New Creative Science and Environment Book 7

Features of vertebrates
Some important features of vertebrates are mentioned below.
Æ Presence of three layers in the skin i.e. triploblastic body.
Æ The body can be divided into two equal halves i.e. bilaterally symmetric
body.
Æ Presence of special features like notochord in embryonic stage.
Æ Presence of a spinal cord.
Æ Pharyngeal gill slits are present.
Æ The body consists of a well-developed body cavity.
Æ They have a complete digestive tract and a well developed nervous
system.
According to their body features and mode of life, vertebrates are classified

into five classes.
1. Pisces 2. Amphibia 3. Reptilia 4. Aves 5. Mammalia

Class: Pisces

This group of vertebrates consists of all kinds of fish. Pisces are totally
aquatic in nature. They are the primitive types of vertebrates. Some examples are
labeos, sea-horses, rohus, asalas, etc.

LivingB einsg 147

General characteristics of pisces
Æ They have a boat-shaped streamlined body which helps them to swim
easily and change the direction by cutting water currents.
Æ They have fins in their bodies which help them to swim in water.
Æ Gills are the respiratory organs which are found under the head on
both left and right parts.
Æ The body is covered with scales.
Æ They are poikilothermic i.e. cold blooded. Their body temperature
changes with the environmental temperature.
Æ They have a two-chambered heart.
Æ They lay eggs, thus known as oviparous.
Æ The body is divided into the head, trunk and tail.
Æ Fertilization is external.

Class: Amphibians

This is a group of vertebrates can live in both water and on land. They are
more developed than pisces. In an immature condition, they live an aquatic life
while they adapt to the terrestrial mode of life after they grow up. Some of the
examples of amphibians are toads, frogs, etc.

General characters of amphibians
Æ They have moist and soft skin.
Æ The body is divided into the head, trunk and limbs.
Æ Four limbs are present. The two limbs in the front are called forelimbs,
and, the two limbs at the back are called hind limbs. Hind limbs are
stronger than forelimbs.
Æ They are cold-blooded i.e poikilothermic.

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Æ Respiration takes place through gills in the tadpole stage, through skin
in water and through lungs on land.

Æ They lay eggs i.e. oviparous.
Æ A three-chambered heart is present.
Æ Fertilization is external.

Class: Reptilia

Those vertebrates that creep on land belong to this class. Most of them are
terrestrial while some may be adapted to an aquatic environment. Some of the
examples of reptilia are snakes, crocodiles, turtle, lizards, etc.

General characters of reptilia
Æ They have dry and rough skin. Some may have thorny scales.
Æ The body is divided into the head, neck, trunk and tail.
Æ Limbs are absent.
Æ They are cold-blooded i.e. poikilothermic.
Æ Respiration takes place in the lungs.
Æ They lay eggs i.e. oviparous.
Æ A three-chambered heart is present.
Æ Fertilization is internal.

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Class Aves

Those vertebrates that are adapted to an aerial mode of life belong to
this class. They are also called flying vertebrates. All the birds are included in
this class. Some of the examples of aves are eagles, hens, parrots, crows, owls,
vultures, ostriches, etc.

General characters of aves
Æ Their body is covered with light and fluffy feathers which help them
to be warm.
Æ The body is divided into the head, beak, trunk and tail.
Æ Hind limbs are modified for a bipedal movement while forelimbs are
modified as wings.
Æ They have a boat-shaped body for flying.
Æ Bones are hollow, light and spongy filled with air sacs, which make
their body light for flying.
Æ They are warm blooded i.e. the body temperature remains constant.
Æ Respiration takes place through lungs.
Æ They are oviparous. Babies are hatched from eggs.
Æ They have a four-chambered heart.
Æ Fertilization is internal.

Class: Mammalia

Those vertebrates that are well developed and have mammary glands on
the female belong to this group. Most of the animals are adapted to a terrestrial

150 New Creative Science and Environment; Book 7

mode of life whereas some very few may have aerial and aquatic a mode of life.
Dolphins, and blue whales are aquatic whereas bats have an aerial a mode of life.

Some of the examples of mammalia are humans, dogs, cows, buffaloes,
monkeys, mice, bats, blue whales, etc. The blue whale is the largest mammal.

General characters of mammalia
Æ The body is covered with small hairs.
Æ The body is divided into the head, neck and trunk while dolphins,
blue whales have tail.
Æ A well-developed limbs are present.
Æ They are warm blooded i.e. homoeothermic.
Æ Respiration takes place through lungs.
Æ Presence of mammary glands in the chest of females which secrete
milk for feeding their young ones.
Æ They give birth i.e. viviparous.
Æ A well-developed and four-chambered heart.
Æ External ears called pinnae are present in a pair.
Æ Internal fertilization takes place.

Aestivation and Hibernation

Some animals do not change their body temperature with the surrounding
temperature. Those animals are known as warm blooded animals. They have a
fixed body temperature. Some of the examples are hens, dogs, monkeys, eagles,
pigeons, humans, etc.

LivingB eings 151

Animals like snakes, fish, crocodiles, lizards, frogs are cold-blooded animals.
They do not have a constant body temperature; so their body temperature changes
with the environmental temperature. So, during summer and winter seasons,
they do not resist very hot or very cold temperature. So to be protected from the
heat of summer season, they go to sleep inside the ground in colder places and
rest there. This summer sleep is known as aestivation. In the same way, in the
winter season, they go down inside the ground in warmer places and become
inactive. This winter sleep is known as hibernation.

Life cycle of frog

The Frog is a
vertebrate. It is an
amphibian animal i.e.
it needs both water and
land to complete its life
cycle. Frogs undergo
summer sleep called
aestivation and a winter
sleep called hibernation
to maintain their body
temperature. During
the rainy season they
wake up from their
summer sleep and go
near to water bodies.
Mature male frogs call
mature female frogs
by croaking. Mature
female frogs are larger
than male frogs. When
a mature female frog
approaches a male frog, mating occurs. During mating the male frog clasps the
female frog underneath an embrace called amplexus which occurs in water. The
female frog releases a large number of eggs in water. These eggs are covered
by jelly like substances that helps to stick them together and arrange them in a
group. The male frogs then produce large number of sperm cells that fall over the
eggs and fertilize the eggs. This type of fertilization that occurs outside the body
is called external fertilization.

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The fertilized egg is called zygote. It undergoes nuclear division continuously
and forms an embryo. Soon, the an embryo looks more and more like cocoons.
Inside cocoon the larva grows and develops. Usually, after about 6- 21 days,
the egg hatches out and tadpole comes out. Shortly after hatching, the tadpole
feeds on the remaining yolk present in its gut. The tadpole at this point consists
of poorly developed external gills, a mouth, and a tail. It usually sticks itself to
floating weeds or grasses in the water. Then, 7 to 10 days after the tadpole has
hatched, it begins to swim around and feeds on algae. After about 4 weeks, the
external gills disappear and internal gills start growing under the skin. Tiny teeth
develop in it to turn solid food into soupy particles. A coiled and long digestive
organ helps to digest its food and provides it energy. After this, tadpoles start to
swim in group. After about 6 to 9 weeks, little tiny legs start to sprout from the
place of gills. Other important organs like a nose, lungs and digestive systems
etc. are develop. The head becomes more distinct and the body elongates. Now,
the diet grows to include larger items like dead insects and even plants. The arms
begin to bulge with the emergance of an elbow at first. After about 9 weeks, the
skin starts to change and the tadpole looks more like a tiny frog with a long tail.
By 12 weeks, the tadpole loses its tail and looks completely like a small adult
frog. Soon, it leaves the water and starts to live on land. When it becomes mature
enough to produce eggs or sperm, it returns to the water bodies and mate with the
opposite sex to form fertilized eggs. In this way, the life cycle of a frog completes.

1. The bat has a aerial mode of life but why is it kept under mammalia?
Ü Bats are viviparous i.e. they give direct birth to young ones. They have

mammary glands on the females and have a pair of external pinna. So the
bat is kept under mammalia.

2. Write any five important features of mammals.
Ü Five important features of mammals are mentioned below.

i) Their body is covered with hairs.

ii) They have mammary glands on the female for secretion of milk.

iii) A pair of external ears called pinna are present.

iv) They have a four-chambered heart.

v) They give birth to the young ones i.e. viviparous.

LivingB einsg 153

F Those animals having a vertebral column or a backbone are called
vertebrates.

F Vertebrates are also known as chordates.
F Vertebrates are divided into five classes. They are pisces, amphibia,

reptilia, aves and mammalia.
F Pisces, reptiles, amphibian are cold-blooded.
F Aves, and mammals are warm-blooded.
F Aestivation is the summer sleep of cold-blooded animals so that they

can protect themselves from a hot environment.
F Hibernation is the winter sleep of cold-blooded animals so that they can

protect themselves from a cold environment.

1. Fill in the blanks with suitable words.

a. The rohu belongs to class _____________.

b. Those animals do not have a vertebral column are known as __________.

c. Egg laying animals are called ____________ animals.
d. Frogs respire in water through their ____________.

e. Aves have ___________ bones filled with _____________.

f. External _____________ takes place in frogs.

2. Select the correct alternative from the following.

a. Salamander is ___________

i) a reptile ii) an amphibian iii) pisces
b. Mammals have

i) a mammary gland ii) a 3-chambered heart iii) gills

c. ____________ has a horn and rough scales.

i) toad ii) salamander iii) crocodile

d. The ____________ is a warm blooded animal.

i) snake ii) sea-horse iii) dolphin

e. The _____________ is the largest mammal

i) elephant ii) rhinocer iii) blue whale

154 New Creative Science and Environment; Book 7

3. Match the following

Labeo hibernation

Dolphin mammals

Tadpole gills

Snake pisces

Eagle internal fertilization

Human aerial mode of life

4. Define the following terms:

a. Vertebrates b. Oviparous c. Viviparous

d. Hibernation e. Aestivation

5. Differentiate between:

a. dolphin and labeo b. bat and eagle

c. snake and fish d. cold blooded and warm blooded animals.

6. Answer the following questions.
a. What do you mean by invertebrates?
b. Name any 2 chordates and classify them as pisces, reptiles, amphibians,
aves and mammals.
c. What are the features that allow birds to fly?
d. Write down five important characters of reptiles.
e. Why is the frog kept under amphibians?
f. What feature makes mammals more developed than other
invertebrates?
h. Write down the characteristics of pisces.
i. What do you mean by vertebrates? List some features of vertebrates.
j. Describe fertilization in frogs.

Aquatic - that live in water

Oviparous - egg producing animals

Creep - to move slowly, quietly and carefully

Fluffy - soft, light and containing air

Bipedal - having two legs

Viviparous - animals producing live babies

‰‰

LivingB einsg 155

(B) Classification of Plants

After the completion of this unit, students will be able to:
Æ classify plants on the basis of similar and dissimilar characters.
Æ explain about flowering plants.
Æ state about the vegetative parts of plants.
Æ explain about the reproductive parts of plants and their

structures.

Introduction

We find different types of plants around us. Some of them are shrubs, some
herbs and some are trees. Some plants have flowers whereas some do not have.
In the same way, the plant body may vary from unicellular to multicellular large
trees. They may contain chlorophyll or they may not contain it. Thus the system
of classification is needed to make their study easier.

General characteristics of plants

Æ They are fixed by their roots.
Æ They prepare their food themselves. They have green pigment

i.e. chlorophyll in them. In the presence of sun-light; water and
carbon dioxide, they conduct photosynthesis. It is a food making
process.
Æ They have developed roots and shoots.
Æ They have continuous growth. New branches, new leaves, new
flowers, roots etc. continuously grow during their lifetime.
Æ They show a great degree of regeneration. If any parts of the plant
like leaves, branches, are injured or destroyed, they themselves repair
it.
Æ Means of reproduction is both sexual and asexual.

Classification of plants

Based on similar and dissimilar features of plants, they are classified as :
non-flowering plants and flowering plants.

156 New Creative Science and Environment; Book 7

1. Non-flowering plants (Cryptogams)

The plants that do not bear flowers are called cryptogams. Cryptogams are
divided into three divisions.

a) Thallophyta b) Bryophyta c) Pteridophyta

a. Thallophyta

In these plants, the plant body is thallus i.e cannot be differentiated into
roots, stems and leaves. They are the primitive plants. Thallophyta are
divided into 3 sub-divisions.

i. Algae ii. Fungi iii. Lichens

i. Algae
These are the green plants. They contain a green pigment called chlorophyll.
In the presence of sunlight, water and carbon dioxide, chlorophyll performs
photosynthesis i.e. a food preparing process. These plants range from
unicellular chlamydomonas to multicellular filamentous spirogyra. They are
found in moist places, lakes, rivers, etc. Some examples are chlamydomonas,
volvox, ulothrix, spirogyra, etc.

ii. Fungi

They are non green plants. They do not contain chlorophyll. So, they cannot
produce their food themselves but depend upon dead and decayed matter
for food. So, they are known as saprophytes. Some of them live as parasites
as they depend on other organisms. Some examples of fungi are mucor,

yeast, mushroom, etc.

LivingB einsg 157

iii. Lichen
Lichen is the mutual association of algae and
fungi. It is found in old rocks, tree barks, etc.
The algae of the lichen prepares food whereas
the fungal part gives protection to the algae
from unfavourable environmental conditions.
Examples are foliose, fructicose, crustose, etc.

b. Bryophyta
Small primitive green plants but
slightly developed than thallophytes
fall under this division. They have a
flat body lying on the soil while some
are erect. They cannot be differentiated
into roots, stems and leaves but the
unicellular or multicellular rhizoids act
as roots. The examples of bryophytes
are moss, marchantia, hornwort,
funaria, liverworts, riccia, etc. They
are also known as amphibious plants
because they need water during
reproduction.

c. Pteridophyta
Well developed non-flowering plants fall under this division. The plant
body can be differentiated into roots, stems and leaves. They are found
in moist, damp and dry places. They reproduce by spores. Their life cycle
shows alternation of generation between sporophytic and gametophytic
stages. The examples are ferns, equisetum, horsetails, etc.

158 New Creative Science and Environment; Book 7

2. Flowering plants (Phanerogams)

Those plants that bear flowers and seeds are called phanerogams. They
are developed plants. They have distinct body parts like roots, a stem, leaves,
flowers, etc.

Phanerogams are divided into two sub divisions:

i. Gymnosperms ii. Angiosperms

i. Gymnosperms (Naked seeded plants)

These are the woody plants usually trees found at higher altitudes. They have
seeds inside a modified flower called the cone. The seeds are not enclosed
in a fruit. They have well developed roots and shoots with differentiating
parts. The examples are pinus, cycas, fir, acacia, juniper, etc.

ii. Angiosperms (Closed seeded plants)

These plants have seeds enclosed in a fruit. They have well developed roots,
a stem, leaves, etc. The flower is well-developed. Most of the plants we see,
like trees, shrubs and herbs fall under this division. These are economically
important plants.

Depending on the number of cotyledons in the seeds, these plants are
classified as monocotyledons and dicotyledons.

a. Monocotyledons

Plants having only
one cotyledon in
their seed are called
monocotyledons.
They have fibrous
adventitious roots. Their
leaves have parallel
venations. They are
comparatively in less number than dicotyledons. The examples are grass,
maize, bamboo, onion, garlic, wheat, oats, etc.

LivingB eings 159

b. Dicotyledons

Plants having two cotyledons in their seed are called dicotyledons. They are
abundant in number. They have a tap root system. Their leaves have net-
like reticulate venation. The examples are pea, gram, bean, mustard, apple,
mango, etc.

A sketch showing classification of plant kingdom.

Kingdom: Plant

Sub-kingdom: Cryptogams Phanerogams

Division: Thallophyta Bryophyta Pteridophyta Gymnosperm Angiosperms
Class

Sub-division: Algae Fungi Lichen Monocotyledon Dicotyledon

160 New Creative Science and Environment; Book 7

Questions

• What do you mean by cryptogams?
• How are bryophyta different from pteridophyta? Write any two points.
• Write two differences between algae and fungi.

Memory Note

Æ Taxonomy is the branch of science that classifies and studies plants.
Æ All plants are given their scientific names using two words i.e. generic

and specific.
Æ Chlamydomonas is the unicellular green plant.

Parts of a flowering plant

A well-developed flowering plant has roots, a stem, branches, nodes and
internodes, leaves, flowers, buds and fruits. Those parts of a flowering plant
responsible for growth and development, respiration, photosynthesis, mechanical
strength, support, conductions of essential materials, etc. are vegetative parts.
Roots, stem, branches, leaves, node and internodes are the vegetative parts of the
plants. Those parts of a flowering plant that are responsible for reproduction are
known as reproductive parts. Flowers are the reproductive part of a plant.

Flower

Fruit

Bud Stem

Shoot system

Root system Node

A mustard plant Main root
Secondary root

LivingB eings 161

1. Root system

The part of a plant that grows under the
soil are called roots. In dicots like mustard, tap
root are present while fibrous roots are present
in monocots like maize. Roots are white or
yellowish brown in colour. They grow from a
radicle of a seed.

The root just below the ground is a
primary root. It is divided into more branches
of secondary roots. A root tip is the delicate
growing point of the root which is protected
by a root cap. The elongation region is behind
the root tip which increases the length of the root. The upper basal region of the
root is mature, and it produces minute root hairs.

Types of roots

According to the structure, roots are of two types. They are:

a. Tap root

In dicotyledenous plants, roots are grown vertically

down in the form of a main root. This root does not divide into

different networks but develops branches from its surface.

The top-most part of this root (apex) bends away from the

main body of the root. The root that develops branches and

does not divide itself from the main axis of the root but

grows continuously is known as the tap root. These roots Tap root
are comparatively stronger than fibrous roots. Some of the

examples of plants having tap roots are mustard, carrot, pea, sunflower, gram, etc.

Example of tap root

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2. Fibrous root

In monocotyledonous plants, the root is Fibrous root
divided into small cluster of roots. These small
and thin roots develop from the basal part of
the stem. Thus the fibrous roots are those roots
that are developed from the basal part of the
stem and lack the main root. Fibrous roots are
comparatively weaker than tap roots since they
donot grow deep inside the soil.

Some of the examples of plants with fibrous
roots are maize, onion, wheat, grass, barley, millet, paddy, etc.

Functions of the roots

Æ Roots absorb water and minerals from the soil.
Æ They fix the plant in the soil and hold it.
Æ In some plants, roots act as the storage of food.
Æ They help to conduct water and soluble salts to the stem.

2. Shoot system

The shoot is the erect part of the plant that grows above the soil. It is
developed from the plumule of the seed. A shoot has various parts like stem,
branches, leaves, stipules, bud, flower and fruits.
1. Stem

The stem is an important part of the plant. It grows above the land surface
bending or straightly towards the sunlight. The stem is usually green in colour.

It helps to produce branches and leaves. The portion from where the branches
or leaves are formed is called a node. The distance between the two nodes of a
stem is called internode. The stem has three types of buds. They are axillary buds,
floral buds and terminal buds. Axillary buds are present in the nodes of a stem.
It forms branches and leaves. Floral buds help to produce flowers in floral axis
while the terminal buds present in the tip or apex of the plant increase the length
of the plant by its continuous growth.

Leaf
Branch
Fruit

Node

Stem

Shoot system
Some stems are not erect but creep on land. Such types of plants are called
creepers. The examples of creepers are pumpkins, watermelons, etc. Some
stems need a support to climb up and those plants are known as climbers. The
examples of climbers are peas, grapes, beans, etc. They creep on land or climb
with a support because they have weak stems that cannot grow erect themselves.

2. Leaf
The leaf is the green flat structure present

on the stems and branches of the plant. The
shape and size of the leaf vary from plants to
plants. A pine has needle-like leaves whereas the
cylindrical leaves are present in garlic and onion-
like plants. Leaves are green due to the presence
of chlorophyll. Leaves are arranged in such a
way that they absorb more light required for
photosynthesis. Leaves are arranged in alternate
opposite or whorled manners. Dicotyledons have
a net-like structure i.e. reticulate venation and
monocotyledons have parallel venation in leaves.

164 New Creative Science and Environment; Book 7

A typical leaf has 3 parts. They are leaf base, petiole and leaf blade (lamina).
The leaf base is the lowermost part of a leaf attached to the branches or the stem.
It bears stipules. The petiole is the stalk of the leaf. If it is absent, the leaf is called
sessile and if it is present, the leaf is called petiolated leaf. The leaf blade is the
thin flattened green structure. It has an upper dorsal and lower ventral surface.
A large number of minute pores called stomata are present in leaves. They help
in respiration and photosynthesis in plants.

3. Flower

Flowers are the Corolla
reproductive parts of the plant. Androacium
They appear on the floral axis Calyx
of the stem. If they have both Gynoecium
male and female parts, they are
known as bisexual flowers. In Thalamus
some plants, flowers may have
only one male or female part. A typical flower
This is called a unisexual flower.

A typical flower has four
parts. They are sepals, petals, androecium and gynoecium.

Sepals

Sepals are the green leafy structures which form the
outermost whorl of the flower. Sepals are free or fused together.
Sepals as a whole is known as calyx. It arranges the petals and
provides protection to petals.

Petals

Petals are the coloured, scented and leafly structures which
form the second whorl of the flower. Petals are also free or fused
together. Petals as a whole is termed as corolla. They also have
a nectar gland in them. The colourful and scented petals attract
insects for pollination.

Androecium

These are the male reproductive parts of the plants and also known as
stamen. It consists of a long stalk called filament and usually a bilobed sac at the
top called anther. Anther contains pollen grains that are fluffy and powder-like.
These pollen grains form the male gamete to fertilize the egg or ovum.

LivingB einsg 165

Anther

Pollen grains

Filament

Pollen grain

Gynoecium stigma

These are the female reproductive parts present in style
the centre of the whorl surrounded by the stamen. It is
also known as pistil. The gynoecium has 3 parts; the ovary, ovary
style and stigma. The ovary is the basal part which encloses ovule
a female gamete, ovule, in the centre. The style is the
cylindrical tube from which pollen grains pass to the ovule.
The stigma is the uppermost part from which pollen grains
enter to the ovary. The stigma is feathery and sticky so as to
allow the passage of pollen grains to the ovary.

Pollination

The process of transfer of pollen grains from the anther of the stamen to the
stigma of the pistil is known as pollination. The dispersal of pollen grains occurs
due to wind, water, explosive mechanism of the anther, activities of man, other
animals and insects.

Cross pollination

Self pollination

Pollination

166 New Creative Science and Environment; Book 7

Fertilization

The process of fusion of male gametes
with female gametes in the ovary is known
as fertilization. A zygote is formed from
fertilization which develops to an embryo.

The fertilized ovule develops into a seed
and the whole ovary develops into the fruit.

Fertilization

1. Why is the flower known as the reproductive part of a plant?

Ü The flower consists of four parts; calyx, corolla, androecium and gynoecium.
Among them the androecium acts as a male reproductive part whereas the
gynoecium acts as the female reproductive part. The androecium develops
the male gametes whereas the gynoecium develops the female gametes.
Therefore the fusion of male and female gametes forms an embryo which
later on gives fruit and seeds. Seeds are germinated producing new plants.
Thus the flower is known as the reproductive part of a plant.

2. What do you mean by the bisexual flower?

Ü The flower which consists of both male and the female reproductive parts
i.e. and roecium and gynoecium is known as the bisexual flower.

3. Write the differences between

a. Cryptogams and phanerogams b. Algae and fungi

Ü (a)The differences between cryptogams and phanerogams are as given below.

Cryptogams Phanerogams

i. These plants do not bear flowers i. These plants bear flowers and

and seeds. seeds.

ii. These are primitive and simple ii. These are highly developed

plants. plants.

iii. All plants do not have iii. All plants have chlorophyll on

chlorophyll in them. them.

iv. Root, stem and leaves are not iv. Root, stem, leaves, flowers, buds

distinct except pteridophytes. etc. all are distinct.

LivingB einsg 167

b. The differences between algae and fungi are as given below.

Algae Fungi

i. They are green plants. i. They are non-green plants.

ii. They are autotrophs. ii. They are heterotrophs.

iii. Chlorophyll is present. iii. Chlorophyll is absent.

Examples are chlamydomonas, Examples are yeast, mucor,

volvox, spirogyra, etc. mushroom, etc.

F Plants are classified on the basis of their similar and dissimilar features.
F Plants which have flowers and seeds are called flowering plants or

phanerogams, e.g. rose, maize, apple, pine, etc.
F Plants that do not bear flowers and seeds are called non-flowering plants

or cryptogams, e.g. moss, mucor, yeast, volvox, fern, etc.
F In thallophyta, the plant body is thallus and cannot be differentiated into

roots, stem and leaves, e.g. spirogyra, ulothrix, etc.
F Algae are green due to the presence of chlorophyll.
F Fungi are non-green plants. They depend upon other living or dead

organisms for parasitic or saprophytic mode of life, e.g. yeast, mucor, etc.
F Pteridophytes are the developed cryptogams. They can be differentiated

into root, stem and leaves, e.g. fern, equisetum, etc.
F Gymnosperms are those plants that do not have seeds enclosed inside a

fruit i.e. the seed is naked, e.g. pinus, cycas, etc.
F Angiosperms have seeds enclosed inside a fruit i.e. the seed is covered,

e.g. apple, mango, rose, maize, etc.
F Monocotyledons have only one cotyledon in their seed, e.g. maize,

wheat, oat, bamboo, etc.
F Dicotyledons have two cotyledons in their seed, e.g. gram, pea, bean,

apple, etc.
F Stems have nodes and antinodes in them. Nodes bear leaves and

branches.
F Stomata are the tiny pores present in the leaf that help in respiration and

photosynthesis in plants.
F The flower is the reproductive part of the plant.
F Pollination is the process of transfer of pollen grains from anther of and

roecium to stigma of gynoecium.
F Fertilization is the process of fusion of the male gamete (sperm) with the

female gamete (ovum) in the ovary to produce the zygote.

168 New Creative Science and Environment; Book 7

1. Fill in the blanks.
a. ____________ acts as a root in the pteridophytes.

b. The exchange of gases during respiration and photosynthesis in plants
is due to ___________ of leaves.

c. ___________ do not bear flowers and seeds.

d. The green pigment called ______________ is present in algae.

e. ___________ are non-green plants.

2. True or false.
a. Lichens are the mutual association of algae and fungi.
b. The fern is a well developed pteridophyte.
c. An androecium is the female reproductive part of a plant.
d. Sepals and petals produce male and female gametes.
e. Lamella is the flat, thin and expanded part of a leaf.

3. Match the following:

Stipules pteridophyte

Riccia fungi

Mucor fertilized ovule

Seed algae

Fern bryophyte

Spirogyra leaf

4. Define the following terms:
a. Unisexual and bisexual flower
b. Pollination
c. Fertilization

5. Differentiate between:
a. Thallophyta and pteridophyta
b. Unisexual and bisexual flowers
c. Dicotyledons and monocotyledons
d. Pollination and fertilization

LivingB eings 169

6. Answer the following questions.

a. What is classification? Why is it necessary to classify plants?

b. What do you mean by thallophytes? Give any 5 examples of
thallophytes.

c. What are the differences between algae and fungi? Write any two.

d. Why are fungi non-green in colour? Why are they called heterotrophs?

e. Write down any 2 important characteristics of bryophytes with 2
examples.

f. What are the important characteristics of pteridophyte? Write any 2
examples.

g. Why are gymnosperms known as naked seeded plants? Write down
its important features with four examples.

h. Write down the names of any five dicots and five monocots.

i. Write short notes on the stem. What are its functions?

j. What types of roots are found in monocots and dicots? Write two
functions of roots.

k. Why are leaves necessary for a plant?

l. Write a short note on the flower and write down its functions.

Primitive - of early stage of evolution (development)
Parasites - that live by feeding on others
Altitude - the height above the sea level
Modified - enlarged, changed, revised
Delicate - tender, soft
Network - a closely connected group of something

‰‰

170 New Creative Science and Environment; Book 7

16 Cell and Tissue

After the completion of this unit, students will be able to:
Æ describe the cell and its structure.
Æ differentiate the structures of the cell.
Æ describe the functions of cell and their parts.

Introduction

All the living organisms, (either plants or animals) are composed of small
microscopic compartments. These microscopic compartments are the minimum
organizations of matter. These minimum units capable to drive all the process
which we refer to as life are known as cells. Thus the cell is the basic unit of life.

The cell can be defined as the structural and functional unit of life.
The cell was first discovered by Robert Hooke in 1665 AD. He observed a
thin section of bottle cork made of wood under a microscope. He found the small
boxes arranged like a honeycomb. All the boxes were similar to each other. He
named cells to those boxes. Cells are very small that cannot be seen with naked
eyes. So an instrument called a microscope is used to view cells.
Questions
‰ Define a cell?
‰ Who descover the cell?
Memory Note

Æ Cytology is the study of cells.
Æ Red Blood Cells are the smallest cells of the human body.
Æ Neuron, a nerve cell is the biggest and longest cell of a human body.

Unicellular and multicellular organisms

On the basis of the number of cells present, organisms are classified as:
unicellular organisms and multicellular organisms.

Cell and Tisseu 171

Unicellular organisms are those organisms whose body is made up of only
one cell. All the life processes like respiration, reproduction, excretion, digestion
etc. occur within a single cell. Their cell is thus delicate and any unfavourable
condition in them leads to death. The examples of such organisms are amoeba,
paramecium, euglena, chlamydomonas, etc.

Examples of unicellular organisms
Multicellular organisms are those organisms whose body is composed of
more than one cells. All the living creatures you see with your naked eyes are
multicellular organisms. The life process in them is carried out by the group of
cells. Any injury or death of one cell does not affect them. Destruction, repair and
formation of cells occur in them continuously. The examples are earthworms,
hydras, fish, birds, humans, animals, etc.

Examples of Multicellular organisms

Shape and size of a cell

The shape and size of cells vary from cells to cells of different tissues or
organs. Some cells are big in size whereas some are small. They may be rectangular,
circular, rod-shaped, discoid, elliptical, cubical, flat or spherical in shapes. Cells
also vary from plants to animals. A plant cell is polygonal in shape while animal
cell is circular. The variation in shape and size of cells depends on their functions
in the body.

172 New Creative Science and Environment; Book 7

Amoeba and white blood cells have no definite shape. They change their
shape according to the condition.

Different types of cells

Structure of the cell

A typical cell consists of a cell membrane and a living substance called
protoplasm. The central nucleus, the fluid of the cell and cytoplasm is collectively
known as protoplasm.

The parts of cells along with important functions are discussed below.

Cell membranes
Centrosome Cell wall

Nucleus

Vacuole

Mitochondria
Plastid

Animal cell Plant cell

Cell wall

It is the outermost covering of the plant cell. It is absent in animal cells. It is
composed of cellulose, hemicellulose and lignin. It protects cell organelles from
external injuries and provides strength to the cell.

Cell membrane (Plasma membrane)

The cell membrane is the outermost layer of cytoplasm. In plant cells,
it lies inside cell wall and in animal cells, it acts as an outer covering. It is a

Cell and Tissue 173

semipermeable membrane. It means it allows some substances to pass in and
out of the cell. It is made up of protein and lipids. It protects the inner structure
of the cell. It permits essential nutrients to pass inside the cell and unnecessary
substances to pass outside the cell. In some organisms like the amoeba it helps in
locomotion.

Cytoplasm

It is a fluid found between the nucleus and the cell membrane. Cell
organelles are found to be scattered here and there in cytoplasm. Cell organelles
like mitochondria, plastids, golgi bodies, centrosome etc. are found in cytoplasm.

Vacuoles

Vacuoles are the space consisting water and minerals. They are found in
various numbers and sizes in plant and animal cells. The central large vacuole is
found in plant cells whereas small and many vacuoles are found in animal cells.
It also helps to balance water and minerals in the cell.

Nucleus

The nucleus is the prominent and very important Nucleus
structure in the cell. It consists of a fluid called Mitochondria
nucleoplasm in which nucleolus and fine thread-like
matters called chromosomes are present. It controls Chloroplast
all the cellular activities. It is a major organ for protein
synthesis and to transfer hereditary characters from
generation to generation.

Mitochondria

A mitochondria is a granular, oval, rod-shaped or
vesicular structure with finger-like projections. It is also
known as the powerhouse of the cell because respiration
takes place in this organ and it releases large amount of
energy.

Plastids

Plastids are the circular protoplasmic
structures scattered in the cytoplasm. It is present
in plant cells and absent in animal cells. It contains
a green pigment called chlorophyll. Plants can
produce their food themselves by the process of
photosynthesis due to the presence of chlorophyll.

174 New Creative Science and Environment; Book 7

Centrosome

It is the circular structure that lies close to the nucleus. It is present in animal
cells and absent in plant cell. It helps in cell division.

Endoplasmic reticulum

It is a network of much branched membranes
distributed in cytoplasm. It helps in protein
synthesis and acts as a passage for transporting
synthesized materials in and out of the cell.

Endoplasmic reticulum

Golgi bodies

These are the flat, plate-like cell organelles
attached to each other through tubules. They
help in the transportation of chemical substances,
formation of cell plates in the cell division and
formation of the cell wall.

Memory Note

Æ Chromosomes is the genetic material for heredity.
Æ Mitochondria is the place of respiration in the cell.
Æ Plastids give colour to a plant and its parts.

How to view an onion cell? Onion cells

Æ Take a piece of onion and peel Cell and Tisseu 175
its skin.

Æ Cut a thin section of the inner
membrane with a sharp blade.

Æ Keep the section in safranine
and transfer to the slide.

Æ Drop glycerin on the material
and cover it with a cover-slip.

Æ View the cells under the microscope.

How to view the cells of the human cheek? Human cheek cells

Æ Scarp out the inner surface of your
cheek with the forceps.

Æ Scatter the scraped substance on
a glass slide and cover it with a
coverslip.

Æ View the slide under the microscope.

Amoeba

Amoeba is a unicellular, microscopic, organism Structure of amoeba
which lives in water or moist places. Some species of
amoeba also live inside the body of other organisms.
As it is a unicellular organism, all of its life processes
like reproduction, excretion, digestion, nutrition,
respiration take place within a single cell.

Structure

The word amoeba means to ‘change’. So, the structure of amoeba is
constantly changing. Its body membrane or cell membrane is elastic and flexible
due to which its body shape constantly changes. Inside the cell membrane, there
is protoplasm. There is a nucleus which controls the whole cell of amoeba.

The cytoplasm is divided into outer ectoplasm and inner endoplasm.
Ectoplasm is denser than endoplasm. It consists of contractile vacuoles and food
vacuoles. The food vacuoles help in the digestion of food and contractile vacuoles
help in the balancing of water inside the cell.

The cell membrane helps to the entrance and exit of materials inside and
outside the cell.

Amoeba sends and withdraws the finger-like projections of its cell membrane
which are called pseudopodia. Amoeba locomotes with the help of pseudopodia.

Effects of amoeba on human beings

There are various species of amoeba. Some are free living and they are not
harmful. Entamoeba coli is found in the large intestine of human beings. They
fed on the undigested food from the small intestine. They are not harmful to us.

176 New Creative Science and Environment; Book 7

Another species Entamoeba histolytica is also found in the human intestine.
They attack the walls of intestine and so they are harmful to us. They cause the
amoebic dysentery.

Entamoeba Gingivalis is found inside the mouth of human beings. They
cause pyorrhea which is characterized by the bleeding gums, foul smell, etc.
These amoebae enter our body through the contaminated foods and drinks.
Thus, we must be careful and avoid eating contaminated food and drinks.

Boil an egg and peel off its shell. Cut it into equal halves. Draw its picture
and write which parts can be compared with nucleus, cytoplasm and cell
membrane.

Hydra

Hydra is a multicellular aquatic animal.
It lies in phylum coelenterata of subkingdom
invertebrates. It can be found in fresh-water ponds,
lakes, and streams in the temperate and tropical
regions.

Its tubular body is made up of tissues. The

body of hydra consists of tentacles, body cavity

and simple adhesive foot. The upper end of the

cavity has an aperture surrounded by one to

twelve thin and mobile structures called tentacles. Hydra
This aperture behaves both as the mouth and anus.

Tentacles help hydra to move from one place to

another, to paralyze prey, to catch it and put it into its mouth. It is also a defensive

organ in hydra. Each tentacle is made with highly specialized stinging cells. They

release neurotoxins which can paralyze the prey. The tentacles of Hydra are

extraordinarily extensible. They can be four to five times the length of the body.

Hydra is able to stretch its body wall that is enough to digest prey twice more

than its size. Its adhesive foot called the basal disc secretes a sticky fluid. This

fluid helps to attach it to the substratum.

Hydra is generally attached to the substratum. But sometime it moves in
search of food. They do this by bending over and attaching themselves to the
substrate with the mouth and tentacles. And then release the foot, which provides

Cell and Tisseu 177

the usual attachment. This process of movement in hydra is called looping. The
body then bends over and makes a new place of attachment with the foot. Hydra
may also move simply by detaching from the substrate and floating away in the
water current.

Locomotion in hydra

Hydra has two main body layers, outer ectoderm and inner endoderm.
These layers are separated by a gel-like substance called mesoglea. Its nervous
system is very simple. Respiration and excretion occur by diffusion through the
epidermis. When there is plenty of food, many hydra reproduce asexually by
producing buds in the body wall. These buds grow like a small adult and simply
break away when they are mature. This process of asexual reproduction is called
budding.

1. Why is mitochondrion called the powerhouse of the cell?

Ü In mitochondria cellular respiration takes place. This releases a large
amount of energy which is needed for metabolic activities of the cell. So
mitochondria are called the powerhouse of the cell.

2. Write down any two major functions of the cell wall.

Ü Any two major functions of the cell wall are as given below.

i) It provides mechanical strength to the cell.

ii) It protects the inner structure of the cell from external injuries.

3. Write down the differences between a plant cell and an animal cell.

Plant cell Animal cell

i. Cell wall is present. i. Cell wall is absent.

ii. Centrosome is absent. ii. Centrosome is present.

iii. Plastids are present. iii. Plastids are absent.

178 New Creative Science and Environment; Book 7

iv. Nucleus is at the periphery of iv. Nucleus is at the centre of the

protoplasm. protoplasm.

v. Cell plate formation takes place v. Cell furrow formation takes place

in cell division. in cell division.

vi. Large central vacuole is present. vi. Small scattered vacuoles are

present.

F A cell is the structural and functional unit of life.
F Unicellular organisms are made up of only one cell, e.g. amoeba,

paramecium etc.
F Multicellular organisms are made up of more than one cells, e.g. hydra,

earthworms, starfish, frogs, snakes, birds, humans, etc.
F A typical cell has 2 main parts: the cell membrane and the protoplasm. In

protoplasm, cytoplasm and nucleus are present.
F Nucleus is the control centre of the cell which controls all the cellular

activities.
F The shape and size of cells vary according to their functions.

1. Fill in the blanks.
a. ____________ is the basic unit of life.
b. The shape and size of cells depend upon their ____________.
c. ____________ is the control centre of the cell.
d. Large central and prominent ___________ are present in plant cells.
e. The powerhouse of the cell is ____________.

2. True or False.
a. The neuron is the largest cell in the human body.
b. Plastids help in respiration in the cell.
c. The cell membrane is the outer covering of an animal cell.
d. Robort Hooke observed the cells of a bottle cork.
e. Vacuoles store fats and proteins in a cell.

Cell and Tisseu 179

3. Match the following:

Amoeba the smallest human cell

RBC nucleolus, nuclear membrane and chromosome

Nucleus small, many and scattered in an animal cell

Vacuoles photosynthesis

Plastids have no definite shape

4. Differentiate between:

a. plant cell and animal cell b. cell wall and cell membrane

5. Answer the following questions.

a. What is a cell?

b. What do you mean by unicellular organisms? Give four examples.

c. What do you mean by multicellular organisms? Give four examples.

d. Describe the parts of a cell with its function.

e. Draw a well labelled diagram of a plant cell and an animal cell.

f. Why is the nucleus the main part of the cell?

g. Describe the structure of amoeba and hydra.

h. How does hydra move? Show with a figure.

i. Describe the effect of amoeba on human beings.

Composed of - made of

Compartments - division

Discovered - found out

Delicate - soft, tender, weak

Counterstrike - face

Permits - allows

Locomotion - movement

Scattered - dispersed

‰‰

180 New Creative Science and Environment; Book 7

17 Life Processes

After the completion of this unit, students will be able to:
Æ describe and understand the meaning of life processes.
Æ define respiration and the organs involving in respiration in

different ways.
Æ describe the process of respiration in humans.
Æ give the meaning of excretion and organs involving in it.
Æ describe the process of excretion in humans.

Introduction

All the living organisms have special body features for their existence.
Plants have chlorophyll in their leaves for food making process. They have small
tiny pores on their leaves for the exchange of gases. In the same way, animals
also have various body features like nerve cells, heart, skin, skeleton, body cavity
for various processes to take place in their body. These processes are respiration,
excretion, digestion, circulation, reproduction, etc. Thus, life process is defined as
the phenomenon that occurs in the living body.

Here, we discuss about the two major life processes. They are respiration
and excretion.

1. Respiration

We need energy to do our daily activities. We eat food to get energy. Do you
know how energy is derived from food?

All the living things respire but their ways are different. Respiration involves
the process of breathing. Taking in and taking out air is the breathing process.
During respiration, oxygen is taken in and carbon dioxide is taken out. The food
items we eat are broken down into simpler forms by the digestion process. The
simple type of foods like carbohydrates and glucose when chemically combine
with oxygen gas releases energy along with carbon dioxide and water. Hence
due to respiration, we obtain energy for other life processes.

Life Processes 181

Thus, respiration is defined as the process of releasing energy due to the
chemical break down of food by oxygen. It can simply be defined as the process
of oxidation of food to release energy.

Ways of respiration

Animals and plants respire in different ways. The organs of respiration also
differ from one type of animal to other types.

1. Stomatal respiration

This is the process of Respiration in plant
respiration in simple plants. The
surface of leaves contains tiny small
pores on them. They are called
stomata. From the opening of the
stomata, exchange of gases between
plants and atmosphere takes place.
Plants diffuse carbon dioxide and
water vapour in the atmosphere
while oxygen is taken from the
atmosphere.

2. Respiration through body surfaces O2

Unicellular organisms like amoeba, CO2
paramecium, etc. respire through their body Respiration through body surface
surface. Their body surface takes dissolved
oxygen from water and carbon dioxide is
diffused into the water from their general
body surface.

3. Respiration through skin O2

Mostly multicellular invertebrates respire CO2
through the skin. Animals like leech, earthworm Respiration through skin
having their moist and thin layer of skin exchange
gases through their skin. In water, frogs also
respire through the skin which is also known
as cutaneous respiration. Oxygen is taken while
carbon dioxide is released through the skin.

182 New Creative Science and Environment; Book 7

4. Respiration through air tubes

Animals usually insects (belonging to class Respiration in butterfly
insecta) have porous and thin tubes in their body. through air tubes
These thin tubes pump out carbon dioxide and pump
in oxygen. Organisms like butterflies, dragonflies,
mosquitoes, etc. respire through the air tubes.

5. Respiration through gills

Vertebrates under the class pisces respire Respiration in fish through gills
through gills. The larval stage of the frog called the
tadpole also respires through gills. Gills absorb the
dissolved oxygen from water and release carbon
dioxide. Fishes respire through gills.

6. Respiration through lungs

Vertebrates like reptiles, birds and mammals Respiration in monkey
respire through lungs. The exchange of gases takes through lungs
place in the part of lungs known as alveoli. Through
this process, oxygen is passed to the blood while
carbon dioxide is released out. Some of the animals
respiring through lungs are snakes, hens, crocodiles,
man, monkeys, tortoises, adult frogs, etc.

Respiration in human beings

Human beings respire through lungs. They Trachea
inhale oxygen and exhale carbon dioxide. The lung Lung
is the main organ of the respiration though human
beings have different body organs involving Bronchus
in the process of respiration. The main organs
involving in the respiration are the nose, trachea Human respiratory organ
(windpipe) and lungs. Further these organs can
be differentiated into the nose, pharynx, larynx,
trachea, bronchi, bronchioles, lungs and alveoli.

When we inhale air, it passes from the nose to the larynx and to the pharynx.
In the nose, the air is filtered by nose-hairs and it is warmed. The pharynx allows
the air to pass from the windpipe or the trachea. During this, the food-pipe is
covered by a cartilage called epiglottis. The air finds its way from the trachea

Life Processes 183

to the left and right bronchi. Bronchi is divided to form bronchioles. Air passes
from these bronchioles to the lungs. Lungs consist of many air sacs called alveoli
which are rich in blood capillaries. The air passes to the alveoli. In each alveolus
oxygen is absorbed by blood and carbon dioxide gas is released out. Carbon
dioxide is thrown out by the nose and oxygen is carried by the blood through
blood vessels. The carbohydrate and glucose chemically combine with oxygen
in the cells releasing energy, carbon dioxide and water as byproducts. Thus the
energy is obtained by the cells. This process is very fast and it continues till the
human being is alive.

Objective
To show that carbon dioxide is evolved during respiration.

Apparatus required
Round bottom flask, test tube, gram seed, moist cotton and lime water

Procedure

Æ Take some gram
seeds, some
boiled and some
soaked in water.

Æ Keep these seeds
into two different
round bottom flasks in moist cotton.

Æ Cover the mouth of both the flasks and leave it for germination.

Observation and conclusion
When the seeds germinate, open the cover of both the round bottom

flasks and tilt it near the mouth of the test tube containing lime water. Then
shake the test tube. What do you observe? Do you observe any change when
the lime water is kept in contact with the mouth of the boiled seeds flask?

The lime water when kept in contact with the germinated seed turns
milky. This shows that there is the evolution of carbon dioxide gas during
respiration.

Digestive system in the human body
Digestion is a catabolic process or the process of breaking down of complex

food materials into simple forms which can be directly absorbed by the body.
The digestive system of the human body consists of the mouth, alimentary canal
and the anus.

184 New Creative Science and Environment; Book 7

Mouth

It is an opening through which food is taken inside the body. The food
mixes with saliva inside the mouth and here the mechanical break down of the
food occurs with the help of teeth and the tongue. Saliva contains the enzyme
ptyalin which helps to break down carbohydrate partially to the glucose.

Question

• Why do we feel sweet when we chew beaten rice for some time in
our mouth?

Alimentary canal

The alimentary canal is basically a long tube extending from the mouth
to the anus. It is necessary to move the food in a regulated manner along the
digestive tube so that it can be processed properly in each part. The linings of the
canal have muscles that contract rhythmically in order to push the food forward.
This peristaltic movement occurs throughout the gut. The alimentary canal has
the following parts:

(1) Food pipe or oesophagus (2) Stomach

(3) Small intestine (4) Large intestine (5) Anus

Tongue Mouth (Buccal cavity)
Oesophagus

Diaphragm Stomach
Small intestine
Liver
Gall bladder Large intestine (Colon)
(stores bile)
Anus
Appendix
Life Processes 185

(1) Food pipe or oesophagus
The food after chewing in the mouth passes to the stomach through the

food pipe or the oesophagus.
(2) Stomach

The stomach is a large organ which expands when food enters it. The
muscular wall of the stomach helps to mix the food throughly with more digestive
juices.

The digestive functions are carried out by the gastric glands present in the
wall of the stomach. The gastric glands release:

(i) hydrochloric acid.
(ii) a protein digesting enzyme called pepsin.
(iii) mucus.
The hydrochloric acid creates an acidic medium which facilitates the action
of enzyme pepsin. It also kills the bacteria present in the food.
The food enters in the small intestine through the stomach.
(3) Small Intestine
This is the longest part of the alimentary canal which is excessively coiled.
The small intestine is the site of the complete digestion of carbohydrates, proteins
and fats. It receives the secretions of the liver and pancreas for this purpose.
The food coming from the stomach is acidic and has to be made alkaline for the
pancreatic enzymes to act. The food is made alkaline by the bile juice secreted by
the liver. The fat globule present in the large intestine is broken down.
The pancreatic juice secreted by the pancreas contains the enzymes like
trypsin for digesting proteins and lipase for breaking down emulsified fats.
The wall of the small intestine contains glands which secrete intestinal juice.
The enzymes present in it finally convert the proteins to amino acids, complex
carbohydrates into glucose and fats into fatty acids and glycerol.

186 New Creative Science and Environment; Book 7

The digested food is taken by the walls of the intestine. The inner lining of
the small intestine has numerous finger-like projections called villi. They increase
the surface area for absorption. The villi are richly supplied with blood vessels.
They take the absorbed food to each and every cell of the body where it is utilized
for obtaining energy, building up new tissues and the repair of old tissues.

Large Intestine

The unabsorbed food materials are sent into the large intestine where more
villi absorb water from these materials. The rest of the materials is removed from
the body through the anus. The exit of this waste materials is regulated by the
anal sphincter. The process of throwing out of the waste materials from the body
is called egestion.

Memory Tips

The small intestine of herbivores are larger than that of carnivores because
meat is easier to digest than the cellulose.

The summary of the digestion of food is given in the table below.

S. Digestive Digestive Digestive Enzymes Products
N. organs glands juices
1. Mouth
Salivary Saliva Ptyalin Starch is converted into maltose.
2. Stomach glands

Gastric HCl - Food changes into acidic medium
gland Gastric Pepsin germicides.
Renin Proteins converted into peptons.
juice Milk protein (Caesein) into curd.

3. Duodenum Liver Bile juice - Emulsifies fat and makes medium neutral

or slightly alkaline.

Prancreas Pancreatic Trypsin Peptones → Peptides

juice Amylase Starch → Maltose

Lipase Fat → Fatty acid & glycerol

4. Small intestine Intestinal Intestinal Erepsin Peptide → Amino acids
Sucrase Sucrose → Glucose
gland juice Lactase Lactose → Glucose
Maltase Maltose → Glucose

5. Large intestine - - - Some important salts and water are
absorbed.

Question

# What is the role of acid in our stomach?
# How is the small intestine designed to absorb digested food?

Life Processes 187

Assimilation

The absorbed food materials are taken to all cells of the body via blood.
These nutrients are used by cells to perform various activities. This process is
called assimilation.

2. Excretion

Life process occurs in the living body for the existence of life. This process
performs their specific function by which the living things can live. This process
forms various types of byproducts. All the byproducts may or may not be useful.
Thus there is another life process which helps in the elimination of unnecessary
and harmful byproducts formed in the body. This process is known as excretion.
Excretion is defined as the process by which unnecessary and harmful substances
are removed from the body.

During respiration, carbon dioxide gas is released. It is excreted out in the
atmosphere by the lung. Ammonia and urea are excreted from our body in the
form of urine. These excretory products are formed from the complete digestion
of food. These poisonous and harmful wastes are removed from the body through
the respective excretory organs like lungs, kidney, skin, etc.

Excretion in plants

In plants, stomata are the sites of excretion. The ways of excretion by stomata
are as follow.

i. In the process of respiration, carbon dioxide gas is diffused out from
the stomata.

ii. During the photosynthesis process, oxygen gas is diffused out in the
atmosphere.

iii. Stomata release excess amount of water into the atmosphere. This
process is known as transpiration.

Except the stomata, stem and leaves of certain plants release gum, resin and
water-like wastes. These substances are not necessarily released out but may be
stored in various plant parts. In guava-like plants, the thin layered barks may also
be detached from the stem and branches. This is also an example of excretion.

Excretion in animals

Animals have different groups. They may be unicellular to multicellular,
invertebrates to vertebrates. Depending on their structure and body feature,
excretion differs in different animals.

188 New Creative Science and Environment; Book 7

i. Unicellular organisms like amoeba, paramecium have no definite
excretory system. They excrete out the wastes by osmoregulation and
diffusion.

ii. Multicellular invertebrates like sycon, sponge, euspongia, etc. excrete
through small pores called ostia.

iii. Invertebrates like hydra, jellyfish, coral have some pores for both
excretion and food drawing.

iv. Invertebrates like the roundworm, tapeworm excrete out from flame
cells.

v. The earthworm, leech, liver fluke excrete from the developed the
excretory system.

vi. Insects like bees, mosquitoes, butterflies etc. excrete out through
malpighian tubules.

vii. Vertebrates have well developed excretory organs. Skin, nose, mouth,
lungs, large intestine, kidneys and liver are the excretory organs. These
excretory organs help in the elimination of waste materials from the
body.

Excretion in human beings

Human beings have a well

developed excretory system. The Kidney
excretory systems in humans are

composed of the kidney, ureter, urinary

bladder and urethra.

i. Kidneys: These are reddish Ureter

brown bean-shaped organs. They

are present in each side of the

vertebral column at the back of

abdominal cavity. A large number Urinary bladder

of coiled and looped structures

called nephrons are present in Urethra
kidneys. They are the structural, Urinary system

and functional units of kidney.

Nephrons function for the filtration of impure blood and elimination of

urea in the form of urine.

ii. Ureter: The two tubes which join the kidneys and the urinary bladder is the
ureter. These are thin walled ducts.

Life Processes 189

iii. Urinary bladder: This is the stretching bag-like structure which holds the
urine. From this bladder urine is passed to the urethra.

iv. Urethra: The urinary bladder has a ring-like construction which opens when
human wants for urination. This opening leads the urine to pour into the
small narrow tube called the urethra. Through this tube, urine is expelled
from the body.

Organs of excretion

Apart from the organs involved in excretion, the human body has different
organs for excretion. Some of the important excretory organs are mentioned
below.

a. Skin: Skin eliminates excess water in the form of sweat. It also helps in the
removal of urea and other mineral salts.

b. Lungs: Lungs help to release carbon dioxide out from the body. It also
eliminates water from the blood.

c. Kidneys: Uric acid, urea, salts, unnecessary water, etc. are removed from
the blood in the form of urine. This is due to the filtration of blood by the
nephrons of kidney.

d. Large intestine: Undigested food materials are removed out from the body
in the form of faeces. Through the anus, the faeces is eliminated out.

e. Liver: It helps in the removal of amino acid, dead red blood cells, and excess
metal ions from the body.

1. What are the excretory organs in tapeworms and hookworms?

Ü Protonephridia (flame cells) are the excretory organs in tapeworms and
hookworms.

2. What is respiration? What are the different organs of respiration in
different organisms?

Ü Respiration is the process of releasing energy due to the chemical break
down of food using oxygen.

The different organs of respiration in different animals are as given below.

a. Stomata b. Body surface

c. Skin d. Air tube

e. Gills f. Lungs

190 New Creative Science and Environment; Book 7

F Phenomena that occur in the living body are called life processes.
F Respiration is the process of oxidation of food to release energy.
F Organs of respiration differ from different types of organisms.
F Different organs of respiration in living things are stomata, general body

surface, skin, air tubes, gills and lungs.
F Excretion is the process of elimination or removal of unnecessary and

harmful wastes from the body.
F Organs of excretion also differ in different groups of organisms.
F Skin, lungs, liver, mouth, kidneys, large intestine are the organs of

excretion.

1. Fill in the blanks.

a. ____________ is derived from food due to respiration.

b. ____________ is the main site of respiration in plants.

c. Respiration through skin is also known as ____________ respiration.

d. _____________ are the excretory organs of insects.

e. _____________ gas is diffused by plants during photosynthesis.

2. Select the correct alternatives.

a. Gills are the respiratory organs of:

i) tadpoles ii) whales iii) snakes

b. Which of them shows cutaneous respiration?

i) turtle ii) crocodile iii) frog

c. Which one of them is the excretory organ?

i) anus ii) stomach iii) liver

d. What covers the food-pipe during respiration?

i) epiglottis ii) bronchioles iii) larynx

e. The lung is the respiratory organ of :

i) birds ii) amoeba iii) insects.

Life Processes 191

3. Match the followings:

Trachea nephrons

Transpiration gills

Fishes windpipe

Kidney loss of water

Skin respiration in human

Lungs sweat

4. Write ‘T’ for true and ‘F’ for false statements.

a. Ostia are the excretory sites of sponge, euspongia, etc.

b. The lung is the respiratory organ of birds.

c. Nephrons are the structural and functional unit of lungs.

d. Alveoli are present in the surface of kidneys.

e. The liver also helps in the excretion of amino acids.

5. Define the following term.

a. Excretion b. Respiration c. Flame cells

d. Alveoli e. Nephrons

6. Differentiate between:

a. Excretion and respiration

b. Flame cells and ostia

c. Gills and lungs

7. Answer the following questions:

a. Describe the process of respiration in short.

b. How is food converted into energy?

c. What are the organs of respiration in different organisms? Write three

examples of each.

d. What do you mean by excretory organs? Write their functions in a

single sentence.

e. What are the forms of excretion in plants?

f. Describe the structure and function of the kidney.

g. Why do people die if both kidneys fail to function?

By product - result, output
Reptiles - animals that crawl
Respire - take in and out air by a living thing
Elimination - process of removing or getting rid of
Respective - concerned, related

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192 New Creative Science and Environment; Book 7

18 Structure of the Earth

After the completion of this unit, students will be able to:
Æ identify minerals and rocks.
Æ explain the characteristics of different kinds of rocks.
Æ identify and explain some common rocks.
Æ name different types of rocks found in Nepal.

Minerals

The chemical substances which are naturally found in the earth’s crust in
solid and crystalline form and which cannot be made by human beings are called
minerals. They are non-living substances and cannot be obtained from living
beings. For example, talc, gypsum, quartz, diamond, ruby, emerald, graphite,
garnet, topaz, etc. There are many types of minerals found in the earth’s crust among
which only few are useful to us.

Memory Tip

Coal, petroleum, natural gases, pearl are not minerals because they are
produced from living beings.

Rocks

Rocks are hard solids composed by the combination of one or more minerals.
Our earth consists of different types of rocks. They are also found in the seabed,
bases of the peak of the Himalayas, etc. Rocks form soil. So, they are usually
found embedded inside the soil.

According to geologists, it is estimated that rocks are made from 92 elements
but their percentage composition may vary from one to another. The rough
percentage of minerals in rocks is as listed below.

Elements Symbol Percentage
Oxygen O 46.6
Silicon Si 27.7
Aluminium Al 8.1
Iron Fe 5.0

Struc tur e of the Earth 193

Calcium Ca 3.6

Sodium Na 2.8

Potassium K 2.6

Magnesium Mg 2.1

Other elements – 1.5

Total 100.0

The table shows that about 98% of the rocks are made up of first 8 elements,
and only 15% is taken by other elements to form crust.

Types of rock
On the basis of their origin and formation, rocks are classified mainly into

three types. They are

i) Igneous rock ii) Sedimentary rock iii) Metamorphic rock

i) Igneous rock

They are the primary rocks formed by the cooling of hot magma inside or
outside the earth’s surface.

We know that it is very hot inside our earth’s crust. Everything is in the
molten state inside the earth due to the excessive temperature and pressure.
When this magma comes outside the earth crust it cools and solidifies or it may
solidify inside the earth’s crust too. Then it forms a hard and crystalline solid
which are known as igneous rocks.

Igneous rocks are again divided into two types:

i) Plutonic or intrusive rocks ii) Volcanic or extrusive rocks

i) Plutonic or intrusive rocks

These types of rocks are formed due to the cooling Gabbro
of hot magma inside the earth while trying to come out. It
has the biggest crystal due to the slow cooling of magma.
Similarly, they are the hardest rocks, e.g. granite, diorite
gabbros, peridiorite, dunite, etc.

ii) Volcanic or extrusive rocks

These types of rocks are formed due to Basalt Pumice
the cooling of hot magma outside the earth
which has come out due to the volcanic
eruption. They have small crystals and their
surface is glassy. Water cannot pass through
these rocks, e.g. basalt, pumice, obsidian, etc.

194 New Creative Science and Environment; Book 7

As igneous rocks are formed from hot lava, they do not contain fossils.

Sedimentary rocks

The materials on the earth’s surface are constantly weathering and breaking
due to wind, water, heat and other forces. These materials are carried away by
rivers, rain, wind, etc. and they are deposited in a certain place. The continuous
deposition of the materials makes many layers and these layers are closely packed
together and become hard by pressure to form sedimentary rocks.

Thus, sedimentary rocks are the rocks formed from the sediments.

Fossils may be found in this rocks. Since the body part of living beings may
be preserved into it during fossil formation process, they are soft compared to
other types of rocks. For example, conglomerate, sandstone, shale, limestone,
dolostone, coal, etc.

Sandstone Conglomerate

Metamorphic rock

These are formed from the igneous, sedimentary or any other types of
metamorphic rocks which remain under great heat and pressure for a long time.
For example, marble, gneiss, slate phillite, quartzite, etc.

Strcu tur e of the Earth 195

Some rocks
(1) Granite

It is a common intrusive or plutonic rock. It is used in the construction of
roads, building and monuments.

(2) Basalt
It is also a plutonic rock which is heavier and darker. It is also used in the

construction works.

(3) Pumice
It is a volcanic rock having the pores of air in it. This is due to the trapping

of hot gases during its cooling process. They are light and spongy rocks.

(4) Conglomerate
It is a sedimentary rock. It is made from sand, pebbles and gravel cemented

together. The quartz binds small pieces of stones to form conglomerates. If the
constituents are bound together by silica then the conglomerates are hard.

(5) Sandstone
It is a sedimentary rock formed by the binding of sand particles by silica. It

may be hard or soft.

(6) Shale
The particles smaller than the grains of sand are called silt and the particles

smaller than silt join to form clay. The rock formed by silt and clay is called shale.
It is a soft rock found in different colours.

(7) Limestone
This is formed from the shells of organisms. It is fine and granular. It may

be red, brown, white or black in colour.

Uses of rocks
Rocks are used for various purposes in our daily life. Some of them are

listed below:
1) They are is used to make houses and buildings. The rocks like marble,
granite and limestone are used for this purpose.
2) They are used to construct roads and buildings.
3) They can be used to make very valuable monuments.
4) Granite is used to build pagodas and temples.
5) Slate is used for writing purposes.
6) They are the sources of valuable minerals and gems.
7) They are used by the scientists to study the history of the earth.

196 New Creative Science and Environment; Book 7