Science and Environment 8

Seeds of wheat, barley, paddy, etc. are also the examples of endospermic monocot
seeds.

Rice Wheat Maize
Fig. 16.21 Some monocotyledonous seeds

2. Dicotyledonous seeds [di - two, cotyledon - seed leaf]

The seeds having two cotyledons are called dicotyledonous seeds. Seeds of pea,
mango, bean, gram, apple, mustard, orange, etc. are some examples of dicotyledonous
seeds. Endosperm is absent in dicot seeds. The cotyledons themselves serve as
storage tissue in dicots.

Gram seeds Pumpkin seeds Mango seed
Fig. 16.22 Some dicotyledonous seeds

Differences between Monocotyledonous seed and Dicotyledonous seed

S.N. Monocotyledonous seed S.N. Dicotyledonous seed
A seed contains two cotyledons.
1. A seed contains only one 1.
cotyledon.

2. Endosperm is present. 2. Endosperm is absent.
Plumule is large.
3. Plumule is very small. 3. Embryo is large.
Micropyle and hilum are distinct.
4. Embryo is small. 4.

5. Micropyle and hilum are 5.

microscopic.

Functions of Seed

The major functions of seed are as follows:

(i) to produce new plants (ii) to store food materials

Seeds serve several functions for the plants. Major functions among these are nourishment
of the embryo, dispersal to a new location and dormancy during unfavourable condition.
Seeds are the means of sexual reproduction in flowering plants. Seeds protect and nourish
the embryo or baby plant.

BIOLOGY Oasis School Science and Environment - 8 245

Seed germination

Seed germination is a process by which a seed embryo develops into a seedling and
subsequently a plant. It is the resumption of the growth of a seed embryo after the period
of dormancy, i.e. resting period. Germination involves the reactivation of the metabolic
pathways that lead to growth and the emergence of the radicle and plumule in it.

(a) Bean seed germination (b) Maize seed germination

Fig. 16.23

Germination does not take place unless the seed has been transported to a favourable condition.
The primary conditions of a favourable environment are adequate water, oxygen and suitable
temperature. Different species of plants germinate best in different temperatures, however
extremely hot or cold temperatures are not suitable for germination. Some seeds also require
adequate exposure to light before germination. Thus, water, air and suitable temperature are
necessary conditions for germination of a seed.

Activity 3

• Take three seeds each of maize, bean, pea, gram, wheat, etc.
• Keep them in the moist soil and allow them to germinate.
• Observe the little plantlet carefully and identify the radical and plumule.

Activity 4

• Take three bean seeds and tie them on a glass slide.

• Keep the slide in a beaker containing water in such

a way that one seed is completely immersed in Seed in air
Water
water, the middle one is half–immersed in water

and upper most one is in air. Seed
partially in
• After 3-4 days, observe the seeds. You can see the water
Seed
germination of only the middle seed as it gets inside

all three conditions air, water and temperature. water

• Write down the conclusion of this experiement. Fig. 16.24

adequate /ˈædɪkwət/ - enough in quantity BIOLOGY

246 Oasis School Science and Environment - 8

Dispersal of seed

Seed dispersal is the movement or transport of seeds away from the parent plant. Seeds
are dispersed by various methods which are as follows:

i. By wind

Seeds of some plants are very light having hairy or fluffy parachute-like structure.
Such type of seeds are dispersed by wind. Seeds of simal, grass, cotton, dandelion,
etc. are dispersed by wind.

(a) Seeds of dandelion (b) Seeds of cotton

Fig. 16.25

ii. By water

Seeds of some plants like coconut, lotus, water lily, betel nut, etc. are dispersed by
water. Seeds of these plants do not decay in water for a long time and germinate in
favourable condition.

(a) Seeds of coconut (b) Seeds of betel (c) Seeds of water lily

Fig. 16.26

iii. By explosion of fruits

Fruits of some plants explode themselves after drying and disperse seeds in their
surroundings with a jerk. Seeds of sesame, pea, myrtle (Tiuri), linseed (Aalas), etc.
disperse by the explosion of fruits.

BIOLOGY Oasis School Science and Environment - 8 247

(a) Pea (b) Sesame (c) Myrtle (d) Linseed
Fig. 16.27

iv. By animals

Seeds of some plants have hooks or sticky structures Fig. 16.28
on their surfaces. These structures attach to the fur
of mammals or clothes of human beings and get
dispersed. Birds and other animals eat the fleshy
fruits and discard the seeds. Similarly, birds and other
animals eat fruits with seeds but the seeds are not
digested and pass out with their droppings far away
from the parent plant. Seeds of tomato, guava, myrtle,
etc. are dispersed by animals.

v. By human beings

Now-a-days, human beings transport fruits and seeds of different plants from one
place to another and help in seed dispersal. Seeds of most fruits, vegetables, crops,
flowers, etc. are dispersed by human beings.

Reasonable fact-3

Different types of plants are found on the banks of rivers.
On the banks of rivers, fertile soil, sufficient amount of water and appropriate climate
is available for the development of plants. Similarly, different types of seeds of
different plants are carried by river water and they get collected on the bank of river.
So, different types of plants are found on the banks of rivers.

Reasonable fact-4

Germination of seed does not occur in dry soil.
Water is necessary for germination of a seed. But in dry soil there will be no water. So,
germination of seed does not occur in dry soil.

Reasonable fact-5

The seed kept in a closed container does not germinate.
Air is necessary for germination of seed. But in a closed container, there will be no
sufficient air. So, seed kept in closed container does not germinate.

corolla /kəˈrɒlə/ - the ring of petals present in a flower

248 Oasis School Science and Environment - 8 BIOLOGY

Reasonable fact-6

A new seed does not germinate though it gets suitable condition.
Seed embryo is not completely developed in a new seed. So, a new seed does not
germinate though it gets suitable condition.

16.7 Life Cycle of a Flowering Plant

Some plants reproduce asexually by different methods whereas most of the developed
plants reproduce sexually. In flowering plants, sexual reproduction is the most common
method of reproduction. Flower is the sexually reproductive organ of all seed bearing
plants. Flowers produce fruits which contain seeds and seeds can develop into new
plants. Flowering plants produce seeds which play a great role to complete their life cycle.
The series of forms into which a living organism changes as it develops is called life cycle.

Flower

Flower is the most attractive part of flowering plants. Most of the flowers have sweet
smell. Some flowers have so strong smell that honey bee and butterfly are attracted
towards them. Some flowers have an unpleasant smell whereas some have no smell at
all. Flowers, like leaves, grow from the stem of a plant. Many flowers have bright colours.
Some are yellow, white, blue, etc.

Anther Stigma
Filament Style

Petal

Ovary Sepal

Fig. 16.29 Structure of a typical flower

Structure of a Flower

Different types of flowers have different shape, size and colour. Most of them have
common structure. Each flower has a stalk called pedicel or receptacle. Pedicel may be
absent in some flowers. The basal swollen part of a flower is called thalamus. The parts
of a flower are arranged in a ring which is called whorl. Most flowers have four whorls
arranged in a definite order, viz. calyx, corolla, androecium and gynoecium.

1. Calyx: It forms the outermost whorl of a flower. It is made up of green leaf-like
structures called sepals. Sepals may be free (i.e. polysepalous) or united (i.e.
gamosepalous). Calyx synthesizes food for flower and protects the flower in the bud
stage.

slender /ˈslendə(r)/ - thin or narrow

BIOLOGY Oasis School Science and Environment - 8 249

calyx

Sepal

Typical calyx Calyx of mustard epicalyx Calyx of pea
Calyx of China rose

Fig. 16.30 Different types of calyx

2. Corolla: The second whorl of a flower is made up of colourful petals which is called
corolla. Petals are usually scented and beautiful. Petals attract insects for pollination
and also protect the reproductive organs of a flower.

petal

limb
claw

Typical corolla Corolla of mustard Corolla of China rose Corolla of pea

Fig. 16.31 Various types of corolla

3. Androecium: It forms the third inner whorl of a flower. Androecium consists of a
group of stamens. Each stamen is the male reproductive organ of a flower. It consists
of a swollen upper part called anther and a slender stalk called filament. Each anther
is made up of four pollen sacs which are connected together by a connective. Each
pollen sac is filled with pollen grains. Pollen grains are fine, powdery structures
containing male gametes.

anther pollen
connective anther

filament nectar gland
A typical stamen
T.S. of an anther Androecium of mustard Androecium of China rose Androecium of pea

Fig.16.32 Various types of androecium

4. Gynoecium: Gynoecium forms the innermost whorl of a flower. It is the female
reproductive part. Each member of the gynoecium is called pistil or carpel. Each

250 Oasis School Science and Environment - 8 BIOLOGY

carpel is made up of three parts, viz. ovary (the lowermost swollen part), style
(middle cylindrical part) and stigma (the uppermost spreading part). The stigma
receives pollen grains, the style supports stigma and the ovary contains ovules. The
ovules are connected to placenta. They produce female gametes and mature into
seeds after fertilization.

Stigma

Style

Ovary Placenta
Ovule

Typical gynoecium Section of an ovary Gynoecium of Gynoecium of China rose Gynoecium of pea
mustard

Fig.16.33 Various types of gynoecium

Differences between Calyx and Corolla

Calyx Corolla

1. It is the outermost whorl of a flower 1. It is the second whorl of a flower made

made up of green leaf-like structure up of colourful petals.

called sepals.

2. It synthesizes food for flower and 2. In corolla, petals attract insects for

protects the flower in the bud stage. pollination and also protect the

reproductive organs of a flower.

Differences between Androecium and Gynoecium

Androecium Gynoecium

1. It is the male reproductive part of a 1. It is the female reproductive part of a

flower. flower.

2. It produces pollen grains. 2. It produces female gametes or ovum.

3. It is made of anther filament and 3. It is made of stigma, style and ovary.
connective.

Pollination

At maturity, anthers begin to dry and burst open to release pollen grains. The pollen
grains are transferred to the stigma of a flower by many external agents like insects, wind,
birds, water, animals, etc. Pollination is the process of transfer of pollen grains from the

zygote /ˈzaɪɡəʊt/ - a diploid cell formed by the fusion of a male gamete and a female gamete

BIOLOGY Oasis School Science and Environment - 8 251

anther to the stigma of a flower. It is of two types– self-pollination and cross-pollination.

Self-pollination is the process of transfer of pollen grains from the anther to the stigma of
the same flower or to the stigma of another genetically identical flower of the same plant.
This process is common in bisexual flowers, e.g. China rose, pea, etc.

Cross-pollination is the process of transfer of pollen grains from anther of a flower of one
plant to the stigma of a flower in other plants of the same species. This process is common
in both unisexual and bisexual flowers. External agents of pollination are essential for
cross-pollination. In flowering plants, pollination is followed by fertilization.

Self-pollination Self-pollination

Cross-pollination

Fig.16.34 Types of pollination

Differences between Self-pollination and Cross-pollination

Self-pollination Cross-pollination

1. It is the process of transfer of pollen 1. It is the process of transfer of pollen

grains from the anther to the stigma grains from anther of a flower of one

of the same flower or to the stigma of plant to the stigma of a flower of

another genetically identical flower another plant of the same species.

of the same plant.

2. External agent of pollination are not 2. External agents of pollination like

required. insects, wind, water, etc. are required.

3. It does not help in variation. 3. It helps in variation.

Fertilization

Fertilization is the process of fusion of a male gamete and a female gamete to form a
zygote. In flowering plants, pollen grains absorb secretions from the stigma and undergo
germination after pollination. The germinating pollen grain produces a pollen tube which
grows down towards style and finally reaches the ovule in the ovary.

252 Oasis School Science and Environment - 8 BIOLOGY

Mature Germinated pollen grain
plant with Anther at tip of stamen
flowers Pollen tube
Ovary (base or carpel)
Seedling Ovule Zygote
Embryo sac Embryo
Egg
Sperm Simple fruit
(develops from
Germinating seed Seed ovary)

Seed (develops
from ovule)

Fig.16.35 Life cycle of a flowering plant

The fertilization in flowering plants involves the fusion of two male gametes separately. One
male gamete fuses with the egg cell (ovum) and forms zygote. Similarly, another male gamete
fuses with the secondary nucleus and forms endosperm nucleus. Therefore, the fertilization
in flowering plants is called double fertilization. After fertilization, the zygote divides and
forms embryo whereas the endosperm nucleus develops into endosperm of the seed.

An embryo is the baby plant in the very early stage of its development before coming
out of its seed whereas the endosperm is the food storage tissue of the seed. The embryo
and endosperm together make a seed. After fertilization, the ovule forms seed and ovary
forms the fruit. A seed is a reproductive unit of a plant which can germinate to produce a
new plant on favourable condition.

Differences between Pollination and Fertilization

Pollination Fertilization

1. The process of transfer of pollen grains 1. The process of formation of a zygote

from anther to the stigma of a flower by the fusion of male gamete and

is called pollination. female gamete is called fertilization.

2. This process is found only in flowering 2. This process is common in both

plants. flowering plants and animals that

reproduce by sexual method.

Activity 5

To observe various parts of flowers
• Visit a garden and collect different types of flowers.
• Separate the sepals, petals, stamens and pistils of each flower.
• Draw diagrams of each flower and label them.
• Also, write down the similarities and differences among them.

BIOLOGY Oasis School Science and Environment - 8 253

Activity 6

• Visit a crop field and uproot a mustard plant or any other flowering plant.
• Observe its root, stem, leaves, flowers and fruits.
• Draw a neat diagram and label the main parts.

SUMMARy

• The organisms which cannot be seen with our naked eyes are called microscopic
organisms.

• Bacteria are the smallest and most widespread single-celled plant organisms.

• Viruses are the smallest and possibly the most primitive, acellular, non-
protoplasmic bodies, which cause various diseases in plants and animals.

• Since viruses can reproduce only inside the living cell of the host, they are called
obligatory parasites.

• Fungi are non-green thallophytes without chlorophyll.

• The root, stem and leaves of plants perform certain functions. Besides these
functions the root, stem and leaves of different plants are modified to perform
various functions and adapt in their habitat. This process is called modification of
parts of plants.

• A seed is a ripened ovule of a flowering plant. It is a small embryonic plant
enclosed in a covering called the seed coat.

• The seeds in which food is stored in endosperm are called endospermic seeds.

• The seeds having two cotyledons are called dicotyledonous seeds.

• The seeds in which food is stored in cotyledons are also called non-endospermic
seeds.

• Seed germination is a process by which a seed embryo develops into a seedling
and subsequently a plant.

• Germination does not take place unless the seed has been transported to a
favourable condition.

• Seed dispersal is the movement or transport of seeds away from the parent plant.

• In flowering plants, sexual reproduction is the most common method of
reproduction.

• Each carpel is made up of three parts, viz. ovary (the lowermost swollen part),
style (middle cylindrical part) and stigma (the uppermost spreading part).

• Pollination is the process of transfer of pollen grains from the anther to the stigma
of a flower. It is of two types– self-pollination and cross-pollination.

• A seed is a reproductive unit of a plant which can germinate to produce a new
plant on favourable condition.

254 Oasis School Science and Environment - 8 BIOLOGY

Exercise

1. Choose the best answer from the given alternatives.

a. Bacteria are found in............................................ .

i. air ii. water iii. soil iv. all of above

b. Which of the following is a viral disease?

i. typhoid ii. AIDS iii. cholera iv. pneumonia

c. Mushroom, yeast and moulds are the examples of...................................... .

i. fungi ii. bacteria iii. viruses iv. animals

d. Which of the following is a monocotyledonous seed?

i. bean ii. pumpkin iii. orange iv. maize

e. Which of the following is the innermost whorl of a flower?

i. corolla ii gynoecium iii. calyx iv. androecium

2. Tick () the correct statement and cross (×) the incorrect one.

a. Bacteria do not have well developed nucleus.

b. Rhino virus is a plant virus.

c. Fungi are autotrophic plants.

d. In cactus, stem is modified to store water.

e. Plumule of a seed develops into stem.

f. Anther produces pollen grains.

g. Embryo develops from a zygote.

3. Fill in the blanks using appropriate words.
a. Viruses show the properties of both ……………… and ……… things.
b. The stem of potato is modified to …………… food.
c. Plumule is larger in ……………. seed.
d. ……… is the second whorl of a flower.

e. Ovary develops into ………… after fertilization.

4. Answer the following questions.

a. What are bacteria? Write any four characteristics of bacteria.

b. What are viruses? What is the literal meaning of virus?
c. What are fungi? Give any three examples.

BIOLOGY Oasis School Science and Environment - 8 255

d. Write any three characteristics of fungi.
e. What is meant by modification of parts of plants?
f. How are roots of plants modified? Describe in brief.
g. How are stems of plants modified? Describe in brief.
h. What is a seed? Write down the function of radicle and plumule of a seed.
i. Write any two functions of seed.
j. What is meant by dispersal of seed? Write any three methods of seed dispersal.
k. What is the source of food for a germinating seed?

l. What is meant by germination of seed? Write down the conditions required
for this process.

m. Define pollination and fertilization.

5. Differentiate between b. Fungi and Bacteria
a. Bacteria and Viruses d. Radicle and Plumule
c. Monocot seed and Dicot seed

e. Hylum and Micropyle f. Androecium and Gynoecium

6. Give reason.
a. Bacteria are called the simplest plants.
b. Viruses are kept in the border line of living and non-living things.
c. Some seeds contain fluffy parachute-like structure.
d. Leaves of desert plants are reduced into thorns.

7. Draw a neat and labelled figure of :

a. Bacteria b. Virus c. Monocot seed

d. Dicot seed e. Flower

8. Describe an experiment to prove that a seed cannot germinate in the absence of
favourable conditions.

9. Draw a neat and labelled figure showing the life cycle of a flowering plant.

256 Oasis School Science and Environment - 8 BIOLOGY

UniT 17 Estimated teaching periods : Th Pr
6 3

Robert Hooke

CeLL and TissUe

Objectives

After completing the study of this unit, students will be able to:

• describe the interrelationship among cell, tissue and organ.
• introduce epithelial tissue and meristematic tissue and describe their

types.
• explain the interrelationship among cell, tissue and organ in human

body.

Course of Study

• Introduction to cell and tissue
• Animal tissue
• Epithelial tissue and its types
• Meristematic tissue and its types
• Interrelationship between cell, tissue and organ in human body

Points to be Focused/Questions to be Discussed

• What are cell, tissue and organ?
• What is epithelial tissue?
• What are the types of epithelial tissue?
• What are the functions of epithelial tissue?
• What is meristematic tissue?
• What are the types of meristematic tissue?
• What is the relationship among cell, tissue and organ in human body?

BIOLOGY Oasis School Science and Environment - 8 257

17.1 Introduction

All living organisms are composed of microscopic units called cells. These cells are called
building blocks of life. A cell is defined as the basic, structural and functional unit of
life capable of independent existence. A cell has a complete set of parts neatly arranged
in a mass of cytoplasm surrounded by a membrane that appears a tiny compartment.
Therefore, the cell is also called basic unit of life. A cell is made up of life giving substance
called protoplasm.

Plasma membrane Nucleus Plastid
Centrosome Nucleolus Gogi bodies
Nucleus
Cytoplasm
Nucleolus
Vacucole Endoplasmic
reticulum
Cytoplasm Cell wall
Mitochondrion

Vacuole

Endoplasmic reticulum Mitochondrion

Golgi complex Cell membrane

(a) Animal cell (b) Plant cell

Fig. 17.1

Face file-1

Cell is considered as the fundamental unit of life.
Cell is called the fundamental unit of life because all life forms are composed of cells.
Some forms of life are made of one cell, other contain trillions.

17.2 Discovery of Cell

Cell was discovered by Robert Hooke in 1665
AD. He observed a thin slice of cork under
his self-built microscope and found that the
cork piece had numerous compartments
connected together in a honey-comb like
structure. He named these compartments as cells
(L., cella-compartments).

Fig. 17.2 Compound microscope

17.3 Tissue

The body of multicellular organisms is made up of a large number of cells. There are
different groups of cells that perform different functions. Group of cells having a common
origin and performing similar function is called a tissue. Each tissue comprises of cells

capable /ˈkeɪpəbl/ - having the ability for doing sth

258 Oasis School Science and Environment - 8 BIOLOGY

that originate from common parent cells and have a characteristic shape, size and
arrangement. A tissue can be defined as a group of cells having a common origin which
are more or less alike in shape, size and performing the same function. Epithelial tissue,
muscular tissue, blood, meristematic tissue, xylem, phloem, etc. are some examples of
tissues. The microscopic study of tissues and their functions is called histology. Plants and
animals contain different kinds of tissues.

Differences between Cell and Tissue

Cell Tissue

1. Cell is the basic, structural and functional 1. A tissue is a collection of similar cells

units of life. The bodies of all living having similar structure and adapted to

organism are made up of cells. perform a function or set of functions.

Animal tissue

Epithelial tissue Muscular tissue Connective tissue Nervous tissue

Pavement epithelium Voluntary muscle

Cubical epithelium Involuntary muscle
Columnar epithelium Cardiac muscle
Glandular epithelium

Sensory epithelium Soft connective tissue Hard connective Fluid connective
Fibrous tissue tissue tissue
Cartilage Blood

Adipose tissue Bones Lymph

17.4 Animal Tissues

On the basis of structure and function, animal tissues are classified into following four
types:

A. Epithelial tissue B. Muscular tissue

C. Connective tissue D. Nervous tissue

In this unit, we will study the epithelial tissue, its types and functions only.

A. Epithelial tissue Oasis School Science and Environment - 8 259

BIOLOGY

Epithelial tissue is a thin, protective tissue composed of one or more layers of cells
covering the external surface and internal body organs. It lines the body cavity and
cavities of hollow body organs, ducts and blood vessels.

Nucleus
Cytoplasm

Cell membrane

(i) (ii)

Fig.17.3 Pavement epithelium (i) layer and (ii) surface view

Characteristics of epithelial tissue

1. The lowermost layer of epithelial tissue is attached to the basement membrane
which separates it from underlying tissue.

2. Cells of this tissue are closely packed without intercellular spaces and matrix.

3. Blood vessels are absent in this tissue.

4. The surface of cells may be smooth or may have hair-like cilia or microvilli.

Functions

1. Epithelial tissue protects the underlying tissues from mechanical injury, entry
of germs and harmful chemicals.

2. This tissue helps in absorption of digested food and excretion of nitrogenous
wastes.

3. It helps in secretion of hormones and enzymes and formation of gametes.

4. Sensory epithelium in sense organs receives sensory stimuli and conveys nerve
impulses to the brain and spinal cord.

Types of epithelial tissue

On the basis of structure and organization of the component cells, epithelial tissues are of
following types:

a. Pavement epithelium b. Cubical epithelium

c. Columnar epithelium d. Glandular epithelium

e. Sensory epithelium

a. Pavement epithelium

Pavement epithelium is a single-layered epithelial tissue in which cells are thin
having centrally placed nucleus. The cells are arranged edge to edge and form

impulse /ˈɪmpʌls/ - a force or movement of energy that causes sth else to react

260 Oasis School Science and Environment - 8 BIOLOGY

delicate lining or covering. Pavement epithelium is also called squamous epithelium.

The cells in this tissue are flat, plate-like and polygonal. They are closely packed
together which resemble flat tiles like that of a mosaic floor or pavement. So, this
tissue is also called pavement epithelium.

Location
Pavement epithelium is found in the form of lining in skin, lungs, heart, kidneys,
oesophagus and blood vessels.

Functions
The major functions of pavement epithelium are protection, filtration and making
passage for flow of liquid and gases.

b. Cubical epithelium

Cubical epithelium is made up of single-layered cubical cells having similar
dimensions on each side. The cells in this tissue are attached with one another by
their lateral surfaces.

Location
Cubical epithelium is found in thyroid gland, terminals of bronchioles, ducts of
excretory organs, inner parts of testes and ovaries.

Functions
Cubical epithelium is responsible for protection, secretion and germination.

Cytoplasm

Nucleus

Basement membrane

Fig.17.4 Cubical epithelium

Differences between Pavement epithelium and Cubical epithelium

Pavement epithelium Cubical epithelium

1. It is a single layered epithelial tissue in 1. It is a epithelial tissue made of single
which cells are thin having centerally layered cubical cells.
placed nucleus.

2. It is responsible for protection, filtration 2. It is found in thyroid gland, terminals of

and making passage for flow of liquid bronchioles, ducts of exretory organs,

and gases. inner parts of testes and ovaries.

BIOLOGY Oasis School Science and Environment - 8 261

c. Columnar epithelium
The single layered cells of this tissue are elongated and placed side by side like
columns. The cells are attached to the basement membrane.

Location
Columnar epithelium is found in the form of lining layer of stomach, intestine,
salivary gland, urinogenital organs and their ducts.

Function
Columnar epithelium is responsible for absorption and secretion.

Cell membrane
Cytoplasm
Nucleus
Basement
membrane

Fig.17.5 Columnar epithelium

d. Glandular epithelium
Glandular epithelium is the modified form of columnar epithelium in which cells

are specialized for manufacture and secretion of chemical substances. These cells
form the structural basis of various glands in the body.
Location
Glandular epithelium is found in various endocrine and exocrine glands.
Function
Glandular epithelium secretes various chemicals like enzymes, hormones, sweat,
saliva and other digestive juices.

Cilia

Mucus

Goblet cell

Nucleus

Fig.17.6 Glandular epithelium
hormone /ˈhɔːməʊn/ - the chemical substance produced in the body that encourages the growth and development

262 Oasis School Science and Environment - 8 BIOLOGY

e. Sensory epithelium
Sensory epithelial tissue is also the modified form of columnar epithelium in which
elongated cells are present along with the sensory hairs at free ends and nerve fibres
at other end.

Location
This tissue is found in olfactory epithelium of nose, retina of eye, etc.

Function
It is sensory in function.

Axons

Cribriform
plate

Olfactory
sensory
neurons
Dendrite

Mucous layer Cilia Basal
cells

Fig.17.7 Sensory epithelium

Activity 1

• Take a toothpick and wash it. Rinse your mouth.

• Gently scrape the inner lining of your cheek with Nucleus

the toothpick. Bacteria

• Put a drop of iodine solution on a slide and trans-

fer the scraping onto the slide. Fig. 17.8

• Put a cover slip over it and observe it under the
microscope.

• Draw a well labelled figure and identify the type of tissue.

Activity 2

• Visit a nearby butcher's shop. Observe the various organs like eye, heart, kidney,
lung, brain, etc. and write their functions.

mitosis /maɪˈtəʊsɪs/ - the cell division that takes place in body cells and causes growth

BIOLOGY Oasis School Science and Environment - 8 263

17.5 Plant Tissues

On the basis of location and function, plant tissues can be divided into following
two types:

A. Meristematic tissue

B. Permanent tissue Apical
meristem
A. Meristematic tissue
Meristematic tissue is made up of simple Lateral
undifferentiated cells which continue to divide meristem
actively to produce new cells. The meristematic
cells are thin-walled cells and are in active state Intercalary
of mitosis. meristem

The meristematic cells are compactly packed Fig. 17.9 L.S. of a shoot showing
without leaving intercellular spaces. The cells meristematic tissue
are small with a distinct nucleus and dense
cytoplasm without vacuoles.

On the basis of location, meristematic tissue are of three types:

i. Apical meristem

ii. Lateral meristem
iii. Intercalary meristem

i. Apical meristem

The meristematic tissue present at the tips of root, stem and their branches is
called apical meristem. It is responsible for axial growth of the plant.

ii. Lateral meristem

The meristematic tissue located along the side of the stem and root is called
lateral meristem. It is responsible for increasing the girth of the plant.

iii. Intercalary meristem

The meristematic tissue located at the base of leaf and fruit is called intercalary
meristem. It increases the length of internodes.

Reasonable fact-1

A plant does not grow when its tip is cut.
Division of cells to produce new cells takes place only at the tip of a plant. So, a plant
does not grow when its tip is cut.

17.6 Organ

An organ is a part of an animal or a plant having a characteristic function, shape and
structure. Eyes, heart, lungs, stomach, kidneys, etc. are examples of some organs of

264 Oasis School Science and Environment - 8 BIOLOGY

animals. Similarly, root, stem, leaves, flowers, etc. are organs of plants. Several organs
may function together which is called an organ system.

17.7 System

In the body of an organism, a set of organs act together to perform a certain function.
This group of organs is called system. Examples: Digestive system, circulatory system,
reproductive system, etc. There are nine systems in human body. In a system, different
types of organs act together. For example, various organs like mouth, oesophagus,
stomach, intestine, salivary glands, pancreas, gastric glands and intestinal glands work
together in digestive system.

17.8 Interrelationship among Cells, Tissues and Organs

Cell is the basic, structural and functional unit of life. The body of all living organisms is
made up of cells. A unicellular organism consists of only one cell whereas multicellular
organisms contain many cells. The single cell of unicellular organisms can perform
various activities like respiration, excretion, reproduction, digestion, etc. But in case
of multicellular organisms, there are separate groups of cells responsible for different
functions. Such group of cells is called tissue. The cells of a tissue show similar pattern
of growth and development. In the developed organisms, there are many functions
being carried out by various tissues in the group. Such group of tissues that performs
a particular function is called an organ. In the body of an organism, a set of organs
acts together to perform a certain function, e.g. digestive system, circulatory system,
etc. Various systems act together and form a complete organism. Thus, there exists a
close relationship among cells, tissues, organs and systems.

Cell + Cell → Tissue

Tissue + Tissue → Organ

Organ + Organ → System

Liver is the main organ of human body which performs many functions in our body.

The major functions of liver are as follows:

i. The bile juice secreted by liver helps to digest fat.

ii. It produces heat in the body.

iii. It destroys red blood cells.

iv. It regulates the amount of sugar in blood.

v. It detoxicates drugs.

vi. It synthesizes vitamins.

vii. It forms urea and uric acid that are excreted in urine.

viii. It converts glucose into glycogen and stores it.

Various systems, organs and tissues of human body and their functions are given in the

BIOLOGY Oasis School Science and Environment - 8 265

table below:

S.N. Systems Organs Tissues Functions

1. Digestive system Mouth, stomach, Columnar Digestion and

liver, pancreas, epithelium, absorption

intestine involuntary muscle

2. Respiratory system Nose, wind pipe, Pavement and To exchange oxygen

lungs cubical epithelium and carbon dioxide

3 Circulatory system Heart, blood, blood Pavement To supply food

vessels epithelium, cardiac and oxygen, fight

muscle, smooth against infection

muscle, connective

tissue

4. Excretory system Kidney, liver, Pavement and To excrete waste
ureter, urinary
bladder cubical epithelium materials

5. Muscular system Various types of Skeletal, smooth To help in
muscles and cardiac muscle movement of body

parts, to give shape

6. Skeletal system Bones and cartilage Connective tissue To give internal
framework, to help
in locomotion

7. Reproductive Testes, ovaries Cubical and Sexual reproduction
system vagina, penis, etc. columnar
epithelium

8. Nervous system Brain, spinal cord Nervous tissue Sensory
and nerves

9. Endocrine system Endocrine glands Glandular To bring about
epithelium harmonious
development of
body

Reasonable fact-2

There is close relationship among cells, tissues and organs.

All life forms are composed of cells. Cell is the basic, structural and functional unit
of life. Tissue is a collection of similar cells having similar structure and adapted to
perform a set of function, i.e. similar pattern of growth and development. An organ
is the group of tissue that performs a particular function. This shows that tissue is the
collection of cells and organ is the collection of tissues which are closely related to each
other. So, there is close relationship among cells, tissues and organs.

Activity 3

• Take a tip of a growing plant. Cut a thin slice of the tip and prepare a slide.
Observe the slide under the compound microscope and draw a neat and
labelled figure.

266 Oasis School Science and Environment - 8 BIOLOGY

SUMMARy

• A cell is defined as the basic, structural and functional unit of life capable of
independent existence.

• Group of cells having a common origin and performing similar function is
called a tissue.

• A tissue can be defined as a group of cells having a common origin which are
more or less alike in shape, size and performing the same function.

• Epithelial tissue is a thin, protective tissue composed of one or more layers of
cells covering the external surface and internal body organs.

• Pavement epithelium is a single-layered epithelial tissue in which cells are thin
having centrally placed nucleus.

• Glandular epithelium is the modified form of columnar epithelium in which
cells are specialized for manufacture and secretion of chemical substances.

• Meristematic tissue is made up of simple undifferentiated cells which continue
to divide actively to produce new cells.

• The meristematic tissue present at the tips of root, stem and their branches is
called apical meristem.

• The meristematic tissue located along the side of the stem and root is called
lateral meristem.

• The meristematic tissue located at the base of leaf and fruit is called intercalary
meristem.

• An organ is a part of an animal or a plant having a characteristic function,
shape and structure.

• In the body of an organism, a set of organs acts together to perform a certain
function. This group of organs is called system.

• There exists a close relationship among cells, tissues, organs and systems.

BIOLOGY Oasis School Science and Environment - 8 267

Exercise

1. Choose the best answer from the given alternatives

a. The basic, structural and functional unit of life is called ....................... .

i. tissue ii. cell iii. organ iv. system

b. Blood vessels are absent in ....................... .

i. epithelial tissue ii. muscular tissue

iii. nervous tissue iv. connective tissue

c. The tissue that helps in growth of a plant is ....................... .

i. connective tissue ii. muscular tissue

iii. meristematic tissue iv. permanent tissue

d. Which of the following is an organ?

i. blood ii. kidney iii. skin iv. muscle

e. The organ that performs many functions in human body is....................... .

i. eye ii. ear iii. liver iv. kidney

2. Tick (√) the correct statement and cross (×) the incorrect one.

a. A group of similar cells that performs a certain function is called
tissue.

b. In cubical epithelium, cells are arranged like flat tiles of a
pavement.

c. Apical meristem helps in axial growth of the plant.

d. Blood, skin and bone are examples of organs.

e. The major function of digestive system is to circulate blood.

3. Fill in the blanks using appropriate words.
a. ………….... is the fundamental unit of life.
b. The group of …..……….. that performs a certain function is called organ.
c. …..…….. epithelium is found in walls of stomach, intestine and ureters.
d. The epithelium that secretes hormones and enzymes is called ……........... .
e. The meristematic tissue that increases the girth of a plant is called ……..... .

4. Answer the following questions.
a. What is a cell? Why is cell called the basic unit of life?
b. What is a tissue? Give any three examples.

268 Oasis School Science and Environment - 8 BIOLOGY

c. Name the four types of tissues found in animals.
d. What is epithelial tissue? Write any three characteristics of this tissue.
e. Write any four functions of epithelial tissue.
f. What is pavement epithelium? Where is it located?
g. Where is columnar epithelium located? Write down its two functions.
h. What is glandular epithelium? Write down its major function.
i. What is meristematic tissue? Write down any two characteristics of this tissue.
j. What is lateral meristem? Write down its function.

k. Define organ and system with any two examples of each.

5. Differentiate between:
a. Pavement epithelium and Glandular epithelium
b. Epithelial tissue and Meristematic tissue
c. Apical meristem and Lateral meristem

d. Tissue and Organ

6. Give reason.

a. Cell is called the functional unit of life.

b. Blood is called a tissue.

c. A plant does not grow when its apical meristem is cut.

7. Draw neat and labelled figure showing:

a. Cubical epithelium b. Glandular epithelium c. Meristematic tissue

8. Name the following tissues. Write down the location and major function of each.

a b. .

9. Name the four types of epithelial tissue and write one major function of each.
10 Describe the relationship among cell, tissue, organ and system in the

human body.

BIOLOGY Oasis School Science and Environment - 8 269

UniT 18 Estimated teaching periods : Th Pr
10 2

Human heart

Life ProCesses

Objectives

After completing the study of this unit, students will be able to:

• explain asexual and sexual reproduction that occurs in plants and
animals.

• introduce blood circulatory system in human body and explain the
process of blood circulation.

• introduce photosynthesis that occurs in plants and perform experiments
based on photosynthesis.

Course of Study

• Reproduction - Introduction
• Asexual reproduction
• Methods of asexual reproduction
• Sexual reproduction in plants and animals
• Blood circulatory system is human body
• Photosynthesis
• Experiments based on photosynthesis

Points to be Focused/Questions to be Discussed

• What is reproduction?
• What is asexual reproduction? What are different methods of asexual

reproduction?
• What is sexual reproduction? How does it occur in plants and animals?
• What is circulatory system? What are its functions?
• What is photosynthesis? What are the raw materials required for

photosynthesis?

270 Oasis School Science and Environment - 8 BIOLOGY

18.1 Introduction

Living organisms perform various activities like respiration, nutrition, transportation
of substances, excretion, movement, reproduction, etc. These activities are essential for
survival of an organism and hence called life processes. Various activities carried out
by living organisms, which are necessary to maintain and continue life are called life
processes. Living organisms cannot survive in the absence of life precesses.

18.2 Reproduction

Living organisms cannot survive for ever. Each living being remains alive in this nature for
a limited period of time and then it dies. So, living organisms produce their own kinds for
continuity of the race of their species on the earth. The biological process in which living
organisms produce their own kinds by asexual or sexual method is called reproduction.
Reproduction can also be defined as the creation or production of new organisms from the
pre-existing organisms of the same species. Living organisms reproduce by two methods
to maintain the life of their species on the earth which are as follows:

(i) Asexual reproduction, and (ii) Sexual reproduction

18.3 Asexual Reproduction

Asexual reproduction is a common method of reproduction in lower plants and animals.
In this method, a single organism is capable of reproduction. The method of reproduction
which takes place from a single parent without the fusion of a male gamete and a female
gamete is called asexual reproduction. In this process, no sex cells, i.e. gametes are
involved. So, this method is called asexual reproduction. The new offspring produced by
asexual method are genetically identical to their parents. Asexual reproduction involves
the production of offspring from a single parent. Binary fission in amoeba, budding in
hydra, regeneration in planaria, vegetative propagation in rose, etc. are some examples of
asexual reproduction.

18.4 Methods of Asexual Reproduction

The various methods of asexual reproduction are mentioned below:

(a) Fission (b) Budding (c) Sporulation

(d) Fragmentation or Regeneration (e) Vegetative propagation

(a) Fission

The method of asexual reproduction in which a parent organism divides into two
or more daughter organisms is called fission. It is common in unicellular organisms
like Amoeba, Paramecium, Plasmodium, Bacteria, Euglena, etc. On the basis of the
number of daughter organisms produced, fission is of two types:

(i) Binary fission

(ii) Multiple fission

fission / ˈ f ɪ ʃ n / - the division of a cell into new cells as a method of reproduction

BIOLOGY Oasis School Science and Environment - 8 271

(i) Binary fission

The fission in which a parent organism divides into two daughter organisms is called
binary fission. In this method, the nucleus divides first into two daughter nuclei.
This process is followed by the division of cytoplasm. Finally, the cell splits into two
daughter cells. In this way, a parent organism divides into two daughter organisms.

Binary fission occurs during favourable conditions of life. Some unicellular plants
like Bacteria, Diatoms, etc. and animals like Euglena, Amoeba, Paramecium,
Plasmodium, etc. reproduce by binary fission.

Parent cell Nucleus divides Cytoplasm divides

Daughter cells

Fig. 18.1 Binary fission in Amoeba

(ii) Multiple fission

The fission in which a parent organism divides into more than two daughter
organisms at the same time is called multiple fission. It occurs in unfavourable
conditions. Many unicellular algae and some unicellular animals like Amoeba,
Plasmodium, Chlamydomonas, etc. reproduce asexually by multiple fission during
unfavourable conditions.

Daughter nuclei

Cyst

Parent cell Daughter
plasmodia

Fig.18.2 Multiple fission in Plasmodium

In multiple fission, a cyst (i.e. a thick protective layer) is formed around cell of unicellular
organism in unfavourable condition. Inside the cyst, the nucleus divides repeatedly to
produce many daughter nuclei. Later on, each nucleus is surrounded by cytoplasm and
cell membrane. As a result, many daughter cells are formed inside the cyst.

On the return of favourable conditions, the cyst breaks and small offspring are
released. In this way, multiple fission takes place in unicellular organisms.

272 Oasis School Science and Environment - 8 BIOLOGY

Differences between Binary fission and Multiple fission

Binary fission Multiple fission

1. The process in which one parent body 1. The process in which one parent body

divides into only two daughter organisms divides into more than two daughter

is called binary fission. organisms is called multiple fission.

2. It is common in amoeba, bacteria, etc. 2. It is common in Plasmodium,
Chlamydomonas, etc.

(b) Budding

It is a method of asexual reproduction in which a bud

arises from the parent’s body which detaches and finally Bud
develops into a new organism. The method of asexual

reproduction which takes place by the formation of

a bud is called budding. This method is common in

unicellular plants like yeast and multicellular animals

like hydra. Fig.18.3 Budding in yeast

In yeast, a bulb-like outgrowth (i.e. bud) is formed on

one side of the cell. The nucleus divides and one daughter nucleus passes into the

bud. The bud grows and finally gets detached from the parent cell which grows in

size and becomes a new yeast.

Bud grows Bud separates
Bud

(c) Sporulation Fig. 18.4 Budding in hydra

In this method, the parent plant produces a large number of tiny spores which
can produce new plants. The method of asexual reproduction which takes place
by means of spores is called sporulation. This method is common in Mucor, Moss,
Marchantia, Chlamydomonas, etc.

sporangium sporangial wall

spores
columella

mycelium (b)
(a)

Fig.18.5 Sporulation in mucor

detach /dɪˈtætʃ/ - to become separated from sth

BIOLOGY Oasis School Science and Environment - 8 273

In mucor, small knob-like structures called sporangia (singular–sporangium)
develop at the top of hyphae. Numerous spores are produced inside the sporangium.
Spores are the microscopic asexually reproductive bodies covered by a hard
protective coat. Spores germinate into new organisms under favourable conditions.
At maturity, sporangia burst open to release spores, which grow into new organisms
on favourable condition.

Activity 1

To observe sporulation in mucor

• Take a slice of bread and keep it in a moist and
warm place for 4-5 days.

• After 4-5 days, you can see a white cottony mass of
mucor.

• Keep the slice of bread in the sunlight for 2-3 days.
• Observe the surface of mucor under the hand lens Fig. 18.6 Growth of mucor on bread

and compound microscope.
• Draw the labelled figures and write a few comments on the basis of your

observation.

(d) Fragmentation or Regeneration
Fragmentation is the method of asexual reproduction in which a multicellular
organism breaks into two or more fragments and each fragment develops into a new
complete organism. The ability of an individual fragment of an organism to replace
its lost parts is called regeneration. It can also be defined as the process of getting
back a complete organism from its body parts.

(a) Regeneration in Planaria (b) Fragmentation in Spirogyra

Fig.18.7

In fragmentation, a parent multicellular organism breaks down naturally to produce
two or more pieces. After a certain time, each piece of the organism regenerates
itself to form a complete organism by growing all missing parts. Filamentous algae

regeneration /rɪdʒenəˈreɪʃn/ - to grow again

274 Oasis School Science and Environment - 8 BIOLOGY

like spirogyra and animals like hydra, planaria, tapeworm, sponge, etc. reproduce
asexually by this method. Please note that the term ‘fragmentation’ is generally used
for plants and the term ‘regeneration’ is used for animals.

(e) Vegetative Propagation

Vegetative propagation is the method of asexual reproduction common in some
higher plants. In this method, a bud grows on the vegetative part of plant like a stem,
root or leaf and develops into a new plant. On maturity, the new plant detaches
itself from the parent plant and lives as an independent plant. Thus, vegetative
propagation is the method of asexual reproduction in which new plants are produced
by vegetative parts of plants like root, stem or leaf.

(i) Vegetative Propagation by Roots

Some flowering plants like sweet potato, dahlia, mint, etc. reproduce asexually by
means of roots. Roots of those plants contain adventitious buds. When such roots are
planted in the soil, new plants are produced.

(a) Dahlia (b) Sweet potato

Fig.18.8 Vegetative propagation by roots

(ii) Vegetative Propagation by Stem

At maturity, the stem of plants develops buds on it. The part of stem having buds
serves as an organ for vegetative propagation. When the stem falls on the ground, it
propagates new plants on favourable condition. For example, bulb of onion, stem of
rose, tuber of potato, etc. reproduce asexually by means of stem.

main root scale leaf
New plant
eye Node
scale leaf bud Intermode
disc Node
root

(a) Tuber of potato (b) Bulb of onion (c) Aerial stem of sugarcane

Fig. 18.9 Vegetative propagation by stem

BIOLOGY Oasis School Science and Environment - 8 275

Activity 2

To observe vegetative propagation by stem in sugarcane
• Bring a mature sugarcane and cut it into small pieces.
• Observe the buds in the nodes of the sugarcane.
• Plant these pieces in the soil and supply water regularly.
• Observe after 2-3 weeks.
• Prepare a report with the labelled figures and submit to your science teacher.

Reasonable fact-1

Vegetative propagation is beneficial for farmers.
Vegetative propagation is beneficial for farmers because of the following reasons:
(i) Gardeners, farmers and botanists can grow a large number of plants by this

method.
(ii) The plants which do not produce viable seeds like rose, sugarcane, potato, etc.

can easily be propagated by this method.

(iii) Vegetative Propagation by Leaf
Leaves of some plants like Bryophyllum, Begonia, etc. produce adventitious buds.

Those buds develop into small plantlets when the leaf falls on the moist soil. These
plantlets get separated from the leaf and grow into new plants.

New plantlets

New plantlet

Leaf of Bryophyllum Leaf of Begonia

Fig. 18.10 Vegetative propagation by leaf

18.5 Significance of Asexual Reproduction

(i) Asexual reproduction produces new individuals with exactly identical qualities as
the parent.

(ii) It is a faster, easier and cheaper method of reproduction.

(iii) The plants produced by vegetative propagation bear flowers and fruits earlier than
those produced from seeds.

(iv) The plants which do not produce viable seeds (like sugarcane, rose, potato, banana,
bamboo, etc.) can easily be propagated by asexual reproduction.

276 Oasis School Science and Environment - 8 BIOLOGY

18.6 Sexual Reproduction

Sexual reproduction is a complex process of reproduction in which both sexes, the male and
female, are involved. Most animals and higher plants reproduce by sexual reproduction.
The process in which reproduction takes place by the fusion of a male gamete and a
female gamete is called sexual reproduction. In this method, a male gamete and a female
gamete unite to form a zygote which finally develops into a new organism.

18.7 Sexual Reproduction in Flowering Plants

In flowering plants, sexual reproduction is the most common method of reproduction. In
higher plants, flower is the sexually reproductive organ. A complete flower contains four
floral whorls, viz. calyx, corolla, androecium and gynoecium.

anther stigma pistil
filament style
ovary
petal

receptacle

sepal pedicel

Fig. 18.11 Structure of a flower

At maturity, anthers begin to dry and burst open to release pollen grains. The pollen
grains are transferred to the stigma of a flower by many external agents like insects, wind,
birds, water, animals, etc. This process is called pollination. Pollination is the transfer of
pollen grains from the anther to the stigma of a flower. It is of two types– self-pollination
and cross-pollination. This process leads to cross-fertilization which brings out variation
in offspring. In flowering plants, pollination is followed by fertilization.

After fertilization, the ovule develops into seed and ovary into the fruit. The seed is a
reproductive unit of a plant which can germinate to produce a new plant on favourable
condition.

In this way, flowering plants reproduce sexually by forming seeds through flowers.

Activity 3

To observe various parts of flowers
• Visit a garden and collect different types of flowers.
• Separate the sepals, petals, stamens and pistils of each flower.
• Draw their figures and label them.
• Also, write down the similarities and differences among them.

whorl /wɜːl/ - a ring of leaves, flowers, etc. around the stem of a plant

BIOLOGY Oasis School Science and Environment - 8 277

18.8 Sexual Reproduction in Animals

Sexual reproduction is the only method of reproduction in vertebrate animals but it is
also found in lower group of invertebrates like paramecium, flatworms, roundworms,
arthropods, molluscs, etc. Among them, some animals are unisexual and some are
bisexual. Bisexual animals can produce both male and female gametes whereas unisexual
animals can produce either male gamete or female gamete. The process by which animals
produce gametes is known as gametogenesis. In animals, gonads are the primary sex
organs which produce gametes or sex cells. Testis is the male gonad that produces sperms
or male gametes by spermatogenesis. Similarly, ovary is the female gonad that produces
ova or egg cells or female gametes by oogenesis.

After the formation of gametes, fusion of a male gamete and a female gamete takes place
which results in the formation of a zygote. The zygote divides mitotically and forms an
embryo which finally develops into a young animal.

Haploid sperm

Diploid zygote

Haploid egg

Fig. 18.12 Gametes and zygote

18.9 Gametes

Sexual reproduction takes place by the fusion of two special type of haploid cells called
sex cells. These sex cells are called gametes. Thus the haploid sex cells involved in sexual
reproduction are called gametes.

Sex cells or gametes are of two types, viz. male gamete and female gamete. The male
gamete is a haploid male sex cell produced by testis/anther. The male gamete of an animal
is called sperm. It is motile and smaller in size. The female gamete or ovum is the haploid
female sex cell produced by female sex organ, i.e. ovary. It is also called egg. It is non-
motile and larger in size. On favourable condition, a male gamete and a female gamete
fuse together and form a diploid zygote.

(a) Sperms (male gametes) (b) Eggs (female gametes)

Fig. 18.13 Gametes or sex cells

gamete /ˈɡæmiːt/ - the sex cell, i.e. sperm or egg

278 Oasis School Science and Environment - 8 BIOLOGY

18.10 Unisexual and Bisexual Organisms

Sexes are separate in most of the developed animals. The organism having only one kind
of reproductive organ (either male or female) is called unisexual organism. Such organism
has one sex only. Human beings, birds, mammals, reptiles, frogs, fishes, etc. are some
examples of unisexual animals. Unisexual organisms produce only one kind of gametes,
i.e. male gamete or female gamete.

Some animals possess both male and female reproductive organs in the same body. The
organism having both male and female reproductive organs in its body is called bisexual
or hermaphrodite animal. Hermaphrodite organism can produce both male and female
gametes. Some animals like tapeworm, liver fluke, earthworm, hydra, leech, etc. and most
of the flowering plants are bisexual organisms.

Reasonable fact-2

The asexual reproduction that occurs in planaria is called regeneration.
When planaria breaks into two or more parts then each part grows into a new complete
planaria. So, asexual reproduction that occurs in planaria is called regeneration.

Reasonable fact-3

The reproduction that occurs in flowering plants is called sexual reproduction.
Reproduction in flowering plants takes place by the fusion of a male gamete and a
female gamete. So, the reproduction that occurs in flowering plants is called sexual
reproduction.

Reasonable fact-4

Earthworm is called a bisexual organism.
Earthworm has both male and female reproductive organs in its body. So, earthworm
is called a bisexual organism.

Reasonable fact-5

The fertilization that occurs in fish and frog is called external fertilization.
The fusion of a male gamete and a female gamete in fish and frog takes place outside
the body of female i.e. in water. So, fertilization that occurs in fish and frog is called
external fertilization.

18.11 Significance of Sexual Reproduction

(i) Sexual reproduction gives continuity to the generations.
(ii) It brings out genetic variation in organisms which leads to evolution.
(iii) Increase in genetic variation in a species results in better survival of that species in

the changing environment.

evolution / ˌ i ː v ə ˈ l u ː ʃ n / - the development of complex organisms from simple organisms over a long period of time

BIOLOGY Oasis School Science and Environment - 8 279

Differences between Asexual Reproduction and Sexual Reproduction

S.N. Asexual Reproduction S.N. Sexual Reproduction

1. It takes place without the fusion 1. It takes place by the fusion of a

of a male gamete and a female male gamete and a female gamete.

gamete.

2. Only single parent is involved in 2. Both male and female organisms are
asexual reproduction. involved in sexual reproduction.

3. This method is common in 3. This method is common in

primitive plants and animals. developed plants and animals.

18.12 Blood Circulatory System in Human Body

Blood circulatory system is an organ system in human body responsible for transporting
various materials inside the body with the help of blood. This system consists of three
main parts: (i) Blood (ii) Blood vessels and (iii) Heart.

The circulatory system supplies food and oxygen to the cells of a body for survival. It
carries away carbon dioxide and other metabolic wastes from the cells. This system is
also responsible for maintaining constant body temperature. In blood circulatory system,
the heart acts as a pumping organ. The arteries, veins and capillaries act as tubes through
which blood flows and the blood itself acts as a circulatory medium.

18.13 Blood

Blood is a red-coloured tissue fluid made up of plasma (55%) and blood corpuscles (45%).
The blood constitutes about 1/30 of the body's weight. The composition of human blood
is given below:

Blood

Plasma Blood corpuscles

Red blood corpuscles White blood corpuscles Platelets

Composition of Blood

Blood is made up of plasma and three types of cellular elements, viz. (i) Red blood
corpuscles (RBCs), (ii) White blood corpuscles (WBCs) and (iii) Platelets. The plasma
occupies about 55% and the blood corpuscles occupy about 45% of the blood by volume.

280 Oasis School Science and Environment - 8 BIOLOGY

RBC
Platelets
WBC
Plasma

Fig.18.14 Blood film under the compound microscope

Plasma

Plasma is a transparent clear yellowish liquid. It forms about 55% of the blood volume.
Plasma contains about 90% water, 8% proteins and 2% other dissolved substances like
minerals, carbohydrates, salts, respiratory gases, waste products, etc. Red blood cells,
white blood cells and platelets are immersed in the plasma.

Functions of Plasma
(i) Plasma transports digested food to the different parts of body.

(ii) It regulates body temperature, amount of water and other chemicals in the
body.

(iii) It transports waste materials like carbon dioxide, urea, etc. to their respective
sites for excretion.

(iv) Fibrinogen (a protein) present in plasma plays an important role in blood
clotting.

Red blood cells or Erythrocytes

Erythrocytes (RBCs) are red coloured (erythros-red),
biconcave cells without nucleus. They are thick and
rounded at the peripheral region and flat in the centre.
Erythrocytes are very small in size (about 7 µ in diameter).
Red blood cells appear red due to the presence of
haemoglobin (i.e. iron-containing pigment).

Red blood cells are produced in the bone marrow. The Fig.18.15 Red blood cells

average life span of red blood cells is about 120 days. They

are destroyed in the liver. The number of RBCs ranges from 5 – 5.5 million per cubic

millimeter in an adult man and 4.5 – 5 million per cubic millimetre in an adult woman.

Function of Red blood corpuscles : RBCs transport oxygen from the lungs to the tissues
and carbon dioxide from the tissues to the lungs.

haemoglobin / ˌ h i ː m ə ˈ ɡ l ə ʊ b ɪ n / - the iron containing pigment found in RBCs

BIOLOGY Oasis School Science and Environment - 8 281

Note: When there is a long-term decrease in the number of RBCs or in the amount of
haemoglobin or in both, the condition is called anaemia.

White blood cells or Leucocytes

White blood corpuscles (WBCs) are larger (8 – 15 µ in diameter) irregular cells having
nucleus. They are capable of amoeboid movement.

Neutrophil Eosinophil Basophil

Monocyte
Lymphocyte

Fig.18.16 Various types of leucocytes (WBCs)

WBCs are produced in red bone marrow and lymph nodes. The average total number of
WBCs is 4000 - 11000 per cubic millimetre. They live for a few hours to a few days. They
are destroyed in the liver, spleen and at the site of infection.

Functions of WBCs

1. WBCs help in destroying solid substances like bacteria and hence they defend
the body from various diseases.

2. They fight against germs (microbes) and destroy the damaged cells.

Platelets or Thrombocytes

Platelets are colourless, oval or round, cytoplasmic fragments without nucleus. They
are formed from the giant cells of bone marrow. The number of platelets varies from
2.5 lakh to 4.5 lakh per cubic millimetre. The average diameter of platelets is about
2.5 µ. They live for about 5 to 10 days and are destroyed in the spleen.

Function

Platelets play an important role in the coagulation or clotting of blood.

282 Oasis School Science and Environment - 8 BIOLOGY

Activity 4

To study the blood film under the compound microscope

• Clean a finger-tip of your friend with a spirit swab.

• Prick the fingertip with a sterilized lancet. Don’t use that lancet to prick
another fingertip as it may transmit dangerous diseases.

• Put a drop of blood on the one end of a slide, spread it throughout the slide
by using another slide and allow it to dry.

• Put few drops of Leishman’s stain on it and dry it for few minutes.

• Wash the slide with distilled water and observe it under the compound
microscope.

• Draw a neat and labelled figure and prepare a short report on the basis of
your observation.

Functions of blood

(i) Blood transports oxygen from lungs to the tissues and carbon dioxide from the
tissues to the lungs.

(ii) WBCs present in blood help to prevent the body from infection.

(iii) Blood helps to regulate the body temperature.

(iv) The metabolic waste materials produced in the body are transported by blood
to the organs meant for their removal from the body.

(v) Blood transports chemical secretions like hormones from the site of their
secretion to the targeted organ.

(vi) Blood maintains water balance in the body to a constant level.

(vii) The digested food materials absorbed by blood are transported to various
parts of the body.

Differences between Red blood cells and White blood cell

Red blood cells White blood cells

1. They are smaller cells having biconcave 1. They are larger cells having a amoeboid

shape.2 shape.

2. Nucleolus is absent. 2. Nucleus is present.

injury /ˈɪndʒəri/ - harm done to a person's or animal's body

vena cava /ˌviːnə ˈkeɪvə/ - either of the two veins that collect impure blood towards the heart

BIOLOGY Oasis School Science and Environment - 8 283

Differences between Red blood cells and Platelets

Red blood cells Platelets

1. Red blood cells are smaller cells having 1. Platelets are cytoplasmic fragments

biconcave shape. having oval or round shape.

2. The average life span of red blood cells 2. The average life span of platelets is

is about 120 days. about 5 to 10 days.

18.14 Heart

Heart is a hollow, conical organ made up of cardiac muscle. It is about the size of a fist of
the owner. It measures about 12 cm in length and 9 cm in breadth. The average weight of
the heart is about 300 gram in adults. The human heart lies near the middle of the thoracic
cavity between two lungs.

External morphology

The human heart contains four complete chambers. It is divided into two halves (i.e. right
half and left half ) by septa. Each half consists of two chambers: the upper, small-sized
auricles and the lower, large-sized ventricles. The human heart remains enclosed in a
double layered membranous sac called pericardium. The space between two pericardial
layers is filled with a slippery fluid known as pericardial fluid. This fluid enables the
heart contract smoothly and also protects from mechanical injury. Various blood vessels
entering and leaving the heart can be seen externally.

Superior vena cava Aorta
Pulmonary artery
Pulmonary veins Pulmonary veins
Right auricle Left auricle
Right ventricle
Left ventricle
Inferior vena cava
Pericardium

Fig.18.17 External structure of human heart

284 Oasis School Science and Environment - 8 BIOLOGY

Internal morphology

The longitudinal cross-section of human heart shows two auricles, two ventricles and
blood vessels entering and leaving the heart.

Auricles are thin-walled chambers which are separated from each other by a muscular
wall called inter-auricular septum. The ventricles are thick-walled chambers which are
separated by a thick muscular wall called inter-ventricular septum. The auricles are thinly
muscled as they pump blood to only short distances to the ventricles. The wall of right
ventricle is more muscular than that of auricles because it has to pump blood to a much
farther distance to the lungs. Similarly, the left ventricle has the thickest wall as it has to
force the blood all the way round the body.

Superior vena cava Aorta
Pulmonary artery
Pulmonary artery
Pulmonary veins
Right auricle Left auricle
Pulmonary veins Pulmonary valve
Tricuspid valve Aortic valve
Bicuspid/mitral valve
Right ventricle Left ventricle
Inferior vena cava
Septum

Cardiac muscle

Fig.18.18 Internal structure of human heart

Three blood vessels are connected to the right atrium. Superior vena cava brings
deoxygenated blood from the upper region (i.e. head, neck and upper limbs) of the body
whereas inferior vena cava brings deoxygenated blood from the lower region of the
body. The left auricle is connected to two pairs of pulmonary veins, one pair from each
lung. Pulmonary veins bring oxygenated blood from lungs to the left auricle. Pulmonary
aorta arises from the right ventricle and it transports deoxygenated blood to the lungs
for purification. Similarly, systemic aorta arises from the left ventricle and transports
oxygenated blood to various parts of the body except the lungs.

Four different types of valves are present in the human heart. They regulate the flow of
blood within the heart and its passage. Tricuspid valve, having three concentric flaps,
is present between the right auricle and right ventricle whereas bicuspid or mitral
valve is present between the left auricle and left ventricle. It has two concentric flaps.
Auriculoventricular valves allow the flow of blood from the auricles to the ventricles and
prevent the backward flow. Similarly, aortic semi-lunar valve is present at the base of

BIOLOGY Oasis School Science and Environment - 8 285

aorta and pulmonary semi-lunar valve is present at the base of pulmonary artery. Each
semi-lunar valve contains three flaps, shaped like a half moon.

Reasonable fact-6

The wall of left ventricle of heart is thicker than that of right ventricle.
Left ventricle pumps out a large amount of blood to the different parts of body through
aorta. For this, a great force is required, which is provided by its thick walls but right
ventricle supplies impure blood towards lungs through pulmonary artery. So, the wall
of left ventricle of heart is thicker than that of right ventricle.

Activity 5

To study the external and internal structure of a heart of a goat
• Visit a butcher’s shop and buy a heart of a goat.
• Keep the heart in a dissecting tray, observe its external morphology and draw a neat

and labeled diagram.
• Cut open the heart longitudinally and observe the internal parts carefully.
• Draw a neat and labelled diagram showing internal structure of the heart.

Differences between Auricles and Ventricles

Auricles Ventricles

1. Auricles are thin walled upper 1. Ventricles are thick walled lower

chambers of heart. chambers of heart.

2. Auricles receive blood from the 2. Ventricles pump blood to the various

different parts of body. parts of body.

Differences between Tricuspid valve and Mitral valve

Tricuspid valve Mitral valve

1. Tricuspid valve guards the right 1. Mitral valve (or bicuspid valve) guards

auriculoventricular aperture (i.e. the the opening of the left auricle into the

opening of the right auricle into the left ventricle.

right ventricle.)

2. This valve consists of three 2. This valve consists of two membranous

memebranous flaps or cusps. flaps or cusps.

18.15 Blood Vessels

Blood vessels are the pipes through which blood flows. They form a system of channels
for blood circulation. There are three types of blood vessels. They are arteries, veins and
capillaries.

(a) Arteries

Arteries are thick-walled blood vessels that carry blood away from the heart to

286 Oasis School Science and Environment - 8 BIOLOGY

different parts of the body. All arteries carry oxygenated blood except pulmonary
artery which carries deoxygenated blood from the heart to the lungs. An artery has
a narrow lumen whereas the wall is thick and more elastic.

Tunica interna

Tunica media

Tunica externa

Fig. 18.19 Structure of an artery

Arteries are deep-seated in the muscle and can bear great pressure. Valves are absent
in arteries except at their origin in the heart. Inside arteries, the blood flows with
high speed and under high pressure. Aorta and pulmonary arteries are two main
arteries of the human body.
(b) Veins
Veins are thin-walled blood vessels which carry blood towards the heart. All
veins carry deoxygenated blood except pulmonary veins. Veins are comparatively
superficial in position and cannot bear great pressure.
Veins are provided with semi lunar valves. These valves open towards the heart.
They stop the reverse flow of blood as the blood moves against the gravity and is
under low pressure. The lumen of veins is much wider than that of arteries through
which blood flows easily with low speed and under low pressure.

Tunica interna

Tunica media
Tunica externa
Valve

Fig. 18.20 Structure of a vein

(c) Capillaries
Capillaries are microscopic, extremely narrow and thin-walled blood vessels. They
can penetrate every part of the body. Capillaries connect arterioles (i.e. branches of
arteries) to the venules (i.e. branches of veins). The wall of a capillary is made up of
a single layer of cells.

BIOLOGY Oasis School Science and Environment - 8 287

Arteriole Venule

Artery

Tunica interna Capillary network
(a) Structure of a capillary (b) Capillaries and their network

Fig. 18.21

The exchange of various materials like oxygen, food, carbon dioxide and waste
materials between the blood and body cells takes place through the capillaries.

Differences between Arteries and Veins

S.N. Arteries S.N. Veins

1. Arteries carry blood away from 1. Veins bring blood towards the

the heart. heart.

2. Their wall is thick and strong. 2. Their wall is thin and weak.

3. They are located deep in the body 3. They are located close to the

away from the skin. skin.

4. They have narrow lumen and no 4. They have wide lumen and have

internal valves. internal valves.

5. All arteries carry oxygenated 5. All veins carry deoxygenated

blood except pulmonary artery. blood except pulmonary veins.

18.16 Blood Circulation in Human Body

In human beings, the blood flows twice through the heart before the oxygenated blood is
pumped to the body. Such circulation of the blood is called double circulation.

The circulation of blood in human body is of two types:
(i) Systemic circulation
(ii) Pulmonary circulation

288 Oasis School Science and Environment - 8 BIOLOGY

Deoxygenated blood is Lung
carried to the lungs
Oxygenated blood is
returned to the heart

Deoxygenated blood Heart Oxygenated blood is
returns to the heart carried to all cells in the
body
CO2 diffuses from the
body cells into the blood Oxygen (O2) diffuses from
the blood to the body cells

Fig. 18.22 Process of blood circulation

(i) Systemic Circulation

The circulation of blood from the left ventricle to the right auricle of heart via body
tissues (except lungs) is called systemic circulation. In this circulation, the left ventricle
contracts and pumps the oxygenated blood into aorta. Aorta gives off branches (i.e.
arteries) and sub-branches (i.e. arterioles) to all the organs of the body except lungs.
From these arterioles, oxygen is diffused into tissues. Finally, deoxygenated blood
from the tissues is brought to the right auricle by superior and inferior vena cavae.
Schematic diagram of systemic circulation is given below:

Left ventricle Aorta Arteries

Right auricle Arterioles

Vena cavae Capillaries

Veins Venules Capillaries Tissues and cells

Fig. 18.23 Systemic circulation

(ii) Pulmonary Circulation
The circulation of blood from the right ventricle of heart to the left auricle via
lungs is called pulmonary circulation. In this process, the right ventricle pumps

photosynthesis /ˌfəʊtəʊˈsɪnθɪsɪs/ - the process of making food by green plants

BIOLOGY Oasis School Science and Environment - 8 289

deoxygenated blood to the lungs through pulmonary artery for purification. The
oxygenated blood from the lungs is brought to the left atrium of the heart by four
pulmonary veins. Schematic diagram of pulmonary circulation is given below:

Right ventricle Pulmonary artery

Lungs

Left auricle Pulmonary veins

Fig. 18.24 Pulmonary circulation

18.17 Heart beat

The continuous rhythmic beat throughout the life which is produced due to the
contraction and relaxation of heart muscles is called heart beat. One complete contraction
and relaxation of the heart muscles makes up one heart beat. The heart of a healthy young
person beats 60 – 72 times per minute. The heart beats vary according to the age, sex and
condition of the body. The rate of heart beat increases with tension, physical exercise,
emotion, fear and fever.

18.18 Arterial pulse

Arterial pulse is the systemic contraction of the heart that can be felt as a jerk in certain
arteries which are superficial in position. Arterial pulse proceeds as a wave of expansion
throughout the arteries and disappears in the capillaries. Pulse rate is the same as the
heart beat rate, i.e. 72 times per minute. Pulse can be felt easily in the radial artery at the
wrist, temporal artery in front of the ear, etc.

18.19 Photosynthesis

Green plants prepare their own food in chlorophyll by using carbon dioxide and water as
raw materials and sunlight as the source of energy. This process is called photosynthesis.
Green plants are called autotrophic plants as they can manufacture their own food. The
presence of chlorophyll is essential for photosynthesis to trap sunlight. In a series of
complex chemical reactions, carbon dioxide taken by leaves through stomata and water
absorbed by roots are converted into glucose. Oxygen is released as a by-product during
this process.

6CO2 + 6H2O CSh luonroligphhtyll C6H12O6 + 6 O2

(Carbon dioxide) (Water) (Starch) (Oxygen)

290 Oasis School Science and Environment - 8 BIOLOGY

Sunlight Glucose to the
plant body

Oxygen to the environment Carbon dioxide Water and minerals
Fig. 18.23 Photosynthesis

Green plants manufacture their own food by means of photosynthesis and plants are in
turn eaten by animals. During photosynthesis, oxygen is given out to the atmosphere
which is utilized by animals in respiration.

18.20 Experiments on Photosynthesis

Experiment 1

TO TEST THE PRESENCE OF STARCH IN LEAF (IODINE STARCH TEST)

Materials required
A fresh green leaf, water, alcohol, iodine solution, burner, test tube, beaker, petri
dish, stand.

Procedure Fig. 18.26 Apparatus to show sunlight is
necessary for photosynthesis
• Pluck a fresh green leaf from a plant
and keep it under the sunlight for
2-3 hours.

• Put the leaf in a test tube containing
alcohol. Place the test tube in a
beaker containing water.

• Heat the water in the beaker with the
help of a burner. Never boil alcohol
directly as it may catch fire.

• Observe the colour of the leaf
carefully. As alcohol starts to boil,
the chlorophyll dissolves in alcohol
and the leaf becomes pale.

BIOLOGY Oasis School Science and Environment - 8 291

• Remove the leaf from the alcohol and wash it in warm water.
• Spread the leaf in a petri dish and put a few drops of iodine in it.

Fresh green leaf Boiling leaf in alcohol Petri dish with Leaf turns blue-black
iodine solution

Fig. 18.24 Iodine starch test

Observation

When the leaf is kept in iodine solution, a blue black colour will be seen on the leaf.

Conclusion

This experiment shows the presence of starch in the leaf. It proves that starch is pro-
duced during photosynthesis.

Experiment 2

TO PROVE THAT OXYGEN IS RELEASED DURING PHOTOSYNTHESIS
Materials required
A few twigs of fresh hydrilla plant, test tube, glass funnel, beaker, water, sodium
bicarbonate, matchbox

Procedure

• Take a few twigs of fresh hydrilla plant in a beaker filled with water.

• Add a pinch of sodium bicarbonate, as a source of carbon dioxide, in the
beaker, which can be used by leaves for photosynthesis.

• Cover the twigs of hydrilla by a glass funnel in such a way that the stems of
hydrilla face upward.

• Cover the end of the funnel with an inverted test tube as shown in the diagram
on the next page

• Keep the apparatus in the sunlight for a few hours.

292 Oasis School Science and Environment - 8 BIOLOGY

water oxygen gas
test tube gas bubbles

beaker water
funnel Hydrilla plant

(a) Before (b) After

Fig. 18.25 Apparatus to show oxygen is released during photosynthesis

Observation
After a few minutes, a stream of small bubbles coming out of stem can be observed. After
a few hours some gas collects in the test tube by downward displacement of water. When
a burning matchstick is inserted inside the test tube containing the unknown gas, it burns
with a bright flame. It shows that the gas is oxygen.

Conclusion
This experiment proves that oxygen is released during photosynthesis.

Experiment 3

TO PROVE THAT SUNLIGHT IS NECESSARY FOR PHOTOSYNTHESIS

Materials required
A potted plant with broad leaves, black paper, cello tape, materials for iodine
starch test.

Procedure

• Take a potted plant with broad leaves and keep it in a dark room for 2-3 days.
It is done to make the leaves starch-free as no photosynthesis will take place in
the dark room.

• Cover a part of the leaf from both sides with a black paper and cello tape as
shown in the figure.

• Keep the plant in sunlight for 5-6 hours.

• After 5-6 hours, pluck the experimental leaf and test it for the presence of
starch.

Observation

The portion of leaf covered with black paper shows the absence of starch as it cannot
get sunlight to make food. But the uncovered portion of the same leaf shows the
presence of starch as it gets sunlight.

BIOLOGY Oasis School Science and Environment - 8 293

Conclusion
This experiment proves that sunlight is essential for photosynthesis.

Experiment 4

TO PROVE THAT CARBON DIOXIDE IS ESSENTIAL FOR PHOTOSYNTHESIS
Materials required
A potted plant with broad leaves, a bottle with wide mouth, cork, caustic potash
(KOH), materials for iodine starch test, etc.
Procedure
• Keep a potted plant with broad leaves in a dark room for 2-3 days to make it
starch-free.
• Put some KOH solution in the bottle as it absorbs the carbon dioxide present
in the bottle.
• Select a broad leaf of the potted plant. Keep a part of the leaf in the bottle
through a split cork as shown in the figure.
• Keep the potted plant under the sunlight for 2-3 hours.
• Remove the experimental leaf and test it for the prpresence of starch.

Potted plant

Cork Starch present
(Blue-black)
Bottle Starch absent
(Pale yellow)

KOH solution

Wooden black

Fig. 18.27 Apparatus to show carbon dioxide is essential for photosynthesis

Observation

The portion of the leaf inside the bottle does not show the presence of starch because
the carbon dioxide present inside the bottle is absorbed by KOH solution. The outer
portion of the leaf shows the presence of starch as it gets carbon dioxide from the
atmosphere.

294 Oasis School Science and Environment - 8 BIOLOGY