cells of plants and Schwann (1839) studied the cells of animals. They proposed the cell theory.

Louis Pasteur

Period: 1822-1895 A.D
Contribution: He proved that microbes are found in the air which spoils the food items.

Edward Jennar

Period: 1796 A.D
Contribution: He invented method of vaccination against Small Pox.

Robert Koch

Period: 1845-1910 A.D.
Contribution: He discovered bacteria as causes of main diseases like Tuberculosis.

Joseph Lister

Period: 1860 A.D
Contribution: He made antiseptic medicines like Iodine and Carbolic acid.

Charles Darwin

Period: 1859 A.D
Book: Origin of Species by Natural Selection
Contribution: He explained concept of evolution in his book.

Gregor Mendel

Period: 1822-1884 A.D
Contribution: He conducted experiments on Pea plants. He formulated the laws of inheritance. He is known as father of modern genetics.

William Lawrence and William Henry

Period: 1882 A.D
Contribution: They discovered X-ray crystallography to understand the structure of deoxyribonucleic acid (DN). They were father and son.

Francis Crick and James Watson

Period: 1953 A.D
Contribution: He discovered the double helix model of DNA and proved that DNA is found in cells of all living organisms.

Significance of Biology or Impact of Biological Study on Human Life

The present high level achievements of man are largely due to the advanced biological research. The study of biology is very important in routine matters of our life as described below.

Food Production

Food has basic importance in our life. Due to researches in biology, there are great achievements in agriculture. For the production of cereal crops; the best varieties of seeds were selected. The yield of wheat corn, rice, sugarcane and cotton has been enormously increased bringing healthy effect and prosperity. Today, the man has overcome the problems of balanced diet, food storage and famine.

Control on Diseases

Health is basic necessity of life. Due to researches in biology, the discovery of new antibiotics for many infectious diseases like plague, cholera, pneumonia, tuberculosis and typhoid has made the life easy. The infant mortality has reduced due to discovery of vaccines for fatal diseases like small pox, polio, tetanus and diphtheria. Today AIDS is problem for world. The germs of this disease destroy the natural resistance and immunities against diseases.
A medicine called AZT has been found effective for AIDS. Similarly many drugs have been discovered for treatment of cancer. Many organisms are used to produce drugs e.g. bacteria and fungi. We have controlled many infectious diseases by using drugs like penicillin and streptomycin. We have eliminated many harmful pests like locusts, flour beetle, termites, fungi, shipworm etc by using pesticides.

Genetic Engineering

Genetic engineering is a technology in which useful genes are inserted into the bacteria etc, to get required beneficial results. Using this technique, manipulation of heredity material is done and new species are produced e.g. Doli sheep. Today human insulin gene is inserted into DNA of bacteria to synthesize insulin on commercial bases. This insulin is found to be very useful in treatment of diabetic patients.

Pollution Control

Due to increasing urbanization, industrialization and automobiles, the man and other organisms have to face a great danger, “the environmental pollution”. due to pollution of air, land and water there is danger to humans aid wild life. Many plants and animals have been maintaining the balance in our environment for millions of years and now at the verge of extinction due to pollution. By biological research, scientists are busy to find out causes and ways to control the pollution. The biology thus, has greatly improved the quality of our life.

Space Biology

On Mars, some evidence of life has been found which is still under further investigation. During exploration of space the scientists have been conducted experiments on different plants, animals, fungi and bacteria in space and they have obtained very useful information.

Islamic concepts About Origin of Life

We have got much information about origin of life by studying the Holy Quran.

Ultimate Creator

The first thing learnt from teachings of Quran is that Allah is the ultimate creator of everything whether plants, animals or non-living things.
“Allah is the creator of all things and He is Guardian of overall things.” – (Surah Zamar-Ayat 62)
Not only plants, animals and non-living things and human beings but also the heavens and whole universe have been created by Allah.

Origin of Life from Water

The second important fact we get from Quran is that Allah has created all living thins from water.
“We made every thing from water.” – (Sura Ambia – Ayat 30)
Viruses, bacteria, algae, fungi, different plants, all animals and humans are all living things. According to Quranic verses, all diverse living things were created from water.
Common Origin
From above mentioned sayings of God there is an indication for common origin of living things or we can at least say that all living things have come out from water.
Creation of Man
Allah also sys in Quran:
“He created man from clay like the potter’s.” – (Sura Rehman – Ayat 14)
It seems that there were following two sages for creation of man:
1. Creation from water.
2. The first created thing, on admixing with clay was transformed into more advanced beings.
The same can also be applied to other animals because there are certain similarities between structure of man and other animals. In vertebrate animals, the structures of digestive system, respiratory system, blood circulatory system, excretory system and reproductive system etc are similar to great extent, although differ in other details. Reproduction in living things.
Once the life had been created, Allah implemented the process of reproduction for the continuity of races of animals and other organisms. The various stages of reproduction have been described in sura in following way:
“Then fashioned we drop a clot, then fashioned we clot a little lump, then fashioned we the lump bones, then clothed the bones with flesh.” – (Sura Almominoon Ayat 14)
Classification and Evolution
“Allah has created every animal from water some of them creep up on their bellies, other walk on two legs, and others on four, Allah creates what the pleases. He has power overall thins.” – (Sura Nur Ayat 45)
“Hath there come upon man (every) any period of time in which he was a thing unrememberd?” – (Sura Dahar Ayat 1)
The close study of above sayings of God reveals that all animals had a common origin but they gradually underwent changes after words and became different from each other i.e. some animals became crawler, some bipedal and some other tetra pods. The present animals are advanced forms of the past animals who achieved this form after passing through many changes.
Concept of Abiogenesis and Biogenesis for Origin of Life on Planet Earth
Scientific Views About Origin of Life
How did life originate on this earth? This may never be know for certain to science because neither it is possible today to make observation of primitive events when the life actually originated nor there is any fossil record of first formed soft bodied organisms. However, in 1950 some scientists created the primitive earth condition (approximately 4 billion years ago) in the laboratory and performed experiments. On the basis of results obtained from these experiments, scientists formulated some ideas. These ideas seem to be close to reality.
Abiogenesis and Biogenesis
In ancient times, there were two views about the origin of life:
1. According to one view, offspring are produced from their parents by process of reproduction, this is called concept of Biogenesis.
2. According to other view, living things are produced spontaneously from non-living things. This is called concept of Abiogenesis.
Because at that time, there was neither so much advancement in science nor scientific tools like microscope and other instruments were invented, which could help in detailed observations about reality. According to some people, insects are produced from dewdrops, rats from debris, frogs from mud, and maggots from putrefied meat. Some scientists like Copernieus, Bacon, Galileo, Harvey, and Descartes also believed this concept.
From 16th to 18th century many scientists performed experiments to test this concept. They found some animals to be developed from non living matter. Therefore this concept seemed to be correct.
Later on, scientists performed experiments with more care. First of all an Italian scientists, Francesco Redi, (1668) proved that this concept was wrong.
Redi’s Experiment
Redi took four bottles. He put a dead snake in one bottle, a few dead fish in second bottle, dead eel in third bottle and a piece of meat in the fourth bottle. All these bottles were left open. The flies could enter these bottles. Then he took four more such bottles. He put some dead animals in all four bottles but covered the mouth of bottles.
(Figure from book)
After few days, maggots were produced in four open bottles. Maggots were not produced in closed bottles. Moreover, no flies were seen. Therefore, it was proved that maggots were not produced spontaneously by produced due to flied which were visiting the open bottles. The maggots were the larvae produced from the eggs of the visiting flies.
Needham’s Experiment
In 1948, an English scientist Needham boiled the meat in the water and prepared gravy. He poured this gravy into the bottles and closes their mouth with corks. After some days, many microscopic organisms were produced. In this way, the believers of abiogenesis were once again gain courage.
(Figure from book)
Experiment of Spallanzani
In 1767, an Italian scientists Spallanzani criticized the experiment of Needham. He said that air entered the bottles through the pores of cork and hence living organisms were produced.
(Figure from Book)
Spallanzani put the boiled meat and vegetables in clean bottles and then sealed the mouth of bottles by heat. He placed these sealed bottles in boiled water to kill the possible germs. After some days, he found no organisms. He left the same boiled meat and vegetables in open bottles at the same time. Some living organisms were produced in these bottles. This supportd the concept of Biogenesis. But the believers of Abiogenesis said that air removed by Spallanzani was necessary for living things so no organisms were produced in sealed bottles. When oxygen was discovered the supporters of Abiogenesis said that Spallanzani had removed oxygen where by no life could be produced in his experiment.
Experiment of Louis Pasteur
The argument on Biogenesis and Abiogenesis continued up to the middle of, 19th century. A well-known French scientist, Louis Pasteur proved, after simple but very careful experiments, that abiogenesis could not occur in present environment of earth. He proved that living organisms could only be produced from their parents.
In 1864, Pasteur performed his experiment in front of the commission formed to solve the issue. He took flasks, which had long curved S-shaped necks. He placed fermentable infusion (Yeast + sugar + water) in flasks and left their mouth open.
(Figure from Book)
He boiled the yeast infusion in the flasks. After this, he allowed to cool them and kept them as such. He observed that no life ws produced even after the lapse of several days, because microscopic organisms entering along with air got stuck up in on the curved walls of the glass necks. Then he broke up the curved necks, so that air containing microscopic organisms could reach the infusion. Now he noted that microscopic organisms were produced within 48 hours. This proved that if care was taken and no microscopic organisms and reproductive structures (eggs or spores) approach the infusion, no life could be produced because thee is no spontaneous generation of life from non life. After Pasteur, no further experiments were performed on origin of life for the next 60 years. In 1920, a Russian biochemist Alexander Oparin and a British biologist J.B.S 1-Ialdane suggested that life on earth was originated after a long and gradual molecular evolution and there was no spontaneous and miraculous origin of life on earth.
Chemical and Organic Evolution of Life on Earth
The modern view of the origin of life stresses on the idea of chemical evolution. According to Oparin and Haldane, the origin of first life had been initiated from the time of the existence of the solar system (the sun with its nine planets). The earth, like the sun was made up of light and heavy elements. Heavy elements like iron, nickel etc were present in the nucleus of the earth, while the light elements and compounds like hydrogen, methane, nitrogen, carbon, ammonia, nitrogen oxide, etc in the form of vapours existed on the surface of the earth. These light elements and compounds were responsible for the first life on earth.
The earth had high temperature and radiation and had frequent and abundant discharges. In these conditions, the first life originated. Oparin and Haldane suggested that simple inorganic molecules slowly and gradually combined to produce complex organic molecules from which the simplest form of life (bacteria) came into existence. This process took a long time.
Haldane proposed that primitive earth’s atmosphere had only carbon dioxide, ammonia and water vapours. If a mixture of these gases is exposed to ultraviolet radiation, it leads to the formation of organic compounds like sugar and amino acids. As free oxygen was not available to check the radiation from reaching the earth so substances like sugar and amino acids went on accumulating under such conditions.
About 15 billion years ago, there was a huge explosion (Big Bag). The universe started expanding and the temperature dropped drastically. In time, about 4.6 billion years ago our earth and other planets appeared as part of the solar system. The primitive atmosphere of the earth was rich in hydrogen.
With the passage of time, the atmospheric temperature gradually dropped. This allowed condensation and heavy rains, which caused formation of oceans. Thunder and lightning sparks together with ultraviolet radiation caused reactions of the atmospheric gases resulting in the formation of simple organic molecules. These molecules came down with the rains and accumulated in the seas, oceans, lakes, rivers and the soil over a very long period of time. These molecules interacted and produced amino acids and proteins which are the body building substances.
The fossil evidence indicates that the earliest forms of organisms lived about 3.8 billion years ago. From this it is speculated that the origin of life started about 4 billion years ago.
The earliest organisms were heterotrophs. The depletion of the pre-existed food from the environment led to the evolution of organisms capable of making their own food. They became autotrophs, and added free oxygen into the atmosphere.
For at least the first 2 billion years of life on earth, all organisms were bacteria. About 1.5 billions years ago, the first eukaryotes appeared.
The idea of organic evolution was supported by scientists like Lamarck and Charles Darwin.
Differentiate between Biogenesis and Abiogenesis
A theory which describes the origin of life on the earth from pre-existing living organisms is called Biogenesis.
It was based on practical experiments and material evidence.
It was supported by the experiments performed by Redi and Pasteur.
It was based on practical basis.
It describes the process of reproduction as an essential ability of living organisms.
A theory which describes the origin of life on the earth from non living things is called Abiogenesis.
It was based on observations and national thoughts.
It was supported by the fungus of bread: and production of frogs in the mud.
It was based on theoretical basis.
It gives no scientific reasoning about the production of life.
Differentiate between Hypothesis and Theory
The process of making some possible answers for the related biological problem is called Hypothesis.
It is the step of biological methods which gives the way to carry on the research.
Hypothesis is an uncertain intelligent statement.
Hypothesis is formed from observations and collected facts.
The final explanation which is given on the basis of hypothesis and deduction if they are found correct is called theory.
It is the step of biological method which gives actual reason to biological method.
Theory is certain intelligent statement.
Theory is formed by experimentation, physical evidence to explain the laws of nature




Structural Organization Of Life

The Discovery of Cell and Cell Theory

Discovery of Cell
In 1665, an English biologist Robert Hooke invented first compound microscope and observed the sections of corks and leaves under this microscope. He noticed in them small box like chambers of same size which he called “cells”. After this, biologists observed different organisms under the microscope. They found that structure of cells was complex.
Cell Theory
In 19th century, the compound microscope was highly advanced and biologists observed things just a micrometer apart. After this, a series of discoveries started, which provided basic information for cell theory.
1. In 1831 – 33, Robert Brown discovered nucleus in cells of plants.
2. In 1838, a German botanist Mathias Scheiden observed that all plants were made up of cells.
3. In 1839, Theoclor Schwann obsrved that the bodies of of animals were made up of cells which were similar to plant cells.
4. Thus, Schleiden and Schwann formulated the “Cell Theory”. According to this, all organisms are made up of cells.
5. In 1840, J. Purkinji gave the name “Protoplasm” to the things found inside the cells. At that time, cell was considered as a bag of thick dense substance containing a nucleus.
Later on, resolving power and quality of microscopes were highly improved. Section cutting of tissues and cells and their staining became easier and better. It revealed that cell was not a simple mass of granular substance; instead it contained many sub cellular bodies called “Organelles”. Each organelle has a definite job in the cell.
6. Human is made up of about 60 trillion cells. From Amoeba and unicellular algae to whales and tallest red wood trees, all’ are made up of similar basic units called cell.s All animals and plants are thus made up of cells and cell products.
Salient Features of Cell Theory
1. All animals and plants are made up of cells and cell products. Among these some organisms are unicellular and some are multicellular.
2. Cell is structural and functional unit of living organisms.
3. New cells come from the divisions of pre-existing cell.

Electron Microscope

This is the most advanced form of microscope. Its resolving power is 250 times or more that of a compound microscope. In this microscope, a beam of electrons under high voltage is passed through the object and its image is reflected on to a screen through an electro magnetic lens to make a photograph.
With the help of microscope, any object an be magnified up to 250,000 its original size.
Comparison of Light Microscope and Electron Microscope
Light Microscope
The radiation source is light so it is called light microscope.
Wavelength of light is 400 – 700 nm.
Maximum resolution is 200 nm.
Maximum useful magnification is X 1500 with eye.
Lenses are used.
Electron Microscope
The radiation source is beam of electrons, so it is called Electron Microscope.
Wavelength of beam of electrons is 0.005 nm.
Maximum resolution is 0.5 nm.
Maximum useful magnification is X. 250,000 on screen as image or photograph.
Electromagnets are used.

Structure of Eukaryotic Cell

Structure of Cell
There are two types of cells:
1. Prokaryotic cell
2. Eukaryotic Cell
Prokaryotic cell lacks a membrane bound nucleus and membraned organelles e.g. bacterial cell while eukaryotic cell has a membrane bound nucleus and membraned organelles e.g. cells of plants and animals.
With the help of light microscope and electron microscope, a typical Eukaryotic cell shows the following structural details.
1. Cell Wall
2. Cell Membrane
3. Nucleus
4. Cytoplasm
1. Cell Wall
It is the outer most boundary of plant cells. It is rigid and non-living. It is chemically composed of Cellulose. The cell wall of fungi is made up of Chitin. The walls of some cells are thick and walls of some cells are thin. For example, in plants, xylem vessel elements and tracheids (which transport water and minerals) have thick walls whereas as parenchyma cells (which store water and food) have thin walls. The primary layer of cell wall is known as primary walls which are further strengthened by an additional layer called secondary wall especially in xylem vessels. Secondary wall is thicker than the primary wall. Electron microscope studies reveal that cellulose fibers in primary and secondary walls have a criss cross arrangement.
Cell wall provides a definite shape, rigidity, protection and support to plant cell.
2. Cell Membrane
It is a thin membrane which is also called Plasma membrane. It is present in cells of all plants and animals. It is outer most boundary of animal cell while in plant cells; it is present inner to cell wall. Both nucleus and cytoplasm are surrounded by cell membrane. According to fluid mosaic model, cell membrane is composed of two layers of lipids in which protein molecules are partially or completely embedded.
Cell membrane is selectively permeable membrane. It means that it allows some things to pass through easily while some not. Thus, it controls the movement of material inside or outside the cell.
3. Nucleus
It is most important and distinct part of the cell. It is present in center of the animal cell while in plant cell it is pushed on one side due to large central vacuole. It is also surrounded by a membrane which is called membrane. Under microscope, it to be doubled and nuclear electron appears porous.
1. The number of chromosomes is fixed for each species. This number is called diploid number (2n). E.g human’s cell has 46 chromosomes, cell of Radish has 18 chromosomes, and cell of union has 16 chromosomes.
2. Chromosomes are composed of protein and DNA.
3. In the nucleolus (plural, Nucleoli) ribosomal RNA is formed which helps in the formation of ribosome.
4. Cytoplasm
It is viscous opaque substance. It is present between nuclear membrane and cell membrane. In a living cell, many types of organelle of different sizes and shapes are found. It contains many insoluble granules of storage substances. There are also present organic compounds like carbohydrates, proteins, lipids (fats), enzymes and inorganic compounds like water and salts.
Cytoplasm provides chemicals, site and environment for different biochemical reactions

Organelles in Cytoplasm

They re oval or rod like in shape. Their membrane is doubled. Outer membrane is smooth while inner membrane has enfolding in the mitochondrial matrix. These enfolding are called cristae. The cristae bear small rounded bodies which are called particles.
There are about one million elementary particles in one mitochondrian. They are involved in oxidative phosphorylation. They also have many respiratory enzymes.
Number of Mitochondria
Their number is different in different cells of different animals. In more active cells, their number is more than 1000 e.g. liver cell.s The cells of ear lobes have a few number of mitochondria.
Mitochondria re very important organelles of Eukaryotic cell.s Many oxidation-reduction reaction occur in the mitochondria. As a result energy is produced. This energy is used by cell in various functions. This the reason that mitochondria are also called “Power house of cell”.
Golgi Bodies
They were discovered by Camillo Golgi. They consist of set of smooth, flattened sacs which are called cristernae. The cristemae are stacked over each other. Golgi bodies are in the form of network in some cells or meshwork or filamentous in other cells.
Golgi bodies store the secretions, convert them into finished products and pack them at their margins into small rounded sacs called Golgi vesicles, which transport secretions outside the cell.
Endoplasmic Reticulum
It is a network of tubules and cristemae extending throughout the cytoplasm from nuclear membrane to cell membrane.
Types of Endoplasmic Reticulum
Following are the two types of Endoplasmic Reticulum:
Smooth Endoplasmic Reticulum
It is also called non-granular endoplasmic reticulum because ribosomes are not attached on it.
Rough Endoplasmic Reticulum
It is also called granular endoplasmic reticulum because ribosomes are attached on it.
1. Smooth endoplasmic Reticulum plays a role in synthesis of lipids.
2. Rough endoplasmic reticulum plays an important role in synthesis of proteins. It also transports materials from one part of cell to other.
3. Endoplasmic reticulum provides support to the cell.
These are tiny granular structures. These re not bounded by any membrane. These are formed in the nucleolus nd re freely dispersed in cytoplasm or attached with endoplasmic reticulum.
Ribosome is involved in protein synthesis. It is the only organelle which is also found in Prokaryotic cell.
These are pigment containing organelles. These are found in plant cells. Many plastids have one or more than one pigments.
Types of Plastids
Plastids are of three types which are as follows:
These are mot important plastids. These re green in colour and found in green parts of plant. These contain chlorophyll which helps in photosynthesis. The study of ultra structure reveals that it is bounded by a double membrane.
Inside the chloroplast there is present a semifluid matrix called called stroma, which is made up of proteins and other chemicals. The inner membrane forms stacked membrane system which becomes suspended in the stroma. Each membrane stack is called granum (plural grana. The membranes of grana are the sites where photosynthesis occurs in the presence of sun light.
In chloroplasts, photosynthesis takes place and food is prepared for plant.
These are second type of plastids. These are of various colours other than green. In plants, colours other than green are due to chromoplasts. These are present in the petals of the flowers and in the ripened fruit.
These help the plants in pollination. These impart various colours to petals and fruits.
These are third type of plastids. These are colourless plastids. These are triangular tubular or of any other shape. These are found in food storage prts of the plant especially the roots and tubers.
In animal cells, two centrioles are present near the nucleus. There are hollow and cylindrical. Each centriole consists of nine triplets of microtubules.
Centrioles help in spindle formation during division of animal cell. Spindle is composed of protein fibers which help the chromosomes to move. Centrioles are absent in cells of higher plants. In some cells, centrioles help in the formation of flagella or cillia.
It is a fluid filled small sac which is bounded by a single membrane. In animal cells, these are comparatively smaller in size but many in number while in plant cells; there is a large central vacuole which is filled with water and salts.
In small organisms, extra water and wastes are excreted through contractile vacuoles, while food is digested in food vacuole. Increase in size of vacuole results in an increase in size of cell

Difference between Prokaryotic Cell and Eukaryotic Cell

Prokaryotic Cell

The organisms made of prokaryotic cells are called prokaryotes e.g. bacteria and cyanobacteria.

These cells lack a membrane bound nucleus. The hereditary material (DNA) is found in cytoplasm.

These cells lack membrane bound organelles.

Ribosomes are of small size in and freely scattered cytoplasm.

Cellulose is absent in cell wall, rather it is made up of peptido-glycan or murein.

These cells are simple and of smaller size (average diameter 0.5 – 10 nm)

Eukaryotic Cell

The organisms mae of Eukaryotic cells are called Eukaryotes, e.g. animals, plants fungi and protists.

These cells have a membrane bound nucleus; and hereditary material is found inside the nucleus.

These cells have membrane bound organelles.

Ribosomes are of large size and are present in endoplasmic reticulum free in cytoplasm.

Cellulose is present in cell wall of plant cells. The cell wall of most of fungi is composed of chitin.

These cells are complex and of larger size (Average diameter 10-100nm)


It is that cell division in which the number of chromosomes in both daughter nuclei remains same as in parent nucleus.
Events of Mitosis
Mitosis has the following phases:
1. Prophase
2. Metaphase
3. Anaphase
4. Telephase
5. Cytokinesis
1. In this phase, coiling of chromosomes starts and their length decreases but diameter increases. It means that chromosomes become shorter and thicker, this process is called condensation.
2. Microtubules arrange to form a structure called spindle.
3. In animal cell, there are also present centrioles on both poles of spindle. From each centriole, small microtubules or fiber arise forming a star shaped aster.
4. Spindle fibers, centrioles and aster collectively form mitotic apparatus. In plants, this apparatus is made up of only spindle fibers as asters are absent in these cells.
5. Nuclear membrane is broken down. Nucleolus disappears and chromosomes scatter over the spindle fiber.
6. Each chromosome consists of two similar threads like structure called chromatids, these chromatids are united to each other by means of centromere.
1. The chromosomes arrange themselves on equator of the spindle to form an equatorial plate. In this condition, chromosomes become more visible.
2. The chromosomes are attached at their centromere to one spindle fiber from each pole.
1. First of all spindle fibers shrink and become short.
2. The centromere of each chromosome then divides and the two chromatids of each chromosome start separating. At this stage these are not called chromatids because these are no in united condition these are called chromosomes.
3. These chromosomes start moving slowly towards the opposite poles. In this way, one set of chromosomes moves towrds one pole while other towards the other pole.
1. The chromosomes reach their poles.
2. The chromosomes uncoil and become less visible.
3. Nuclear membrane reforms and nucleolus appears too. Therefore two nuclei are formed. Each daughter nucleus has the same number of chromosomes as the parent cell.
The division of cytoplasm is called cytokinesis. It begins at the last stages of nuclear division. In plant cell, cytoplasm divides by formation of cell plate which is also called phragmoplast. It gradually extends outward and finally two daughter cells are separated.
In animals, cytoplasm divides by furrowing. During this, there occurs inward pinching of cell membrane resulting into two daughter cells. In mitosis, two daughter cells are formed from one parent cell which are identical to their parent cell.
Significance of Mitosis
1. Mitosis occurs in all types of somatic cells.
2. Daughter cells formed as a result of mitosis have same number of chromosomes as that of parent cell. In this way, all cells of body of an organism have same number of chromosomes.
3. Zygote divides by mitosis to form embryo and after hatching or birth, mitosis continues up to maturity of an individual.
4. Mitosis also results in growth and repairing of damaged or worn out tissues.
5. Healing of wounds is also due to mitosis


It is that type of cell division in which cytoplasm and nucleus divides twice and as a result of this, four daughter cells are formed and chromosome number is reduced to half. It means that one diploid (2n) parent cell divides to form four haploid (n) daughter cells.
Meiosis consists of two sub divisions:
1. Meiosis I
2. Meiosis II
1. Meiosis I
It has following stages:
Prophase I
1. It is lengthy than prophase of mitosis. It is very important phase. It is divided into five stages during which there is continuous condensation of chromosomes.
2. The important process of this phase is synapsis in which homologous chromosomes pair with each other length wise.
3. Each pair consists of four chromatids or two chromosomes.
4. After synapsis, the process of crossing over takes place. In this, homologous chromosomes exchange their chromatids parts at certain places.
5. At end of this phase, nuclear membrane breaks up. Nucleolus disappears and chromosomes scatter over the spindle.
6. Like mitosis, mitotic apparatus is also formed here.
Metaphase I
1. The chromosomes arrange on scatter of the spindle.
2. Here, homologous bivalents arrange at equatorial plate of spindle.
3. Only one spindle fiber is attached to each chromosome.
Anaphase I
1. Homologous pairs of chromosomes are separated.
2. Spindle fibers contract.
3. Chromosomes begin to move towards the opposite poles.
4. This phase is different from metaphase of mitosis because half the number of chromosomes moves towards each pole and each chromosome still has two chromatids.
Telephase I
1. Half the number of chromosomes reach at opposite poles.
2. Chromosomes again increase their length.
3. Nucleolus reappears. Nuclear membrane is reformed and in this way two daughter nuclei are formed.
4. Now cytoplasm divides and two daughter cells are formed. Each cell is haploid (n).
2. Meiosis II
It is similar to mitosis. The haploid cells formed in meiosis I pass through phases of meiosis II and ultimately four haploid (n) daughter cells are formed. These cells afterwards change into spores (in plants or gametes (animals)
Significance of Meiosis
1. Meiosis takes place only in germ mother cells which form gametes or spores.
2. It maintains the chromosome number of a species constant generation after generation.
3. If gametes had the same number of chromosomes as in somatic cells, the number of chromosomes would have doubled after each generation in a species.
4. The number of chromosomes is constant for each species. During meiosis; gametes (both and) formed are haploid.
5. Gametes unite to form a diploid zygote.
6. During meiosis, pairing of chromosomes takes place which is called synapsis.
7. Exchange of genetic material occurs during meiosis. In this way variations are produced which are raw material for evolution.


A group of cells which perform same function is known as tissue. The tissues are divided into different types on the basis of their form and structure or function.
Plant Tissues
Following are the types of tissues in plants:
1. Simple Tissues
2. Compound Tissues
1. Simple Tissues
Simple tissues consists of only one type of cells. In plants, they are of following types:
i. Meristematic or embryonic tissues
ii. Permanent Tissues
i. Meristematic Tissues
1. Cells of this tissue have ability to divide.
2. Cytoplasm is dense nd nucleus is big in these cells.
3. Vacuoles are smaller if present other wise absent.
4. All cells are identical.
5. There are no intercellular spaces.
6. Their walls are thin and nucleus is present in centre of cell.
7. These tissues found on apex of root or shoot are called apical meristems. The cells of these tissues divide; and redivide to add primary tissue for elongation of setm or root.
This type of growth is called primary growth.
8. Meristematic cells are also found on the lateral sides of roots and stems as lateral(cambium) or intercalary meristem, and these add, secondary tissues. In this way, thickness of stem or root is increased. This type of growth is called secondary growth.
ii. Permanent Tissues
The cells of this tissue lack the ability to divide and they originate from meristems. These are given below:
a. Epidermal Tissues
b. Ground Tissues
(a) Epidermal Tissues
1. They are found as the outermost covering of leaf, stem or root.
2. There are non intercellular spaces.
3. Cells are rectangular in shape.
4. In the epidermal tissues of stem and leaves, there are small openings called stomata for gaseous exchange.
(b) Ground Tissues
1. Most of the portion of body of herbaceous plants consists of ground tissues i.e. parenchyma.
2. They are thin walled.
3. Cells are large in size.
4. Cells sometimes may develop the ability to divide.
5. Their main functions are to prepare and store food and water.
Supporting or Mechanical Tissues
These provide strength flexibility to the plant. They are of following two types:
a. Collenchyma Tissues
b. Sclerenchyma Tissues
(a) Collenchyma Tissues
1. These consist of living cells.
2. Their walls are not uniformly thickened.
3. Usually walls are thickened at angles.
4. These are more flexible or elastic than sclerenchyma.
5. These tissues are found in stem, in midrib of leaves and in cortex of petiole.
(b) Sclerenchyma Tissues
1. These consist of dead cells.
2. Their walls are highly thickened due to deposition of lignin.
3. Lignin provides hardness and strength to the cell.
4. These cells are without protoplasm.
5. Sclerenchyma cells are of two types,

Stone cells having uniformly thick cell walls; found in testa of seeds.

Fibrous cells which are elongated cells found in xylem and phloem for strength and transport of water

  1. Compound Tissues
    These are the tissues which consists of two or more than two types of cells. But all cells perform a common function.
    These Tissues are of following types:
    Xylem Tissue
    1. This vascular tissue transports water in the plants and provides strength to the plant.
    2. In this tissue, there are present xylem parenchyma and two types of thick walled dead cells.
    Long cells which are called vessel elements or cells. They are joined together to form long pipe-lines. These transport water from roots to leaves.
    Spindle shaped cells, which are called tracheicts. These provide strength to root and shoot etc.
    3. Xylem conducts water in one direction that is from roots towards the stem and leaves.
    Phloem Tissues
    1. This vascular tissue transports food in the plants.
    2. It helps in two directional conduction of food material i.e. from leaves to roots and vice-versa.
    3. This tissue mostly consists of living cells. There are three types of cells
    (a) Phloem Parenchyma
    (b) Sieve Tube Cells
    (c) Companion Cells
    (a) Phloem Parenchyma
    These cells store surplus water and food. They can start to divide when needed.
    (b) Sieve Tube Cells
    Their end walls have small pores called sieve plates. These cells join to form long pipelines, which are called sieve tubes. There is no nucleus in these cells. Their main function is to transport food.
    (c) Companion Cells
    In some plants, each sieve tube cell is accompanied by a companion cell. The companion cell has a nucleus. The corn cell controls the movement of food through sieve tubes.
    Animal Tissues
    Following are four types of tissues that are found in animals:
    1. Epithelial Tissues
    2. Connective Tissues
    3. Muscle Tissues
    4. Nerve Tissues
    1. Epithelial Tissues
    1. these are found as outer most layers of an organ or as lining of body invaginations.
    2. Their cells are long and flat.
    3. These may form one or more layers of epithelial tissues of skin which is called squamous epithelial cells.
    4. Squamous Epithelium provides protection to skin.
    5. Some cells are cubical in shape and known as cuboidal epithelial cells.
    6. Cuboidal epithelial cells from the lining of glandular ducts and help in the production of cell secretions.
    7. Some cells are small and elongated which are found at certain places in the inner lining of different organs and secret juice. These are called columnar epithelial cells e.g. cells of gastric glands in stomach which secrete the gastric juice.
    8. Some columnar cells have cilia at their free surface. These are called ciliated columnar epithelial cells e.g. cells present in trachea. Due to movement of these cilia, mucous and other materials are expelled.
    2. Connective Tissues
    1. This tissue is made up of semi fluid matrix.
    2. These matrixes contain a variety of cells and fibers.
    3. These tissues provide support to different body parts and bind them together. These also protect the organs from germs and help in the production of blood cells.
    4. These are of two types:
    Soft connective tissues e.g. fatty tissues and tendons.
    Hard connective tissues e.g. cartilage and bone.
    5. Blood is also a special connective tissue with cells suspended in the fluid medium. It transports materials in the body.
    2. Muscular Tissues
    1. This tissue is made up of special contractile cells or fibers.
    2. The cells are elongated and are called muscle fibers.
    3. These cells have the ability to contract and relax which results in movements of body and the organs.
    4. Following are the three types of muscles in our body.
    Skeletal Muscles
    These are attached to cartilage and bones. These seem to be striped fibers under the microscope. Therefore these are striped or striated muscles. Their movements are under our control so these are voluntary muscles e.g. muscles of arm and legs which move these parts.
    Smooth Muscles
    These are found around hollow organs such as blood vessels, gut. These produce slow, sustained contractions but do not fatigue. These re composed of spindle shaped unstriated muscles. These are involuntary and are under the control of the autonomic nervous system.
    Cardiac Muscles
    These are found in the heart. These are composed of branched fibers and are capable of sustained contraction but do not not fatigue. These are also involuntary in action.
    4. Nervous Tissues
    1. These are composed of nerve cells which are called neurons.
    2. Each neuron consists of a cell body, axon and dendrites.
    3. These productive nerve impulse to conduct messages.
    4. By this tissue, different body parts have coordination with each other.
    5. This tissue also forms brain and spinal cord

Unicellular Organism (Amoeba)

The organisms consisting of only one cell are called unicellular organisms e.g. Amoeba, Paramecium etc.
1. It is mostly found in fresh water pond or pool.
2. In the ponds, it is found moving about around the weeds and stones. Some species are found in the moist soil.
3. Amoeba is a large protist.
4. It does not have the permanent shape.
5. Its size is about the end of pin or it measures about 0.25mm. Therefore it is observed under the microscope.
6. Its structure is very simple.
7. It consists of nucleus and cytoplasm, which are surrounded by a cell membrane.
8. Cell membrane protects it.
9. Cytoplasm is divided into two parts. Outer clear and transparent part is called ectoplasm while the inner, viscous, translucent and granular part is called endplasm.
10. Endoplasm contains food vacuoles of different sizes. These food vacuoles help in the digestion of food.
11. The food of Amoeba consists of microbes present in the water of pond.
12. Contractile vacuole maintains the concentration of water in the body. It removes surplus water out of the cell.
13. In Amoeba, the exchange of gases and removal of waste.
14. In Amoeba, there are also present mitochondria, golgi bodies and ribosomes.
15. Nucleus changes its place with the movement of the organism.

Multicellular Organism (Brassica Plant)

Multicellular Organism
The organisms consisting of many cells are called multicellular organism. e.g. Brassica Plant, frog, man etc. diagram?
Brassica Plant (Mustard Plant)
1. This plant is sown in winter and at the end of season, it produces seeds and then dies.
2. This is an annual plant.
3. An oil is extracted from seeds of this plant which is known as mustard oil.
5. The scientific name of this plant is Brassica Campestris.
Non-Reproductive Parts or Vegetative Parts
These parts do not directly take part in sexual reproduction e.g. root, stem, branches and leaves.
Reproductive Parts
These parts directly take part in sexual reproduction e.g. flower, fruit and seed.
Root of Brassica
The root is that part plant which is present inside the soil. It is produced from radical of seed. The first formed root is called Primary root. During its growth, it gives off secondary and tertiary root. Each root has a root cap at its tip or apex. Behind the root cap, root hairs are present which absorbs water and salts from the soil. Roots also anchor the plant firmly in the soil.
Internal Structure of Root of Brassica
When transverse section of root of Brassica is observed under the microscope, the following parts are very prominent.
It is outermost and protective layer. It is single celled. Some cells grow outward to form root hair.
It is present inner to epidermis. It is made up of several layers of thin walled living cells (parenchyma cells). There are present intercellular spaces. These cells store food.
it is the innermost layer of cortex. There are no intercellular spaces. There are thickenings of special materials around the cell which check diffusion of water from xylem to cortex.
The layer present inner to endodermis is called pericycle. There are also no intercellular spaces. All the branches of roots arise from pericycle.
Vascular Bundles
Xylem is present in middle of root which extends to pericycle in the form of four rays and controls one way transport of water and salts. In between the xylem rays, phloem bundles are present which transport food in two directions.
Stem of Brassica
The stem is that part of the plant which grows above ground. It arises from plumule of seed. It is herbaceous and branched. It bears leaves and flowers. The part of stem or its branch from where a leaf arises is called node. The part between two nodes is called internode. the important function of stem is the conduction of prepared food from leaves to other parts and that of water absorbed from roots to leaves. It supports leaves, flowers and fruits like a pillar. It keeps the leaves in such a position that they can get light to prepare food.
Internal Structure of Stem of Brassica
When transverse section of stem of Brassica is observed under the microscope, following parts are visible.
It is the outermost protective layer of stem. Outer to epidermis, there is layer of cutin which reduces loss of water from stem. The cells are compactly arranged and there are no intercellular spaces.
It is inner to epidermis. It is made up of many layers of parenchyma and collenchyma tissues. The main function of cortex is storage of water and food.
It is innermost layer of cortex. It is not prominent in stem. It allows suitable quantity of waer to enter cortex from xylem.
It is in the form of bundles in between the endodermis and vascular bundles. It is composed of sclerenchyma cells. It forms bundle cap.
Vascular Bundles
In stem, vascular bundles are arranged in the form of ring. Vascular bundle consists of phloem and xylem. Phloem is towards outside and xylem is towards inside. Few layers of cambium are present between the xylem and phloem. Cambium causes increase in diameter of the stem with passage of time.
Medullary Rays
There are present few layers of thin walled living cells between every two layers. These are called medullary rays. The medullary rays connect the cortex with pith for the transport of food.
The central part of stem consists of living, rounded, thin walled parenchyma cells. This part is called pith. Here food is stored.
Leaf of Brassica
1. Leaf is produced on node of stem or its branch.
2. Each leaf consists of two parts. The stalk of leaf is called petiole and upper broad part is called lamina.
3. Young leaves are without petiole and their margins are entire or smooth.
4. Lower leaves are large in size. These are also without petiole but there margins are wavy.
5. In the middle of leaf there is a thick midrib.
6. From midrib, arise veins of different thickness and form a network in leaf. This arrangement of veins is called reticulate venation.
7. Veins are composed of xylem and phloem.
8. The angle formed between stem and leaf is called axil. In this axil, buds are present which gwo and become branches.
9. The dorsal and ventral surfaces of leaves are different from each other. Such leaves are called bifacial leaves.
10. The main function of leaf is the preparation of food by process of photosynthesis.
Internal Structure of Leaf
When transverse section of leaf is observed under the microscope, following structure are visible.
This layer of cells covers both upper and lower surfaces of leaf. Upper layer is called upper epidermis and lower layer is called lower epidermis. There are more number of stomata in lower epidermis than upper epidermis. This results in less transpiration and CO2 enters according to need. Each stomata consists of two guard cells, which are bean shaped, or kidney shaped. There is a pore between guard cells through which exchange of gases takes place and water vapours come out of leaves.
The tissue present between upper and lower epidermis is called mesophyll. It consists of two parts.
Palisade Mesophyll
Uper part consists of elongated cells which hare lying vertical. These are double layered closely packed cells and are called Palisade Mesophyll.
Spongy Mesophyll
The lower part is sponge like and has more intercellular spaces. This is called spongy mesophyll.
Both types of cells have chloroplasts containing chlorophyll. So, photosynthesis takes place here. The function of mesophyll is to manufacture food for the plant.
Vascular Tissue
It consists of midrib and veins. The midrib is bundle. Upper part of midrib is xylem and lower part is phloem. Pericycle and endodermis surround this bundle. Besides this Lamina has other bundle which are called veins.
Flower of Brassica
The flower is reproductive part. With the maturation of age, the plant bears yellowish flowers. Many flowers are arranged on a branch in a special way. This branch is called peduncle. This arrangement of flowers on the peduncle is called Inflorescence.
Parts of Flowers
Flower consists of a stalk and floral leaves. The stalk is called Pedicel. The upper part of pedicel is comparatively swollen and flattened. This is called thalamus. On the thalamus, floral leaves are arranged in four whorls.
The details of floral leaves is as follows:
It is the outermost whorl of floral leaves. It consists of four sepals. On maturation, its colour changes to yellow. In young flowers sepals cover the inner parts of the flower. The main function of calyx is to protect inner parts of the flower.
It is the second whorl of floral leaves. It consists of four free petals. Its yellow colour is conspicuous and can attract insects, honey bees and butterflies which help in pollination.
It is the third whorl present inner to petals. It is the male reproductive part. It consists of six free stamens. These are arranged in two whorls, the outer whorl has two small stamens and inner whorl has four long stamens. Each stamen consists of two parts. Lower stalk is called filament. Upper swollen part is called anther, Inside anther, a large number of pollen grains are produced. When anther matures, a longitudinal slit appears in its walls from which pollen grains escape. AT the base of filament, four nectaries are present. These nectaries secrete nectar. To get nectar, insects visit the flowers. In this way, pollen grains get attached to the bodies of insects and are transferred from one flower to the other. This process is called pollination.
It is the inner most part of flower. It is female reproductive part. It consists of two carpels, which are fused. Each carpel has three parts. The basal swollen part is called ovary. The stalk like part above the ovary is called Style. The top of style is somewhat swollen and it is called Stigma. Overy contains many ovules. Ovules are ripened to form seeds while ovary is ripened to form fruit. The fruit of Brassica is called Siliqua.


Frog is found in he water or near the water. It belongs to class Amphibia. it passes a specific part of life in water and remaining life on land. Its bilogical name is Rana Tigrina. It is a cold blooded animal i.e. blood temperature changes with that of the environment. At the start of winter, water is decreased and temperature is lowered, the frog lives buried in the mud to over come winter.
The body cavity of frog is called Coelom. It contains many organs which form different systems.
Digestive System of Frog
This system consists of alimentary canal and accessory glands like liver and Pancreas.
Alimentary Canal
It is a coiled tube through which food passes. It consists of buccal cavity, pharynx, oesophagus, stomach and intestines.
Buccal Cavity and Pharynx
Mouth is present between upper and lower jaws. Upper jaw has a row of pointed maxillary teeth. Lower jaw lacks teeth. There is a pair of set of vomerine teeth on the roof of the buccal cavity. Frog does not chew the food with teeth. But teeth are used only to grasp the food. The old teeth are continuously replaced by the new teeth through its life. Near the vomerine teeth, internal nostrils are present on the roof of the buccal cavity. These open outwards into external nostrils. Behind them, two large bulges indicate the position of eyes. The tongue of frog is sticky. The tongue is attached at anterior end of buccal cavity. The posterior end of tongue is free and bifid. the frog feeds on different insects. To capture its prey, it suddenly throws its tongue on to the prey, which sticks to the tongue and is brought to the buccal cavity, when the tongue is drawn back.
Near the maxillary joints, pair of opening of eustachian tubes are present. In male frog, there is also, present a pair of opening of vocal, sacs on the lateral side of floor of the buccal cavity which help the croaking. Buccal cavity narrows, posteriorly to form pharynx. The digestive system, respiratory system and ears are linked to pharynx. In posterior part of pharynx, there is another opening called Glottis. This leads to lungs through tachea. It closes at the time of digestion of food but remains open when animal is respiring.
Oesophagus, Stomach and Intestine
Pharynx leads into a small but wider tube called oesophagus or gullet. The oesophagus opens into the stomach. The anterior end of stomach is called Cardiac end while the posterior end is called Pyloric end. The walls of stomach are muscular and glandular.
The muscles of walls of stomach contract and relax, by which food is broken down into tiny pieces. The secretions of stomach have different enzymes which help in chemical digestion. In stomach, digestion of protein of food is started. After stomach, first part of intestine begins which is called duodenum. The ducts from liver and pancreas open into the duodenum. These ducts bring juices from these glands. The second part of intestine is Ilium are called Small intestine. The secretion of pancreas is called Pancreatic Juice. Pancreatic juice enters the bile duct by small duct. This juice digests the food and brings in such form which can be absorbed by the blood through intestine. Digested food is absorbed by illium and surplus water is absorbed by recturm. Remaining undigested food is expelled though cloacal aperture. A membrane keeps the intestine intact at a place and prevents strangulation of small intestine. This membrane is called mesentery.
Respiratory System of Frog
There are three methods of respiration in frog.

Pulmonary Respiration

Cutaneous respiration

Buccal Respiration

Pulmonary Respiration
The exchange of gases through lungs is called pulmonary respiration. In this process, frog keeps its mouth closed. Air reaches buccal cavity through nostrils. Nostrils are closed floor of buccal cavity is raised; glottis opens, and air is pushed into the lungs. The intake of air is called inspiration. In frog, there is a pair of balloon shaped lungs. Each lung consists of small thin walled chambers called alveoli which greatly increase the surface area of the lungs. On each alveolus, there are many blood capillaries. When lungs are filled with air, then exchange of gases occurs between blood and air in lungs at the site of alveoli. During this, the exchange of gases occurs between blood and air present in buccal cavity. After this air is removed from the lungs. Frog uses its nostrils and floor of buccal cavity for inspiration and expiration.
Oxygen present in the air is dissolved in moisture present on lining of lungs. Then oxygen is diffused into the blood where it combines with hemoglobin to form oxyhaemoglobin. This oxygenated blood goes to all parts of the body by means of capillaries. Where oxygen separates from oxyhaemoglobin molecules and is absorbed by the cells. Carbon dioxide from cells comes out into the blood, which carries it to the lungs, and from here carbon dioxide is expelled.
Cutaneous Respiration
In frog, exchange of gases occurs through skin during hibernation and swimming. This is called cutaneous respiration. Skin is richly supplied with capillaries. Skin is moist. Oxygen diffuses through skin to capillaries and is carried by blood and CO2 diffuses back to blood from cells and is discharged out.
Circulatory System of Frog
It consists of blood vascular and lymphatic systems.
Blood Vascular System
The blood vascular system of frog consists of following parts:





Structure of Heart
Heart is conical organ. It is muscular. It has three chambers. It is present in the body cavity between the oesophagus and sternum. Like a pump, it contracts and is relaxes. As a result of this, blood continuously circulates in the body. The heart is surrounded by a membrane which is called pericardial which protects the heart.
The three chambers of heart are as follows:
1. Right Atrium
2. Left Atrium
3. Ventricle
the two atria form the broader interior part of the heart. The right atrium is larger than left atrium. Both atria are thin walled. The posterior conical thick walled part of the heart is called ventricle. A broad vessel, which is called truncus artenosus, arises from dorsal side of the ventricle and then divides into two branches near the atria. A thin walled triangular sinus venosus opens into the right atrium. Some biologists consider truncus arteriosus and sinus venosus as chambers of the heart.
Function of Heart

The chambers of the heart beat in a rhythmic way.

First of all sinus venosus contracts. Then, the two atria contract. After this ventricle and finally truncus arteriosus is contracted.

The deoxygenated blood from the whole body except lungs is carried to sinus venosus by two precavals and one post caval.

Sinus, venosus opens into the right atrium through an opening.

Oxygenated blood from the lungs is brought into the the left atrium by two pulmonary veins.

Both the atria open into the ventricle and push their blood collectively into the ventricle by a common aperture, which is guarded by a valve.

This valve maintains the unidirectional flow of blood in the heart and prevents the back flow of blood.

In the middle of ventricle some mixing of oxygenated and deoxygenated blood takes place. On the two sides the blood remains unmixed due to rapid flow of blood.

When ventricle contracts the blood goes to the truncus arteriosus through an aperture. This aperture controls the speed and direction of the blood by a spiral valve present at the start of truncus arteriosus.

Arterial System of Frog
The blood vessels which carry the blood from heart to different parts of the body are called arteries. The system consisting of arteries is called arterial system.
It starts from truncus arteriosus. It is divided into two main branches each of which further divides to form three small branches.
Carotid Arch
It supplies blood to lower jaw, tongue, eye and brain.
Pulmocutaneous Arch
It carries blood to lungs and skin.
Systemic Arch
Right and left systemic arches joint posteriorly to form dorsal aorta. But prior to their union, each systemic arch gives out arteries supplying blood to vertebral column, oesophagus and fore limbs.
Dorsal Aorta
It runs along the vertebral column towards hind limbs. It gives off following branches.
Coeliacomesenteric Artery
It supplies blood to digestive system.
Renal Arteries
These supply blood to kidneys and general organs.
Posterior Mesenteric Artery
It supplies blood to rectum.
Illiac Arteries
These supply blood to hind limbs of their sides.
After reaching their specific organs, all the arteries divide and redivide to form capillaries. The walls of capillaries are very thin. Due to this reason, the exchange of materials take place between blood and tissues. The capillaries join to form venules. These venules join to form veins. Then these veins carry blood back to heart.
Venous System
The blood vessels which bring the blood from different body parts, back into the heart are called veins. The system containing of veins is called Venous system.
Following are the major veins in frog.
Pulmonary Veins
Blood from right and left lungs goes to left atrium through pair of pulmonary veins. These have oxygenated blood.
Right and Left Precavals
Each precaval is formed by union of three veins which bring blood from tongue, lower jaw, head, shoulders, forelimbs and skin. Both veins open in sinus venosus. From here blood goes to right atrium.
It is formed by union of five or six pairs of renal veins from the kidney and the genital veins. While passing through the liver, it receives two hepatic veins. Then it enters the sinus venosus. Therefore, venous blood from different body parts enters the heart.
Renal Portal Vein
The veins which bring blood from the hind limbs and pelvic region combine to form Renal portal vein. The renal portal vein enters the kidney of its side and form capillaries. Blood from kidney goes to the post caval through renal veins. Post caval caries the blood to the heart.
Abdominal Vein
The Pelvic veins of two sides combine to form abdominal vein. Before entering the liver, it divides into branches. In liver, it is further divided to form capillaries. The blood from the liver is drained into post caval by hapatic veins of both sides.
Hepatic Portal Vein
The blood vessels (veins) bringing blood form various organs of digestive system (stomach, duodenum, illiums, rectum, pancreas and spleen etc) combine to form a large vein. This is known as hepatic portal vein. Near the liver a branch of abdominal vein combines with it. Then it enters the liver and divides and redivides to form capillaries. The, blood entering the liver through hepatic portal veins goes to the post caval by means of hepatic veins. The blood from post caval goes to heart through sinus venosus.
The blood coming back into the heart is of two types.

Oxygenated blood which comes from lungs by pulmonary veins.

Deoxygenated blood from all parts of the body enters sinus venosus through precavals and post caval and then enters the right atrium.

Lymphatic System of Frog
In circulatory system, due to blood pressure, many components of blood plasma come out of the capillaries and fill the inter cellular spaces. These components are also in the form of fluid and called tissue fluid or interstitial fluid. Much of it reenters the capillaries and some of it enters the lymph vessels where it is known as lymph. The flow of lymph is unindirectional. Through lymph “vessels” lymph goes to big veins. Thus, lymph again enters the blood.
1. The lymph keeps the tissues wet.
2. The lymph helps in transport of various substances from blood to tissues and vice versa.
Excretory System of Frog
In frog, waste materials are removed in different ways e.g. through skin, lungs, liver digestive system etc. But for removal of nitrogenous wastes, there are two kidneys. Kidneys are attached to dorsal wall of body cavity. These are present close to vertebral column in posterior part of body cavity. These are elongated and made up of urinary tubules. Urinary tubules combine to form collecting ducts which open into Ureter. The urine from kidneys comes into ureters after illustration. Both ureters which start from edges of kidneys open into the cloaca. From here, urine is excreted directly or stored in the urinary bladder, which on opening of cloacal aperture is expelled. The carbon dioxide and water are excreted through lungs and skin while through liver and digestive system; undigested food and some wastes are excreted.
Reproductive System of Male Frog
The reproductive system of male frog consists of a pair of testes and reproductive ducts. Each testis is attached to kidney by means of a membrane. At anterior end of testis, there is present fat body. Each testis is composed of small ducts called seminiferous tubules in which sperms are produced. Sperms enter the kidney via vesa efferentia. Sperms reach the cloaca through ureter. From here, these are dischaged in the water through cloacal aperture in this way, ureter in male frog does two jobs, one is removal of urine and other is removal of sexual material, so it is called urinogenital duct and the urinary system and genital system are collectively call urinogenital system.
Reproductive System of Female Frog
The reproductive system of female frog consists of a pair of ovaries and reproductive ducts. Ovaries are present close to the kidneys. At their anterior ends, there are present fat bodies. Each ovary contains many follicles in which eggs (ova) are produced. During breeding season, ovaries are enlarged. Ova are released into the body cavity through the coelomic fluid, these enter the oviduct. The anterior part of oviduct is funnel like called oviducal funnel and reach the uterus. The uterus opens into the cloaca. At last, ova are discharge in the water through cloacal aperture. In water, union of sperm with egg results in formation of zygote. From zygotes, offsprings are formed and in this way continuity of race is ensured.
Nervous System of Frog
It consists of three parts:
1. Central Nervous System
2. Peripheral Nervous System
3. Sympathetic Nervous System
Central Nervous System
It consists of brain and spinal cord.
Brain is enclosed in protective layers and is located in cranium or brain case, which is major part of skull.
Brain is divided into three parts:
(a) Fore Brain
(b) Mid Brain
(C) Hind Brain
(a) Fore Brain
This is anterior part of brain. This is associated with sense of smell. It controls the secretion of many hormones. It also receives messages from internal and external environment of the body.
(b) Mid Brain
This is central part of brain. This is associated with eyes and vision.
(c) Hind Brain
This is the posterior part of brain. It controls and coordinates body movements and maintains balance of the body. It also controls respiration, circulation, taste and digestion.
Spinal Cord
The posterior part of the brain is continuous with spinal cord. It runs through the vertebral column. The spinal cord controls the movements of trunk region.
Peripheral Nervous System
It consists of nerves. These nerves connect the central nervous system (CNS) with various parts of the body. Some nerves originate from brain. These are called cranial nerves other nerves originate from spinal cord. These are called spinal nerves. In frog, there are 10 pairs of cranial nerves and 9 or 10 pairs of spinal nerves.
Basically, nerves are of three types:
Sensory Nerves
These take messages from sensory organs to CNS.
Motor Nerves
These take messages from CNS to glands and muscles.
Mixed Nerves
These do both above mentioned functions.
Cranial Nerves
In these nerves, first, second and eight pairs are sensory nerves which are associated with senses of smell, sight and hearing. Third, fourth and sixth pairs are motor nerves which carry message from brain to the eye. Nine and ten pairs are mixed nerves, which are supplied to jaw, face, tongue and heart.
Spinal Nerves
These are all mixed nerves. These control functions of different organs.
Ear of Frog
The organ of hearing in frog is “Ear” like other vertebrates.
Structure of Ear of Frog
The ear of frog consists of following three parts.
1. External Ear
2. Middle Ear
3. Internal Ear
1. External Ear
External ear consists of a bone. The vibration is produced in external ear when sound waves strike with it.
2. Middle Ear
Middle Ear consists of a tympanic membrane. On the inner side of the membrane is a cavity known as tympanic cavity. The cavity contains small rod like bones called ossicles. The middle ear is connected to internal ear by a tube which is called Eustachian tube; it transfers the vibrations towards the internal ear.
3. Internal Ear
The internal ear is a very delicate organ. It consist of three semi circular canals. These canals are filled with a fluid and sensory cells are located at special places in these canals.
Function of Ear of Frog
When sound waves strike the tympanic membrane, it is set into vibration, this is in turn vibrates the internal ear and thus sound waves stimulate the hearing receptors in the inner ear. The internal ear, in addition to hearing also keeps the balance of the body.
Eye of Frog
The frog has two eyes one on each side of the head. If we make vertical section of the eye, we find that the innermost layer of the ball is the sensory retina. The retina contains photoreceptor cells. Outside the retina is the choroid, which is richly supplied with blood capillaries supplying nutrients to the retina. The sclerotic is the hard, outer most layer of the eye. It provides shape to the eye ball. The anterior transparent part of the eye is called cornea. Behind the cornea is Iris. The Iris has a window called the pupil. Behind the pupil is the lens of the eye. The cornea, pupil and lens focus light on the retina. A watery fluid is present in between the cornea and lens. Similarly a jelly like fluid is present between the lens and retina, through which light passes before it strikes retina. Optic nerve takes the sensory messages from the eye to the brain.




Classification of Living Organisms

Classification The arrangement of organisms into groups and subgroups on the basis of similar characters is called classification.
Basis of Classification
The classification of organisms is based on such features or characters, which are similar in one kind of organisms and different in different kind of organisms. These characters may be about internal morphology, (anatomy), external morphology, physiology, cell structure, especially the number of chromosomes and chemical composition (especially of proteins) and embryology of the organisms. These characters help in study of intra specific (within the same species) and intra specific (between different) species differences.
The presence of similar characters in different organisms indicates their common ancestory. This similarity because of common ancestral origin is called Homology e.g. arm of a monkey, flipper of a whale and wing of a bat show homology. They are dissimilar apparently but their internal structure (arrangement of bones and muscles) is same. These organs are called homologous organs. Due to this homology, we can, say that monkey, whale and bad had common ancestors and are placed in same large group “vertebrate”. This homology is proved to be very helpful in classification.
Aims/Objectives of Classification
These are given below:
1. To determine similarities and differences between different organisms.
2. To arrange organisms on the basis of similarities and differences.
3. To identify the organisms on the basis of their structure and other prominent characters and study them systematically and logically.
4. To find out inter-relationships of organisms.
First of all, Aristotle classified the organisms on the basis of their resemblances. After this, Theophrastus classified the plants. Then, after a long time, Carolous Linnaeus (1707-1778), suggested a new system of classification. In this way, he started modem taxonomy.
Units of Classification
The basic unit of classification is specie (Plural specie). A species is a group of organisms that can breed with one another in nature and produce fertile offspring. All members of a species have same number of chromosomes and also have many other features in common. All the mustard plants belong to one species. All the human beings belong to another species. The members of one species differ from members of other species and do not breed naturally with each other. Such different species, which are closely related, they are grouped in large group called genus (plural; genera) e.g. Brassica is a genus. It includes several species like mustard, cabbage and turnip. Similarly, Felis is a genus. It includes several species like lion, tiger and cat. Similarly, many closely related genera are placed in a bigger group called Family, families are grouped into an order, orders are grouped into a class and classes are grouped into a phylum (plural, phyla) or division (plural; division) in case of plants. The phyla or divisions are grouped into kingdom. All these units are divided into subunits e.g. sub genus, sub phylum and sub kingdom etc. The smallest the group or unit, the organisms found in this group, would be more similar, they have more number of of similar character.
Difference between Homologous and Analogous Organisms
The fruit of all plants, whether sweet, or sour, small and dry or large and fleshy, all are the homologous structures because they develop from ovary of flower. Their origin is common. On the other hand, wings of an insect, and a bird, despite having same function, are not homologous because their origin is different. Similarly green leaf of moss plant and that of any vascular plant are not homologous. These organs are similar in function but different in basic structure and origins are called analogous organs.
Biological Classification of Mustard Plant
Common Name —————– Mustard
Phylum or Division ———- Anthophyta
Class ———————– Dictyledonae
Order ———————– Capparales
Family ———————- Brassicaceae
Genus ———————– Brassica
Species ——————— Brassica Campestris
Classification of Human Beings
Common Name —————- Human
Kingdom ——————– Animalia
Phylum ——————— Chordata
Class ———————- Mammalia
Order ———————- Primates
Family ——————— Hominidae
Genus ———————- Homo
Species ——————– Homo sapiens
Scientific Name ———— Homo sapiens
Kingdoms of Organisms
The classification is not static, nor has only one system of classification been followed rather it is dynamic. Whenever any new knowledge is available about organisms, it is used in classification. Therefore, many systems of classification have been used. Living organisms are classified into two to five kingdoms.
Two Kingdom Systems
All organisms were classified into two kingdoms before present time.
1. Plant Kingdom (Plantae) – It includes all the small and large plants.
2. Animal Kingdom (Animals) – It includes all the animals.
Important Characters of Plants and Animals
Presence of cell wall and ability to prepare their own food were considered the most important characters of plants.
Lack of cell wall and inability to prepare food and characteristic mode of nutrition and especially the ability to locomote were considered the most important characters of animals.
Plant kingdom and animal kingdom were divided into large groups.
Binomial Nomenclature
The method of giving scientific names to organisms is called nomenclature. Same animal or same plants may be known by different names. It must have one scientific name so that there may be no confusion. To give such names to living organisms, the method was formulated by carolous Linnaeous (1753). This method is called Binomial Nomenclature. Because tis system is simple and comprehensive, so it is accepted and used in whole world.
Rules of Binomial Nomenclature
1. According to this method, every species of living organisms is given a Latinized scientific name consisting of two parts.
2. The first part is the name of genus and is called generic name. It starts with a capital letter.
3. The second part is the name of species and is called specific name. It starts with a small letter.
4. Both parts of scientific name of a species are either underlined separately or italicized.
The scientific name of mustard plant is Brassica campestris. The scientific name of rose plant is Rose indica. Similarly the scientific name of frog is Rana tigrina and that of human is Homo sapiens.
Significance of Binomial Nomenclature
Before establishment of binomial nomenclature, the names of organisms consisted of many words. These words were based on the characters of these plants or animals. In different countries, even in different parts of same country; local names were used for plants and animals. The same organism may be given different names e.g. turnip, shaljam, gongloo, thipar, and gogroon are all names of same plant. In England, there are at least fifty names for pansy. Similarly a single common name may be used for different kind of organisms e.g. the word “raspberry” is used for about 100 kinds of plants. This confusion can be avoided by giving each organism a scientific name according to binomial nomenclature proposed by Carolous Linnaeus in 1753. It is adopted by all taxonomists.
Biological Classification of Man
Common Name —————– Man
Kingdom ——————— Animalia
Phylum ———————- Chordata
Class ———————– Mammalia
Order ———————– Primates
Family ———————- Hominidae
Genus ———————– Homo
Species ——————— Homo sapiens
Biological Classification of Frog
Common Name —————– Frog
Kingdom ——————— Animalia
Phylum ———————- Chordata
Class ———————– Amphibia
Order ———————– Salientia (Anura)
Family ———————- Ranidae
Species ——————— Rana tigrina





Virus, Bacteria and Cyano Bacteria

Micro-Organisms A large number of living things are present in this world. Some of them are large and some are small. Majority of the organisms are so small that they re not seen with naked eyes. For their observation, we need a light microscope or even an electron microscope. These microscopic organisms are called micro-organisms.
Micro-organisms As a Heterogeneous Group
Micro-organisms are a heterogeneous group. It includes different kinds of organism viruses, bacteria, cyanobacteria, protozoa, certain algae and some fungi. On the basis of structure they range from sub-cellular to cellular for example, viruses are sub-cellular and all other micro-organisms are cellular. Bacteria, and cyanobacteria are prokaryotes (without nucleus) where as algae, fungi and protozoa are eukaryotes (with nucleus). On the basis of mode of nutrition algae are autotrophic while fungi and protozoa are heterotrohic. Therefore, micro-organisms differ in their structure and mode of characteristics of viruses, they are studied in a separate group where as bacteria and cyanobacteria, being prokaryotes, are included in kingdom Monera.
1. Virus is a Latin word which means “Poison”. Viruses are so small that they can only be seen with electron microscope.
2. Viruses have charcteristics of both living and non-living things.
3. Structurally they are not like, cell and are only made up of proteins and nucleic acids.
4. When they enter the body of any living organisms, they reproduce there like living organism.
5. They look like non-living crystals when they are out of the body of a living organism.
6. That is why they are placed between living and non-living things.
7. All viruses are parasites and cause different diseases in their hosts.
8. Viruses were discovered by Iwanowsky in 1892 from infected tobacco leaves. In 1935 W.M. Stanley isolated viruses in crystalline form from infected leaves of tobacco and observed them under electron microscope.
Size of Virus
Viruses are of different sizes. Their size varies from 0.01um to 0.03um(um is micrometer = 1/10,00,000 meter)
Shape of Virus
Viruses are of different shapes some are rounded, few are rod shaped, few polyhedral while some viruses look like tadpoles.
Structure of Virus
Viruses have same biochemical nature. In spite of their different shapes, they are made up of only two parts, an outer “coat”, and an inner “core”. The core is made up of DNA or RNA (never both) and the coat is made of protein. The outer protein coat determines the shape of viruses. e.g. in bacteriophage (virus that lives in bacteria) protein coat consists of two parts, head and tail. DNA is present in the head region but the tail has only protein. Most of the animal viruses contain DNA whereas plant viruses have RNA core bacteriophage is also called phage virus.
Viral Diseases in Plants
Ring spot in different plants, yellow in sugar beet and mosaic disease in tobacco, potato, tomato, bean and cabbage are the various diseases of plants, caused by viruses.
Viral Diseases in Animals
Mouth and foot disease in cattle and cowpox in horses, buffalo and cows are caused by viruses.
Viral Diseases in Humans
In human beings, viruses produce common cold, influenza, small pox, yellow fever, polio, infectious hepatitis, cancer and AIDS.
Ways of Viral Transmission
1. Through droplets produced during coughing and sneezing.
2. Through contact.
3. By air, contaminated water and food.
4. Through insects.
5. By reuse of already used syringes.
6. By un-sterilized surgery equipments.
Bacteria are found every where in air, water, living and dead bodies of organisms and even in glaciers and hot springs. These are unicellular micro-organisms.
Discovery of Bacteria
Leeuwenhoek discovered bacteria in 1697 for the first time. Later, Louis Pasteur and Robert Koch worked on them. They discovered that bacteria produce many diseases in men and animals.
Size of Bacteria
Bacteria (singular : bacterium) range from 1um to 10um in length and from 0.2um to 1um in width and can be observed under light microscope.
Types of Bacteria
On the basis of shape and form, bacteria are of four types. These are as follows:
1. Rounded – Cocci (singular; coccus)
2. Rod-like – Bacilli (singular; bacillus)
3. Spiral shaped – Spirilla (singular; spirillum)
4. Comma like – Vibrios (singular; vibrio)
Bacteria occur both singly and in colonies. Cocci bacteria are found in groups of two or four, or in irregular groups and even in the form of long beads. Baccilli are found singly or may join end to end to form long threads. But Spirilla and Vibrios occur singly.
Structure of Bacteria
1. Bacteria are single celled prokaryotic organisms.
2. Bacterial cell is surrounded by a cell wall which is made of carbohydrates and amino acids.
3. Some bacteria have an additional slime capsule around their cell wall, which protects them and prevents them from drying.
4. Ribosomes help in synthesis of proteins. Nucleus is absent in bacterium. However, only a single large circular molecule of DNA is present which is surrounded by a clear zone of cytoplasm. It is known as nucleoid. This is not bounded by a nuclear membrane.
5. In addition to main bacterial DNA small, circular molecules of DNA called plasmids are also found. Plasmids play an important role in transmission of some heredity characteristics. Plasmids are also used a vectors in genetic engineering.
6. Motile (which can move) bacteria like bacilli are spirilla have one or more thread like flagella (singular; flagellum) which help them in their locomotion. Non motile bacteria like cocci lack flagella.
Economic Importance of Bacteria
It is generally thought that bacteria are fatal and harmful organisms and there is no beneficial aspect. But this is wrong impression. There are number of bacteria which are not only beneficial for mankind but are also essential for living system. Bacteria play very important role in the life of living organisms.
Beneficial Bacteria
Ecological Importance
These, along with fungi, help to decompose dead organisms and their refuse into simpler substances replenishing the raw materials in the soil and atmosphere and can thus purify the environment.
Bacteria and Nitrogenous Compounds in Soil
These bacteria are called nitrogen fixing bacteria. Another kind of bacteria live in the soil, called nitrifying bacteria which convert ammonia into nitrite and then to nitrate, enhancing the amount of nitrogen in the soil. In this way fertility of soil is increased.
Industrial and Commercial Purposes
1. These are used in manufacturing butter, cheese and yogurt.
2. These are used in processing of commercial fibers, leather, coffee, tobacco and vinegar.
Bacteria Synthesize Enzymes
Bacteria synthesize cellulose enzyme in the stomach of herbivore animals which helps in the digestion of food. Some bacteria also synthesize vitamin “B” and “K” in the large intestine of man and other mammals.
Bacteria as Bio-Insecticides
Recently the use of bacteria in bio-insecticides has become popular.
Harmful Bacteria
1. Bacterial decomposition on one hand is beneficial but on other hand causes damage to food, wood, clothes and other things.
2. Denitrifying bacteria in soil decrease the amount of nitrogen in soil and reduce the soil fertility. These are called identifying bacteria.
3. Many bacteria are harmful and cause many diseases in plants, such as canker disease in citrus fruits, rot and fire blight in peach, pear and apple, and potato scab in potato.
4. In animal like cattle bacteria cause T.B and anthrax. Bacteria also cause many diseases in man like T.B, Whooping Cough, Diphtheria, Typhoid, Pneumonia, Tetanus, Plague, Bacterial Dysentery, Cholera, Leprosy etc.
Ways of Bacteria Transmission
1. Whooping cough, Diphtheria, T.B and Pneumonia causing bacteria are transmitted from one person to other person through sneezes and cough droplets released in air.
2. Bacteria causing Typhoid and Cholera, are transmitted from one organism to another through contaminated water and food.
3. Plague and bacterial dysentery read through vectors like flies and animals.
1. Cyanobacteria are also called blue green algae. They are simplest living organisms which have the ability to manufacture their own food by photosynthesis.
2. Structurally they resemble bacteria. Bacteria and Cyanobacteria are prokaryotes and they are placed in kingdom Monera.
3. Generally Cyanobacteria are found in moist places like of trees, rocks and soil, fresh water and oceans.
4. Some of them are symbionts and some are epiphytes.
5. Cyanobacteria are usually unicellular and solitary.
A common example of cyanobacteria which has filamentous structure which is found in the form a ball is called Nostoc.
Characteristics of Nostoc
The important characteristics of Nostoc are:
1. It has a filamentous structure which form a ball like structure of Nostoc.
2. It floats on water.
3. Each filament of Nostoc is unbranched and has a single row of rounded or oval cells.
4. Each cell of Nostoc has double layered wall.
5. The protoplasm is differentiated into two parts.
6. Endoplasmic reticulum, mitochondria, golgi bodies and vacuoles are not present in the structure of Nostoc.
7. Heterocyst are found which help in nitrogen fixation.
8. Nostoc is an autotroph like other Blue-green-Algae.
Taxonomic Position of Nostoc
According to new classification, Nostoc belongs to kingdom prokaryota or Monera.
Structure of Nostoc
The structure of Nostoc is filamentous. The filaments are interring mixed in agelatinuous mass forming a ball like structure. It floats on water. A single filament looks like a chain of beads. Each filament is unbranched and has a row of rounded or oval cells




Fungi and Algae


During rainy season, a large number of umbrella-shaped mushrooms emerge on dung-piles. Fluffy mass of tangled threads like structure with black-dots of molds is also often seen growing on orages and bread, these mushrooms and molds are fungi.
Characteristics of Fungi
1. Fungi are simple heterotrophic eukaryotes which cannot manufacture their food and have absorptive mode of nutrition (e.g. absorbed prepared food).
2. Cell wall is made up of Chitin instead of cellulose.
3. Some fungi are parasitic while others are saprotrophs.
4. Parasitic fungi obtain their food from other living organisms.
5. Saprotrophic fungi get their food from dead animals, plants, their wastes and decaying materials.
Economic Importance of Fungi
Fungi are useful as well as harmful to humans. e.g.
Useful Aspects of Fungi
Saprotrophic Fungi
Saprotrophic fungi chemically break down dead bodies of organisms and their wastes into simple components. They clean the environment and also cause the recycling of nutrients.
Mycorrhizal Fungi
Mycorrhizal fungi improve the growth production of crop plants.
Edible Fungi
Mushrooms and some other fungi are edible.
Some antibiotics are also obtained from some fungi. For example, Penicillin, the first antibiotic discovered in 1928 by Alexander Flemming. Penicillin is obtained from the fungus penicillium.
Yeasts are used in making bread and alcohol.
1. During rainy season, a large number of umbrella like mushrooms emerge on dung piles.
2. Mycelium of mushroom is saprotrophic, spreading under group in the soil that contains, decaying and organic matter.
3. When spores are to be formed, many hyphae of mycelium come out of the soil to form umbrella shaped fruit bod, the familiar mushroom. It can be 3,4 inches in height.
4. Fruid body consists of two main parts; a lower stalk or stripe, and an upper umbrella shaped cap or pilens which bears annulus around it just below the cap.
5. On maturation, many radial plates or gills are seen on the underside of the cap on which enormous numbers of spores are produced.
6. Some mushrooms, like Agaricus, can be used as food before their fruit bodies become overripe. Agaricus is rich in protein. Some mushrooms, like Amanita, are deadly poisonous.
Algae are a group of simple eukaryotes in which, like plants, chlorophyll is found. They are photosynthetic autotrophs and have cellulose in their cell wall. However unlike plants but ike fungi, their organs are unicellular and body is simple, thallus. Therefore they are placed in another kingdom, the Protista.
Algae, are mostly (found in water). A large number of algae are found in vast saltwater oceans. These are called marine algae, other are found in lakes, ponds, puddles, streams and rivers. These are called fresh water algae. Some marine algae, called the helps and grow as long as 60 meters or more in a season. Some of them are used as food.
Characteristics of Algae
1. All the algae have chlorophyll so they are autotrophic; they make their own food by photosynthesis.
2. Their cell walls are made up of cellulose.
3. Algae are mostly marine found in the sea. While others are found in fresh water lakes, ponds, puddles, streams and rivers and they are also found in damp soil.
4. Their plant body is called a thallus without a true root, stem or leaf.
5. Algae are sometimes classified on the basis of the pigments they contain. Their green colour can be masked by the presence of other pigments.
6. Their reserved food material is starch.
7. Algae have a wide variety from unicellular algae, e.g. chlamydomanas and spirogyra to multicellular large seaweeds like sargassum.
8. Previously algae were regarded as plants and were placed in thallophyta.
It is fresh water green alga, commonly found in fresh pond and drains. It is single celled green algae which are seen only under a microscope.
1. Chlamydomonas is spherical, oval or pear-shaped.
2. The cell is enclosed by a cell wall which maintains its shape.
3. In the anterior part, the cell wall forms an outgrowth called apical papilla.
4. Two flagella (singular flagellum) arise from the cytomplasm below the apical papilla and come out through the cell wall. These help in swimming.
5. A thin cell membrane lies beneath the cell wall, it represents the ourter surface of cytoplasm.
6. In cytoplasm, there is, a cup shaped chloroplast, which is involved in production of food by process of photosynthesis.
7. The chloroplast contains, a spherical structure called pyrenoid in its posterior part, and a single red orange light-sensitive eye-spot on one side in its anterior regions.
8. The pyrenoid is supposed to store carbohydrates in the form of starch grains.
9. The eye spot helps chlamydomonas to determine its position nd direction according to changes in the intensity of light.
10. There are two contractile vacuoles near the base of flagella ‘which periodically expel excess water and waste from the cell.
11. A nucleus is present in the middle of chloroplast in the cytoplasm.
12. Although body, of chlamydomonas consists of a single cell, yet it performs all the basic functions of life. It reproduces both sex and asexual.
1. Spirogyra is a multicultural filamentous green alga. It is found in great abundance in fresh water ponds, lakes and streams. Its filamentous thallus consists of cylindrical cells.
2. These cells are joined end to end, to form un-branched filaments. Usually the filaments are found occurring in a large number.
3. The filaments are surrounded by a layer of mucilage that makes them slippery.
4. During day time, the oxygen produced during photosynthesis stores in the mucilage and the filaments start floating on the surface of water.
5. Each cell of Spirogyra is usually twice as long as broad.
6. The cell is surrounded by cellulosic cell wall. A peripheral layer of cytoplsm is present just inside the cell wall and around a large, central vacuole.
7. The vacuole is filled with cell sap.
8. A single nucleus is suspended near the vacuole by cytoplasmic strand.
9. The most prominent part of cell is its chloroplast. There may be one ore more than one chlrorplasts in each cell. The chloroplasts run along the; length of the cell in the form of spiral ribbon in the peripheral cytoplasm.
10. Numerous pyrenoids are located in a row in the chloroplast and are meant for storing starch. Spirogyra continually grows in length by cell division.
11. Each cell can be divide into two, so filament increases in length. The Spirogyra reproduces both sexually and asexually.




Bryophytes and Tracheophytes

Bryophytes Bryophytes are on of the two main groups of kingdom ‘Plantae’ the second being the ‘tracheophytes’. Bryophytes is a group of plants which are multicellular, photosynthetic eukaryotes; and their reproductive organs are multicellular; their zygote develops into small, protected embryo that develops into a complete new hence bryophytes have also been called embryophytes. The cell of these plants is made up to cellulose.
Characteristics of Bryophytes
The important characteristics of Bryophytes are as follows:
1. Bryophytes are plants without vascular tissue (xylem a phloem), whereas tracheophytes have vascular tissue. Therefore tracheophytes are vascular plants, whereas bryophytes are non-vascular plants.
2. Bryophytes are the simplest land plants. Bryophytes divided into three groups. Liverworts, hornworts, and mosses.
3. Marchantia is an example of liverworts; its plant body is a thick branched green thallus.
4. Anthoceros is a horn wort, and Funaria is a moss.
5. All bryophytes and generally found growing in moist habitants such as damp soil and rocks, moist brick walls, and along the banks of streams.
Life Cycle of Funaria Moss
It is a common moss found grwoing t moist places. Green leafy, moss plant of Furania, as like all Bryophytes, Funaria is haploid gametophyte, its height is about 0.5 – 1 inch.
Gamatophyte Generation
It consists of 3 parts:
1. A vertical stem like structure.
2. Leaf like photosynthetic structures arranged on the stem, which are composed of a single layer of cells, and without stalk.
3. Numerous multicellular rhizoids, arising from the lower side of the stem and which absorb water and salts, and anchor the plant to the soil.
Male sex organs, called antheridia (singular antheridium) are located at the tip of male branch, and the female sex organs, called archegonia (singular archegonium) are located at the tip of female branch.
Fertilization takes place in the presence of water within the archegonium located at the tip of female branch. The zygote develops into the embryo (2n). The embryo forms the sporophyte (2n). The sporophyte remains attached to the tip of female branch. The sporophyte gets water, slts and also part of its food, from the parent gametophyte plant.
Sporophyte Generation
The sporophyte consists of three parts:
1. A foot
2. A long stalk like seta
3. Capsule
The foot is anchored to the female branch and absorbs nutrients from the gametophyte. The seta elevates the capsule in the air. Within the capsule, haploid spores are produced by meiosis. The spores are dispersed by wind. Each spore develops eventually into new haploid gametophyte plant, and the life cycle continues.
Like other bryophytes, Funaria also has well defined alteration of generations; haploid gametophyte generation is dominant, whereas diploid sporophyte is attached to and more or less dependent on the gametophyte.
1. Unlike bryophytes the plant body in Pteridophytes is differentiated into root, stem and leaves.
2. In contrast to other vscular plants Pteridophytes do not bear flowers, fruits and seeds.
3. Due to presence of vascular tissues, they are similar to gymnosperms and angiosperms.
4. Although the dominant generation in Pteridophytes is also the sporophyte but unlike gymnosperms and angiosperms both sporophyte and gametophyte generations are independent and free living. However, the gametophyte in much reduced and smaller in size.
Seed plants or Spermatophytes are that group of vascular plants which produce seeds. Seed is a ripened ovule. It contains a young plant with embryonic root, stem and one or more leaves, which has stored food material and is protected by a resistant seed coat or testa.
Spermatophytes like pteridophytes possess vascular tissues. They also have life cycles with alternation of generations. Unlike bryophytes and pteridophytes, spermatophytes do not have free living gametophyte; instead the gametophyte is attached to and nutritionally dependend upon the sporophyte generation.
Main Groups of Spermatophytes
They produce seeds which are totally exposed or borne on the scales of cones.
They are flowering plants which produce their seeds within a fruit.
Pinus and Thuja – The Typical Gymnosperm
Pinus is normally grows at an altitude of 5000 ft to 8000 ft. It has many types e.g. chir, kail, chilghoza etc. However, some species are found in the plains. It is also grown as ornamental plants. Pinus tree is a sporophyte, which is evergreen and quite tall. It consists of an extensive root system and a strong, stout and woody stem and its branches. The upper branches progressively become shorter in length. In this way, the tree assumes a symmetrical conical shape.
Thuja (common known as Mor Pankh) is a short tree. It has profuse branches, which are covered with small, dark green scale leaves. It is conical in appearance. It is grown as ornamental plant in parks and homes.
Leaves of Thuja
Thuja has small scale like green leaves that cover the stem.
Female Cone of Thuja
In Thuja the female cones are spherical or oval in shape. These are about the size of a bair (berry). They consist of hard, brown colour scales with triangular apices.
Pinus has two types of shoots.
Shoots of Pinus
Long Shoots or Shoots of Unlimited Growth
They are formed on the main stem and continue growth indefinitely by buds borne at their apices. They are covered by scale leaves.
Dwarf Shoots or Shoots of Limited Growth
These shoots originate in the axils of the scale leaves on the long shoots. They are very short (only a few millimeters in length). Each dwarf shoot bears 1 t 5 foliage leaves in addition to scales leaves.
Leaves of Pinus
Scale Leaves
These are small, membranous and brown in colour. They cover the stem.
Foliage Leaves or Needles
These are commonly long and narrow, tough, and leathery. In contrast to scale leaves they are green and photosynthetic. Depending upon the type of species, a cluster of 2 to 5 needles is produced on each dwarf shoot. Each dwarf shoot with its cluster of needles is called a spur.
Reproduction in Pinus
Pinus tree produces reproductive structures known as cones every year. Cones are of two types, male and female c9ones. Both male and female cones are produced on the same tree but on different branches.
Male Cone of Pinus
Male cones, usually 1 cm or less in length, are much smaller than the female cones. They are produced in clusters. These are generally born on the lower branches of the tree. Each male cone is composed of spirally arranged leaf-like structures called scales or microsporophylls. Each microsporophyll has two long sacs called pollen sacs of microsporangia on it are under surface. Asexual reproductive cells, microspores or pollen grains are produced by meiosis in the microsporangia. Pollen grains are haploid. After being transferred to the ovule, the pollen grain forms pollen tube. It is the male gametophyte in which male gametes or sperms are produced.
Female Cone of Pinus
The female cones are much larger than the male cones. These are usually found on the upper branches. Each female cone is also made of spirally arranged scales which are called megasporophylls. These scales become woody on maturity. Two ovules are present side by side at the base of each scale. Haploid megaspores are formed in the ovule by meiosis. Measpores give rise to female gametophytes which produce female gametes. Fertilization results in the formation of embryo after which the ovule is ripened to form seed. Female cones normally remain attached for three years on the plant. On maturity the cones open up and the seeds are set free and dispersed.
Angiosperms are the flowering plants which are most successful plants. They are more important than the gymnosperms. They have adapted to almost every type of environment. There are about at least 235,000 species. They are dominant plants. Angiosperms are vascular plants which bear flowers. Their seeds are produced within fruits. The fruit protects the developing seeds and also helps in their dispersal. Seed and fruit producing habit have helped flowering plants in their evolutionary success.
Angiosperms are found in wide variety of sizes and forms. Ensize they range from over 300 ft in height (some species of Eucalyptus) to searcely 1mm in length (duckweed, Woiffia).
On the basis of size and woody texture, angiosperms are classified as herbs, shrubs (bushes) and trees. Herbs are the plants which are small in size. Their stems are Herbs which are then cut or pulled from the soil. In contrast shrubs and trees have hard woody stems, which retain their shape even after being cut. Shrubs are shorter than trees but have more branches. In addition to tracheids, angiosperms have efficient water conducting structures known as vessels in their xylem.
Classes of Angiosperms
On the basis of the number of cotyledons in the seed, angiosperms are divided, into two classes.
1. Monocotyledons or Monocots
2. Dicotyledons or Dicots
1. Monocot seeds have only one cotyledon or embryonic leaf.
2. A nutritive tissue called “endosperm” is usually present in the mature seed.
3. Monocots are mostly herbs with long narrow leaves.
4. Leaves have parallel veins i.e. in the lamina of the leaf veins run parallel to one another.
5. The floral parts of most flow3ers usually occur in threes or multiples of three (i.e. 3, 6, 9 …)
6. Monocots include different grasses, cereals (wheat rice, maize etc) ,palms, onions and lilies.
1. Dicot seeds have two cotyledons.
2. In mature seed, te endosperms is usually absent.
3. Their leaves vary in shape but usually are broader than monocot leaves.
4. Leaves have reticulate veins i.e. branched veins resembling a net. The flower parts are four or five in number or multiples of 4 or 5.
5. Dicots include rose, peas and pulses, sheesham, Kiikar (Acacia), sarsoon (mustard), cacti, mango, orange and sunflower etc.





Protozoa 1. According to two-kingdom classification, protozoa are the first phylum of invertebrate animals but according to five kingdom classification it is placed in a separate kingdom, “protista” in which all other eukaryotic unicellular organisms are also placed.
2. Body of all protozoans consists of one cell and istherefore called unicellular.
3. They are so small in size that they cannot be seen with naked eye. They can be seen with the help of a microscope.
4. They are unicellular but they intake food, respire, reproduce.
5. Protozoans mostly live in damp, watery places. Their habitat is mostly moist soil, decaying matter of animals and plants. Most of them live singly but some form colonies. In a colony, unicellular organisms become partially interdependent and limit themselves to perform specific functions in a group. If separated from group they still can perform all life activities and can live independently.
6. Some protozoans are parasites and causes different diseases e.g. a type of Amoeba causes dysentery, plasmodium causes malaria.
7. Protozoans are also useful for man because they feed and destroy bacteria which are harmful for human health, for example Amoeba can feed on bacteria.
It is unicellular animal which is found in pools and ponds. It is slipper shaped its body is covered with cilia. Cilia are small hair like out structures arising from protoplasm. Their lashing movement in water acts as oars and help in swimming (locomotion) of the animal. Paramecium feed on algae. Bacteria and other small protozoans, through an oral groove provided with cilia. Cilia push food inside the protoplasm through a canal called gullet making a food vacuole in the protoplasm. There are two contractile vacuoles, one at each end of the body for discharging surplus water there are two nuclei one large, mega nucleus which controls almost all functions of cell other small, micro or reproductive nucleus which controls reproduction. Many protozoa like Amoeba and Paramecium are unicellular but they respond to the intensity of light like all other multicellular organisms. They can detect high intensity of light and move towards the area having low intensity of light.
Phylum Porifera
1. This phylum is called porifera because animals belonging to this phylum have numerous small pores on their bodies.
2. They are also called sponges.
3. They are multicellular but they have no organs or true tissues.
4. Every cell performs its all function.
5. Sponges are aquatic animals. Most of them are found in sea water but some live in fresh water.
6. Sponges have different colours.
7. Green colour of sponge is due to algae that live in their body. Algae produce oxygen during photosynthesis which is used by sponges and the sponges release carbondioxide, which is used by algae for photosynthesis. This association in which both the organisms benefit from each other is called mutualism.
Phylum Cnidaria
1. Animals belonging to this phylum have a special cavity in their body which is called coelenteron and due to this reason they are called coelenterates.
2. They are diploblastic animals as their bodies have two layers of cells. Outer layer is called ectoderm and inner layer is called endoderm. Between these layers a jelly like substance the mesoglea is present.
3. Coelentrates are aquatic animals. They are mostly marine but few live in fresh water.
4. Most of the animals of this phylum can move freely but a few remain attached to stones or rocks throughout their life.
5. Hydra, Jellyfish and Sea anemone are common examples of this phylum.
Phylum Platyhelminthes
They are triploblastic animals because their body is made of three layers, an outer ectoderm, a middle mesoderm and an inner endoderm layer. They are also called flat worms because their body is thin, flattened and tape like. Some animals are free living but most are parasite. Parasites live in liver, stomach and intestine of other animals. They attach themselves to the walls of intestine of their host by sucker and suck blood and food. Tape worm sucks food from intestine and sometimes grows up to 40 feet in length. Liver fluke, tape worm and planaria are common examples of this phylum.
Phylum Mollusca
1. This phylum is one of the largest phyla of animal kingdom. It has about fifty thousand species.
2. Mollusca are a latin word which means “soft”. Their body is soft so in most of the animals and external shell is present for support and protection.
3. Some animals have internal shell and some lack shell. They are also known as shell fish.
4. They are found in aquatic and moist habitat.
5. Most of Mollusca are used as human food.
6. Buttons are made from their shell.
7. The pearls are produced by these animals.
8. Their body is quite complicated.
9. They have a muscular foot for locomotion and gills for respiration.
10. Snails, Fresh water mussel, Cuttle fish, Octopus and Oyster are common examples of this phylum.
Phylum Arthropoda
1. The bodies of these animals are also segmented but these segments are external.
2. Their bodies are covered with the hard shell composed of chitin, forming an exoskeleton.
3. They have jointed legs on their body and therefore they are called arthropoda (arthro means jointed and poda means foot)
4. These animals are found in all habitats, in air, water and on land.
5. Common examples are Prawn, Crab, Spider, Scorpion, Centipede, Millipede and Insects.
Phylum Echinodermata
1. The animals of this phylum are exclusively marine.
2. They are called echinoderms because their bodies are covered with spines or spicules.
3. All animals have internal skeleton consisting of dermal caleareous ossicles.
4. They have a water vascular system and dermal gills.
5. These animals are considered to be closest to the chordates from evolutionary point of view, Sea star (known as star fish). Brittle star, Sea urchin and Sea cucumber are examples of this phylum.
Phylum Annelida
1. Animals in this group have elongated segmental body.
2. Annelids occur in water as well as on land.
3. They have well developed systems in their bodies.
4. They have close type circulatory system.
Phylum Nematode
1. Nematodes or round worms have long smooth cylindrical body which is pointed at both the ends.
2. The body is un-segmented.
3. Nematodes have a complete and one way digested tube.
4. They are free-living as well as parasites of animals, man and even plants




Chordata and Vertebrata

Characters of Class Pisces (fishes) 1. The class of fishes is called Pisces. They are aquatic vertebrates.
2. According to their size and shape, the fishes are of many kinds.
3. They have a head, a trunk and a tail.
4. The head and trunk are directly jointed together and neck absent.
5. Body of fish is flexible tapering at both ends and streamlined. This type of body helps in swimming.
6. They can swim with fins, which are attached to the trunk.
7. They body is covered with scales which remain moist by special type of secretion of body.
8. Breathing organs are gills which are present in the hollow spaces found on both sides of the head for exchange of gases i.e. oxygen and carbon dioxide.
9. Mouth has teeth, which is used for grasping instead of grinding of food.
10. In some fishes air pouch is present, which is called air bladder. The air bladder is used for buoyancy.
Class Amphibia
1. This group of animals can live both in water and on land.
2. They need water for reproduction. Therefore they are called Amphibians.
3. The skin is thin, moist and slimy.
4. Small teeth are present in the upper jaw which is only used for grasping the prey.
5. Breathing organs are two lungs. Skin is also used for the exchange of gases.
6. Eggs are laid in water or moist places and their outer shells are not hard.
7. They are cold blooded animals e.g. they cannot maintain their body temperature constant.
8. They become very slow and bury themselves in the mud. This process is called hibernation.
9. During the process of reproduction fertilized egg is changed into adult passing through a number of physical changes. This process is called metamorphosis.
10. The fertilized egg develops into larva. The larva of frog is called Tadpole. It has tail and gills. This larva later changes into adult.
Class Reptilia
The animals of this class are called reptiles. They have following features.
1. Most of the reptiles are terrestrial and only a few five in water.
2. They are also called crawlers.
3. They have thick, dry and rough skin.
4. The skin is covered with scales which originate from the ectoderm.
5. There are present lungs for respiration.
6. Teeth are present in their buccal cavity, which are used for cutting and biting.
7. The locomotary organs are legs but snakes and a few types of lizards have no legs.
8. Most of the lizards are not poisonous except members of the genus Heloderma which are found in American desert.
9. All the reptiles lay their eggs on land. Water dwelling reptiles e.g. turtle also lay their eggs on land.
10. Their eggs have a tough outer shell of calcium carbonate.
Class Aves
The animals included in this class are called Birds. Their distinguishing characters are as follows.
1. Birds have a single unique feature, which makes them different from other animals which is the presence of feathers. Their forelimbs are modified to form wings while hind limbs help in walking, wading and sitting on the branches.
2. All the birds have horny beaks without teeth.
3. All the birds lay eggs.
4. All the birds must have two wings for support and propulsion, strong but light and hollow bones.
5. Their digestive system is able to digest high caloric food.
6. They have a higher blood pressure and higher metabolic rate.
7. Nervous system and especially eye sight is very well developed so that they can track their path even at a very high speed.
8. They migrate during winters towards warmer places covering thousands of miles.
9. It is the most studied and most observable class in the world.
10. The birds are very beautiful and have melodious voices.
Types or Groups of Birds
Running Birds (Ratitae)
They have following characters:
1. They have flattened sternum.
2. Their pectoral muscles are weak.
3. Their examples are Ostrich, Emu, Rhea and Casso wary.
Flying Birds (Carinatae)
They have following characters:
1. A keel is present on sternum in these birds.
2. Keel is vertical bony part that is present below the sternum in the centre from anterior to posterior end.
3. Pectoral muscles are very strong, powerful and are inserted on the keel. These muscles help them to fly.
4. Their common examples are pigeon, hen, crow, kite etc.
Class Mammalia
All the animals included in this class are called “mammals”. These animals are highly advanced vertebrates. There are almost four thousand species of mammals including man.
Characteristics of Mammals
Their distinguishing characters are given below:
The body of mammals is covered with hair. In most of the mammals hair may cover the whole body but in a few may be restricted to some areas. The hair conserves heat of the body.
Their skin is provided with sweet glands, scent glands, sebaccous glands and mammary glands.
Two occipital condyles, secondary bony palate, three bones in middle ear and fused pelvic bones and seven cervical vertebrae are present in their skeleton.
External Ear
Fleshy external ears are present in mammals.
Moveable eyelids are present in mammals.
Two sets of teeth are present. Milk teeth are replaced by permanent set of teeth.
Brain is higly developed. It perform more functions than that of other vertebrates.
Cranial Nerves
Twelve pairs of cranial nerves are present.
Circulatory System
Circulatory system has four chambered heart, persistent left aorta and non-nucleated biconcave red blood corpuscles are present in female.
Sexes are separate i.e. there are two individuals, male and female.
Most of them have internal fertilization and fetus developed inside the uterus of female giving birth to their children.
Breast Feeding
They feed the children by milk from mammary glands.
They are endothermic i.e. they can maintain their body temperature according to the environment. It means that they are warm-blooded animals.
Egg Laying Mammals
These mammals lay eggs. Mostly two eggs are laid in one year. Fertilization of egg is internal i.e. inside the body of mother. Eggs are laid in burrows of animals. Young ones are hatched from the eggs. Mother feed their children with milk. Their egg laying character shows their relationship with reptiles. Duck bill platypus and Spiny ant eater are the examples of egg laying mammals.
Pouched Mammals or Marsupial Mammals
These mammals have a pouch outside the belly called marsupium, this is the reason that they are also known as Marsupial mammals.
1. Fertilization of eggs and development of embryo is internal.
2. The embryo is at first encapsulated by shell membrane and floats free for several days in the uterine fluid.
3. There is no placenta.
4. After hatching from the shell membranes, the embryo does not implant or “take root” in the uterus and absorb nutrient secretions from the vascularized yolk sac.
5. The gestation period is brief and the marsupials give birth to tiny young that is effectively still an embryo.
6. These young creeps into the marsupium where it gets milk from mother through nipple.
7. It lives in marsupium until it can take care of itself.
8. Examples are Kangaroo, Koala, Tasmanian wolf and Wombat etc. These are found in Australia and Tasmania, Opossum is found in America. It lives on trees.
Placental Mammals
This is common group of mammals in which embryo completes its development inside the mother’s uterus. After gestation period young ones are born. Embryo remains in the uterus and gets its nourishment from mother through umbilical cord and placenta. Gestation period of these mammals is longer than those of other mammals. Pregnancy is called Gestation Period. In man it is of 9th months.
In mice it is 21 days, in rabbit 30 to 36 days, in cats and dogs 60 days, in cattle 250 days and in elephants 22 months. It is lengthier in large mammals.
The conditions of young ones at time of birth are different in different mammals. For example in antelope, at the time of birth, the body of young is covered over, with heavy fur, eyes are open and it can walk about. In case of rat, young is very weak, eyes are closed and has no hair on the body.
Flora and Fauna of Pakistan
“Different types of plans present in a particular region constitute its flora.”
1. Hilly regions of Pakistan have snow fall and low temperature. These regions have thick forests where trees of Juniper (Sanober), Cedar, Chir, Chalghoza, Olive Apple, Plum Peach and Loqaut are very common.
2. Plain areas of Pakistan have fertile and less fertile soils. In areas where rainfall is low, desert environment is present in which Aeacia (Babool), Kikar, Ber, Pilas etc grow.
3. Fertile plains have trees of Sheesham, Bakain, Cane, Bamboo and Eucalyptus. These are source of timber whereas; fruit trees include mango, banana, Kino, Orange, Grapes, Jamman etc.
4. Plain and hilly areas have natural pasture lands that provide fodder for cattle.
5. In sea, rivers, ponds, canals and streams, algae are abundant, which on one hand are the source of food for aquatic animals and on the other hand they provide oxygen to atmosphere.
6. A large number of plants are used as ornamental plants. These include flowering plants like rose, motia, jasmine, lady of night, chrysanthemum etc.
7. Besides this wheat, maize, rice, oats, burley, grams garlic, onion, potatoes, carrots, cabbage and turnips etc are cultivated in plains and hilly areas to meet our food requirements.
“Different kinds of animals present in a particular region are known as its Fauna.”

1. In the seas adjoining our coastal areas numerous types of animals are found starting from protozoa to mammals. The most noticeable are octopus, mussels, star fish, sea urchins, crabs, prawns, fishes, amphibians, whale, dolphin etc.
2. Many animals are used as food e.g. prawns, crabs and fish etc. Our rivers are rich in fish life particularly Rohu, Khagga, Malhi, Trout, and carps are abundant and used as human food, as well as a source of earning lively hood.
3. Frogs and toads are abundant.
4. The tortoises, turtles, snakes, crocodiles are also common.
5. On the plains of Pakistan we have very rich wild life. There is a great diversity of land fauna starting from earthworms, almost all kinds of insects, spiders, myriapods, snails, slugs to toads, lizards, snakes and enormous variety of birds and mammals.
6. Some of the birds peculiar to Pakistan are Houbara bustard, partridge, pheasant, falcons etc.
7. The mammals peculiar to Pakistan include Black buck, Blue ball, Brown bear, Musk deer, Urial, Ibex, Asiatic ass.etc.
8. Most of the animals provide milk, meat, hide and wool. Some are used for transportation. Some of the animals are now endemgered species because of their excessive hunting and pollution.
The animals which do not change their body temperature with the change of temperature in environment are called as Warm Blooded Animals. Their body temperature remains constant.
Common examples of warm blooded animals are following.
(i) Parrot
(ii) Sparrow
(iii) Pigeon
(iv) Ostrich
(v) Kiwi
(vi) Duck billed platypus
(vii) Kangaro
(viii) Oppossum
(ix) Elephant
(x) Whale
(xi) Monkey
(xii) Man
The animals in which the body temperature is changed with the changes of temperature in the environment are called Cold Blooded Animals.
Common example of cold blooded animals are following.
(i) Shark
(ii) Labeo (Rohu)
(iii) Trout
(iv) Hilsa (Pullah Fish)
(v) Cat Fish (Khagga)
(vi) Frog
(vii) Toad
(viii) Snake
(ix) Wall-Lizard
(x) Crocodile





Food And Nutrition

Need for Food

Everything needs energy to do some job e.g. to operate machines, electricity, steam, fuels like coal, petrol, wood etc are burned to get energy. Similarly, living organisms require energy to carry out their diverse activities of life. They maintain the complex structure of cells, excrete waste material, and reproduce for continuation of their race. They grow in size during their life span as they are small when born and are large when adult. A considerable amount of energy is required to carry out the functions of life. The organisms, therefore, need to have some source of energy in order to maintain their life. Organisms get their energy from food. The type of food depends upon the kind of organism using the food. Some organisms use inorganic compounds to get their energy requirements. Some organisms use vegetables (plants) while some others require flesh (animals) as their food.
The organisms burn up their food (metabolize) to get a special form of energy called ATP (Adenosine triphosphate) which is used by them to carry out their functions of life.

Nutrients of Food and Their Importance

The food of organisms and the organic compounds, building their bodies are almost same. Their bodies are composed of carbohydrates, proteins and fats etc. These substances are used by organisms as their food. They get energy from these substances. They use the components of food in growth and repairing of damaged tissues. Thus substances acquired by organisms to obtain energy are called nutrients and the process by which they are obtained is called nutrition. The food of all organisms which depends upon already prepared food has been found to consist of six basic components. These are as follows:
1. Carbohydrates
2. Proteins
3. Fats, Oils
4. Vitamins
5. Minerals
6. Water


They are organic compounds. They are found in all organisms. They are commonly known as sugars. They contain three elements carbon, hydrogen and oxygen in which hydrogen and oxygen exists in 2:1 ratio that is why they are called hydrates of carbon or carbohydrates. One gram of carbohydrates provides 3800 calories of energy.
Forms of Carbohydrates
Carbohydrates occur in three forms.
1. Monosaccharide
2. Disaccharides
3. Polysaccharides
1. Monosaccharides
Monosaccharides are simple sugars. Their common example is glucose. Glucose is main source of energy in our body cells.
2. Disaccharides
Disaccharides are formed by condensation of two monosaccharide units e.g. sucrose is formed by the combination of glucose and fructose. Maltose is another disaccharide.
3. Polysaccharides
Why many monosaccharides link together, they form polysaccharides. A single polyusaccharide may have many hundred units of monosaccharides. The common examples of polysaccharides are glycogen and starch. Glycogen occurs in animals and starch in plants. Another polysaccharide is cellulose, present in the cell walls of plants. It is the most abundantly occurring carbohydrate.
Sources of Carbohydrates
Carbohydrates containing starch are obtained from cereals and their products like wheat, rice, maize, oats and barley. They are also obtained from carrots, radish, turnip, beet, beet root and potatoes. Simple sugar called glucose is obtained from grapes. The sugar derived from fruit is called fructose. Then from beet and sugar cane is called sucrose and that from milk is lactose.
Importance of Carbohydrates in Human Body
One gram carbohydrate food provides 3800 calories to our body. The Carbohydrates are the cheapest and easy source of energy. Surplus carbohydrates are stored as glycogen in the liver and muscles, or converted to fats and stored in the fat cells beneath the skin and causes obesity.
Children, laborers and people, involved in physical labor need more carbohydrates in their daily diet whereas other should avoid them because their excess in the body can cause blood pressure, diabetes, obesity and heart diseases, therefore, carbohydrate products should be taken with care.


Proteins are very important organic compounds found in all organisms. Proteins contain carbon, hydrogen, oxygen and nitrogen and sometimes some amount of sulphur. There is no 2:1 ratio between hydrogen and oxygen. A protein molecule is composed of many building units linked together to form a chain. A chain of amino acids is called polypeptide. Amino acids are building units of a protein molecule. About twenty different amino acids occur in nature that combines in different manners to make different type of proteins. Proteins are structural part of the cell membrane. Some proteins are fibrous. They form different structures in the body like muscles, bones and skin. They also occur in our blood and cells. The enzymes which control different chemical reactions in the body are also proteins in nature. As a result of protein catabolism, energy is released. One gram of protein produces 4.3 kilo cal of energy which is used to synthesize ATP.
Amino Acids
Plants can synthesize all the amino acids they need from carbohydrates, nitrates and sulphates but animals can not synthesize all amino acids. Amino acids are the building units of proteins.
There are about twenty different types of amino acids which are used in the synthesis of protein found in the human body.
Non-Essential Amino Acids
There are many amino acids which a human body can synthesize within the body. These are called non-essential amino acids.
Essential Amino Acids
There are approximately ten amino acids, which human beings cannot make. These are called essential amino acids and can be obtained directly from proteins in the diet.
Sources of Proteins
Following are the sources of proteins:
Animal Sources e.g. meat, fish, chicken, milk and cheese.
Plant Sources e.g. legumes, pulses, dry fruit and cereals.
Importance of Proteins in Human Body
1. Proteins are essentially required for growth and development.
2. Growing children ,pregnant women and lactating mothers need a lot of proteins.
3. An adult requires 50-100 gms of proteins daily.
4. Protein deficiency in children and cause a disease called Kwashiorkor.
5. Proteins play an important role in the building of cellular protoplasm.
6. They also play an important role in the building of muscles and connective tissues.
7. Many proteins are required for making enzymes, hormones and antibodies.
8. If proteins are eaten in excess than needed by body, the excessive amino acids are converted into carbohydrates by the liver, which are either oxidized to release energy and converted into glycogen and fat and stored.


Lipids are obtained from two sources:
Animal Sources
Ghee, butter, cream, animal fat and fish oil.
Plant Sources
Oils from mustard, olives, coconut, maize, soya beans, sunflower and peanuts.
Importance of Lipids
1. The use of fat rich products increase in winters because they provide double the amount of energy as compared to carbohydrates.
2. They provide 9000 cal/gm energy to the body.
3. In plants fats are stored in seeds, and in animals, they are found beneath the skin and around the kidneys where they are not only stored but also protect these parts.
4. They provide materials for building new protoplasm and cell membrane.
5. Some fatty acids are essential for man.
6. Saturated fats (animal fats) should be used with, great care in our diet as they lead to rise in the cholesterol level, which accumulates in the blood vessels, and thus affects the flow of blood in the arteries This can result in heart attack


Vitamins are very complicated compounds. When vitamins were discovered, their chemical nature was not well known. Therefore, they were denoted with English letters as A, B, C, D, E and K. Now it is known that vitamin B is not a single vitamin but a group of vitamins call ed as vitamin B complex. It has eight different compounds as B1, B2 etc although they have no energy value but they are essential in small quantities for the normal activities of life. It has been observed that when animals were given a diet rich in carbohydrates, fats and proteins but lacking vitamins, the growth and development of the organisms were affected and the animal suffered from various diseases. Vitamins are needed for healthy growth and development of the body. They also serve as enzyme.
Plants can prepare their vitamins from simple substances but animals obtain it directly or indirectly from plants. Fifteen or more vitamins have been isolated and most of them seem to act as essential part of coenzyme involved in chemical changes taking place in the body.
If our diet has variety and consists of fresh fruit and vegetables, our body will receive all those vitamins which are necessary for us.
Fat Soluble Vitamins
Some vitamins are fat-soluble and can be stored along with fat.
Water Soluble Vitamins
Some vitamins are water soluble and hence cannot be stored in the body, thus their in take is required continuously.


Mineral Salts
Mineral salts are inorganic compounds. They do not provide energy to the body. However, they are required for the normal chemical activities of the body. Man can obtain them from animals or plants which absorb them from the soil. Some minerals are needed by man and mammals in relatively large quantities, other are required in very small quantities.
Trace Elements
The mineral required by organisms in minute quantity are called Trace Elements.
Few Important Minerals
Calcium, Sodium, Potassium, Magnesium, Chlorine, Iron, Phosphorous and iodine etc.
Role of Minerals
Sodium Chloride
It helps to make hydrochloric acid in the stomach which is very important for the digestion of food. Along with potassium it helps to conduct messages through nerves.
It is found in the living cells especially in the red blood cells and muscles and it helps in the growth of the organism. The body acquires it through cereals.
It is an important component of the bones. It is obtained by eating different vegetables. It helps the enzymes which control different metabolic reaction.
It plays an important role in strengthening the bones and teeth. It helps in blood clotting, muscular contraction and in the conduction of nerve impulse. It is found in milk, eggs, fruit, cereals and green leafy vegetables.
It is very important mineral. It helps in making hemoglobin in the red blood cells. It occurs in meat, liver, eggs, peanuts, spinach and other vegetables.
It helps in the growth and development of the bones and teeth. If it is mixed in drinking water in suitable amounts, dental decay (caries) can be reduced in children. The body can obtain this mineral from vegetables and fish.
Note: In addition to these mineral trace elements like cobalt, manganese, zinc and copper are also necessary for the better health of the human body.

Role of Water

Water makes approximately 70% of the body tissues. It is an essential component of the protoplasm. One can live without food for more than a week but a person can die within two to three days due to lack of water.
Importance of Water
1. It plays an important role in digestion.
2. It helps in transport of digested food and other materials in dissolved form.
3. All the chemical reactions inside the cell take place in the presence of water.
4. It helps in excretion of urine, removal of faeces.
5. Enzymes become more active in solution form.
6. It keeps the blood thin and so that it can be easily circulated.
7. Water regulates the body temperature.
8. Its deficiency in tbe body causes dehydration, which can prove fatal.
9. Plants cannot photosynthesize without water.
10. The people living in hot and dry places need more water. By breathing, sweating and urination about 2-3 liters of water is lost per day.

Dietary Fibers

Dietary Fiber (Roughage)
These are foods which provide fibers to our body.
Sources of Dietary Fibers
All fruit and vegetables provide fibers to the body for example, citrus fruits, cereals, spinach, cabbage and salads. The cell wall in plant cells are largely made of cellulose which cannot be digested by man. Bacteria living in the gut of ruminants digest the cellulose and convert it into fatty acids, which renders it absorbable.
Importance of Dietary Fibers
1. Roughage adds bulk to the food enabling the muscles of the alimentary canal to grip it and keeps the food moving by peristalsis.
2. Absence of roughage in our diet may lead to constipation and related disorders.
3. Fibers keep the intestines in a healthy condition, thus our daily diet must contain a lot of fruit and vegetables

Nutrition and Food Technology

For thousands of years, man has been making efforts to grow more food for storage so that it can be used when needed. Modern man knows how to preserve food for use subsequently when needed. Man has adopted modern techniques of food preservation in which its nutritional value and taste are preserved. Foods are damaged by bacteria; fungi and other micro-organisms, which occur everywhere. These organisms make food unsafe for use and storage, so it is necessary to kill bacteria or other organisms as soon as they enter food.
Early methods of preservation affected the taste of the preserved food, but modern scientific techniques prevent contamination of food, keep the taste and make it consumable even after a long period of storage. To achieve this, temperature plays an important role.
Food that we take is usually made up of dead tissue and it can be spoiled for two reasons, either the food is contaminated and destroyed by bacteria or fungi or the enzymes still active in tissue start breaking down the cells, thus making food poisonous and tasteless to eat.
All bacteria, fungi and micro-organisms must be killed or their growth must be retarded in order to protect the food from spoilage. Heat is the best source, as extreme increase in temperature retards bacterial growth and enzymes can also be denatured. Thus temperature extreme can be useful in the preservation of food

Methods of Food Preservation

This method was discovered by famous biologist, Louis Pasteur. By this method milk is prevented from turning sour. In this process, milk is heated to 71 C for a few seconds and then cooled rapidly. This kills most of the bacteria. The bacteria which survive this treatment may become retarded in growth. In this way, the milk is preserved for a few days.
In this methods, food is kept at very low temperature usually below freezing point. It retards the action of enzymes and the growth of bacteria. In deep freezers food can be preserved for many years. Quick freezing helps to maintain the taste and texture of meat, fruit and vegetables.
In this method food is dried. Such food can be kept safe for a long period at normal temperature. Bacteria do not grow without water, therefore when water content is removed from meat and vegetables, they can be preserved for long durations. Pickling of food is another common indigenous technology in which taste and texture of pickled food is maintained for long.
In this method the food is first heated at a high temperature. This kills bacteria and destroys enzymes. Then, the food is sealed in a metallic container. In this way; food becomes safe from contamination. Metallic cans are usually lacquered to prevent food from chemically reacting with metals and producing toxic substances

Health Problems Related to Nutrition

Under Nutrition
During under nutrition a person’s diet is deficient in the required calories. children are mostly affected due to availability of less than normally required diet and they suffer from a disease called marasmus. In this disease, children are reduced to a skeleton as the body becomes completely depleted. Some of the countries like Ethiopia are famine stricken. Although international community does try its best to rescue the famine inflicted areas yet it is not possible for them to meet their complete nutritional requirements on such a large scale. The world population is continuously and rapidly increasing each year. It has been estimated that by 2025, the world population will rise to ten billion, whereas water and soil resources are being continuously depleted by increasing use by the continuously growing population. The experts therefore envisage that increasing human population if not checked will soon eat up all the food resources of the world which may lead to destruction of human race.
If malnutrition (a diet missing in one or more essential nutrients) continues for a prolonged period, particularly under special circumstances, such as during pregnancy or immediately after childbirth, it is found to be very harmful.
If malnutrition occurs during lactation period, it causes irrepairable damage to the infant. During the last quarter of pregnancy when foetus is rapidly developing its cerebral tissues, the protein deficient diet of the mother results in mental retardness and nervous abnormalities in foetus, which may prove fatal or lead to permanent disorders. These abnormalities may also occur in infants if the lactating mother is taking a protein deficient diet during the first year of breast-feeding.
If a human diet lacks essential elements or nutrients, the body will fail to prepare vital compounds, and thus the person will suffer from various diseases. Deficiency of a few amino acids, vitamins, fatty acids (about thirty compounds) and 21 mineral elements, called as essential nutrients in diet are responsible for various diseases.
In the poor countries like ours packaged or junk food(sugar coated cumin seeds, betal nuts, chewing gums and drinks) are not prepared under proper care. The food colours scents and flavours are added to make them commercially attractive. But these are substandard and harmful for human health. The use of food additives may be the cause of dangerous diseases like cancer and ulcer etc. These items should, therefore, be avoided.
Over Nutrition
It is the problem of the developed countries where people eat too much. Obesity is the most common disorder due to over nutrition. Obesity is the cause of a large number of diseases too

Balanced Diet

A diet containing essential dietary components in the correct proportion, which helps to maintain health and fulfills the body requirements of organisms, is known as balanced diet. The degree to which any particular meal is adequate in providing energy from food depends on the nature of the job of a person.
A common man’s diet is said to be suitable if it provides 50% calories from carbohydrates, 40% from fats, and 10% from proteins. Carbohydrates are abundantly used foods because they are readily available and cheaper as compared to fats and proteins. We can live without carbohydrates it our diet has all the components of food and is capable to provide total calories required by the body. Fats are taken in our diet to obtain energy. Our daily food requirement varies with sex, age and occupation e.g. children need more food because they are growing. Youth need more food than elderly people due to physical exertion. Men need more food than women. Pregnant women, lactating mother’s convalescents need more food as compared to others.


God has blessed animals and human beings with teeth. They help in breaking and chewing of the food. They are present in oral cavity.Teeth are attached to the upper and lower jaws.
Kinds of Teeth
Humans have two sets of teeth during their lives.
Milk Teeth
The first set of teeth begins to come through the gums when the baby is about six months old. these are called the milk teeth and all twenty teeth are formed over a period of two years.
Permanent Teeth
The milk teeth begin to drop out at the age of six years and are gradually replaced by the second set of teeth called the permanent teeth. In man the milk teeth do not fall off simultaneously, they fall off one by one and similarly permanent grow one by one as well. Healthy teeth are strong and give a beautiful and lustrous look. You must brush your teeth at least twice a day.
Structure of a Tooth
A tooth has two permanent parts, the Crown and the Root. The crown is that part of tooth which projects out of the gum and jaws. The root the the tooth is embedded into the gums and is therefore, hidden.
This is the outer most part of tooth which is very hard and lustrous. It is deposited on the outside of the crown of the tooth by cells in the gum. The enamel is a non-living substance. It is made up of calcium salts. It imparts beauty to the tooth and protects the tooth. If the enamel gets removed then the teeth start decaying.
It is the part of teeth present under the enamel which is hard. But it wears off if the enamel gets removed. Running through the dentine are strands of cytoplasm arising from the cells in the pulp. These cells keep on adding more dentine to the inside of the tooth.
The innermost part of the tooth is hollow and is made up of soft connective tissue which is called the pulp. The strands of cytoplasm in the dentine derive their food and oxygen from the pulp which enables the tooth to live and grow. The pulp contains sensory nerves and blood capillaries. These nerve endings are sensitive to heat and cold and can produce the sense of pain e.g. toothache.
Cement is a thin layer of very hard material which covers the dentine at the root of the tooth. the fibers holding the tooth in the jaw are embedded in the cement at one end and in the jaw at the other. In this way teeth remain firmly embedded in the jaws.
Protection and Cleanliness of Teeth
Teeth are a gift of nature. For a good health, presence of clean, good healthy teeth is necessary if we wish our teeth to remain healthy; we should wash and clean them after every meal. Our tongue helps in cleansing the upper portion of teeth to some extent. If food particles are firmly trapped up between the teeth, or between gums and teeth, then it becomes difficult to remove them with the tongue. The main cause of tooth decay is a sugar coating left by sugary food on the teeth, which is converted into acid by bacteria. The acid damages the enamel and allows the bacteria to infect the soft dentine and reach the pulp cavity. The dentine begins to decay and causes toothache. Sugary foods such as sweets, toffees and chocolates, the bacteria which cause decay, form a thin layer of scum over the surface of the teeth. This layer becomes very hard with the passage of time and becomes difficult to remove. This scum is called plaque.
The teeth should be cleansed properly and regularly with a miswaak or a tooth brush. So that there is no formation of plaque. We should eat less sugar or sweet and sticky foods and also cleanse the teeth afterwards. Balanced diet should be taken, especially by young people who have growing teeth

Digestion of Food

First of all food comes in the oral cavity where the teeth crush and break the food and convert it into small particles. The tongue rolls the morsel of food and pushes it under teeth again and again so that the food is evenly divided into fine particles and the saliva secreted from the salivary glands gets mixed with the food. The saliva lubricates the food and makes the particles adhere to one another, forming a ball of food called bolus. Now the chemical digestion of food begins. Saliva contains an enzyme to digest starch in the food. The combined action of teeth, tongue and saliva pushes the bolus through the throat into the oesophagus, and then it reaches the stomach.
Definition of Digestion
Digestion is the process in which the insoluble and non-diffusible components of food are broken down and by the action of enzymes are converted into soluble and diffusible substance to be absorbed into the blood stream.
Types of Digestion
1. Mechanical digestion
2. Chemical Digestion
1. Mechanical Digestion
In mechanical digestion, the food consisting of large sized particle is broken into fine pieces by cutting, grinding, chewing and churning up, so that enzymes can act upon it efficiently and effectively. Mechanical digestion of food takes place in the mouth and stomach.
2. Chemical Digestion
In chemical digestion, the digestive enzymes mix with the food and act upon it to break it down further into simple and diffusible chemical forms. The enzymes act on carbohydrates, proteins and fats separately. Chemical digestion takes place in all the major parts of the digestive system. The digestive glands such as liver and pancreas also play very important role in this digestion.
Digestive System
All living things require food to live and carry on their life functions. Animals are unable to synthesize their food.
Digestion is the process in which the non-diffusible molecules of food are changed to diffusible ones by the action of enzymes. All the organs which take part in this process make a system which is called the digestive system.
Human Digestive System
The process of digestion takes place in the alimentary canal. It starts from the mouth and ends at the anus. The tube assumes different shapes according to their role in the process of digestion. It consists of the mouth, oesophagus, stomach, small intestine, and large intestine. Besides these organs liver and pancreas, also play important roles in digestion.
The muscles of alimentary canal produce rhythmic waves of contraction which is called peristalsis. Due to this process, food is carried through various parts of the alimentary canal.
The food of animals and human is in the solid form and may be bulky. Taking in of the food in the oral cavity and swallowing is called ingestion.
Digestion of Food in the Mouth
During mastication, the food is mixed thorougly with the saliva while the food is in the oral cavity (buccal cavity). The saliva is secreted by three pairs of salivary glands located in the buccal cavity. The saliva is continuously secreted by the salivary glands in response to the presence of food in the buccal cavity.
Saliva is alkaline and contains an enzyme ptyalin. This enzyme converts starch into sugar (maltose). The morsel of food after being chewed and thoroughly mixed with the saliva is called a bolus. It is rolled down by the swallowing action into the oesophagus which conveys it to the stomach by the wave of peristalsis. The end of stomach lined with oesophagus is called cardiac end.
Digestion of Food in the Stomach
Stomach is a thick sac like structure, in which food is stored for some time. Its wall is strong and muscular. Its inner surface has numerous glands called gastric glands. These glands secrete a juice called gastric juice. Human stomach secretes about one to two liters of this juice daily; Gastric juice contains Hydrochloric acid and two enzymes, renin and pepsin. Hydrochlroic acid changes the medium of food to acidic. This medium kills the bacteria that may be found in the food. the pepsin acts on proteins and breaks them down into peptones. Renin helps to curdle milk in infants. There is no chemical action on carbohydrates and fats present in food. the regular movements of the stomach churn up the food. the food is changed into a thick fluid called chyme. When digestion in the stomach is complete, the distal end of the stomach called the pyloric end relaxes, and allows a small amount of chyme to pass into the first part of the small intestine. Food stays in stomach for about 2-3 or 3-4 hours.
Digestion of Food in the Small Intestine
Food from stomach enters the duodenum which is the first part of the small intestine. An alkaline pancreatic juice from the pancreas and bile juice from the liver and poured into the duodenum by a common duct. Both the juices contain bicarbonates which neutralize the acidic chyme and make. It rather alkaline besides these juices other intestinal juices from the walls of the small intestine are also poured. These entire juices act on food and help in digestion of food.
It is largest gland, in the body. Its colour is reddish brown. It lies just below the diaphragm on the right side of the body under the ribs. It has five lobes, three on the right side and two on the left. The cells of the liver secrete a greenish yellow alkaline fluid which is called the bile juice. It contains bile salts and bile pigments which give greenish yellow colour to the juice. Bile contains no digestive enzymes, but it does contain bile salts which break down the large molecules of fats to small fat droplets. This process is called emulsification. This process helps in the digestion of fats. Bile juice also contains bile pigments that are by products of red blood cells, these pigments are eliminated from the body along with the faeces, and the colour of faeces is due to these pigments. Besides this, bile juice also kill the germs in the food.
Functions of Liver
1. Liver stores glycogen and regulates the level of glucose in the blood.
2. It breaks down excess amino acids. this process is called deamination.
3. It is involved in detoxification.
4. It produces and secretes bile juice which is stored in the gall bladder.
5. It metabolizes carbohydrates, fats, proteins and other compounds.
6. As a result of chemical changes a lot of heat is produced, therefore liver helps to keep the body warm.
7. It makes fibrinogen and other blood proteins.
8. It decomposes the damaged red blood cells.
It is a leaf like organ. It lies below the stomach and between the two arms of duodenum. The pancreas produces a juice which is called the pancreatic juice. This juice flows down the pancreatic duct into the duodenum. It contains three enzymes.
1. Pancreatic amylase which acts on undigested starches of the food and converts them into maltose.
2. Enzyme trypsin which breaks down proteins into peptides.
3. Lipase which splits fats into fatty acids and glycerol.
If any of the constituents of food still remain undigested, enzymes secreted by the glands in the small intestine act upon them and complete the digestion by converting peptides to amino acids, maltose and other sugars to glucose and fats to fatty acids and glycerol.
The enzymes secreted by the intestinal walls are amino-peptidases and disaccharidase,(which form glucose from maltose, lactose and sucrose). In this way food is completely digested at intestine.


Definition of Enzymes
Enzymes are chemical compounds. They are protein in nature. They are formed in living cells. They are not consumed in a reaction but act as a catalyst as they only speed up the chemical reactions.
Types of Enzymes
There are two types of enzymes:
1. Intracellular Enzymes
2. Extracellular Enzymes
1. Intracellular Enzymes
They work within a cell, in which they are produced.
2. Extracellular Enzymes
Some enzymes are secreted out of the cells where they work. They are called extracellular enzyme. Bacteria and fungi secrete such extra cellular enzymes into the medium in which they are growing. The higher organisms secrete extracellular enzymes into the lumen of alimentary canal to act on the food.
The enzymes acting on the starch are known as Amylases; those acting on proteins are known as Proteinases, while those acting on fats are known as Lipases.
Characteristics of Enzymes
The characteristics of enzymes are as follows:
1. All enzymes are protein in nature; they can be destroyed by heating.
2. They act best within a narrow, temperature range.
3. They work efficiently in narrow range of acidity or alkalinity.
4. A particular enzyme forms the same end-product, because it acts on a particular/specific substrate

Light and Dark Reactions

Light Reactions
When light falls on the leaves, it is absorbed by chlorophyll. The solar energy is used to split water into oxygen and hydrogen and this is called photolysis (photo means light and lysis means to break). The oxygen is released into the atmosphere as by-product of photosynthesis. As this process takes place only in the presence of light, it is called light reaction.
During light reaction, two compounds are formed when the solar energy is converted into chemical energy these are:
1. NADPH (Nicotinamide Adenine Dinucleotide Phosphate)
2. ATP (Adenosine Triphosphate)
NADP, already exists in the cells of the leaf. The hydrogen released on the splitting of water molecule is accepted by this compound and it is reduced to NADPH.
ADP (Adenosine Diphosphate) is already present in the cell; it combines with the phosphate group using light energy to form a compound called ATP.
These compounds are energy rich compounds which are needed for the dark reactions of the process. Light reaction is called high dependent reaction.
Dark Reactions
Using the energy of ATP and the NADPH, water combines with carbon dioxide to form carbohydrate. Thus the solar energy is now converted into chemical energy to form glucose. Other organic compounds are also synthesized from this glucose.
This stage is completed in a series of chemical reactions with the help of enzymes. Neither light energy nor chlorophyll is needed for dark reactions. Therefore dark reaction is also called light independent reaction.
Various steps of the dark reactions were studied by a scientist called Melvin Calvin so the dark reaction is also called the Calvin’s Cycle.






The oxidation of the absorbed food material in order to obtain energy is called respiration.

There are two types of Respiration in the organisms:
1. Aerobic Respiration
2. Anaerobic Respiration
1. Aerobic Respiration
In most of the higher and larger organism, the glucose etc is oxidized by using molecular oxygen. This type of respiration is known as Aerobic Respiration. In aerobic respiration a mole of glucose is oxidized completely into carbon dioxide and water releasing enormous amount of energy. One glucose molecule in this resnpiration produces 686,000 calories of energy. Aerobic respiration thus produces 20 times more energy than the anaerobic respiration.
In aerobic respiration food is oxidized in presence of molecular oxygen.
Stages of Aerobic Respiration
There are two stages of Aerobic Respiration:
(a) External Respiration
In this stage, the organisms take the air (containing oxygen) into their bodies. This is called external respiration. this stage includes the transport of oxygen obtained from the inhaled oxygen to each cell of the body.
(b) Internal Respiration
The second stage is called internal respiration. It consists of the oxidation of glucose, amino acid and fatty acids etc, with molecular oxygen. In this stage all these reactions are included which extract the chemical energy of glucose and other compounds and store it in the form of ATP molecule, this respiration is also called cellular respiration as it occurs within cells.
In the internal or cellular respiration glucose and other compounds are passed through such enzymatic reactions which release the chemical energy gradually in small amounts with the help of which ATP molecules are synthesized.
2. Anaerobic Respiration
Some organisms oxidize their food without using any molecular oxygen. This is known as Anaerobic Respiration. In this type of respiration considerably less amount of energy is released as compared with the other type of respiration.
In anaerobic respiration a glucose molecule is broken down into two molecules of lactic acid with a release of only 47,000 calories of energy.
Glucose ——–> 2 Lactic Acid + Energy (47,000 calories)
Importance of Anaerobic Respiration
1. When earth came into being its environment was totally devoid of oxygen. The aerobic organisms cannot lie in anaerobic environment. The early organisms started respiration in the absence of oxygen to produce energy for survival of organisms.
2. Some existing organisms like bacteria and parasites which live in oxygen environment have anaerobic respiration.
3. Many useful bacteria and yeasts are anaerobic.
4. Even in the aerobic respiration of the first phase is anaerobic. The glycolysis which is the first phase of carbohydrate metabolism involves reaction which does not require the expenditure of molecular oxygen. This proves the idea that aerobic organisms have evolved from anaerobic organisms.
5. In our skeletal muscles, although aerobic metabolism takes place but in sustained activity when the oxygen supply cannot keep pace with energy demand, anaerobic respiration supplies the energy continuously by the breakdown of glucose to lactic acid.
ATP (Adenosine Triphosphate)
It is a chemical compound. ATP is an abbreviation of adenosine triphosphate. Its name indicates that it contains adenosine and three phosphate groups. Adenosine is formed of a nitrogenous base called adenine and a sugar called ribose. In ATP three phosphate groups are attached to the adenosine in a series one after the other.
Significance of ATP
ATP is a big source of energy. The two terminal bonds between the phosphate groups contain large amount of the chemical energy. When these bonds are broken in enzymatic reaction, large amount of energy is released by which energy requiring activities are accomplished, like synthesis of various compounds of carbohydrates, fats, proteins and hormones etc or for carrying out any physical work like muscle contraction, heat production or transport of substances etc.
When the terminal bond is broken the ATP is changed into ADP and phosphate 7300 calories of energy are released.
Gaseous Exchange in Plants
Plants get their energy from respiration. Plants have no special organ or system fro exchange of gases. The gaseous exchange in plants occurs in cells, of every part of the plant i.e. roots, stems and leaves etc according to their energy demand. The conducting system (xylem and phloem) of plants transports water and nutrients but plays no role in the transport of gases. The air spaces present between the cells of parenchyma of leaves, stem and roots are involved in the gaseous exchange.
Gaseous Exchange in Leaves and Young Stems
In the leaves and young stems, gaseous exchange occurs through stomata. Some gaseous exchange also occurs through cuticle.
Gaseous Exchange in Woody Stems and Roots
In woody stem and roots, there are present dead cells beneath the epidermis which form cork tissue. Later on, this tissue becomes porous. The pores are called lenticels. These are involved in gaseous exchange.
Gaseous Exchange in Leaves
The aquatic parts obtain oxygen for their respiration by diffusion from the dissolved oxygen in water. Whereas the land plants get their oxygen from air directly through their stomata which are more abundant on the lower surface than the upper surface of leaves.
Gaseous Exchange in Roots
The roots get their oxygen for gaseous exchange through diffusion from the air existing in the space between soil particles.
Process of Respiration in Plants
The respiration in plants continues day and night. In this process, the oxygen from the airspaces in the leaves and stems is diffused into tissues and cells after getting dissolved in the film of water which is present over the cells. In the cells this oxygen oxidizes the carbohydrates and other organic compounds into carbon dioxide and water to produce energy. Some of the water (vapours) comes in the airspaces from where they diffuse out to the atmosphere through lenticels and stomata. The elimination of carbon dioxide is more evident from the parts without chlorophyll like growing seeds and buds. The water produced in this process becomes a part of the already present water in the body of plants. The various chemical reactions of respiration are controlled by the specific enzymes. This process occurs at a faster rate in the parts of the plant having rapid growth like growing seeds, buds, apical meristem of roots and shoots, because these parts require more energy to accomplish the growth process.
Relationship between Respiration and Photosynthesis
The gaseous exchange in plant is not very evident during the day time as the products of respiration i.e. carbon dioxide and water are used in the process of photosynthesis. In the bright sunshine, because of high rate of photosynthesis the carbon dioxide produced in respiration falls short and therefore, some carbon dioxide has to be taken into the plant from outside for photosynthesis.
In the day time the plants therefore, take in carbon dioxide and expel out oxygen. The process of photosynthesis occurs in chloroplasts whereas the process of respiration takes place in cytoplasm and mitochondria.
Gaseous Exchange in Animals
The gaseous exchange in different animals takes place by different methods and organs. In unicellular aquatic animals like amoeba, the dissolved oxygen in water diffuses directly through their cell surface into the interior of the animal and the carbon dioxide similarly diffuses out from their bodies into the external water. This is the simplest way of gaseous exchange and it can occur only in small animals with a diameter of less than one millimeter. These animals have greater surface area of volume ratio and have low rate of metabolism.
During evolution, as the animals became complex and complex and grew in their size, their skin or external body surface become impervious to water. Thus the gaseous exchange became impossible through diffusion. In large animals certain organs were developed for exchange of gases w.g. the moist vascular skin, gills, lungs and tracheoles. These large animals have developed blood vascular system which transports oxygen from the respiratory surface to the deep cells and tissues in all parts of the body. The blood in all animals has some respiratory pigments like haemoglobin which carry large amount of oxygen efficiently from respiratory surface to the interior cells.
Properties of a Respiratory Surface
1. Respiratory surface should have large surface area.
2. Respiratory surface should be moist.
3. Respiratory surface should be thin walled.
4. Respiratory surface should have blood supply.
Gaseous Exchange Through Skin
For the exchange of gases through the skin the skin must be moist and richly supplied with blood. The oxygen is diffused from the external water to the blood and the carbon dioxide is diffused from the blood to exterior water. In amphibia and fishes the gaseous exchange occurs through the skin besides through the gills or lungs. The frogs and tortoises breath through the skin during their hibernation period.
Gaseous Exchange by Gills
The gills are very effective for gaseous exchange in aquatic animals. Gills are of two types:
(a) External Gills
(b) Internal Gills
(a) External Gills
Some animals have external gills which project out of body of animals. These gills have very thin and highly vascularized surfaces e.g. the dermal papillae of star fish and arthropods.
(b) Internal Gills
These are present inside the body inner to skin e.g. in fishes and arthropods. Have you ever examined a fish closely? How ill you know that the fish is fresh or not? If the colour of gills is red then it is fresh but if the colour of gills is changed, it is definitely not fresh. The red colour of the fish gills shows the presence of oxygenated blood.
Gills of Fish
In fishes the gills are present in the branchial cavity present on lateral sides of the body behind the head. This branchial cavity is covered over by an operculum. There is a counter current flow of water and blood in gills which ensures maximum exchange of oxygen and carbon dioxide between the blood and the bathing water. Water enters through the mouth, flows over the gills and goes out of the body from the opercular aperture.
Human Respiratory System
In humans, there is very efficient respiratory system. It consists of certain organs which are called respiratory organs these include nose, pharynx, larynx, trachea, bronchi and bronchioles.
The air enters through the external nostrils into the nasal cavity. This is lined with mucous secreting epithelium and ciliated epithelium. The nostrils are lined with hairs. The nasal cavities, located above the oral cavity and behind the nose are covered with epithelial tissue.
The beating of cilia creates a current in the mucus that carries the trapped particles towards the back of the nasal cavity. From here the mucus drips into the throat and is swallowed. Mucus keeps the nasal cavities moist. Bones of the nose warm up the air. Mucus moistens the air. Hair filter the air and stop the dust particles bacteria and any other foreign substance from going to next part of respiratory system. In this way air is purified and is then pushed into the pharynx.
A number of cavities called sinuses open into the nasal cavity. The sinuses are lined with mucus secreting epithelium. The opening of sinuses into the nasal cavity is very narrow. If these openings are closed due to cold or inflammation, the sinuses get filled up with mucus this results in headache and changed voice.
The nasal cavity opens into the pharynx (throat) through two small apertures which are called internal nares or internal nostrils. The pharynx is muscular passage which extend from behind the nasal cavities to the opening of oesophagus and larynx. The air goes from the pharynx into the larynx.
The upper most part of the wind pipe (trachea) is called the larynx. The larynx is a cartilaginous box. Two fibrous bands called vocal cords are located in this box. These vibrate to produce sound. Larynx is, also called sound box or voice box. The air enters the larynx through a small aperture called glottis which is guarded by a muscular flap called epiglotis which fits into this opening while the food is being swallowed into the oesophagus. It prevents the food from entering into the trachea and choking it. During breathing epiglottis keeps the glottis open so that air goes to trachea.
The air tube (wind pipe) is known as trachea. It is about 12 cm long and lies in front of the oesophagus. It has incomplete C shaped cartilagenous rings which are regularly placed in its wall and all along its length. These rings prevent the collapsing of the tube nd thus keep the air passage wide open all the time. Trachea is also lined with ciliated mucous epithelium. Any foreign particles present in the inhaling air get trapped in the mucous that is moved out of the trachea by breathing of the cilia in the upward direction. In trachea air is further cleansed and filtered and then moved towards the lungs.
The trachea while passing the chest cavity divides into two smaller tubes which are called bronchi (single bronchus). Bronchi are similar in structure to the trachea but are smaller in diameter and they have in their walls small irregular catilageuous plates. Each bronchus enters into the lungs of its own side. The right bronchus divides into three secondary bronchi and the left bronchus divides into two secondary bronchi which serve the 3 right and 2 left lobes of the lungs respectively.
the secondary bronchi further divide into very fine branches until they end in thousands of passage ways called respiratory bronchioles. The bronchioles have not cartilaginous plates in their walls. They have smooth muscle and elastic fibers.
The walls of the respiratory bronchioles have clusters of tiny branches(like bunches of grapes) that along with the respiratory bronchioles re the sites of gaseous exchange, these pouches or air sacs are called alveoli (singular: alveolus). The alveoli are enormous in number. Each lung has about three hundred million alveoli.
Pulmonary artery brings deoxygenated blood from the heart into the lung. Here, it divides and re-divides until it forms a network of fine capillaries over the wall of each alveolus. The walls of alveoli are very thin (1/1000 mm thick) and moist. Thus, alveoli are efficient site for gaseous exchange.
The Lungs
There is a pair of lungs present in the chest in man. Actually, the masses of alveoli constitute lungs and their lobes. The lungs re protected by the chest box from sides and by a doem shaped muscular diaphragm from below. Chest box or ribcage is made up of ribs. Between the ribs, there are present inter-costal muscles. The diaphragm is a muscular sheet which partitions the chest and abdomen.
The two lungs re covered by a double layered membrane called pleural membrane. There is a thin film of fluid in between the two layers. This watery fluid makes the movements of the lungs (expansion and contraction) easy. It also protects the lungs from external injuries.
Mechanism of Breathing
Breathing occurs in two phases:
1. Inspiration
2. Expiration
1. Inspiration
1. During inspiration, the dome-shaped diaphragm contracts and becomes flat some what and thereby lowering the floor of the thoracic cavity.
2. The external inter-costal muscles contract raising the ribcage. A combined action of these two events expands the thoracic cavity, which in turn expands the lungs.
3. The air pressure within the lungs decreases.
4. Thus air from the environment outside the body is pulled into the lungs to equalize the pressure of both sides.
2. Expiration
1. The diaphragm relaxes and assumes dome like shape. During expiration, the external inter-costal muscles relax and the internal inter-costal muscles contract as a result of which ribcage drops.
2. The combined action of these two event decreases the volume of the thoracic cavity which in turn decreases volume of lungs.
3. The air pressure with in the lungs increases.
4. The air is thus forced out of the lungs.
Bad Effects of Smoking on Heath
Smoking is injurious to human health. The smoke contains many chemical and gases. Dried tobacco leaves are used in cigarettes. The tobacco on burning produces a number of dangerous and toxic compounds.
Chemicals Present in Cigarette Smoke and Their Harmful Effects
(a) Nicotine
1. Man is addicted to cigarette damages brain tissues.
2. Causes blood to clot more easily.
3. Harden walls of arteries.
(b) Tar
1. Kills cells in air passages and in lungs.
2. Increases production of mucous and phlegm in lungs.
3. Causes lung cancer.
(c) Carbon Monoxide
Prevents red blood cells from combining with and transporting oxygen around the body.
(d) Carcinogens
promote the growth of cancerous cells in the body.
(e) Irritants
1. Irritate air passages and air sacs in the lungs.
2. Kill cells at the surface of air passages.
3. Causes smoker’s cough and lung cancer.
A chemical reaction in which a substance combines with oxygen and produce heat, light and flame is called Combustion.
A process that liberates chemical energy from organic molecules when oxidized is called Respiration. It occurs in all living cells. In fact respiration is a series of complex oxidation and reduction reactions in which energy is released bit by bit.
The process in green plants by which green plants manufacture their own food by using carbon dioxide and water with the help of energy absorbed by chlorophyll from sunlight is called photosynthesis.
Relation of Combustion, Respiration and Photosynthesis
Combustion is the process of burning in which wood, coal, methane, gas etc are burnt in the presence of oxygen, producing carbon dioxide and water accompanied with the release of energy. It is an exothermic chemical reaction.
Cellular respiration can be compared to burning of fuel in which organic food (carbohydrates, fats and proteins) rich in carbon burn in the presence of oxygen producing carbon dioxide, water and energy.
Respiration like combustion is a catabolic exothermic chemical process. However, the difference between the combustion and respiration is that the combustion takes place in one go, releasing the entire energy as the heat, which may be utilized or is lost into the environment. the respiration completes in several small steps. Each step is under the control of a specific enzyme, releasing energy in small amounts which can be stored in the form of ATPs. Photosynthesis, another metabolic process, is just opposite to combustion. Combustion is a catabolic process; the photosynthesis is an anabolic process. In photosynthesis organic substance is synthesized from carbon dioxide and water in the presence of sunlight energy and chlorophyll. The molecular oxygen is evolved as the by-product combustion is exothermic and releases energy, photosynthesis is endothermic and absorbed energy.
Photosynthesis and respiration are the two metabolic reactions opposite to each other. Photosynthesis takes place only in the gree parts of the plant body having chlorophyll, whereas respiration takes place in all the living cells of plants and animals. Mitochondria are the cellular organelles where respiration takes place while the organelles for photosynthesis re chloroplasts. Photosynthesis takes place during the day time only, whereas respiration takes place day and night. In photosynthesis body weight is increased but in respiration weight is decreased. Respiration is an oxidation reaction whereas photosynthesis is a reduction reaction and can be well understood by comparing their chemical reactions.
Chemical Equation in Respiration
Glucose + Oxygen ——-> Carbon dioxide + Water + Energy (In presence of mitochondria and enzymes)
Chemical Equation In Photosynthesis
Carbon dioxide + Water ——–> Glucose + Oxygen (In presence of chloroplast and solar energy)
Respiratory Organs of Insects
The respiratory system of insects is called the Tracheal system. It is a network of interconnecting air filled tubes called trachea delivering air directly to the body tissue cells. Trachea open outside through pores called spiracles.
Each trachea has chitinous cuticle lining which prevents it from collapsing.
A pair of spiracles is usually located on the sides of each segment of the thorax and abdomen. Spiracles have valves to open or close them regulated by special muscles. This controls water loss from internal body tissue.
Trachea break up into numerous smaller tubes called tracheoles which ramify among the body tissues ending blindly. Tracheoles lack a chitinous lining. At rest the tracheoles are filled with watery fluid through which gaseous exchange tkes place in dissolved state.
Ventilation is brought about by contraction and relaxation of abdominal muscles which result in a rhythmic pumping of air into and out of the trachea.
Gas exchange takes place in tracheoles which are permeable to gases and are filled with a fluid in contact with the body tissue. Since oxygen diffuses directly into the tissue cells, blood of insects does not have hemoglobin so it is white. However, removal of carbon dioxide is dependent on blood plasma which takes it up for removal via spiracles






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