Optional Science Book Class 10

The common disaccharides are maltose (glucose + glucose), lactose (glucose + galactose)
and sucrose (glucose + fructose). It is sweet in taste and soluble in water.

~ ON M HOT H' ~ HOCH2

HO 0 ~CIH HH o "-J OH H ~ 0
H
H OH
H OH H' OH H OH H OH OH H
Galactose Glucose Fructose
Glucose Glucose I Glucose
lactose
I Sucrose
Maltose

Polysaccharide (Gk: poly- many)

A polysaccharide is a polymer formed by many monosaccharides joined together by a
glycosidic bond. It is also called a complex carbohydrate. They are usually tasteless and
insoluble in water. The common polysaccharides are starch, glycogen, cellulose and chitin.

Sources of Carbohydrates

The large number of carbohydrates stored by plants are a rich source of food and energy for
all life. A number of complex carbohydrates in plants are formed from glucose. The foods
that are rich in carbohydrates are known as starchy foods. They are found in legumes, rice,
wheat, corns, whole grain breads, cereals and starchy vegetables like potato, carrot, sugar beet,
etc. They are also found in fruits like sugarcane, pineapple, milk and milk products. Some
processed foods like candy, carbonated beverages and table sugar also contain carbohydrates.

Importance of Carbohydrates

Carbohydrates are of great importance in biology. The biological breakdown of carbohydrates
into glucose supplies energy to every living organism in conducting various metabolic
processes.
The importance of carbohydrates are:

1. Carbohydrates are macronutrients that build body strength and serve as excellent
energy providers.

2. Cellulose fiber (i.e., a polysaccharide) is the primary structural component of plants.
cell walls are primarily made up of cellulose.

3. The fibers present in carbohydrates promote regular bowel movement and help to
control constipation.

4. Cellulose is the major component of cotton fiber and wood. Paper and clothes are made
from cellulose.

Memory Plus

The calorific value of carbohydrate is 4.1 kcal/g, i.e. one gm of carbohydrates gives 4.1
kcal energy on its complete breakdown or oxidation. In case of a normal healthy person,
the average intake of carbohydrates is 500g per day (i.e., 2050 kcal/day).

Lipids

Lipids are the naturally occuring organic compounds commonly known as fats or oils and

their derivatives. Chemically, lipids are esters of fatty acids. They are non-polar organic

compounds. So lipids are insoluble in polar solvent like water but soluble in organic solvents

like alcohol, ether, etc. Lipids are the energy storing molecules. They provide energy for life.

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Classification of Lipids
Based on structure, lipids are broadly classified into simple, complex and derived lipids.

1. Simple lipids : Simple lipids are esters of fatty acids with alcohols. Fats (monoglyceride,
diglyceride, triglyceride etc.) and waxes are simple lipids. Oils are fats in the liquid state.

2. Complex lipids: Complex lipids are esters of fatty acids with alcohol and containing other
groups like phosphate, carbohydrates, proteins, nitrogenous base, etc. They are formed
by the combination of lipid with the non-lipid molecule. For example: phospholipids
(lipids + phosphates), glycolipids (lipids + carbohydrates), lipoproteins (lipids + protein),
etc.

3. Derived lipids: Derived lipids are the compounds derived from simple and compound
lipids by hydrolysis. For example: glycerol, fatty acids, steroids (cholesterol), hormones.

Sources of lipids
Both plant and animal sources contain different types of lipids. Lipids can be obtained in a
large amount from meat, butter, cheese, milk, eggs, ghee, nuts, avocados, etc.

Importance of lipids:

1. Lipids are an excellent reservoir of energy for the body.

2. Lipids are a source of fat-soluble vitamins (A, D, E and K).

3. Lipids protect the internal organs.

4. Lipids (fat) act as an insulator.

5. Lipids form the cell membrane. Phospholipids regulate the permeability of the cell
membrane.

Protein

Proteins are large, complex nitrogen-containing organic compounds composed of one or more
long chains of amino acids. They are important macromolecule in a living organism. Protein
builds and repairs body tissue. It also forms antibodies, hemoglobin, enzymes and hormones.
So proteins are also known as the building blocks of life. It protects and provides structure
to the body of a multi-cellular organism in the form of skin, hair, cartilage, ligaments and
tendons.

Proteins are found throughout the body. Trypsin, pepsin, collagen, keratin, insulin, thrombin,
fibrinogens, albumin, globulin, hormones, etc. are some biologically important proteins.
Proteins are made up of 20 different amino acids. When proteins are broken down into amino
acids, the body uses these amino acids to make new proteins.

Fact with reason

Proteins are known as building blocks of life, why?

Proteins are required for structure, function and regulation of each and every organ,
tissue and cells of the body. They are essential to make new cells, repair the damaged
tissue and cells. Proteins are engaged in all the biochemical reactions taking place in the
cells. The body needs proteins for growth and development. So proteins are known as
building blocks of life.

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Amino Acids

Amino acids are organic biomolecules that are attached to each other to form long chains
of proteins. They are known as the building blocks of proteins. Proteins are made up of
carbon, hydrogen, oxygen, nitrogen and with, or without, sulphur. Amino acids perform
several biological and chemical functions in a human body. Amino acids colourless crystalline
substances. They are generally soluble in water and insoluble in non-polar organic solvents.

Classification of amino acids

Most of the amino acids are not synthesized by the body. They must be obtained from food.
Therefore, 20 different amino acids can be classified on the basis of that whether people can
acquire them through diet or not. On the basis of nutrition, amino acids are of three types:

1. Essential amino acids: Amino acids that cannot be synthesized in the body and should
be supplied through diet are called essential amino acids. The essential amino acids are
obtained from eggs, milk, meat, fish and poultry. The eight essential amino acids are
valine, leuine, methionine, lysine, isoleucine, phenylalamine, threonine and tryptophan.

2. Non-essential amino acids: Amino acids that are synthesized in the human body either
from essential amino acids or from normal protein breakdowns are called non-essential
amino acids. Ten non-essential amino acids include: alanine, serine, glycine, glutamine,
tyrosine, aspartic acid, cysteine, proline, glutamic acid and asparagine.

3. Semi-essential amino acids: Amino acids which can partly synthesized in adult human
body but are necessary to supply through diet in infants are called semi-essential amino
acids. These amino acids are only required by lactating or pregnant women and growing
children. The two semi-essential amino acids are histidine and arginine.

Classification of Proteins

Proteins can be classified in different ways. On the basis of nutritional value of dietary proteins,
they are classified as first class proteins and second class proteins.

1. First Class Proteins : Proteins that contain all the essential amino acids are called first
class proteins. These are also known as complete proteins. First class proteins are of
animal sources like meat, fish, dairy, eggs, etc.

2. Second Class Proteins : Proteins that are deficient in one or more essential amino acids
are called second class proteins. These are also known as incomplete proteins. Plant
proteins are generally second class proteins.

Sources of Protein

Proteins should be included in our daily diet for proper growth of our body. Foods rich in
proteins include vegetables like beans, carrot, cabbage, onion, cucumber, beetroot and green
leafy vegetables. Fruits like melon, orange, pineapple, papaya, grapes and pomegranate
contain protein. Eggs, groundnuts, peanuts, whitefish, pork, mustard seeds, chia seeds,
almond, walnut, cashew are also good sources of proteins.

Memory Plus

The calorific value of protein is 5.65 kcal/g, The average adult needs about 70-100 grams
of protein per day.

Marasmus and kwashiorkor usually occur in young children and babies due to deficiency
of protein.

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Fact with reason

Vegetarians must take special care of dietary to meet their protein need, why?

Plants, by themselves, do not provide all the essential amino acids, but they provide
amino acids in combination with other vegetarian food sources. For example, when
cereals are combined with pulses, they provide most of the essential amino acids.
Vegetarians must take special care to ensure that their body requirement of protein is
sufficiently met by their diet.

Importance of Protein

1. Some proteins are hormones. They regulate many body functions.
3. Some proteins act as antibodies. They protect our body from infections and disease

causing germs.
4. Proteins are the structural elements of cells and tissues. They help in building and

repairing cells.
5. Proteins make up bones, muscles, hair and other parts of the body.
6. Proteins act as enzymes. They catalyze the biochemical reactions in the body.

Activity

Food Tests

Students can test a variety of local fresh and dried foods for the following nutrients: fats,
protein, starch and glucose.

Test for fats:

Rub the food sample onto a piece of paper. If fat is present, it will make a translucent stain
on the paper.
Test for proteins (Biuret test)

1. If the food sample is not in liquid form, mash it up and add a little water to make a
suspension.

2. Add 2 - 3 drops of biuret reagent.

3. Shake well.

4. A purple color is seen if protein is present.

Test for starch

1. Add a few drops of iodine solution to the food sample.

2. If it turns into blue-black color, starch is present.

Test for glucose (Benedict’s test)

1. If the food sample is not in liquid form, mash it up and add a little water to make a
suspension.

2. Place about 2ml of the food sample into a test tube and add an equal volume of
Benedict’s solution.

3. Place the tube in very hot water for a few minutes or heat the test tube directly for
a few minutes.

4. A yellow/green/orange or brick red precipitate develops if glucose is present.

...... ......... :

0254 Optional Science - 10 BIOLOGY

Enzymes

Enzymes are large biomolecules that act as catalysts for biochemical reactions within living cells
in every plant and animal. They are involved in many chemical reactions that are necessary to
sustain life. Enzymes catalyse the chemical reactions that are involved in growth, respiration,
digestion, reproduction, etc. They only increase the rate of reaction without themselves being
changed. All enzymes are protein molecules. Some examples of common enzymes are lipases,
amylase, pepsin, protease, catalase, maltase, sucrase, rennin, etc.

Fact with reason

Enzymes are known as biological catalyst, why?
Enzymes are known as biological catalyst because they speeds up the chemical reaction
in cell. These reactions include respiration, digestion, photosynthesis, etc..

Enzyme Activity
Enzyme activity is affected by factors that disrupt protein structure. Factors that disrupt
protein structure include temperature and pH (high level of acid). The degree of temperature
and the level of acids required to break down the molecules of enzymes depends on the
strength of the bonds between amino acids. Once the bonds are degraded enzymes become
inactive or non-functional. The part of enzyme which acts as the catalyst is called active site of
the catalyst, whereas remaining part is called substrate.

Classification of Enzymes
Based on catalyzed reactions, the nomenclature committee of the International Union of
Biochemistry and Molecular Biology (IUBMB) classified enzymes into 6 groups as

1. Oxidoreductase: Oxidoreductage helps in oxidation-reduction reaction. It catalyzes the
transfer of electrons from the reductant (electron donor) to the oxidant ( electron acceptor).

2. Tansferase: Transferase enacts the transfer of specific functional groups (e.g. a methyl or
glycosyl group) from one molecule (donor) to another (acceptor).

3. Hydrolase: Hydrolase uses water to break a chemical bond. This results in a division of a
larger molecule to smaller molecules.

4. Lyases: Lyase Catalyzes the breaking of various chemical bonds and forms a new double
bond or a new ring structure.

5. Isomerase: Isomerase catalyzes the formation isomer from the substrate of enzyme
molecule. It facilitates the transfer of specific functional groups intramolecularly without
adding or removing atoms from the substrate.

6. Ligases: Ligase catalyzes the joining of two large molecules by forming a new chemical
bond. It plays an essential role in DNA replication.

Characteristics of Enzymes
Enzymes have some characteristics as follows.

1. Enzymes are protein molecules.

2. They act as a biological catalyst.

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4. Enzyme activity can be controlled. Their activity is high at optimum temperature.
Most human enzymes have an optimum temperature around 40°C.

5. Enzymes denature at high temperatures, in alcohol, in concentrated acids, etc.

Sources of Enzymes
Enzymes are present in the food we eat. Raw fruits and vegetables are a good source of
enzymes. Fruits and vegetables rich in enzymes are apples, apricots, asparagus, avocados,
bananas, beans, beet, broccoli, cabbage, carrots, celery, cherry, cucumber, figs, garlic, ginger,
grapes, green barley grass, kiwi.

Memory Plus

Canned or processed (drying, freezing, irradiation) food kills the enzymes. Food that is
whole and uncooked and unpasteurized milk will provide enough enzymes.

Functions of Enzymes
Enzymes have various biological functions in living organisms. They also have industrial
applications when extremely specific catalysts are required.

Biological Functions of Enzymes

1. Enzymes like amylase and protease play an important role in digestion.
2. Some enzymes get activated as a part of signal transduction possess.
3. They help in the muscle contraction.
4. Enzymes present in pathogens are for infecting cells.
5. Enzymes can break large molecules into small molecules.

Industrial Applications of Enzymes

Enzymes are mostly used in the food, beer and dairy industry.
1. Enzymes from barley are widely used in breweries.
2. Rennin is used to manufacture cheese.
3. Enzymes like cellulose and pectinase are used to clarify fruit juices.
4. Enzymes are used in forensic science and molecular biology.
5. Amylases convert starch into glucose. They are used in the production of sugars from

starch.
6. Catalase is employed in the rubber industry to form oxygen, which converts latex to

foam rubber.

Memory Plus

The human body contains about 3,000 enzymes that are constantly regenerating, repairing
and protecting us. Enzymes are specific in function. They function with only one reactant
to produce a specific product.

Nucleic Acids

Nucleic acids are large organic compounds found in the chromosomes of living cells and
viruses. They are also one of the most important biological macromolecules in all living
beings. Nucleic acids are found either in a free-state or bound to proteins as nucleoproteins.
They are a linear polymer of nucleotides.

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Nucleotides and their structure . ~xs
I N NH
Nucleotides are made up of pentose sugar,
a nitrogenous base and a phosphate group. O= r - O - C2 ~ Nitrogenous
Nucleosides are structural subunits of nucleic
acids. It is made up of nitrogenous base attached 0- HH (adb:~i~e)
to a pentose sugar. A nitrogenous base is simply Phosphate HH

group OH H

a nitrogen-containing molecule that has the same General Structure Sugar
chemical properties as a base. There are five types Structure of Adenine

of nitrogenous bases. Two of these bases are purine and the other three are pyrimidine.

Purine: Purine bases have a double-ring structure. These are adenine(A) and guanine(G).

Pyrimidine: Pyrimidine bases have a single-ring structure. These are cytosine(C),
thymine(T), and uracil(U).

Types of Nucleic Acids

There are two types of nucleic acids: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).

DNA (deoxyribonucleic acid): DNA is a double helical macromolecule. It contains
genetic information. The nitrogenous bases in DNA are A, C, G and T. The DNA
segments carrying genetic information are called genes. DNA is found inside the cells
in long structures called chromosomes.

RNA (ribonucleic acid): RNA is a single stranded macromolecule that is essential for
protein synthesis in organisms. It contains genetic information in some viruses. The
nitrogenous bases in RNA are A, C, G and U. There are three types of RNA: transfer
RNA (tRNA), messenger RNA (mRNA) and ribosomal RNA (rRNA).
Importance of nucleic acids

1. Nucleic acids store and transfer genetic information.
2. They control the development of an individual.
3. Mutation results from deletion, addition and replication of nitrogen bases of DNA,

which help to form variants.

4. DNA controls the synthesis of RNA in a cell and RNA directs the synthesis of proteins.

Inorganic Compounds

Minerals

Minerals are essential inorganic nutrients for organisms to perform functions necessary for

life. Inorganic biomolecules are minerals. There are 24 elements that are used in our body.

There are eight major elements essential for growth and development of living beings.

Such elements are called essential elements. They are sodium, chlorine, potassium, calcium,

phosphorus, nitrogen, sulphur and magnesium. These elements are also known as macro

elements. Some elements like fluorine, zinc, iodine, iron are needed in trace amounts. These

elements are known as trace elements. These minerals are important for the well-being of

the human body. They have various functions like formation of tissues, conduction of nerve

impulses, formation of blood, etc. We obtain minerals from plants as they absorb them from

the soil.

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Water

Water is the main components of cell. It makes about 60-90% of the total chemical content of
the cell. It is responsible for the living nature of cell. It is found in two forms: free form that can
be used for metabolic processes and bound form that is bound with other molecules. Nearly
95% of water occuring in cells is found in the free state. While 5% is in the bound state to other
molecules.

Importance of water

1. It is the universal solvent.
2. Different metabolic reactions like digestion, photosynthesis requires water.
3. It aids in the movement of plant organs like opening and closing of stomata, dehiscence

of fruits, etc.
4. Water helps to transport materials from one cell to another.
5. Water maintains turgidity of cell.

Answer writing skill

1. Define biomolecules.

Biomolecules are organic molecules present in living things and are involved in the
growth, repair and metabolic process of living organism. For example: carbohydrate,
protein, lipid, etc.

2. What are polysaccharides?

Polysaccharidesarea complex carbohydrate formed by many monosaccharides joined
together by a glycosidic bond. They are usually tasteless and non-soluble in water.
Example: starch, glycogen, cellulose and chitin.

3. List the name of essential aminoacids.

Essential amino acids are valine, leuine, methionine, lysine, isoleucine, phenylalamine,
threonine and tryptophan.

4. Write down the differences between monosaccharides and disaccharides.

Monosaccharide Disaccharide

Monosaccharide consists of a single sugar Disaccharide consists of two

molecule. monosaccharides.

It is the simplest form of carbohydrate. It is a complex form of carbohydrate.

Example: glucose, frutose, galactose, etc. Example: maltose (glucose + glucose),

lactose (glucose + galactose) and sucrose

(glucose + fructose).

5. Write short notes on minerals.

Minerals are inorganic biomolecules. Minerals are important for the well-being of

the human body. We obtain minerals from plants as they absorb them from the soil.

Essential minerals may be categorized into macro elements and micro elements.

Macro elements are the major minerals required in sufficient amounts in our diet.

0258 Optional Science - 10 BIOLOGY

They are sodium, chlorine, potassium, calcium, phosphorous, sulphur and magnesium.
Some elements needed in trace amounts are known as micro elements. They are
fluorine, zinc, iodine, iron etc. The functions of minerals are:

1. Formation of tissues. 2. Conduction of nerve impulses.

3. Formation of blood.

6. Differentiate between simple and derived lipids.
Simple lipids are esters of fatty acids with alcohols,whereas derived lipids are obtained
by the hydrolysis of simple and compound lipids. Examples of simple lipids are fats,
oils and waxes while derived lipids are glycerol, fatty acids, steroid hormones, etc.

7. What is the significance of enzymes?
Enzymes are biocatalysts, which help to speed up the chemical reaction during different
metabolic processes like digestion, respiration, photosynthesis, etc. inside the cells. The
significance of enzymes is as follows:
1. Enzymes like amylase and protease play an important role in digestion.
2. Enzymes present in pathogens are usedfor infecting cells.
3. Enzymes from barely are widely used in breweries.
4. Rennin is used to manufacture cheese.
5. Enzymes like cellulose and pectinase are used to clarify fruit juices.
6. Enzymes are used in forensic science and molecular biology.

8. What is a carbohydrate? What are its types? Write any two importances of carbohydrates.

A carbohydrate is the most abundant biomolecule that contains carbon, hydrogen and
oxygen as its main elements. The general formula of carbohydrate is written as (CH2O)
n. Carbohydrates are often referred to as sugars or saccharides.

There are three main types of carbohydrates on the basis of the number of sugar units.
They are monosaccharides, oligosacharides and polysaccharides.

Monosaccharide: A monosaccharide is the simplest group of carbohydrate. It consists
of a single sugar molecule. It is sweet in taste and soluble in water. Example: glucose,
fructose, galactose, ribose and deoxyribose.

Oligosacchaside: Oligosacchasids si a type of sugar containing a .2-10 monosccnorides.

Disaccharide: Disaccharides are formed by two monosaccharides joined together by a
glycosidic bond. It is sweet in taste and soluble in water. Example: maltose (glucose +
glucose), lactose (glucose + galactose) and sucrose (glucose + fructose).

Polysaccharide: A polysaccharide is a complex carbohydrate formed by many
monosaccharides joined together by a glycosidic bond. It is usually tasteless and non-
soluble in water. Example: starch, glycogen, cellulose and chitin.

The two importances of carbohydrate are:

1. Carbohydrates are macronutrients that build body strength and serve as excellent
energy providers.

2. The fibers present in carbohydrates help to control constipation.

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Exercise

Section "A"

1. Define biomolecules with example.

2. What are carbohydrates?

3. Define each of the followings:

a. monosaccharides b. disaccharides

c. oligosaccharides d. polysaccharides

4. Write two examples of each of the followings:

a. Monosaccharides b. oligosaccharides c. Polysaccharides

5. What are the component sugar molecules in each of the followings:

a. Maltose b. lactose c. sucrose

6. What are lipids?

7. What are derived lipids?

8. Write two examples of each of followings:

a. Simple lipid b. complex lipid c. derived lipids

9. What are proteins?

10. Give name of some biologically important proteins.

11. What are amino acids?

12. How many types of amino acids are there that make up proteins?

13. What are semi-essential amino acids?

14. What is the calorific value of each of protein and carbohydrates?

15. Name two malnutrition in young children and babies due to deficiency of protein.

16. What are enzymes? Write two examples?

17. What is nucleic acid?

18. Name two essential elements and two trace elements that are found in human body.

Section "B"

1. What are the sources of lipid?
2. Differentiate between essential amino acid and non-essential amino acid.
3. Write two differences between simple lipids and complex lipid.

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4. Egg is considered as a reference protein, why?
5. Why do athletes, laborer, etc. need high carbohydrate in their diet?
6. Proteins are known as building blocks of life, why?
7. Write any two importance of each of protein, carbohydrate and nucleic acid each.
8. Write two differences between essential amino acids and non-essential amino acids.
9. Write two differences between first class protein and second class proteins.
10. Write importance of enzymes.
11. Vegetarians must take special care of dietary to meet their protein need, why?
12. Write any four characteristics of enzymes.
13. List six different groups of enzymes.
14. Write two differences between essential elements and trace elements.

Section "C"

1. What roles do the proteins play in our body?
2. Write a brief note on carbohydrate.
3. Write in short about sources of carbohydrates.
4. How can we fulfill the need of proteins in our body through diet? Write on the

basis of its different sources.
5. Explain in short about the factors that affect enzyme activity.
6. Write three biological functions of enzymes.
7. Write three industrial applications of enzymes?
8. Write three importance of nucleic acids.

Section "D"

1. What is the role of enzymes in the body of living organisms? Explain in brief.
2. Explain in brief about the importance of biomolecules in our daily life.
3. Enzymes are called bio-catalyst. Explain.
4. ‘Human diet must be a balanced diet’. Justify it on the basis of your learnings

about biomolecules.
5. Explain in brief about nucleotide and its structure.
6. Mention the role of inorganic compounds in the body of living organisms.

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Multiple choice questions

1. There are ……… types of essential amino acids in the nature.

a.8 b. 12

c. 20 d. 10

2. Lactose is a combination of

a. glucose + glucose b. fructose + galactose

c. glucose + fructose d. glucose + galactose

3. In which of the following group are all polysaccharides?

a. sucrose, glucose and fructose b. maltose, lactose and fructose

c. glycogen, sucrose and maltose d. glycogen, cellulose and starch

4. In RNA, thymine is replaced by

a. adenine b. guanine

c. cytosine d. uracil

5. Glycogen is an example of

a. monosaccharides b. disaccharides

c. oligosaccharides d. polysaccharides

6. Kwashiorkor is due to the deficiency of:

a. carbohydrates b. lipid

c. proteins d. nucleic acid

Project Work

Work in a group to make a chart on a cardboard. Collect information of different
biomolecules including their structure, sources, types, functions, etc. Finally present your
work in the classroom.

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UNIT

14 CELL BIOLOGY

Rudolf Ludwig Carl Virchow (1821-1902) was a German physician, anthropologist,
pathologist, prehistorian, biologist, writer, editor and politician, known for his advancements
in public health. He is known as the Father of modern pathology as his work brings more

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Syllabus issued by CDC Learning objectives:

Theory 9 At the end of this unit, the students will be able to:
Practical 3 • describe the types and functions of plant tissue

and animal tissue.
• describe the structure of the root and stem of a

monocot and dicot plant by observing them.

Key terms and terminologies of the unit

1. Cell biology: Cell biology is a branch of life science that deals with the study of cell
structure, its functions and its chemistry.

2. Tissue: A tissue can be defined as a cluster of cells, similar in structure and performing
a particular function.

3. Epithelial tissue: Epithelial tissue is the membranous animal tissue with one or more
layers of closely packed cells that forms the outer covering or lining part of the body,
including bodily cavities and vessels.

4. Simple epithelium: An epithelial tissue with a single layer of epithelial cells that are
in direct contact with the basement membrane is called simple epithelium.

5. Compound epithelium: An epithelial tissue formed of several layers of epithelial
cells is called compound or stratified epithelium.

6. Connective tissue: Tissues with cells embedded in an amorphous matrix that connect,
support, bind, or separate other tissues or organs are called connective tissues.

7. Tendon: A parallel array of closely packed white fibrous tissues is called tendon.
8. Ligament: A band of dense bundles made of yellow elastic fibers is called ligament.

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9. Muscular tissue: Muscular tissues are the soft tissues capable of contraction and
relaxation which are made up of long cylindrical fibers arranged in a parallel way.

10. Nervous tissue: Nervous tissue or neural tissue is the primary tissue composed of the
cells in the central nervous system and peripheral nervous system which is responsible
for receiving stimuli and transmitting signals to and from different parts of an organism.

11. Stem: Stem is the vascular part of a plant above the ground consists of nodes and
internodes.

12. Pectin: Pectin is a carbohydrate found mostly in the skin and core of a raw fruit.

13. Lignin: An organic substance binding the cells, fibers and vessels, which constitute
wood and the lignified elements of plants.

14. Vascular cambium: The secondary meristematic tissue that forms the vascular tissues
(xylem and phloem).

15. Vascular bundle: A vascular bundle is a part of the transport system in vascular plants

16. Root: A root is a vascular part of plant present normally underground.

17. Cell division: Cell division is the process by which a mother cell divides into two or
more daughter cells.

18. Cell cycle: The cell cycle is the sequence of changes that takes place in the cells during
cell growth and cell division.

19. Interphase: Interphase is the stage during which a cell prepares, grows and accumulates
nutrients needed for cell division.

20. Cytokinesis: Cytokinesis is the division of cytoplasm into two separate cells which
occurs concurrently with nuclear division in M-phase of cell cycle.

21. Centriole: Centriole is a minute cylindrical organelle near the nucleus in animal cells,
occurring in pairs and involved in the development of spindle fibers in cell division.

22. Chromatids: The two thread like strands into which a chromosome divides
longitudinally during cell division are called chromatids.

23. Sister chromatids: 'one-half' of a duplicated chromosome is called sister chromatid.

24. Mitosis: Mitosis is the division of a mother cell into two daughter cells with equal
number of chromosomes to that in mother cell.

25. Somatic cells: All the body cells of an organism that are responsible for growth and
development of the body, except the gametes (sperm or ovum) are called somatic cells.

26. Meiosis: Meiosis is the division of a mother cell into four daughter cells (sex cells or
gametes) each having half number of chromosomes than that in the mother cell.

27. Synapsis: The process of pairing up of homologous chromosomes to form a bivalent is
called synapsis.

28. Chiasmata: The points of contact between two non-sister chromatids are called the
chiasmata

29. Crossing-over: The process of exchange of genetic material from the chiasmata in
between two non-sister chromatids of homologous pair is called crossing over.

30. Terminalization: The process of movement of chiasmata towards the end of the

chromosome and disappear is called terminalization.

0264 Optional Science - 10 BIOLOGY

Introduction

The cell is the structural and fundamental unit of life. Cell biology is a branch of life science
that deals with the study of cell structure, its functions and its chemistry. Cell biology is also
termed as cytology. The term cytology was derived from two Greek words; kytos, which
means hollow, vessel an logos, which means study.

Cell biology is concerned with the physiological properties, metabolic processes, signaling
pathways, life cycle, chemical composition and interactions of the cell with their environment.
Cells organize in a specific way to give structure of tissues. In this unit we will learn about
animal tissues, plant tissues, structure of roots and stem of each of monocot plants and dicot
plants. We will also learn about the two different types of cell division (mitosis and meiosis)
that occurs in body cells with their significance in life processes.

Tissue

Tissues are absent in unicellular organisms. Multicellular animals and plants have tissues that
organize and regulate their response to their environment. The word tissue is derived from a
latin word 'tissu' which means 'weave'. Cells are woven together to form tissues. A tissue consists
of a group of structurally and functionally similar cells. Therefore, a tissue can be defined as a
cluster of cells, similar in structure and performing a particular function. The study of tissues
is called histology.

Animal Tissue

There are four types of tissues found in animals. They are: epithelial tissue, connective tissue,
muscular tissue and nervous tissue (Nevral tissue).

Animal Tissues

Epithelial Tissue Connective Tissue Muscular Tissue Nervous Tissue

Simple epithelium Stratified epithelium Skeletal muscle Smooth muscle Cardiac muscle

Simple Simple Simple Loose connective Dense connective Specialized connective Fluid connective
squamous cuboidal columnar

Areolar Adipose White fibrous Yellow fibrous Cartilage
.___•_ ___.I .__It_ __.I ._.~_I~--_-L_=_=_=_=. =~--------~=~-I=~==I-'..-~=;==I=-=-1=:=:~===Ciliated cuboidal Brush bordered Stratified squamous Stratified cuboidal Stratified columnar TransitionalepitheliumBones

f* i
Keratinized epithelium Non-keratinized epithelium

Ciliated columnar Brush bordered columnar Glandular columnar ~ Blood Lymph

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A. Epithelial Tissue (Epithelium)

There are group of cells in our body that cover the surface of organs, such as the surface of
the skin, reproductive tract, airways and inner linings of the digestive tract, etc. Such a group
of cells forms an epithelial tissue. Epithelial tissue is the membranous animal tissue with one
or more layers of closely packed cells that forms the outer covering or lining part of the body,
including bodily cavities and vessels. This tissue provides a barrier between the external
environment and the organ it covers.

Characteristics: Epithelial tissue is composed of tightly packed cells. It lacks blood vessels but
supplied with nerve fiber. It has a high regenerative ability.

Types of epithelial Tissue: On the basis of layers of cells in the epithelial tissues, there are two
types of epithelial tissues: simple epithelium and compound epithelium.

1. Simple epithelium

An epithelial tissue with a single layer of epithelial cells that are in direct contact with the
basement membrane is called simple epithelium. It functions as a lining of cavities of
body, ducts and tubes. On the basis of structural modification the simple epithelium is
divided into three types: Simple squamous epithelium, Simple cuboidal epithelium and
Simple columnar epithelium.

a. Simple Squamous epithelium: This tissue contains thin, flat fig: Simple squamous epithelium
and polygonal cells in a single layer with irregular margins.
Cells have an oval nucleus in the middle part. They are
arranged like the tiles on a floor. Therefore, it is also known
as pavement epithelium.

It forms the lining of the coelom, buccal cavity, walls of blood vessels, Bowman’s capsule
of nephron in kidney and alveoli of lungs. It helps in the protection, absorption,
ultrafiltration and exchange of gases.

Fact with reason

Simple squamous epithelium is also called pavement epithelium, why?

In simple squamous epithelium, cells are flat with flattened and oblong nuclei. It has a
tile-like appearance. So, it is also called pavement epithelium.

b. Simple Cuboidal epithelium: This tissue contains cubical fig: Simple cuboidal epithelium
cells in a single layer. Cells have a round nucleus at the
center. It is found in the lining of many ducts of the
kidney, glands, testis, ovary, etc. and tubules of nephrons.
It helps in secretion, absorption and excretion. There are
two types of cuboidal epithelial tissue: ciliated cuboidal
and brush bordered cuboidal.

i. Ciliated cuboidal: The cuboidal cell having cilia on the free surfaces is called a ciliated
cuboidal cell. Cilia help in the conduction of mucus and other substances. It is located
on the ducts of nephrons.

ii. Brush bordered cuboidal: The cuboidal cell having microvilli on the free surfaces is
called a brush bordered cuboidal cell.

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c. Simple Columnar epithelium: This tissue contains elongated cells

in a single layer. They are placed side by side like columns. An

elongated nucleus is located at the basal end of the cell. The free

surface of these cells may have microvilli. It forms the lining of the

stomach, gastric glands, intestinal glands, gall bladder, ureter and

uterine wall. There are three types of columnar epithelium: fig: simple columnar
epithelium
i. Ciliated columnar epithelium: Columnar cell having cilia cilia
on the free surface is called a ciliated columnar cell. It is

present in the fallopian tubes, bronchioles, spinal cord. It nucleus

secretes mucus and helps in the movement of particles in a fig: Ciliated columnar epithelium

specific direction.

ii. Brush bordered columnar epithelium: Columnar cell having microvilli on the free
surfaces is called a brush bordered columnar cell. It is present in intestinal mucosa. It
helps to increase the surface area for absorption.

iii. Glandular columnar epithelium: It is made up of modified columnar or cuboidal
cells. It helps in the secretion of chemical substances. It is found in the liver, pancreas,
mammary glands, sweat glands. It forms glands.

Memory Plus

Pseudostratified columnar epithelium is formed by a single layer of cells that
gives an appearance of being made from multiple layers when we look at
cross-section. The nuclei of such epithelial cells are at different levels leading
to the illusion of being stratified. Pseudostratified columnar epithelium
tissue is found mostly in the inner walls of upper respiratory tract (nose,cfoiglu: mPsneaurdeopsittrhaetliifiuemd
trachea, bronchi) and hence also called as respiratory columnar epithelium.

2. Compound or stratified epithelium

An epithelial tissue formed of several layers of epithelial cells is called compound or
stratified epithelium. It is also called multi-layered tissue. Basement membranes are usually
absent in compound epithelium. Its main function is to protect underlying structure from
mechanical wear and tear. Compound epithelium covers dry surface of skin, moist surface of
buccal cavity, pharynx and inner lining of salivary glands. Compound epithelium are of
following types:

a. Stratified squamous epithelium: It is made up of several layers

of cells. The upper layer is made up of squamous cells. The

lower layer is made up of germinative columnar or cuboidal

cells. The stratified squamous epithelium is of two types: fig: Stratified squamous epithelium

i. Keratinized epithelium: This tissue contains a protein called keratin in its upper layer.

This layer is hard. It makes the layer water proof. It is present in outer dry surfaces of

the body like hair, claws and nails. Keratinized epithelium is resistant to friction and

bacterial infections.

ii. Non-keratinized epithelium: The upper layer of this tissue contains living cells. Due
to the absence of keratin, this layer becomes wet. It is present on wet surfaces like
buccal cavity, pharynx, oesophagus and vagina. Non-keratinized epithelium protects
the surface from drying.

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b. Stratified cuboidal epithelium: The upper layer of this tissue is

made up of cuboidal cells. The lower layer is made up of either

germinative columnar or squamous cell. The word germinative

indicates the outward growth of cells to the surface. Stratified

cuboidal epithelium is found in the lining of ducts of sweat glands,

salivary glands, mammary galnds, conjunctiva of eyes, etc. It helps fig: Stratified cuboidal
to circulate nutrients and increase absorption. epithelium

c. Stratified columnar epithelium: The upper layer of this tissue is Dome Cell
made up of columnar cells. The lower layer is made up of germinative
cuboidal cells. It is found in the lining of vasa deferntia, male urethra,
trachea, bronchii, etc. It helps in protection and secretion.

d. Transitional epithelium: This tissue is made up of several layers of

cells. The cells in the upper layer are dome shaped. The cells in the

middle layer are club shaped. The cells in the basal layer are cuboidal

in shape. This tissue has the ability to stretch and relax. It helps in Basement Basal
Membrane Cells

the expansion of the organ. It is found in the urinary bladder and fig: transitional epithelium

ureter.

Function of epithelial tissue

Following are the important functions of epithelial tissues:

1. It covers the body and makes lining of organs like lining of the mouth, alimentary canal, etc.

2. It helps to protect organs from microorganisms, injury and fluid loss.

3. It helps in absorption of water and nutrients. For eg., epithelial tissues in the wall of
intestine help in absorption of water and nutrients.

4. It helps in the elimination of waste from the body. For eg., epithelial tissues in kidneys
help to excrete wastes).

5. It secrets enzymes and hormones in the glands. For eg., epithelial tissues in glands help
to secrete hormones or enzymes.

B. Connective tissue

The tissues with cells embedded in an amorphous matrix that connect, support, bind, or
separate other tissues or organs are called connective tissues. Connective tissues are fibrous
tissues. They are made up of a non-living material called extracellular matrix. This matrix can
be either liquid or rigid solid. Connective tissues give shape to organs and hold or connect
them in place. Example: blood, bone, tendon, ligament, adipose and aerolar tissues.

Types of Connective Tissues

There are four types of connective tissue: Loose connective tissue, Dense connective tissue,
Specialized or supportive connective tissue and Fluid connective tissue.

1. Loose connective tissue: Loose connective tissue is the most common type of connective
tissue in vertebrates. It holds organs in place and attaches epithelial tissue to other
underlying tissues. A loose connective tissue has cells and fibres that are loosely arranged
in a jelly like substance containing white collagen fibers or yellow elastic fibers or both.
There are two types of loose connective tissue: Areolar tissue and adipose tissue.

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a. Areolar tissue: Areolar tissue contains loosely arranged matrix having fibers (white

collagen fibers and yellow elastic fibres) and cells. It contains cells like fibroblast,

macrophages, mast cell, fat cells and Ret ic ula r Mast cell
lymphocytes. It is present beneath the fibers
skin, between and around the muscles, Elastic
blood vessels, alimentary canal, Fixed fibers
respiratory tract, etc. It forms the macrophage
basement membrane of epithelium. Free
Antibody macrophage
Functions: producing cell Collagen
fibers
Blood in
vessel Fibroblast
Stem cell
A~~1r:)

i. It binds the skin with the muscles. Ground - White blood
ii. It helps in healing wounds. s u bstance cell

fig: Areolar tissue

b. Adipose tissue: It contains large Adipose T issue
amounts of fat cells (adipocytes).
Fibers are fewer in amounts or absent
in adepose tissue. This tissue is found
below the skin, around the heart, kidney
and eye ball.

Functions: Nucleus _ _ _ ___,
i. It regulates the body temperature.

ii. It stores fat.

iii. It protects the organs from injury. fig: Adepose tissue

2. Dense connective tissue: Dense connective tissue has fibers as its main matrix element.
Fibers and fibroblasts are packed compactly in dense connective tissue. It forms strong,
rope-like structures such as tendons and ligaments. Dense connective tissue also make up
the lower layers of the skin (dermis). There are two types of dense connective tissue: white
fibrous tissue and yellow fibrous tissue.

a. White fibrous tissue: It is a modified form of areolar tissue. It contains a thick layer
of white collagen fibers which are tough but non-elastic. These tissues are found as
a sheath in the pericardium of the heart, in brain (duramater), cornea of the eyeball,
coverings of the cartilage and bones. A parallel array of closely packed white fibrous
tissues is called tendon. It is a flexible but inelastic cord. Tendon attaches skeletal
muscles to bones.

Function: It provides mechanical protection when muscles are stretched.

b. Yellow fibrous tissue: It is also a modified form of areolar tissue. It contains a thick
layer of elastic, flexible and closely packed yellow elastic fibers. These fibers are
straight and branched. A band of dense bundles made of yellow elastic fibers is
called ligament. They are more stretchy and contain more elastic fibers than tendons.
Ligaments connect bones to other bones at joints.

Function: It allows stretching and elasticity.

3. Specialized connective tissue (Supportive connective tissue): These tissues form the
endoskeleton of vertebrates. They protect the delicate organs from different kinds of
injuries. Cartilage and bones are skeletal connective tissues.

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a. Cartilage: It is a tough, smooth and flexible connective tissue. It is made up of
cartilage cells called chondrocytes. It is found on the tip of the nose, outer ear joints,
etc.

b. Bones: It is a hard connective living tissue. It is made up of living bone cells called
osteocytes. It gives the structural frame to the body of vertebrates. The bone marrow
in some bones is the site of production of blood cells.

Memory Plus

Bones contains inorganic salts mainly calcium, phosphate and calcium carbonate.

4. Fluid connective tissue: Fluid connective tissues are present in liquid form. They circulate
materials in the body, regulate the body temperature, minerals and water. They also
protect the body. Blood and lymph are fluid connective tissues.

a. Blood: Blood is a red, viscous fluid connective tissue. It is slightly alkaline (pH 7.2-7.3)
in nature. It contains pale yellow plasma and three kinds of blood cells, or corpuscles.
The blood cells are the red blood cells (RBC), white blood cells (WBC) and platelets.

Functions:

i. It transports digested food materials, excretory
waste, hormones and respiratory gases inside
the body.

ii. Platelets help in the coagulation of blood and _ • ._ ___,,~white blood
Blood sample cells
protect the body from excessive blood loss.

iii. WBC provides defence against various diseases platelets
and infections.
fig: composition of blood
iv. Blood helps to keep the body temperature stable.

b. Lymph: Lymph is a transparent, slightly yellowish, alkaline fluid connective tissue.
It contains glucose, salts, amino acids and vitamins. Lymph is similar to the blood but
RBCs and some other proteins of blood are absent. It circulates in the body through
the lymph vessels.

Functions:

1. It transports respiratory gases, food materials, hormones to the blood.

2. It brings antibodies from the lymph nodes to the blood.

3. It destroys pathogens and foreign particles.

Functions of connective tissue:

1. It binds and supports various tissues and organs in the body.
2. It helps to lessen the friction during the movement of the body organs.
3. It protects the body against infection.
4. Fat stored in adipose tissues forms an insulation in the body against heat loss.
5. Cartilage and bone give a definite shape to the body.
6. It stores and transports chemical substances in the body.

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C. Muscular tissue

Muscular tissues are the soft tissues capable of contraction and relaxation which are made
up of long cylindrical fibers arranged in a parallel way. These very fine contractile fibres
in muscular tissues are known as myofibrils. These are the basic functional unit of skeletal
muscle. The function of the myofibril is to perform muscle contraction.

Types of Muscular Tissues

There are three types of muscular tissue: Skeletal muscle, smooth muscle, and cardiac muscle.

1. Skeletal muscle: Skeletal muscle Smooth
is a voluntary muscle. It is closely muscle
attached to the bones. It helps in fibers
the movement of the structures of
the body. It gives general support Junction
and maintains the body’s posture. between
It is also known as striated, or adjacent
striped, muscle.
cells

(a) (c)

fig: (a) skeletal muscle (b) smooth muscle and (c) cardiac muscle

2. Smooth muscle: Smooth muscle is an involuntary muscle. It is found in the inner linings
of organs visceral organs like blood vessels, urinary bladder, stomach, intestine, etc. It
helps in passing food materials and fluids. It is also known as unstriated, or unstriped
muscle.

3. Cardiac muscle: Cardiac muscle is only found in the wall of heart. It is the most important
involuntary muscle. It works continuously without fatigue. Cardiac muscle helps our
heart to contract and relax. It helps the heart to pump blood through the heart. Cardiac
muscle looks like skeletal muscle (i.e. looks striated or striped). Unlike skeletal muscle the
contraction of cardiac muscle tissue is not in our control, so it is called involuntary.

Fact with reason

Skeletal muscle is called a voluntary muscle, why?

Skeletal muscle is called a voluntary muscle as the movement of this muscle is under
the control of our will.

Skeletal muscle is called a straited muscle, why?

Skeletal muscle has a repeating functional units. The presence of repeating functional
units results a series of bands visible along the muscle fibers. So, skeletal muscle is also
called a straited muscle.

Smooth muscle is also known as visceral muscle, why?

Smooth muscle is found in the walls of all visceral organs (the internal organs in the
main cavities of the body) except the heart. So, it is also known as visceral muscle.

Smooth muscle and cardiac muscle are called involuntary muscle, why?

The movement of smooth muscle and cardiac muscle is not in our control but under the
control of autonomic nervous system. So these muscle are called involuntary muscle.

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Function of Muscular Tissue

1. The main function of muscular tissue is movement. Contraction of skeletal muscle
fibers causes the bone movement in our body.

2. The muscle provides the framework for the body and also helps in maintaining the
body posture.

3. The contraction of muscle produces heat, it helps to maintain a constant temperature of
the body.

4. Muscular tissue assists with the movement of cardiovascular and lymphatic vessels
through contractions.

5. Muscular tissue protect internal organs and contribute to joint stability.

D. Nervous Tissue Dendrite
Nucleus
Nervous tissue or neural tissue is the primary tissue Cell body
composed of the cells in the central nervous system Axon
and peripheral nervous system which is responsible for
receiving stimuli and transmitting signals to and from Myelin sheath
different parts of an organism. In the central nervous Node of ranvier
system, neural tissues form the brain and spinal cord.
In the peripheral nervous system, neural tissues form Direction
the cranial nerves and spinal nerves. Nervous tissue of impulse
consists of two main types of cells: Axon terminal
Synapse

fig: Neuron

1. Nerve cell: It is also known as neuron. It transmits electrical nerve impulses that move
information around the body.

2. Neuroglia: Neuroglia are also known as glia. These are non-neuronal cells in the central
nervous system and peripheral nervous system. They provide support and protection
for neurons. Astrocytes, ependymal cells, microglial cells, oligodendrocytes and Schwann
cells are examples of glia.

Function of Muscular Tissue

1. Nervous tissues transmit message of external and internal stimuli. Neurons receive
signals from dendrites and send out through axon.

2. Neuroglia provide support, nutrition and insulation for the neurons.
3. Nervous tissues are responsible for controlling movements of specific parts of the body.

For example, for arm movement the nerve impulses are send to effector muscles in the
arm.
4. Nervous tissues work to stimulate activities that can occur at rest such as digestion,
waste excretion, etc.

Activity

Study the histological/permanent slides of different types of animal tissues under a

microscope. Draw a diagram along with the labelling and explain about the observed

tissues.
··cs-····································· .............................................................

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Stem

Stem is the vascular part of a plant above the ground consists of nodes and internodes. It
comes under shoot of a plant that describes the new plant growth including stem, leaves and
flowers. Stem provides a pathway for transporting waters and miners in the plant body. It acts
as a storage site for carbohydrates.

The forms of stem may vary with plants: Cylindrical (it shows circular outline in transverse
section), Angular (it reveals three or four-angles in transverse section), Fistular (solid at the
nodes and hollow at the internodes), etc. On the basis of position with respect to the ground,
there are three types of stems: aerial, sub-aerial and underground stem.

Internal structure of a monocot stem

The internal structure of a monocot stem can be studied by taking a transverse section through
the internode of a monocot plant like grass, maize, bamboo, etc. A transverse section of a
monocot stem shows the following structure:

1. Epidermis 2. Hypodermis 3. Ground tissues 4. Vascular bundles

1. Epidermis: The epidermis is the outermost covering of the stem. It is made up of a single
layer of compactly arranged barrel shaped parenchyma cells. Therefore, intercellular
spaces are absent. It is covered with a thick cuticle. It lacks trichomes (multicellular
hairs). It contains numerous openings called stomata. It plays a significant role in
protection.

2. Hypodermis: The hypodermis Epidermis Epidermis
lies below the epidermis. It Hypodermis Hypodermis
is made up of two or three Va s c u l a r
layers of compactly arranged bundles Vascular
sclerenchyma cells. Intercellular Ground bundles
spaces are absent in hypodermis tissue Xylem
too. It provides mechanical Phloem
support to the plant. fig: Internal structure of moncot stem Ground
tissue

3. Ground tissue: Ground tissue surrounds the vascular bundles. The major cells of the

ground tissue are parenchyma cells arranged in several layers which store nutrients.

In a monocotyledon stem, the ground tissue is not differentiated into the endodermis,

cortex and pericycle. It is represented by several layers of loosely arranged parenchyma

cells. It stores food.

Memory Plus

In some grasses, wheat, etc. the central portion of the ground tissue is hollow and is called
Pith cavity.

4. Vascular bundles: A vascular bundle is a part of the transport system in vascular plants.
In monocot stem, vascular bundles are irregularly scattered in the ground tissue. The
bundles are younger and smaller in size towards the periphery and older and larger
towards the center. This type of arrangement of the vascular bundle is called centrifugal
arrangement. Each vascular bundle is covered by a single layer of sclerenchyma cells,
known as a bundle sheath.

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On the inner surface of the vascular bundle, xylem is found and towards its outer
surface phloem is found. Cambium is absent. These vascular bundles are described as
conjoint, collateral and closed.

a. Xylem: Xylem consists of tracheids, Bund le Sheath
vessels, xylem parenchyma and
xylem fibres. In the xylem, there are ;;;::i,r;~~C:::Ji:ur - Phloem
two metaxylem and two protoxylem
vessels. These vessels are arranged in ....;~ ff'~:"'.:l~- - Metaxylem
the shape of 'Y'. The lower protoxylem
vessel are fused to form a cavity which Protoxylem lacuna
remains filled with water. It is known as Ground tissue
protoxylem cavity or lysigenous cavity.
fig: Vascular bundles in monocot stem

b. Phloem: Phloem consists of sieve tubes, companion cells and phloem fibers. Phloem
parenchyma is absent in monocot vascular bundles.

Characteristic features of a monocot stem

1. Epidermis is single layered and presence of a thick cutical.

2. Absence of epidermal hairs (trichomes).

3. Epidermis consists of stomata with guard cell.

4. Presence of hypodermis made up of sclerenchyma cells.

5. Ground tissues not differentiated into endodermis, cortex and pericycle.

6. Vascular bundles are oval, conjoint, collateral and closed.

Internal structure of a dicot stem

A transverse section of a dicot stem shows the following structures:

1. Epidermis 2. Hypodermis 3. Cortex

4. Endodermis 5. Pericycle 6. Vascular bundles

7. Cambium 8. Medullary rays 9. Pith

1. Epidermis: The epidermis is Epidermis

the outermost covering of the Epidermal hair Collenchyma
stem. It is made up of a single Parenchyma
layer of compactly arranged Epidermis Endodermis
barrel shaped parenchyma Hypodermis Pericycle
cells. Therefore, intercellular
spaces are absent. The cells are Parenchyma Phloem
slightly thick walled. It consists Endodermis Cambium
of numerous multicellular Pericycle Metaxylem

Vascular Protoxylem
bundle

Medullary rays

projection called trichomes Pith Pith
(epidermal stem hairs). The

epidermis is covered by a thin fig: Internal structure of dicot stem

transparent waxy covering called cuticle. This cuticle helps to prevent water loss. It also

contains stomata. Stomata are mainly involved in transpiration.

0274 Optional Science - 10 BIOLOGY

2. Hypodermis: The hypodermis is present just below the epidermis. It is made up of
four-five layers of collenchyma cells. These cells are compactly arranged. Therefore,
intercellular spaces are absent. The cells are thick walled due to the deposition of
cellulose and pectin. These cells contain chloroplast. Hypodermis provides mechanical
protection and additional support to the epidermis.

3. Cortex: The cortex is made up of several layers of loosely arranged parenchyma cells.
Therefore, intercellular spaces are prominent. It may contain chloroplast which helps in
photosynthesis. Cortex is the major storage organ in the stem.

4. Endodermis: The innermost layer of the cortex is called endodermis. It is wavy in
appearance. It is made up of compactly arranged barrel shaped parenchymatous cells.
Therefore, intercellular spaces are absent. These cells deposit more starch in the stem of
a dicot. Thus, the endodermis is also called a starch sheath.

5. Pericycle: The pericycle lies just below the epidermis. It is made up of a few layers of
compactly arranged sclerenchyma and parenchyma cells. The pericycle forms a cap like
structure above each vascular bundle, known as a bundle cap.

6. Vascular bundles: Vascular bundles are arranged in the form of a ring and are eight in
number. The vascular bundles are conjoint, collateral and open. Each vascular bundle
is made up of the phloem, cambium and xylem. The xylem is found on its inner surface
and phloem on the outer surface.

a. Xylem: Xylem lies toward the pith or center and composed of xylem vessels, tracheids,
xylem fibres (wood fibres) and xylem parenchyma (wood parenchyma). Protoxylem is
smaller with annular, reticulate or spiral thickenings, while metaxylem is wider with
pitted vessels.

a. Phloem: Phloem lies outside of the vascular bundle and composed of sieve tubes,
companion cells and phloem parenchyma. Companion cells are associated with sieve
tubes.

7. Cambium: The phloem and xylem are separated by a meristematic tissue known as
cambium. Cambium is a thin strip of two or three layered cells which are radically
arranged. It forms a thin strip between xylem and phloem. Cambium is a type of
lateral meristematic tissues. So cambium increases the thickness of the plant through
secondary growth.

8. Medullary rays: Medullary rays are parenchymatous, radially elongated or polygonal
cells. They are arranged radially. Medullary rays are part of the pith found between
vascular bundles. Their main function is to conduct food and water radially.

9. Pith: It is the innermost part of the stem. The pith is made up of loosely arranged
parenchyma cells. So, intercellular spaces are prominent. Pith helps in the storage of
food materials.

Characteristic features of a dicot stem

1. Cuticles and trichomes (epidermal stem hairs) are present.

2. Hypodermis is made up of collenchyma cells.

3. Chloroplast is present.

4. Presence of a wavy endodermis.

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5. Presence of eight vascular bundles arranged in the form of a ring.
6. The vascular bundles are conjoint, collateral and open.
Anatomical differences between monocot stem and dicot stem

Monocot stem Dicot stem

The vascular bundles are scattered across the Vascular bundles are arranged in the form of

stem without any definite arrangement. a ring.

Bundle sheath is present. Bundle cap is present.

Hypodermis is made up of two or three layers Hypodermis is made up of four-five layers of

of compactly arranged sclerenchyma cells. compactly arranged collenchyma cells.

Phloem parenchyma, Pith and pericycle are Phloem parenchyma, Pith and pericycle are

absent. present.

Vascular bundles are conjoint, collateral and Vascular bundles are conjoint, collateral and

closed. open.

Activity

To study the internal structure of a monocot and dicot stem.

Take any two stems: one of a monocot and another of a dicot. Cut fine sections of both the
stems. Put it in a watch glass, wash it and transfer a fine section or the thinnest cut onto
another watch glass and cover it with safranin for 1-2 minutes. Pick up the section, wash
it gently with water and keep on the glass slide. Put one drop of glycerine. Cover it with
a coverslip and observe it under a microscope. Draw a diagramand explain about the
observed structure.

Root

A root is a vascular part of plant present normally underground. Some plants (like money
plant, maize,etc.) have aerial roots. Root's function is to anchorage the plant and absorb water
and dissolved minerals from the soil and conduct it towards stem. It also acts as a reserve
material of food. There are two types of roots: Tap root and adventitious root.

Internal structure of a monocot root

A transverse section of a monocot root shows the Root hair
following structure: Epiblema
(Rhizodermis)
1. Epiblema 2. Cortex
Cortex
3. Endodermis 4. Pericycle

5. Vascular bundles 6. Conjunctive tissue

7. Pith

1. Epiblema: It is the outermost covering of the root

without cuticle. It is formed by a single layer of Pericycle
compactly arranged barrel shaped parenchyma
cells. These cells absorb water. Some of the Pith Epidermis
epiblema cells develop long unicellular hair like Pcealslsage Phloem
projections called root hairs. Protoxylem

Casparing

Thickening

fig: Internal structure of monocot root

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2. Cortex: The cortex is made up of several layers of loosely arranged parenchyma cells.
Therefore, intercellular spaces are prominent. It is a major component of the ground
tissue and helps in storage of water.

3. Endodermis: The endodermis is made up of compactly arranged barrel shaped cells.
It is the innermost layer of the cortex. Some cells of the endodermis are thin walled.
These cells allow water to pass into the xylem vessels. These cells are known as passage
cells. In the wall of the remaining cells of the endodermis, a waxy substance called
suberin gets deposited and makes it thick. These depositions are known as casparian
thickenings. It creates and maintains a physical force called root pressure.

4. Pericycle: The pericycle is formed by a single layer of parenchyma cells. It gives lateral
roots.

5. Vascular bundles: Vascular bundles are radially arranged in the form of ring. The
xylem and phloem are numerous in number. They lie on different radii alternating with
each other.

6. Conjunctive tissue: Conjunctive tissue is formed by loosely arranged parenchyma cells.
These cells are found between the vascular bundles. Conjunctive tissue stores water.

7. Pith: The pith is the central portion of the root. It is made up of loosely arranged
parenchyma cells. Therefore, intercellular spaces are present. It is well developed in a
monocot root. It stores food.

Characteristic features of monocot root

1. Presence of unicellular root hairs.

2. Presence of passage cells.

3. Presence of casparian thickenings in the endodermis.

4. Presence of conjunctive tissue.

5. Presence of radial vascular bundles.

Internal structure of a dicot root

A transverse section of a dicot root shows the following structures:

1. Epiblema 2. Cortex Root hair
3. Endodermis 4. Pericycle Epiblema

(Rhizodermis)

5. Vascular bundles 6. Conjuctive tissue Cortex
7. Pith

1. Epiblema: The epiblema is formed by a single layer of Epidermis
barrel shaped parenchyma cells. These cells are thin
walled and compactly arranged. Therefore, there are Phloem
no intercellular spaces. They absorb water. Some of Pericycle
the epiblema cells develop long unicellular hair like Protoxylem
Conjnctive tissue
Metaxylem

Casparian strip
Passage cell

projections called root hairs. It gives protection to the frofimg: Instoeriln.aSl sttorumctautrae oaf ndidcotcruotoitcle
roots and also helps in absorption of water and minerals

are absent.

2. Cortex: The cortex is made up of several layers of loosely arranged parenchyma cells.
Therefore, intercellular spaces are prominent. It is a major component of the ground
tissue meant for storing starch. The cells of the cortex allow free movement of water into
the xylem vessels.

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3. Endodermis: The endodermis is made up of compactly arranged barrel shaped cells.
It is the innermost layer of the cortex. Some cells of the endodermis are thin walled.
These cells allow water to pass into the xylem vessels. These cells are known as passage
cells. In the wall of the remaining cells of the endodermis, a waxy substance called
suberin gets deposited and makes it thick. These depositions are known as casparian
thickenings. It creates and maintains a physical force called root pressure.

4. Pericycle: The pericycle is formed by a single layer of parenchyma cells. Intercellular
space is absent.

5. Vascular Bundles: Vascular bundles are radial in arrangement. There are four bundles
each of xylem and phloem. They lie on different radii alternating with each other.

6. Conjunctive tissue: Conjuctive tissue is formed by loosely arranged parenchyma cells.
These cells are found between the vascular bundles. Conjunctive tissue stores water.

7. Pith: The pith is the central portion of the root. It is made up of loosely arranged
parenchyma cells. Therefore, intercellular spaces are present. It is reduced in dicot roots
or even absent in older roots. It helps in storage of food.

Characteristic features of a dicot root

1. Presence of unicellular root hairs.
2. Presence of passage cells.
3. Absence of hypodermis
4. Presence of casparian thickenings in the endodermis.
5. Presence of conjunctive tissue.
6. Presence of radial vascular bundles.
7. Absence of pith in older dicot plant.

Anatomical differences between monocot root and dicot root

Monocot root Dicot root

Xylem vessels are oval or rounded.. Xylem vessels are polygonal or angular in
Pith is large and well developed. shape.

Pith is absent or insignificant.

Conjunctive tissue does not form vascular Conjunctive tissue forms vascular cambium.
cambium.

Secondary growth does not occur. Secondary growth occurs.

Xylem and phloem are numerous in number. Xylem and phloem are limited in number.

Activity

To study the internal structure of monocot and dicot roots.

Take any two roots, one of a monocot and another of a dicot. Cut fine sections of both
the roots. Put themon a watch glass, wash and transfer a fine section or the thinnest cut
onto another watch glass and cover it with safranin for 1-2 minutes. Pick up the section,
wash it gently with water and keep on a glass slide. Put one drop of glycerine. Cover it
with a coverslip and observe under a microscope. Draw a diagramand explain about the
observed structure.

·o ······························································································································

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Cell Division

Life of an organism begins from a single cell (zygote formed Sperm- .-Egg
by fusion of gametes in sexual reproduction). There is

a continuous process of division in cells which gives a

structure to the body of multicellular organism. In a living

organism, the growth and multiplication of cells are the

basic necessities for its proper growth. The process of cell

division is similar in all living organisms. The cell which is

undergoing cell division is called mother cell and the new

cells formed from cell division are called daughter cells. Cell

division is the process by which a mother cell divides into

two or more daughter cells. Cell division was first studied

by Prevost and Dumas (1824 AD) when they described cleavage in fertilized egg of Frog.

Cell Cycle

The cell cycle is the sequence of changes that takes place in the cells during cell growth and
cell division. In cell division, a mother cell divides into daughter cells. The daugher cell grows
into a mature cell and prepares for cell division. So, every cell is derived from the preexisting
cell. All the changes that occur between two consecutive cell division come under cell cycle.
The division of nucleated cells completes with cytokinesis (division of cytoplasm)followed
after Karyokinesisis (nuclear division). Sometimes cytokinesis does not follow the karyokinesis,
as a result multinucleated cells are formed. In eukaryotes, the cell cycle can be divided into
three phases – Interphase, M phase (mitotic or meiotic phase) and cytokinesis.

fig: cell cycle

Phases of Cell Cycle

1. Interphase

Interphase is the stage during which a cell prepares, grows and accumulates nutrients
needed for cell division. It is the stage between the end of one cell division to the
beginning of another cell division. The interphase is the longest phase of a cell cycle.
This stage is also known as resting stage as cell division does not take place in this phase.
Though it is called a resting stage, cell is metabolically active in interphase. This phase
is the preparatory phase. The cells grow, develop and carry out their metabolic function.
There are three distinct phases in the interphase of the cell cycle - G1 phase, S phase and
G₂ phase.

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G₁ phase (Gap one/first growth phase): This is the first phase in the interphase. Here
G indicates gap. This phase is also called the growth phase. Cells carry out normal
metabolic activities. The changes that occur in the cell in this sub-phase are:
i. Carbohydrates, lipids and proteins are synthesized. RNAs are formed.

ii. The cell matures and increases in size due to high rate of biosynthesis.

Sphase (Synthesis): The S or synthesis phase follows the G1 phase. The changes that
occur in the cell in this sub-phase are:
i. The genetic material of the cell (DNA) is copied or replicated.

ii. The synthesis of the vast majority of histones occurs during the S-phase.

G₂ phase (Gap two/second growth phase): The G₂ or second Growth Phase occurs after
the S phase. The changes that occur in the cell in this sub-phase are:

i. Cell grows rapidly during this sub-phase. The cell makes all the structures needed to
divide.

ii. Protein synthesis during this sub-phase prepares for the energy required in M-phase.

Fact with reason

Interphase is also called resting phase,why?
In interphase, the division of nucleus and cytosol does not occur. Any of the cellular structure
does not divide, the cell just prepares for division. So, interphase is called resting phase.

2. M-phase
The M phase consists of nuclear division (karyokinesis). The M-phase copletes in four
distinct stages, namely prophase, metaphase, anaphase and telophase. At the end of
M-phase the nucleus of a cell divides itself into two or four distinct nuclei, known as
'daughter nuclei'. This process of division of the mother cell nucleus into daughter nuclei
is called karyokinesis.

3. Cytokinesis:

Cytokinesis is the division of cytoplasm into two separate cells which occurs concurrently
with nuclear division in M-phase of cell cycle. It is the final phase in cell cycle followed
after karyokinesis, where there is division of cytoplasm to form daughter cells. The
process of cytokinesis differs in plant and animal cells. Cytokinesis occurs by two
methods: cell plate formation and constriction (furrowing/cleavaging) methods.

Cytokinesis in animal cells
In an animal cell, cytokinesis takes places by contraction/furrowing/cleavaging methods.
In this process, a peripheral constriction appears in the cytoplasm at the equator. Slowly,
it continues and deepens towards the center and constricts the cytoplasm to divide it into
two equal halves

Cytokinesis in plant cells
In plant cells, cytokinesis takes place by cell plate formation method. In this process, the
granular bodies produced by the golgi complex or endoplasmic reticulum are arranged
in the equatorial region, form a cell plate and divide the cytoplasm into two equal halves.

0280 Optional Science - 10 BIOLOGY

Memory Plus

The period of the cell cycle varies in different cells. It is 20 minutes in a bacterial cell and 8-10
minutes in an epithelial cell.

The cycle of cell division is a vital process by which a fertilized egg that is single-celled develops
into a mature organism. It is the process by which the skin, hair, blood cells and some internal
organs are renewed.

Types of Cell Division
There are two types of cell division:

a) Direct cell division: amitosis.

b) Indirect cell division: mitosis (equational cell division) and meiosis (reductional cell
division)

Amitosis

Amitosis is a simple type of cell division. It is a means of asexual reproduction. It occurs in
unicellular organisms like bacteria, amoeba, etc. In this cell division, the nucleus elongates
and then takes a dumb-bell shaped appearance. The depression and constriction in the nucleus
divides the nucleus into two nuclei. Therefore, it is also called direct nuclear division. The
division of the nucleus is followed by the constriction of the cytoplasm, which divides the cell
into two equal or approximately similar halves.

In amitosis, the two daughter cells do not receive Constriction
equal amount of nuclear and cytoplasmic materials.
They do not resemble with their parents as well as Nucleus
with each other.Amitosis occurs during binary fission
in bacteria, cyanobacteria and some protozoans like Parent cell Parent cell Daughter cells
amoeba, paramecium, euglena, etc. It is frequently
found in the fast growing cells of cancer. dividing

fig: Stages in amitosis

Fact with reason

The two daughter cells do not look identical in amitosis,why?

During the division of cells in amitosis the chromatin fibres do not replicate as in mitosis. The
genetic material does not get equally distributed when the nucleus divides into two nuclei. Thus the
two daughter cells do not look identical.

Amitosis is called direct cell division, why?

Amitosis takes place by simple cleavage of the nucleus and division of the cytoplasm
without spindle formation or appearance of chromosomes. So amitosis is called direct cell
division.

Mitosis

Mitosis is the division of a mother cell into two daughter cells with equal number of
chromosomes to that in mother cell. These daughter cells are genetically identical to each other
and to the parent cell. It is also called equational cell division. The term mitosis was coined by
Walter Flemming in 1882 AD. Mitisis occurs in somatic cells. So, mitosis is also called somatic
cell division. The word ‘somatic’ is derived from the Greek word ‘soma’ which means body.

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Hence, all the body cells of an organism that are responsible for growth and development
of the body, except the gametes (sperm or ovum) are called somatic cells. A diploid somatic
cell contains two complete sets of chromosomes. It is denoted by '2n'. For example, a human
somatic cell contains 23 pairs (2n= 2*23=46) of chromosomes. On the other hand, the gamete
with single set of chromosome is called haploid cell. It is denoted by 'n'.

Fact with reason

Mitosis is also called an equational cell division, why?

In mitosis, the chromosomes replicate and get equally distributed into two daughter cells.
The daughter cells have the same number of chromosomes as present in the mother cell.
i.e., number of chromosomes in mother cell(2n) = number of chromosomes in daughter
cell(2n). Therefore, it is also known as equational cell division.

Mitosis is also called somatic cell division, why?

Mitosis takes place in somatic cells (body cells except gametes) for the growth, development
and repair. So, it is also called somatic cell division.

Stages of Mitosis

Mitosis is followed by cytokinesis. This process divides the nuclei, cytoplasm, cellular
organelles and cell membrane into two daughter cells. It is divided into the following three
stages: interphase, karyokinesis, cytokinesis.

Interphase: Interphase is the time during which preparations for mitosis are made by the
cell. Following are the changes that occur in the cell in interphase:

i. The cell matures and increases in size.

ii. DNA replicates to form exact two copies of DNA. Centrosomes
with centrioles
iii. Chromosomes are in the form of
chromatin. Aster

iv. RNA and proteins (histone proteins and Nucleolus Chromatin
spindle proteins) are also synthesized. Nuclear netweork
membrane Cell membrane
v. Cell replicates its organelles in fig: Interphase
preparation for mitosis.

Karyokinesis:

It is the division of the nucleus into two identical daughter nuclei. The division of the
nucleus takes place in four different phases:
1. Prophase 2. Metaphase 3. Anaphase 4. Telophase

1. Prophase: Following are the changes that occur in the Nucleolus
cell in prophase:
Centriole
i. The chromosomes become shorter and more Nuclear
compact. membrane
A pair of
ii. Inside the nucleus, the nucleolus starts to chromatids
disappear.
Centromere

iii. The centrioles begin to move to opposite ends of fig: Prophase

the cell, and the spindle fibers extend from the centromere.

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iv. At the end of the prophase, the membrane around the nucleus in the cell dissolves
away, releasing the chromosomes.

v. Each replicated chromosome consists of two identical sister chromatids held
together by a centromere.

2. Metaphase: Following are the changes that occur in the cell in metaphase:

i. The chromosomes are arranged neatly end-to-end along the center (equator) of

the cell. Metaphase
ii. The centrioles are at opposite poles of the cell plate

with the spindle fibers extending from them. Spindle fibres

iii. The chromosomes start pulling the chromosomes Centriole
towards the ends of the cell.

iv. The centromeres of the chromosomes are Centromere
arranged along the metaphase plate, also
known as the equatorial plane. This process fig: Metaphase
of arrangement of all the chromosomes at the
equator is called congression.

3. Anaphase: Following are the changes that occur in the cell in anaphase:

i. Centromere splits and two sister chromatids Chromatids move apart
separate as daughter chromosomes with their (now called daughter chromosomes)
own centomeres.

ii. There is repulsion between two sister fig: Anaphase
chromosomes. The sister chromatids are then
pulled apart by the spindle fiber, which pulls one
chromatid to one pole and the other chromatid to
the opposite pole.

iii. The daughter chromosomes appear as U, V, L and J during the migration of the
daughter chromosomes.

4. Telophase: This is the last stage of karyokinesis. Following are the changes that occur
in the cell in telophase:

i. Chromosomes reach at the poles. Nucleolus
Centriole
ii. The chromosomes spread and overlap Nuclear
to form a chromatin network. membrane
Constriction in
iii. The spindle fibers disappear, whereas cell membrane
the nuclear membrane and nucleolus
reappear. fig: Telophase

iv. At the end of the telophase, two daughter nuclei are formed, each having an
equal number of chromosomes to the mother cell.

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Cytokinesis: Chromatin Network
After karyokinesis, cytokinesis takes
place to divide the cytoplasm to form
two identical daughter cells.

Significance of Mitosis fig: two diploid daughter cells formed after cytokinesis

1. Mitosis division is responsible for the growth and development of a single-celled zygote
into a multicellular organism.

2. The chromosome number remains the same in the daughter cells produced by this
division. They have the same characters as those of the mother cell. So, mitosis maintains
genetic stability.

3. Mitosis replaces wounded, old, decaying and dead cells.

4. It helps unicellular organisms in asexual reproduction.

5. Artificial vegetative propagation like grafting and the modern method of tissue culture
are possible due to mitosis.

Memory Plus

The cells undergoing mitosis are called mitocytes. In plants, the mitocytes are mostly
meristematic cells. In animals, the mitocytes are stem cells, germinal epithelium and embryonic
cells.

Roughly 5×109 cells are lost from the surface of skin, alimentary canal, etc. daily in our body
which are replaced by the new cells formed by mitosis cell division.

Meiosis

Meiosis is the division of a mother cell into four daughter cells (sex cells or gametes) each
having half number of chromosomes than that in the mother cell. The word ‘meiosis’ was
originated from greek word meioum which means to reduce. It was given by Farmer and
Moore in 1905AD. Whereas this process of cell division was first demonstrated by Van Benden
in 1883AD. The number of chromosomes is reduced by half in meiosis cell division. It is also
called reductional cell division. Meiosis division occurs only in diploid reproduction cells or
germ cells and produces four haploid sex-cells or gametes. A germ cell is any biological cell
that gives rise to the gametes of an organism that reproduces sexually. So, meiosis cell division
is necessary for sexual reproduction in eukaryotic organisms.

Fact with reason

Meiosis is also called reductional cell division, why?

In meiosis, only half number of the chromosomes are distributed from diploid mother cell to
the daughter cells (sperm and ovum). i.e.,

number of chromosomes in daughter cell(n) = ¹/2 number of chromosomes in mother
cell(2n). Therefore, meiosis is also known as reductional cell division.

Stages of Meiosis

Meiotic division includes two complete divisions (meiosis I and meiosis II). It can be studied
in the following three stages: Interphase, karyokinesis and cytokinesis.

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Interphase: Before entering meiosis I, a cell first goes through the Interphase. As in mitosis,
the cell grows during the G1 phase (Growth phase), copies all of its chromosomes during
the S phase, and prepares for division during the G2 phase. The replicating process in
S-phase is longer than that occurs in mitosis.

Karyokinesis: In meiotic cell division, the nucleus divides twice. In meiosis I, one diploid
mother nucleus is divided into two haploid daughter nuclei. In meiosis II, each haploid
nucleus formed as a result of meiosis I divides into two haploid daughter nuclei. As a
result, four haploid nuclei are formed from one diploid nucleus at the end of meiosis.

Meiosis I: In meiosis I there are four stages:

1. Prophase I 2. Metaphase I 3. Anaphase I 4. Telophase I.

1. Prophase I:

It is a very complex and long phase in meiosis I. Prophase I is further divided into 5 sub-
phases: Leptotene, Zygotene, Pachytene, Diplotene and Diakinesis.

a. Leptotene (Gk: leptonema- thin threads): Following changes occur in the cell in
leptotene:

i. In this stage, the chromosomes condense into thin, elongated, single stranded
thread like structure.

ii. Size of the nucleus increases.

iii. Centrosome splits into two centrioles, and each centriole starts to move towards
its respective poles.

iv. Nuclear membrane and nucleolus remain intact.

lnterphase leptotene Zygotene Astral rays
Chiasmata
Synapsis of homologous Nucleolus
chromosomes (Disappearing)

Pachytene Crossing Diplotene Diakinesis
over in
Pachytene

fig: Stages in Prophase I

b. Zygotene (Gk: zygonema- paired threads): Following changes occur in the cell in

zygotene:

i. The homologous chromosomes line up with each other to form a pair called

bivalent. These paired chromosomes are called bivalent chromosomes. This

process of pairing up of homologous chromosomes to form a bivalent is called

synapsis.

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ii. Shortening and thickening of chromosomes continues.

c. Pachytene (Gk: pachynema- thick threads): Following changes occur in the cell in
pachytene:
i. In this stage, each chromosome splits longitudinally into two sister chromatids.
The two bivalent chromosomes split to form 4 arms. The structure so formed is
called a tetrad.

ii. Non-sister chromatids overlap or coil with each other. During this process sister
chromatids remain attached at some points. These points of contact between two
non-sister chromatids are called the chiasmata.

iii. Crossing-over begins in this stage. There is an exchange of genetic material
between the non-sister chromatids, and this results in a recombination of
information. The process of exchange of genetic material from the chiasmata in
between two non-sister chromatids of homologous pair is called crossing over.

Memory Plus

Chromosomal cross-over is a significant source of genetic variation. As the DNA
created is of new combinations.

d. Diplotene (Gk: diplonema- two threads): Following changes occur in the cell in
Diplotene
i. Crossing-over takes place.

ii. The bivalent homologous chromosomes remain tightly bound at the region of the
chiasmata, where crossing over occurred.

iii. Nuclear membrane and nucleolus start to dissolve.

iv. Non-sister chromatids start to separate from each other except at the chiasmata.

e. Diakinesis (Gk: Diakinesis- moving through): Following changes occur in the cell in
diakinesis:
i. During the diakinesis stage, the chromosomes condense further.

ii. This stage is the first part of meiosis, where the four arms of the tetrad are visible.

iii. Nuclear membrane and nucleolus dissolve completely. Spindle fibers start to
appear.

iv. Chiasmata move towards the terminal end of the chromosome. This process of
movement of chiasmata towards the end of the chromosome and disappear is
called terminalization.

Metaphase I: Following changes take place in this phase:
i. The homologous pairs of chromatids are arranged on equatorial region known as
the metaphase plate in such a way that the two members of a pair lie on opposite
sides of the equatorial plane.

ii. The centromeres are directed towards the poles, and the arms of chromosomes
face the equatorial plate called co-orientation.

iii. The chromosomes are attached to the spindle fibers by their centromeres.

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iv. As centromere does not split in this phase, the number of chromosomes moving
towards the opposite pole is reduced into half of that in the mother cell. As a
result a haploid nucleus is formed in each pole.

Anaphase I: Following changes take place in this phase:

i. Homologous chromosomes are pulled towards the opposite poles, which results
in the formation of two haploid sets. This process of separation of homologous
chromosomes is called disjunction.

ii. This process of separation of homologous chromosomes is called disjunction.

iii. The centromere does not split. Each chromosome contains a pair of sister
chromatids. These chromosomes are called dyads.

iv. As centromere does not split in this phase, the number of chromosomes moving
towards the opposite pole is reduced into half of that in the mother cell. As a
result a haploid nucleus is formed in each pole..

Telophase I: Following changes take place in this phase:

i. The daughter cells now have half the number of chromosomes. The chromosomes
consist of a pair of chromatids.

ii. The network of spindle fibers disappears. Nuclear membrane and nucleolus
appear.

iii. The chromosomes uncoil and form chromatin threads.

iv. At the end of telophase-I, two haploid nuclei are formed. In some cases, telophase-I
may be absent.

Cytokinesis-I:

Cytokinesis takes place through cell plate formation in the plant cell and by the furrowing
method in the animal cell. This completes the formation of two haploid daughter cells.

Interkinesis:
i. It is a period of rest between meiosis I and meiosis II.

ii. There is no DNA replication, i.e., S-phase is absent.

I PROPHASE I METAPHASEI ANAPHASEIiii.

INTERPHASE

Centrosomes Chiasmata Microtubule iv.
(with centriole attached to Metaphase
pairs) Spindle kinetochore plate Sister chromatids
remain attached

+

Nuclear Sister Tetrad Centromere
envelope (with kinelochore)
chromalids
Chromosomes Tetrads line up
duplicate Homologous Pairs of homologous
chromosomes chromosomes
pair and exchange split up
segments

fig: Stages in meiosis I

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Meiosis II (equational cell division): It is the second part of the meiosis cell division.
Meiosis II is similar to mitosis. But meiosis II occurs in haploid cells instead of diploid
cells as that in mitosis. It results into four haploid cells from two haploid cells produced
in meiosis I.

Fact with reason

Meiosis II phase is also called meiotic mitosis,why?
All the changes that occur in meiosis II phase are similar to that which occurs in mitosis. So,
this phase is also called meiotic mitosis or homotypic division.

In meiosis II, there are four stages:

1. Prophase II 2. Metaphase II 3. Anaphase II 4. Telophase II.

telophase & prophase II metaphase II anaphase II telophase II
cytokinesis

Cleavage
furrow

Two haploid cells

form; chromosomes During another round.of cell division, the sister chromatids finally
are still double separate; four haploid daughter cells result, containing single

chromosomes

fig: Stages in meiosis II

Prophase II : Following changes take place in this phase:

i. During this stage, the nucleoli and the nuclear envelope disappear.

ii. Chromatids become short and thick.

iii. The centrioles move to the polar region.

iv. The spindle fibers appear for the second meiotic division.

Metaphase II: Following changes take place in this phase:
i. During this stage, the centromeres attach to the spindle fibers at each pole.

ii. Nuclear membrane and nucleolus completely disappear.

iii. Dyad chromosomes arrange themselves in an equatorial plane.

Anaphase II: Following changes take place in this phase:
i. In this stage the centromeres are cleaved, pulling apart the sister chromatids.

ii. The daughter chromosomes move towards the opposing poles.

Telophase II: Following changes take place in this phase:
i. In this phase there is uncoiling and lengthening of the chromosomes.

ii. The spindle fibers disappear.

iii. Nucleolus and nuclear envelope reappear.

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Cytokinesis II: Cytokinesis II takes place by cell plate formation in the plant cell and by
furrowing in the animal cell. As a result, four haploid daughter cells are formed at the
end of cytokinesis-II from a single diploid nucleus.

Memory Plus

The cells undergoing meiosis are known as meiocytes. In animals, the meiocytes are the primary
spermatocytes and primary oocytes, while in plants, these are represented by sporocytes.

Significance of meiosis 0 Haploid (n) Haploid gametes (n = 23)
O Diploid (2n)
1. Meiosis produces haploid cells (i.e. male and @ Ovum (n)
female gametes or spores). So, it is responsible
for sexual reproduction in organisms. &=~
IFertlllzallonl
2. Reduction in chromosome number. Each gamete
has only half the number of chromosomes of the ~Testis
parent cell. ~ Diploid
zygote
3. Meiosis reduces the number of chromosomes Mitosis and (2n=46)
into half during gamete formation. When male
gamete and female gamete fuse then the number development
of chromosomes in zygote remains fixed to the
parental organism. Thus, meosis maintains Multicellular diploid
genetic stability in the offspring by keeping fixed adults (2n = 46)
number of chromosomes in the offspring. In
other words, meiosis maintenance the number fig: significance of meiosis in sexual reproduction
of chromosome fixed in somatic cells.

4. Meiosis causes genetic variation. New
individuals do not resemble their parents closely.

Activity

Study the permanent slides showing different stages of mitosis and meiosis. Observe
through microscope and copy the diagrams observed on the permanent slide. Also
comment on different stages of mitosis and meiosis.

Difference between Mitosis and Meiosis

Mitosis Meiosis

Mitosis occurs in somatic cells. Meiosis occurs in reproduction cells.
It produces two daughter cells. It produces four daughter cells.

It completes in one division. It completes in two divisions.

In mitosis cell division, genetic constitution In meiosis cell division, genetic constitution

remains same in the daughter cell. is different in the daughter cells

It takes place during growth, repair, It takes place during formation of gametes
regeneration and development

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Answer writing skill

1. Define cell biology.
Cell biology is defined as a branch of life science that deals with the study of the cell
structure, its function and its chemistry.

2. Define bone.
Bone is defined as a hard connective tissue made up of living cells called osteocytes.

3. What is a cell cycle?
A cell cycle is the sequence of changes that take place in the cells during cell division.

4. Mitosis is called equational cell division. Why?
Mitosis is the division of the mother cell into two daughter cells. These daughter cells
are genetically identical to each other and to the parent cell. Both the daughter cells
contain the same number of chromosomes as the parent nucleus. Therefore, it is also
known as equational cell division.

5. Write short notes on cuboidal epithelial tissue.
Cuboidal tissue
Cuboidal tissue contains cubical cells. It forms the lining of ducts of the kidney, salivary
gland, pancrease, testis and ovary. It helps in secretion, absorption and excretion. There
are two types of cuboidal epithelial tissue:

a. Ciliated cuboidal: The cuboidal cell having cilia on the free surface is called a
ciliated cuboidal cell. The cilia help in conducting mucus and other substances.
They are located on the ducts of nephrons.

b. Brush bordered cuboidal: The cuboidal cell having microvilli on the free surface
is called a brush bordered cuboidal cell.

6. What are the main identifying characteristics of a dicot stem?
The main identifying characteristics of a dicot stem are as follows:

1. Cuticles and trichomes are present.
2. Hypodermis is made of up collenchyma cells.
3. Chloroplast is present.
4. Presence of a wavy endodermis.
5. Presence of eight vascular bundles arranged in the form of a ring.
6. The vascular bundles are conjoint, collateral and open.
7. Describe anaphase in mitosis.
In anaphase of mitosis, the following changes occur:

1. Each chromosome is divided into two sister chromatids as separate daughter
chromosomes with their own centomeres.

0290 Optional Science - 10 BIOLOGY

2. The sister chromatids are then pulled apart by the spindle fiber, which pulls one
chromatid towards one pole and the other chromatid towards the opposite pole.

3. The daughter chromosomes appear as U, V, L, and J during the migration of the
daughter chromosomes.

8. What is a compound epithelium? What are its types? Give two functions of it.

A compound epithelial tissue is a type of epithelial tissue which is made up of several
layers of epithelial tissue.

Compound epithelial tissues are of following types:

1. Stratified squamous epithelium: It is made up of several layers of cells. The upper
layer is made up of squamous cells. The lower layer is made up of germinative
columnar or cuboidal cells. The stratified squamous epithelium is of two types:

a. Keratinized epithelium: This tissue contains protein called keratin in its
upper layer. This layer is hard. It makes the layer water-proof. It is present
inthe hair, claws and nails.

b. Non-keratinized epithelium: The upper layer of this tissue contains living
cells. Due to the absence of keratin, this layer becomes wet. It is present in the
buccal cavity, pharynx, oesophagus and vagina.

2. Stratified cuboidal epithelium: The upper layer of this tissue is made up of
cuboidal cells. The lower layer is made up of either germinative columnar or
squamous cells. It is found in the lining of ducts of sweat glands, salivary glands,
conjunctiva of the eyes, etc.

3. Stratified columnar epithelium: The upper layer of this tissue is made up of
columnar cells. The lower layer is made up of germinative cuboidalcells. It is
found in the liningof vasa deferntia, trachea, bronchi, etc.

4. Transitional epithelium: This tissue is made up of several layers of cells. The cells
in the upper layer are dome shaped. The cells in the middle layer are club shaped.
The cells in the basal layer are cuboidal in shape. This tissue has the ability to
stretch and relax. It helps in the expansion of organs. It is found in the urinary
bladder and ureter.

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Exercise

Section "A"

1. What is a tissue?
2. Define connective tissue.
3. What is cartilage?
4. What is a nerve cell called?
5. Give an example of neuroglia.
6. Define epithelial tissue.
7. What do you understand by glandular epithelium?
8. What is compound epithelium tissue?
9. What is keratinized epithelium?
10. What is cell division?
11. What do you mean by cytokinesis and karyokinesis?
12. Define amitosis.
13. What is mitosis cell division?
14. What is meiosis cell division?
15. What is crossing over?
16. What is a homologous chromosome?

Section "B"

1. What are the types of animal tissues?
2. What are the types of connective tissue?
3. Give two differences between white fibrous and yellow fibrous tissue.
4. Distinguish between striated and unstriated muscle.
5. Describe in brief cardiac muscle tissue.
6. What are the types of epithelial tissue?
7. Name any two organs in our body which contain ciliated epithelium.
8. Name any two organs in our body which contain columnar epithelium.
9. Write the anatomical differences between a dicot root and monocot root.
10. Write the anatomical differences between a dicot stem and monocot stem.
11. Give the names of the different stages of cell division.
12. Name the phases of the cell cycle.
13. What are the changes that occur during G1, S and G2 phase.

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14. Give reason
a. Meiosis is called a reductional cell division
b. Mitosis is called an equational cell division
c. Meiosis brings variation in offsprings
d. Cell division is a necessary phenomenon

15. What are the stages of mitosis?
16. What are the stages of meiosis cell division?
17. Mention the differences between metaphase and anaphase.
18. Mention the differences between anaphase in mitosis and anaphase in meiosis.
19 Write differences between cytokinesis in plant cell and cytokinesis in animal cell.
20. Write differences between haploid cell and diploid cell
21. Write the differences between Prophase I and Prophase II.
22. Give the differences between mitosis and meiosis.
23. Write down the sub-phases of Prophase I.
24. Give difference between mitosis and meiosis cell division.
25. What is the basic difference between mitosis in plant cell and that in animal cell.

Section "C"

1. Write any three function of connective tissue.
2. Write the function of blood.
3. State the function of lymph.
4. What is the function of epithelial tissue?
5. Write functions of muscular tissue.
6. Write functions of nervous tissue.
7. Explain the significance of mitosis.
8. Explain the significance of meiosis cell division
9. Meiosis and mitosis both maintain the genetic stability. Explain how do they maintain

genetic stability.

Section "D"

1. Describe in brief the internal structure of a dicot root.
2. Describe in brief the internal structure of a monocot root.
3. Describe in brief the internal structure of a dicot stem.
4. Describe in brief the internal structure of a monocot stem.
5. Draw a sketch of the transverse section of a monocot stem.
6. Draw a sketch of the transverse section of a monocot root.
7. Draw a sketch of the transverse section of a dicot stem.
8. Draw a sketch of the transverse section of a dicot root.
10. Describe the process of mitosis.
11. Describe the types of epithelial tissue.
12. What are the types of connective tissue? Explain.

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13. Give a short account about nervous tissue and muscular tissue.

14. Draw labelled diagrams to show metaphase and anaphase of mitosis.

15. Describe the somatic cell division and mention its significance.

16. Explain with diagram about the prophase-I.

17. Give a detailed account of meiotic I cell division.

18. Describe the process of meiotic II cell division?

19. Describe the changes that occur in the nucleus during anaphase of mitosis. How is it
different from the anaphase-I of meiosis? Explain along with a diagram.

20. Complete the following table.

Animal tissue Function Occurrence
Areolar tissue
Adipose
Squamous epithelial
cuboidal epithelial
Columnar
Glandular columnar epithelial
Transitional epithelial

Multiple choice questions

1. The science that deals with the study of cell structure, its function and its chemistry is

a. Morphology b. Cytology c. Physiology d. Biology

2. Study of tissue is called

a. Tissue culture b. Cell biology c. Histology d. Cytology

3. Blood is an example of

a. Loose connective tissue b. Dense connective tissue

c. Fluid connective tissue d. Skeletal connective tissue

4. Which muscle tissue works continuously without fatigue?

a. Skeletal muscle tissue b. Smooth muscle tissue

c. Cardiac muscle tissue d. Nervous tissue

5. Which tissue forms the lining of the coelom, buccal cavity, blood vessels and kidney?

a. Epithelial tissue b. Connective tissue c. Nervous tissue d. Skeletal tissue

6. Multicellular hair is absent in

a. Monocot stem b. Dicot stem c. Monocot root d. Dicot root

7. In which phase does the genetic material of the cell (DNA) get replicated?

a. G0 phase b. G1 phase c. S phase d. G2 phase

8. Binary fission is an example of

a. Mitosis b. Meiosis c. Amitosis d. All of the above

9. Equational cell division is

a. Mitosis b. Meiosis c. Amitosis d. Cytosis

10. The points of contact between two non-sister chromatids are called

a. Crossing over b. Chiasmata c. Centroiles d. Synapsis

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0294 Optional Science - 10 BIOLOGY

UNIT Life and Life
Processes
15

Antonie van Leeuwenhoek (1632-1723AD)

He was born in Holland. He was the first to observe the bacteria and protozoa, and proved
that the doctrine of spontaneous generation was wrong on the basis of his research on lower
animals. He was the first acknowledged microscopist and microbiologist because of his
microscopic discovery of microorganisms (animalcule).

Syllabus issued by CDC Learning objectives:

Theory 10 At the end of this unit, the students will be able to:
Practical 3
• describe different physiologies present in a
mouse like the digestive system, respiratory

Atomic mass, molecular mass and system and urogenital system.

mole concept • describe the structure and life cycle of a

Quantum numbers flowering plant (rice).

Concentration (Normality, molarity, • describe different endocrine glands, their
gram per litre and percentage) secretion, functions and their respective
effects.

Key terms and terminologies of the unit

Life processes: The basic essential activities performed by an organism to keep it alive and
functioning are called life processes.

Digestive system: The digestive system is a long tract found inside the animal, start from
the mouth and ends with the anus, and helps in digestion.

Digestion: The process of enzymatic breakdown of macromolecules in food materials into
the simplest molecules required for maintaining cellular function is called digestion.

Alimentary canal: The alimentary canal is a pathway by which food enters the body and
solid wastes are thrown out. It is a tube running from the mouth to the anus.

Viscera: The internal organs of digestive system in the main cavities of the body are called
viscera.

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Peristalsis: The involuntary constriction and relaxation of the muscles of the intestine or
another canal, creating wavelike movements that push the contents of the canal forward.

Respiratory system: The respiratory system is the set of organs that helps to inhale oxygen
(for oxidation of food) and exhale carbon dioxide.

Exocrine glands - The glands that secrete enzymes and juices and pour this secretion in the
duct (vessel) to an organ are called exocrine glands.

Endocrine glands: The glands that secrete hormones and pour directly into the bloodstream
without passing through ducts are known as endocrine glands.

Hormones: Hormones are the chemical messengers produced by the endocrine system that
activate, inhibit or control the function of a certain organ or a group of organs.

Endocrine system: The endocrine system is a chemical messenger system of an organism
consisting of hormones, the group of glands that secrete those hormones directly into blood to
regulate the function of distant target organs.

Endocrinology: The branch of science that deals with the study of the structure, secretion and
functions of different endocrine glands is called Endocrinology.

Introduction

We all have observed in our surrounding that living organisms doing respiration, feeding,
reproducing an individual of their own kind, growing in their dimensions, etc. There are
certain basic vital processes which are essential to perform for an organism to survive. These
processes include nutrition, transportation, metabolism, respiration, reproduction, excretion,
etc. The basic essential activities performed by an organism to keep it alive and functioning
are called life processes. All living things perform life processes. In this unit we will learn
about rat, structure and life cycle of rice and endocrine system in human in this unit.

Rat

A rat is found all over the world and almost everywhere. It is a Kingdom: Animalia
fossorial animal living in burrows. It is usually herbivorous in
diet. A rat is a mammal that belongs to the genus Rattus. The Phylum: Chordata
most common rate are the black rat, Rattus rattus, and the brown
rat, Rattus norvegicus. Rats are more closely related with human Subphylum: Vertebrata
beings. They have some similar characteristics to human beings.
Physically, both have similar nervous system, circulatory system, Class: Mammalia
muscle structure, organs like liver and heart, etc. In this unit, we
will learn about digestive system, respiratory system, urogenital Order: Rodentia
system in rat.
Family: Muridae

Genus: Rattus

Fact with reason

Why are rats widely used as a model in medical testing by researchers?

Rats are more closely related with human beings. Their genetic, biological and behavior
characteristics closely resemble those of humans. Many symptoms of human conditions can
be replicated in rats. So they are widely used as a model in medical testing by researchers.

0296 Optional Science - 10 BIOLOGY

External features of Rat

The body of a rat is elongated and covered with thick fur with stiff hairs. The body of a rat can
be divided into four distinct regions: head, neck, trunk and tail.

The head is elongated tapering at the terminal end. It bears two bulging eyes, two nostrils,

mouth, external ears (pinnae) and vibrissae projecting from the side of the mouth. The neck

connects the head to the trunk. The trunk is the External nares Vibrissae
largest part of the body. It is divided into the thorax Upper incisor
and abdomen. In a female rat, there are six pairs of tooth External auditory
nipples on the ventral side; three pairs in the thoracic Upper arm meatus
region; and three pairs in the abdominal region. A rat Pinna

bears two pairs of forelimbs and hind limbs. Claw Forearm

The anus is present just below the tail. In the male rat, Prepuce Thigh
there are two scrotal sacs containing the testis and a covering
penis ventral to the anus. In a female rat, a genital penis
aperture known as the vulva lies just in front of the Urethral
anus. The urethral orifice is present in front of the orifice
vulva. Excretory matter is passed out through the
urethral orifice. The tail is elongated, cylindrical and Scrotum
tapering. It is slightly longer than the body. The tail Position of anus
lies above the anus. It is used as a balancing organ.
fig: External features of a rat
Digestive system in rat

Animals ingest food in a complex form. A body trachea esophagus
system in animals must convert the ingested food into heart aortic arch
simple molecules required for maintaining cellular
function. The conversion of the food consumed liver lung
to the nutrients required is a multistep process bipleyldouricct
involving digestion and absorption. Finally, there diaphragm
is elimination of undigested molecules. This overall sphincter stomach
biological process is completed by a group of organs duodenum spleen
in digestive system. The digestive system is a long pancreas
tract found inside the animal, start from the mouth jejunum
and ends with the anus, and helps in digestion. The ileum descending
process of enzymatic breakdown of macromolecules colon
in food materials into the simplest molecules required caecum rectum
for maintaining cellular function is called digestion. anus

Alimentary Canal

The digestive system of a rat consists of the alimentary fig: digestive system of rat
canal and its associated glands. The alimentary canal,

also called the digestive tract, is a pathway by which food enters the body and solid wastes are

thrown out. It is a tube running from the mouth to the anus. The alimentary canal includes the

mouth, pharynx, oesophagus, stomach, small intestine, large intestine and anus. Alimentary

canal of rat is divided into two parts: Mouth and pharynx and Viscera.

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1. Mouth and pharynx

Mouth: The mouth is the large opening at the anterior end of the snout. It is bounded
by two lips. It opens into the buccal cavity, or oral cavity.

Buccal cavity: The buccal cavity contains a long narrow bony jaw with a palate, tongue
and teeth set in a socket. The teeth of the rat are like those of other mammals. The teeth
are heterodont, i.e. they are not all similar to each other. Rats have 16 teeth. A rat’s teeth
consist of incisors (4), canine (0), premolars (0) and molars (12).

Pharynx: It is a small passage between the buccal cavity and the oesophagus. It is the
common chamber for food and air. Pharynx is divided into: Nasopharynx (receives air
from the external nares and is not directly in the oral cavity), Oropharynx (space ventral
to the soft palate) and Laryngopharynx (space posterior to the soft palate and anterior
to the esophagus). From the oral cavity, only food diverges in the laryngopharynx and
directed towards the oesophagus

Oesophagus: It is a long narrow straight tube that passes through the neck and thoracic
region. It opens into the stomach.

2. Viscera

The internal organs of digestive system in the main cavities of the body are called
viscera. It includes following organs:

Stomach: The food from oesophagus enters to stomach. It is a bean-shaped sac-like
structure on the left side of the abdominal cavity, which is partially covered by the liver.
It acts as a storage organ so that fewer and larger meals can be consumed.

Small intestine: The food from stomach enters to small intestine. It is a long and coiled
slender tube. It is divisible into duodenum, jejunum and ileum. The duodenum is the
first part of the small intestine and forms a U-shaped loop.

Large intestine:The small intestine is followed by the large intestine. It is comparatively
shorter and wider than the small intestine. It is divisible into three parts: caecum, colon
and rectum.

Caecum: It is a thick tube that lies at the junction of the small and large intestine. The
terminal part of the caecum forms the vermiform appendix.

Rectum: It is a straight tube that opens outside through the anus. It temporarily stores
fecal matter before it is thrown out of the body.

Associated digestive glands

Salivary glands: Salivary glands are found in the buccal cavity. There are three pairs of

salivary glands. They are: paratoid gland (below the external ear), submaxillary gland
(near the lower jaw) and sublingual gland (below the tongue). The salivary glands
secrete saliva, which contains the enzyme amylase or ptyalin that helps to digest the
starch in the food. Enzymes in saliva begin the digestion of carbohydrates and mucus
moistens the food and sticks it together to facilitate swallowing.

Gastric glands: Gastric glands are found in the mucosal wall of stomach the stomach
and secrete gastric juice. Gastric juice contains dilute hydrochloric acid (HCl), mucus,

and the enzymes (pepsin, renin and lipase).

0298 Optional Science - 10 BIOLOGY

Liver: The liver is the largest gland of the body. It lies below the diaphragm. It is a large
reddish brown gland. It contains five lobes. The cells of the liver are called hepatocytes,
which secrete bile. Bile emulsifies fats (breaks them into minute droplets) and makes it
easier to digest them. It also eliminates waste products from the blood. It is carried to
the duodenum by a bile duct. The gall bladder is absent in the rat.

Memory Plus

In humans, the bile is stored and concentrated in gallbladder before it is released
into the small intestine. But rats lack a gall bladder. Therefore, the bile is released
through a duct directly into the small intestine in rats.

Pancreas: The pancreas is situated between the stomach and the duodenum. It secretes
pancreatic juice, which contains digestive enzymes like trypsin, chymotrypsin,
peptidases, amylase, lipase, sucrase, maltase, lactase, etc. These enzymes break down
protein, fat and carbohydrates from the food we eat. Islets of langerhans in the pancreas
secrete certain hormones like insulin, which converts glucose in the liver and muscles.

Intestinal glands: They are present in the mucosal wall of small intestine. They secrete
intestinal juice containing digestive enzyme like erepsin, lipase, nuclease, etc. These
enzymes help in the digestion of food.

Digestion

Digestion is a process by which food is broken down and chemically converted into simple
diffusible form, so that it can be absorbed by the cells of an organism. The absorbed nutrients
are used for energy, growth and cell repair.

In mouth: The mouth is the beginning of the digestion process. As soon as the rat takes the
food through the mouth, it starts chewing. Chewing breaks the food into pieces so that it can
easily be digested. While chewing, saliva mixes with the food and breaks it down into a form
the body can absorb and use. The food travels to the oesophagus through the pharynx. By
means of a series of contractions, called peristalsis, in the oesophagus, the food is delivered to
the stomach.

In stomach: Digestion of proteins begins in stomach. The lining of stomach secrete pepsin
which converts proteins into peptones. Dilute hydrochloric acid is secreted by cells lining
of the stomach to make the environment acidic for activation of pepsin. The muscular walls
of the stomach not only hold the food but also churn the food and mixes it with acids and
enzymes. When the food leaves the stomach, it is in the form of a liquid or paste. The stomach
leads to the duodenum of the small intestine.

In small intestine (duodenum, jejunum and ileum): The actual digestion and the absorption
of the products occur here. The glands present near to it secrete enzymes which help to
breakdown protein and carbohydrate. Liver secretes bile juice and pancreas secretes pancreatic
juice.

In duodenum, the food get mixed with bile which emulsifies the fat and alkaline nature of
bile inactivates the pepsin from the stomach and neutralicex the acid food. Pancreas secrete
enzymes to breakdown fats, carbohydrates and proteins. It continues in the jejunum too.

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Then the digested food or nutrients are absorbed in the small intestine (ileum). The walls
of small intestine are made up of columnar epithelial tissues containing villi. These villi
help in the absorption of digested substances and pass them on to the blood capillaries for
distribution. The absorbed nutrients are transported to the rest of the body through the blood
stream or circulatory system.

In caecum: The undigested food (cellulose) and waste materials now come to the rat’s caecum
where fermentation of the plant cellulose takes place due to the bacteria present over there.
Due to this special process to form caecum product rats produce a special feces. They again
ingest this feces to digest for a second time. This behavior is called coprophagy.

Memory Plus

All mammals do not have caecum. Humans have a short caecum provided with the
appendix. The human caecum provides space for digestion, but does not have the
microbes for cellulose fermentation.

In large intestine: After absorption of most of the nutrients and minerals in small intestine
and caecum, the remaining are transported to the large intestine (colon). The water again get
reabsorbed in the large intestine and prepares the solid fecal material for removal from the
body. When the colon becomes full of stool or feces, it empties its contents into the rectum to
begin the process of elimination through the anus.

Differences between the digestive system of a rat and a human:

Digestive system of rat Digestive system of human

Rats do not have a gall bladder as they rarely In humans, the bile is stored in the gall bladder

take large amounts of fatty food. before being released into the small intestine

Such stored bile is used to digest fatty foods.

Rats have an enlarged caecum to break Humans have a short caecum provided with

down the cellulose into nutrients present in the appendix. It does not have the microbes

the grains and seeds they feed for cellulose fermentation.

Activity

With the help of your teacher, dissect a rat carefully. Observe the digestive tract of the rat.
Draw the observed digestive tract of the rat, label it and discuss its digestive system.

Respiratory system in rat
The respiratory system is the set of organs that helps to inhale oxygen (for oxidation of food)
and exhale carbon dioxide. The respiratory system of rat is similar to that of most other
mammals, including humans. It consists of external nares, nasal chambers, internal nares,
pharynx, larynx, trachea, primary bronchi and lungs.

External nares: These are the paired openings that open into the nasal chambers.
Nasal chambers: The nasal chambers are separated from one another by the nasal
septum and from the buccal cavity by the palate.

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