Class 9 Science_clone

through optic nerves. The brain translates the inverted image to
the erect one in the proper size of the object.

Activity 19 .1 To observe the change in size of pupil.

a) Ask any one of your friends to close his/her eyes for about 10 seconds.
b) Tell him/her to open the eyes. Then see the size of pupil of his/her eye.
c) Observe the pupil with torch light. What changes do you observe in the

size of pupil?
d) Ask him to see near object then the distant object. What changes do you

observe in the size of pupil?
2EVHUYDWLRQ
Size of pupil decreases when the bright and near objects are observed.

Care of eyes
:H VKRXOG QRW ORRN DW RU UHDG DW YHU\ GLP RU EULJKW OLJKW
2. We should eat Vitamin ’A’ rich foods such as JUHHQ YHJHWDEOHV

\HOORZ IUXLWV PLON HJJ ILVK HWF
3. We should wash our eyes with clean water before going to bed.
4. We should not rub our eyes when any foreign bodies enter

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FOHDQ ZDWHU RU ZLWK D SLHFH RI FOHDQ FORWK
5. We should use eye medicine only after consulting with eye-
doctor RSKWKDOPRORJLVW
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Ears: organs of hearing Pinna
Ears are the sense organs
which help us in hearing Auditory Canal Semi-circular
as well as balancing canal

the body. The ears have
two types of receptors.
They are phonoreceptors Aneurdvietory
Helix Cochlea
Eustachian
and statoreceptors. Middle Ear tube
Phonoreceptors receive sound
and convert them to auditory
impulses. Statoreceptors Tympanic
balance our body. The human Lobule membrane
ear is divided into three Cartilage Structure of Ear

parts. They are:

i. external ear ii. middle ear iii. internal ear

347 Times' Crucial Science Book - 9

a) External ear
External ear is a cartilaginous skin-covered oval projection from
the temporal side of head. It has two parts: pinna and auditory
canal.
Pinna
Pinna is funnel shaped portion of external ear. It has ridges and
grooves. It collects and directs sound waves to the auditory canal.
Auditory canal
It is an oblique and tubular canal which leads towards eardrum
or tympanic membrane. The wall of the auditory canal in the
outer part is covered with hairs which prevent the dust particles
from entering inside the ear. Its wall in the inner side contains
ceriminous glands which secrete earwax. It prevents entry of
dusts, insects and protects the eardrum from damage.
b) Middle ear
Middle ear lies internal to the external ear which is separated
by a membrane of skin called ear drum or tympanic membrane.
Middle ear consists of air filled cavity called tympanic cavity
which is connected to pharynx with eustachian tube. Eustachian
tube balances the air pressure on the both side of ear drum. This
prevents distortion of ear drum due to difference in air pressure.
This tube normally opens when we chew or yawn. We need to
chew or yawn when we go to higher altitude or go deeper mines.
We chew chocolates while travelling through higher altitude by
aeroplanes. Tympanic cavity consists of a chain of three bones
called ear ossicles. They are malleus (hammer), incus (anvil) and
stapes (stirrup). They are joined with each other side by side.
Outer end of the malleus is joined with the ear drum and inner
end of the stapes is joined with internal ear through oval window.
c) Internal ear
The internal ear is complicated and important part of ear. It has
mainly two parts i.e. cochlea and semi-circular canal.
Cochlea is a bony coiled tube similar to the structure of snail’s
shell. It is filled with fluid called endolymph. It contains a series
of nerve cells and hair cells which join to the auditory nerves. The
auditory nerves carry the sound impulses to the brain. Cochlea is
concerned for hearing.
Semicircular canals are three in number and are arranged
perpendicular to each other in three planes - one horizontal and

Times' Crucial Science Book - 9 348

two vertical. They contain liquid named endolymph. Each canal
swells up to form an ampulla on each side. Semicircular canals
have no role for hearing but play important role for balancing the
body.
Working of ears
Hearing
The external ear collects the sound waves and directs towards
auditory canal. The sound wave passes through the auditory canal
and strikes the ear drum. As a result, vibration is produced in
the ear drum which is transmitted to the inner ear by the three
bones (ear ossicles). The ear ossicles also magnify the sound waves.
Magnified vibration of sound waves are transmitted to the fluid of
cochlea. The vibrations of the fluid in the cochlea are transformed
to the impulses and sent to the brain by auditory nerves. The brain
interprets the auditory impulses. Thus, sound is heard.
Balancing
Sensory cells which are responsible for the balance of a human
body are present in the semicircular canals. Movement of the fluid
inside semicircular canals causes the vibration of sensory cells.
Such impulses are passed to the brain. Since three semicircular
canals are perpendicular to each other at three different planes,
slight tilting in any direction also can be detected and balance can
be done.
Care of ears
1. We should not insert SRLQWHG DQG VKDUS REMHFWV LQWR RXU HDU

They may damage our eardrum.
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take it out with a soft wet cotton bud when it is GHSRVLWHG in
large amount.
3. If any foreign body RU LQVHFWV HQWHU WKH HDUV ZH VKRXOG QRW WU\
WR SXOO WKHP E\ XVLQJ VKDUS WKLQJV :H KDYH WR FRQVXOW ZLWK
a SK\VLFLDQ in such cases.
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WR JR WR KRVSLWDO IRU FKHFN XS
:H VKRXOG NHHS RXUVHOYHV DZD\ IURP ORXG QRLVHV

349 Times' Crucial Science Book - 9

Activity 19 .2 To test the balance of body after spinning

1. Spin round and round for about 1 minute
2. Stop spinning. What do you feel?
2EVHUYDWLRQ
<RX IHHO GL]]\ DQG GLIÀFXOW WR EDODQFH WKH ERG\
Reason:
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continues to move even you stop spinning. Due to this, we feel dizzy

Tongue- The organ of taste

Tongue is a flat muscular organ found Teeth

in the buccal cavity. It is the organ
which is responsible for the sensation
of the taste as well as the movement of
food during chewing and swallowing. Bitter taste

Its undersurface remains attached Sour taste
to the floor except the free anterior
end. Numerous papillae containing Salty taste

taste buds are present on the dorsal Sweet taste
surface. Gustatory cells are the sensory Tongue
cells present in the taste buds. Each
gustatory cell contains a hair like projection which opens outside
through an opening in the taste bud called taste pore. When
substances in solution form enters the taste pores of taste buds,
the sensory hairs are stimulated and the sensations are carried
to the brain. Thus, taste is detected. There are four types of taste
buds. Different parts of tongue are occupied by different types of
taste buds and are responsible for the detection of different tastes.
Sweet: Sweet taste is detected by the taste buds located at the
tip of tongue.
Sour: Sour taste is detected by the taste buds located at the
side of tongue.
Salty: Salty taste is also detected by the taste buds located at
the lateral tip of tongue.
Bitter: Bitter taste is detected by the taste buds located at the
backside of tongue.

Times' Crucial Science Book - 9 350

Care of tongue
a. We should clean our tongue by using tongue cleaner after
EUXVKLQJ WKH WHHWK %XW ZH VKRXOG QRW UXE ZLWK PRUH IRUFH
it may affect the taste buds.
b. Very hot or cold foods may hurt WKH WDVWH EXGV 7KHUHIRUH
we should not eat too hot or cold foods.
c. Plague on the tongue should be cleaned using common salt
in luke warm water.
G :KHQ WRQJXH LV LQIHFWHG RU ZRXQGHG ZH VKRXOG FRQVXOW WKH
doctors.

Activity 19 .3 To identify the regions of tongue to detect different tastes

Materials required:
Little amount of sugar, salt, vinegar (sour food), bitter substance (bitter
gourd), ear buds, watch glasses, tissue papers, etc.

Procedure:
i. Take a little amount of sugar, salt, ground bitter gourd and vinegar in

separate watch glasses.
ii. Put little water on each watch glass to dissolve the above substances.
iii. Put one earbud in each solution.
iv. Ask one of your friends to dry his/her tongue by using tissue paper.
v. Put the end of the earbud dipped in sugar solution on the different

parts of the dry tongue of your friend and ask him which part of the
tongue can detect the sweet taste.
vi. Repeat the step ’V’ for each solution. But, the tongue should be dried for
each test.

2EVHUYDWLRQ
Sweet and salty tastes are detected by the taste buds located at the tip. Sour
taste is detected by the taste buds located at the side and bitter taste is
detected by the taste buds located at the back of the tongue.

Nose- organs of smell
Nose is the sense organ for smell. The nose contains a cavity called
nasal cavity which is divided into two nostrils by a vertical septum.
Hairs are present on the walls of the nostrils which prevent the
entry of dusts and dirts. The inner surface of the cavity is covered
by epithelial tissue. On the roof of nasal cavity, there are free
endings of sensory nerves called olfactory nerves. These nerves

351 Times' Crucial Science Book - 9

carry the impulses of the smell to Nerve Fibres (No Brain) Smell Receptors
the brain.
When microscopic particles or Sensory Epithlium
vapour of substances are carried Nasal Cavity

by the air to the nose, they get
dissolved or mixed with the mucus
of the nose. When they come in
contact with olfactory nerves, the
nerves are stimulated forming
sensory impulses. These impulses Nose

are carried to the brain. Thus, sensation of smell is experienced.
Common cold affects the sense of smell. When a person suffers
from common cold, the epithelium of the roofs of nasal cavity
is swollen. The particles or vapours of the odorous substances
cannot reach the olfactory nerves easily. Thus, the person cannot
smell properly. The sense of smell is closely related to the sense of
taste. Flavour is the combination of taste and smell in which both
senses should be activated simultaneously. Therefore, we cannot
take real taste of foods during common cold.

Care of nose
1. We should not insert fingers or VKDUS substances inside

nose.
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by mask.
3. We should not SOXFN KDLUV SUHVHQW LQ WKH QRVWULOV
,Q FDVH RI LQIHFWLRQ RU DQ\ SUREOHP LQ WKH QRVH ZH KDYH WR

consult with doctors.

Skin- organ of touch Nerve
Skin is the outermost covering of
human body. It is the organ for the Hair
sensation of touch, pressure and Hair Follicle
temperature. The skin contains Epidermis
three layers -epidermis, dermis and
sub-cutaneous layer. Dermis

Epidermis Root of Hair
Sweet Gland

It is the outermost layer of skin Blood Vessels
IRUPHG E\ HSLWKHOLXP ZKLFK LV
Skin

SURYLGHG ZLWK KDLUV DQG SRUHV It does not contain blood vessels.

Times' Crucial Science Book - 9 352

Dermis
It is the middle layer of skin which contains blood vessels, nerve
endings, sweat glands, sebaceous glands, etc. The blood vessels
play important role for regulating body temperature. The nerve
endings are sensitive to touch or pain. The impulses of touch or
pain are carried by the sensory nerves to the brain for sensation.
Subcutaneous layer is the layer of fat supplied with blood vessels.
It retains the heat inside the body.

Care of skin
a) We should take bath twice a week.
b) We should not wear tight and dirty clothes.
F :H VKRXOG SURWHFW RXU VNLQ IURP GLUHFW VXQ OLJKW
G :H VKRXOG WUHDW VNLQ GLVHDVHV OLNH VFDELHV VNLQ ZRXQGV RU
sores immediately.

Learn and Write

1. A person cannot balance his/her body after spinning. Why?
When a person spins, the endolymph contained inside the
semi-circular canal continues to spin even after stopping
the spinning. Due to this, the person feels dizzy and cannot
balance his/her body.

2. Sweet taste can be felt faster than the sour taste. Why?
Taste buds for detecting sweet taste are located at the tip of
the tongue. But the taste buds for sour taste are located at the
side of the tongue. So, the sweet taste is felt faster than the
sour taste.

3. Chocolates are given to passengers while travelling by
aeroplane. Why?
When an airplane flies to a height, the atmospheric pressure
decreases and thus the pressure of the ear outside the
eardrum too. But the air pressure inside the eardrum remains
more. When chocolates are chewed, the eustachian tube opens
and the air pressure outside and the inside of the eardrum
equalizes and prevents the distortion of eardrum.

4. When we suffer from common cold, we cannot smell properly.
Why?
When we suffer from common cold, the epithelium on the roof
of nasal cavity gets swollen. This prevents the reaching of

353 Times' Crucial Science Book - 9

vapour or minute particles of the odorous substance to the
olfactory nerves. Therefore, smell cannot be detected easily.
5. A person having a hole in eardrum does not hear properly.
Why?
The eardrum having a hole does not vibrate properly when
sound waves hit it. Due to this, sound cannot be heard
properly.

Glossary : coloured
: having the structure and form like a crystal
Pigmented : having the consistency of jelly
Crystalline : converts or transforms
Gelatinous : a natural substance that the ears produce to help protect
Translates
Earwax the ear canal and eardrum
: a signal that travels along the length of a nerve fiber
Impulses : small rounded protuberance on a part or organ of the
Papillae
body

Main points to remember

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FDOOHG VHQVH RUJDQV

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retina.

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(DU FRQWDLQV H[WHUQDO HDU SLQQD PLGGOH HDU DQG LQWHUQDO HDU
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13. 6HQVH RI WRXFK SDLQ DQG WHPSHUDWXUH GLIIHUHQFH HWF DUH GHWHFWHG E\ VNLQ.

Times' Crucial Science Book - 9 354

Exercise

1. Answer these questions in very short.
a. What are sense organs? Name them.
b. Draw a diagram of eye ball and label its parts.
c. What are various layers of eye ball. Explain them briefly.
d. What is eye lens? How is its shape and size changed ?
e. What is night blindness ? Why does it occur ?
f. How does an eye work ? Explain in brief.
g. How do you take care of your eyes?
h. What are various types of photoreceptor cells in an eye ?
What are their functions?
i. What are various parts of an ear? Describe them briefly.
j. What is an eustachian tube ? Mention its function.
k. What are ear ossicles? What are their functions?
l. Mention functions of cochlea and semi-circular canals.
m. What things are done to take care of ears?
n. What are taste buds? Where are the locations of various
types of taste buds?
o. How do you smell odour of any substance?
p. How do you take care of tongue?
q. What are olfactory nerves?

2. Write short note on:
(i) Aqueous humour (ii) Vitreous humour (iii) Optic nerves

3. Give reasons:
i. Cornea is called window of an eye.
ii. We should not pluck hairs from nostrils.
iii. Sweet taste can be felt faster than the bitter taste.
iv. Common cold affects smelling of a person.

Project Work

Draw the labelled diagrams of sense organs in a chart paper and describe
them briefly. Compare your job with that of your friend.

355 Times' Crucial Science Book - 9

Chapter

20 (YROXWLRQ
Charles Darwin
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Objectives

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Mind Openers

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Introduction

We see various kinds of plants and animals around us. They
differ from each other in shape, size, physiology, habitat etc.
Some of them live in water while others live on the land. Some
are microscopic whereas other some are gigantic. When a person
studies about the plants and animals, one question arises in his or
her mind about the origin and development of organisms. How did
they originate? When did they originate? Whether the organisms
were originated in the same present form or not? What caused
diversity of organisms?

No one could give clear cut reply to the above questions. There are
two main theories regarding the origin of organisms on the earth.
They are:

(i) Theory of special creation (ii) Organic evolution

Theory of special creation

According to this theory, the origin of all organisms took place as
a special creation by god. The organisms of the present forms were
created by the god in the same forms. This theory is not accepted
nowadays due to lack of scientific evidences.

Times' Crucial Science Book - 9 356

Organic evolution

According to this theory unicellular organisms were developed at first
in aquatic forms from non-living things. Micromolecules like carbon,
hydrogen, oxygen, nitrogen, etc united to produce macromolecules
like proteins, carbohydrates, nucleic acids etc. From macromolecules,
protoplasm (the basis of life) was formed. Then unicellular organisms
were developed from protoplasm. From unicellular organisms,
multicellular organisms were developed gradually.

This process is called organic evolution. According to this theory,
advanced forms of life at present were developed from simple and
primitive organisms of the past. There are many evidences to
support this theory. Therefore, it is more convincing theory about
the origin and development of organisms.

Fact Reason

Why had dinosaurs evolved before human?
Dinosaurs are reptiles and the humans are mammals. Evolution
always occur from simpler form to complex form. Hence, simpler
animals i.e. dinosaurs (reptiles ) had evolved before human.

Evidences of organic evolution
Major evidences of organic evolution are as follows:
1. (YLGHQFH IURP fossils 3DODHQWRORJLFDO HYLGHQFH
2. (YLGHQFH IURP FRPSDUDWLYH PRUSKRORJ\ and anatomy
3. (PEU\RORJLFDO HYLGHQFH
4. (YLGHQFH IURP YHVWLJLDO organs
5. (YLGHQFH IURP distribution of organisms
6. (YLGHQFH IURP connecting animals

a) Evidence from fossils (Palaentological evidence)

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LPSUHVVLRQV RI GHDG SODQWV
RU DQLPDOV SUHVHUYHG LQ
the rocks. A fossil is the
evidence of the existence of
past life. Study of fossils is
called palaentology.

When animals or plants die Fossil
and their dead bodies along
with soil, stones, etc are

357 Times' Crucial Science Book - 9

carried by water of any source to the ocean. These bodies settle
at the bottom. This process continues. Thus, layer of one above
another is formed. The soft parts of the dead bodies decay but
hard parts like bones of animals or veins of leaves, or stems do
not decay and leave impressions on the sedimentary rocks. Such
impressions are fossils.

When fossils were dug out and studied, it has been found that lower
strata contain fossils of simple and primitive organisms whereas
the upper strata contains the fossils of advanced organisms. It was
also found that the fossils of one strata show close resemblance to
the fossils of next lower or upper strata. This shows that there
is a relation between the organisms which appeared through the
successive time period.

Thus, fossils show the direct evidence of evolution.
b) Evidence from comparative morphology and anatomy
0RUSKRORJ\ LV WKH VWXG\ RI H[WHUQDO VWUXFWXUH RI DQ RUJDQLVP
whereas anatomy is the study of internal structure of an organism.
Morphological and anatomical similarities of organisms suggest
that they have common ancestry.

Human Cat Whale Bat Bat Bird Insect

Homologous organs Analogous organs

When forelimb of human, flipper of whale, wing of bird, forelimbs of
horse and patagium of bat are studied, they contain almost similar
type and number of bones, blood vessels and muscles arranged in
same pattern. All of them contain humerus, radius, ulna, carpels,
metacarpels and phalanges. But these organs are not used by all
organisms in the similar way and their morphological structure
were modified according to their adaptations. Those organs which
are similar in anatomical structure but different in morphology

Times' Crucial Science Book - 9 358

Fishand functions are called homologous organs. Forelimbs of human,
Frogflippers of whales, wings of birds, forelimbs of horses, patagia
Tortoiseof bats, etc are homologous organs. The presence of homologous
Chickorgans in various organisms shows that these organisms must
Rabbithave common ancestry.
HumanSimilarly, there are some organs present in different organisms
which have similar functions but different structure. Such organs
are called analogous organs. Wings of insects, wings of birds,
patagia of bat, etc are examples of analogous organs. Presence of
analogous organs shows that they must have evolved from common
ancestors.
Embryological evidence
Embryos are multicellular
structures which are developed
from zygote and give rise to
new offspring. Generally, they
grow inside the females’ uterus
or inside eggs. The study of
development of embryos is called
embryology.
When embryos of different
vertebrates such as fish, frog,
tortoise, chick, calf and human
are studied in various stages
of their development, they
resemble very close to each other.
It is very difficult to distinguish
one from another. When they grow gradually later they differ from
each other and finally change into respective animals which are
similar to their parents.
The similarities in the embryonic stages of those animals indicate
that these animals must have evolved from the same ancestors.
Evidence from vestigial organs
There are some organs in an organism which are functionless
whereas they are fully functional in other organisms. The organs
ZKLFK DUH UHGXFHG LQ VWUXFWXUH DQG IXQFWLRQOHVV DUH FDOOHG YHVWLJLDO
organs. Human body has many vestigial organs such as vermiform
appendix, nictitating membrane of eye, muscles of external ear,
canine teeth, tail vertebra, etc. Vermiform appendix is remaining
as undeveloped part of large intestines in human being. But this

359 Times' Crucial Science Book - 9

is fully developed and functional in herbivorous animals such as
cow, rabbit, goat, etc. Similarly, canine teeth are more developed
and functional in carnivorous animals like tiger, lion, cat, dog, etc,
whereas these teeth are useless in humans.

Nictitating Membrane Body Hair Muscles of Pinna

Segmental Muscles of Abdomen

Vermiform Appendix Tail Bone

The animals which have vestigial organs and the animals which
are still using the same organs must have originated from the
common ancestors. Thus, presence of vestigial organs supports
the organic evolution.
Evidence from distribution of animals
There are various types of plants and animals on the earth.
Organisms found in one place cannot be found in other places.
Some organisms are commonly found in a particular place only.
Similar types of organisms are not found in all places of the earth
having similar climatic conditions. For example, elephants found
in Africa and Nepal are not found in Brazil even though climatic
conditions in all of those places is similar. Variation occurs in
organisms due to geological factors such as ocean, river, mountain,
forest, etc. If a certain region is separated from another region
for a long time, variation occurs in the organisms of these two
regions even though they have common ancestors. They change
themselves when they migrate and do not come to the previous
place for long time.

Thus, geographical distribution of organisms also causes the
variation.

Times' Crucial Science Book - 9 360

Evidence from connecting (bridge) animals
Some animals have both characteristics of the organisms of lower
group and higher group. Such organisms are called connecting or
bridge animals. For example, platypus is a bridge animal because
it has some characters as those of birds and some as those of
mammals. It lays eggs similar to birds. Its body is covered by hairs
and contains mammary gland similar to mammals.
Similarly, a fossil animal of
Jurassic period Archeopteryx is
also regarded as bridge animal
between a reptile and a bird. It
shows presence of teeth, long
tail with caudal vertebrae, each
finger ending into claw as reptiles
whereas feathery body, forelimb
modified to wings, presence of
four toes, etc as birds.
From above bridge animals, it can Platypus

be said that birds must have developed from reptiles and mammals
must have developed from birds. This is a process of evolution.
Thus, bridge animals also support for organic evolution.
Theory of evolution
Many scientists put forward their views regarding evolution and
development of different kinds of organisms. Among them French
biologist Jean Baptiste de Lamarck, American Scientists Charles
Darwin and Russel Wallace, Dutch scientist Hugo de Vries are
more prominent and notable. Their theories are as follows:
Lamarck’s theory
Jean Baptiste de Lamarck (1744-1829),
a French biologist, put forward theory of
evolution in 1908 A.D.
His theories can be explained in following
points.
(QYLURQPHQWDO LQIOXHQFH RQ RUJDQLVPV
Lamarck

2. Effect of use and disuse of organs
3. Inheritance of acquired characters

1. Environmental influence on organisms

According to Lamarck, environmental factors have direct influence
on the modifications of an organism. He believed that living things

361 Times' Crucial Science Book - 9

need to change themselves to adjust in the new environment. For
example, yaks have thick fur on their body to protect themselves
from cold, people of equatorial regions are more black to protect
themselves from direct sunlight, etc.
2. Effects of use and disuse of organs
According to Lamarck, when some organs are used continuously,
they become more developed and their size increases. But they
become less developed and their size decreases in case they are
not in use for long time. A constant disuse of organ causes the loss
of the an organ ultimately. For example, a wrestler has developed
and increased size of biceps and triceps muscle due to more use of
such muscles. Similarly, a snake living in the cave for long time
loses the power of vision and becomes blind.
3. Inheritance of acquired characters
The characters which are gained by the organisms due to
HQYLURQPHQWDO LQIOXHQFH DQG XVH DQG GLVXVH RI RUJDQV DUH FDOOHG
acquired characters. According to Lamarck, acquired characters
gained by an organism get inherited to the next generation. The
continuous inheritance of acquired characters leads to origin of
new species.
Lamarck’s theory can be explained with the help of following
example. Modern long-necked giraffes are considered to be
developed from short-necked giraffes. The short- necked giraffes
used to graze on grasses available on the ground. Their size was
similar to those of deer. When the number of animals increased,
there became the scarcity of food. Then, they started to depend
upon the leaves of the tall plants. They stretched their neck and
legs constantly for getting leaves of taller plants. The small gain
in the length of leg and neck inherited generation to generation.
Thus, long necked giraffes with long legs were ultimately developed
from short necked giraffes.

Ancient Middle-sized Modern
Giraffe Giraffe Giraffe

Times' Crucial Science Book - 9 362

Criticism of Lamarck’s theory

Main criticisms of Lamarck’s theories are as follows:
a) The change in the structure of a body by use and disuse of
RUJDQV KDV QRW EHHQ SURYHG H[SHULPHQWDOO\
b) It is not absolutely correct that new organs can be formed

according to the will of organisms.
c) All the acquired characters DUH QRW LQKHULWHG LQWR WKH QH[W

generations.

Weismann cut the tails of white mice continuously for 21
generations, but their offspring continued to have tails. Thus,
inheritance of acquired characters was proved untrue.

Darwin’s theory of evolution

Charles Darwin (1809-1882 AD), a famous Charles Darwin
English naturalist put forward his theory in
a book named Origin of Species which was
published in 1859 AD. His theory is known
as Darwinism or Theory of Natural Selection.
Darwin visited many places of the world
through voyage on a ship named Beagle
and studied the nature of organisms. Then
he proposed the theory of natural selection
which can be summarized in following points.

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LL 6WUXJJOH IRU H[LVWHQFH

iii. Variation and heredity

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Y 2ULJLQ RI QHZ VSHFLHV

i. Over reproduction

Each organism has the tendency of reproducing a large number of
offspring. But their number remains fairly constant. For example,
elephant is a slow breeder. It matures in 30 years and survives for
100 years. Each female produces six offsprings in its lifetime. It has
been estimated that a single pair produces 29 million descendants
in 800 years. But, it is found that the number of elephants remains
fairly constant.

363 Times' Crucial Science Book - 9

ii. Struggle for existence
All the offspring do not survive and reproduce. They have to
struggle for food, shelter, water, mating, etc. It is called struggle for
existence. The struggle may be intraspecific (among the members
RI VDPH VSHFLHV or may be interspecific (among the members of
GLIIHUHQW VSHFLHV or environmental ZLWK WKH HQYLURQPHQWDO IDFWRUV
VXFK DV FROG ZLQG HWF .
iii. Variation and heredity
Organisms of the same or different species do not resemble totally
with each other. They are different from each other in size, shape,
colour, behavior, etc. It is called variation. Because of the variation
in structure and functions, some are more capable and fitter than
others. According to Darwin, these variations are preserved and
inherited to the offspring.
iv. Survival of the fittest or natural selection
In the course of struggle for the existence, the organisms which
are the best fitted to the environment can survive and increase
their numbers. Those organisms which have favourable variations
are best fitted to the environment. The organisms which do not
have favorable variations cannot survive and vanish ultimately.
Darwin used the term natural selection for the survival of the
fittest. It means survival of an organism depends upon the
nature. The nature sorts out unfit organisms and favours more
progressive organisms.
v. Origin of species
According to Darwin, organisms should have favorable variations
to survive in the nature. These favorable variations are preserved
and inherited to the offspring from generation to generation.
The process of development of favourable variations continues
from generation to generation. Thus, the offspring become quite
different from the ancestors after many generations. Thus, origin
of new species occurs.

Criticism of Darwinism
Some of the main criticisms of Darwinism are as follows:
a) Natural selection is not the sole cause for the evolution of new

speries. The origin of new species occurs by mutation also.

Times' Crucial Science Book - 9 364

b) It is not always sure that the favourable variations are
inherited.

c) Darwin did not explain about the process of development of
variations in organisms.

d) Darwin could not explain the presence of useless parts if only
the favourable variations are inherited.

Hugo de Vries’ theory of mutation
A Dutch biologist Hugo de vries propounded a theory of mutation in
1901 AD. According to him, the changes in the shape, size, functions,
etc of organisms do not occur gradually but spontaneously. The
sudden and drastic changes that occur in organisms is called
mutation. Black patch on body, six fingered limbs, etc are some
examples of mutation. According to him, evolution of new species
occurs by mutation.

Learn and Write
1. Platypus is considered as a bridge animal. Why?

Platypus has some characters as those of birds and some
characters as those of mammals. Like birds it lays eggs. Its
body is covered by hairs and contains mammary gland similar
to mammals. Thus, it is a bridge animal.
2. Wrestlers have developed and increased size of biceps and
triceps muscles. Why?
Wrestlers use biceps and triceps muscles more. They perform
exercises to build up their muscles. Therefore, they become
more developed and increased.
3. Fore limbs of humans, wings of birds, flippers of whale, etc are
homologous organs. Why?
Forelimbs of humans, wings of birds and flippers of whale
contain similar type and equal number of bones, blood vessels
and muscles arranged in same pattern. But, these organs are
not used for same functions and their morphological pattern is
not identical. Therefore, they are homologous organs.

365 Times' Crucial Science Book - 9

Glossary

Physiology : a branch of biology which studies functions of various
organs in a body
Originate : get started
Micro molecules : smaller molecules like carbon, hydrogen, etc.
Macromolecules : larger molecules like protein, glucose, etc.
Convincing : capable of causing someone to believe
Strata : layers
Successive : next or following others
Patagium : a membrane or fold of skin between the forelimbs and
hind limbs on each side of a bat
Descendant : an animal or plant that is produced from a particular
ancestor

Main points to remember

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VHUYHG LQ WKH URFNV

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LQ PRUSKRORJ\ DQG IXQFWLRQV DUH KRPRORJRXV RUJDQV

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JURZ LQVLGH IHPDOHV· XWHUXV RU LQVLGH HJJV DUH FDOOHG HPEU\RV

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RWKHU RUJDQLVPV DUH FDOOHG YHVWLJLDO RUJDQV

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,W LV FDOOHG YDULDWLRQ

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XQIDYRXUDEOH YDULDWLRQ E\ WKH QDWXUH

7KH VXGGHQ DQG GUDVWLF FKDQJH WKDW RFFXU LQ RUJDQLVPV LV FDOOHG PXWDWLRQ.

Times' Crucial Science Book - 9 366

Exercise

1. Answer these questions in very short.
a. What is organic evolution?
b. What are the theories regarding the origin of organisms
on the earth?
Explain in brief.
c. What are the evidences of organic evolution?
d. What is fossil? How does it support organic evolution?
e. What are homologous organs? How do they support
organic evolution?
f. Differentiate between homologous organs and analogous
organs.
g. How do embryos of vertebrates support for organic evolution?
h. What are vestigial organs? How do they support for
organic evolution?
i. What are bridge animals? How do they support for organic
evolution?
j. What are the main assumptions of Lamarckism? Explain
them.
k. What are the weaknesses of Lamarckism?
l. What are the main assumptions of Darwinism? Explain
them.
m. What is struggle for existence?
n. Mention the weaknesses points of Darwinism.
o. What is natural selection? How does it lead to organic
evolution?
p. What is mutation? How does it lead to origin of new species?

2. Give reasons:
a) Vermiform appendix is a vestigial organ in human beings.
b) Wings of insects, wings of birds and patagia of bats are
analogous organs.
c) Archeopteryx is a bridge animal.

Project Work

Compare the similarities and differences between Lamarckism and
Darwinism. Why do their views need modification? Write your view.

367 Times' Crucial Science Book - 9

21Chapter 1DWXUH

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(QYLURQPHQW
Arthur George Tansley

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Objectives

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• H[SODLQ WKH GHSHQGHQFH RI KXPDQV XSRQ RWKHU DQLPDOV DQG SODQWV IRU EDVLF QHHGV

IRRG VKHOWHU DQG FORWKHV

Mind Openers

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Introduction

There are different kinds of living and non-living things in the
environment. Soil, water, rock, air, light, etc are non-living things
whereas bacteria, virus and different types of plants and animals
are living things. All the non-living things of the environment
constitute the physical component and all the living things of
the environment constitute the biological component. Biological
components depend upon physical components for water, sunlight,
carbon dioxide, oxygen and other minerals. Similarly, physical
components also depend upon biological components. Thus,
physical and biological components of the environment are closely
related.

A group of organisms which depend upon each other and live
together in a particular place is also known as biological community.
In a biological community, each organism shares the same habitat.
All members of the community interact with each other and are
closely interdependent. Similarly, there is a close relationship
and interdependence between biological community and physical
environment. Such relationship is called ecosystem.

Times' Crucial Science Book - 9 368

Thus, an ecosystem is defined as integration of biological community
DQG WKHLU SK\VLFDO HQYLURQPHQW LQ D SDUWLFXODU DUHDV In other
words, it can be defined as an ecological unit which consists of both
biotic (living) and abiotic (non-living) factors of the environment.

Ecology is the branch of science which deals with the study of
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SK\VLFDO HQYLURQPHQW LQ ZKLFK WKH\ OLYH.

Components of ecosystem

The components of ecosystem are mainly divided into two factors.
They are i. abiotic factors ii. biotic factors

A. Abiotic components or factors

Non-living things like air, water, sunlight, soil, minerals,
temperature, etc make abiotic components of the ecosystem.

Air

7KH OD\HU RI WKH DLU ZKLFK VXUURXQGV WKH HDUWK LV FDOOHG DWPRVSKHUH
The atmosphere consists of gases like nitrogen (78%), oxygen
(21%), carbon dioxide (0.03%) and other gases (0.97%) It also
contains water vapour and droplets of water.

All living things use oxygen from atmosphere for respiration. By
respiration process, energy is provided for the organisms.

Plants use carbon dioxide gas supplied by the atmosphere for the
photosynthesis process. The foods prepared during photosynthesis
are used by both plants and animals.

Nitrogen is also used by plants for the synthesis of various
chemicals in plants.

Solar energy

7KH HQHUJ\ SURYLGHG E\ WKH VXQ LQ WKH IRUP RI KHDW DQG OLJKW LV FDOOHG
solar energy. The solar energy plays a vital role in the life of plants
and animals. Plants prepare their foods through photosynthesis
which needs solar light. The sun provides heat to the earth and
maintains suitable temperature. In such suitable temperature,
life is possible on the earth.

Soil

Soil is one of the important abiotic factors of ecosystem. It forms the
top most part of the earth’s crust. All terrestrial animals use soil as
shelter. Soil contains water, minerals, air, etc which make it suitable
for the survival of living things. Terrestrial plants grow on the soil.

369 Times' Crucial Science Book - 9

It provides them the substratum. Plants absorb water and minerals
contained in the soil for the preparation of food. Even the free floating
aquatic plants get the essential nutrients from the soil.
The quality of soil differs from place to place. The quality of the
soil is determined by the amount of water, air, different minerals,
humus and other organic substances. The distribution of the plants
and animals depends upon the quality of soil.
Water
Water is the most abundant natural resource. It covers about 70%
of the earth surface. Water dissolves various types of minerals and
organic substances.

Therefore, it is also called a universal solvent. It is essential for
maintaining the various activities taking place in organisms.
Plants take nutrients from the soil in the form of solution in water.
Plants use water for pollination also. Water provides the habitat
for aquatic plants.

Animals use water for dissolving the food materials. The dissolved
foods are distributed to various parts inside the body through
blood vascular system. Water provides shelter to the aquatic
animals. Moreover, water maintains optimum temperature on the
earth. The distribution and growth of organisms depend upon the
availability of water in a particular geographical region.

Activity 21 .1

a) Visit a nearby grassland.

E 2EVHUYH LW DQG PHQWLRQ LWV YDULRXV FRPSRQHQWV

c) Classify them as abiotic and biotic components.

B. Biotic components or factors
All living things of an ecosystem constitute biotic components or
factors of an ecosystem. On the basis of nutritional relationship,
biotic components are broadly categorized into three classes. They
are:

i. Producers ii. Consumers iii. Decomposers
a. Producers
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ZDWHU VXQOLJKW DQG FDUERQ GLR[LGH DUH FDOOHG SURGXFHUV They are

Times' Crucial Science Book - 9 370

also called autotrophs. The food making process in plants is called
photosynthesis. The plants convert solar energy into chemical
energy during this process. The chemical energy is stored in the
food. The foods prepared by the green plants are not the foods
for them only but also for the animals. It is because all animals
directly or indirectly depend upon the green plants for their foods.
Herbivorous and omnivorous animals directly depend upon plants
for food whereas carnivorous animals depend upon herbivores or
omnivores for foods. Thus, green plants are the producers of foods
for all animals.

b. Consumers

7KH RUJDQLVPV ZKLFK GHSHQG XSRQ Sunlight
other organisms for their foods are Energy
Oxygen

called consumers. They are also called
heterotrophs. Consumers are also divided
into three categories:
Carbon
i. Primary consumers Dioxide

The organisms which directly feed on
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They are also called first class consumers. Soil Water and
Hebivores belong to this type of consumers. Process of Photosynthesis Nutrients
Protozoans, crustaceans, molluscans,
zooplankton, etc are primary consumers of aquatic ecosystem
whereas elephant, deer, sheep, goat, rabbit, grasshopper, etc are
the examples of primary consumers of terrestrial ecosystem.

ii. Secondary consumers

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are called secondary consumers. They are carnivores. Dog, cat, fox,
frog, snake, wild cat, etc are examples of secondary consumers.

iii. Tertiary consumers

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are called tertiary consumers. Physically these animals are very
strong. Tiger, lion, vulture, owl, whale, crocodile, etc are examples
of tertiary consumers.

c. Decomposers

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and decayed bodies of organisms. They convert complex organic
matters into simple matters which can be used by green plants

371 Times' Crucial Science Book - 9

easily. During this process, they absorb some of the products as
food. Bacteria, fungi and other some microbes are examples of
decomposers. They play important role for balancing the various
components of ecosystem.
The interrelationship among producers, consumers and
decomposers
There is a close relationship between biological community and
physical factors of an environment. Various members of biological
community like plants, animals, micro-organisms, etc are also
interrelated.
Green plants absorb water and minerals from soil and take
carbon dioxide from atmosphere. By using these chemicals, plants
prepare their foods in the presence of sunlight by the process of
photosynthesis. All animals depend upon the green plants directly
or indirectly for foods. Green plants are eaten by herbivorous
animals which in turn are eaten by carnivorous animals.
Both herbivorous and carnivorous animals are eaten by omnivorous
animals. When plants and animals die, their dead bodies are
decomposed by microbes like bacteria and fungi into simpler
inorganic compounds. These compounds are mixed to the soil to
make it fertile. These inorganic compounds are absorbed by the
green plants to prepare foods. This type of natural phenomenon
occurs continuously.
Food circulation process in an ecosystem

Energy is needed for all living things for survival and carrying out
various life processes. The energy is obtained by all living things
through nutrition. Energy comes in an ecosystem from solar
energy. Solar energy is used by green plants for the production
of foods during photosynthesis. Non-green plants and animals
cannot prepare their foods themselves. They depend upon green
plants and other organisms for their foods. Foods prepared by
green plants circulate to the animals through primary consumers,
secondary consumers, tertiary consumers and so on. Decomposers
get their food by decomposing dead bodies of plants and animals.
Thus, food transfers from plants to the animals. In the process
of transferring food in the ecosystem, a relationship between
producers and consumers exists in the form of food chain and food
web.

Times' Crucial Science Book - 9 372

Trophic level

During the transfer of foods from plants to decomposers through
different animals, an organism occupies a certain level or position,
such level or position is called trophic level.

Green plants produce the foods for Ecological pyramid
whole ecosystem. Thus, they belong to
the first trophic level. Similarly, the
primary consumers feed on plants.
Therefore, they belong to the second
trophic level. The secondary consumers
feed on primary consumers. Thus,
they belong to the third trophic level.
The tertiary consumers feed on the
secondary consumers and belong to the
fourth trophic level.

Food chain

In an ecosystem,
foods are prepared
by the green plants
during photosynthesis.
Consumers get their
foods from plants.
Foods prepared by the
plants are transferred
to the consumers of
different trophic levels
by the process of eating
and being eaten and finally transferred to the decomposers. Thus,
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GHFRPSRVHUV WKURXJK D VHULHV RI FRQVXPHUV FDOOHG IRRG FKDLQ Thus,
food chain can be defined as the transfer of foods from organism
of one trophic level to the organisms of another trophic level by
the repeated process of eating and being eaten. Plants form the
base of food chain because the plants are the source of foods in
an ecosystem, whereas the organisms of higher trophic levels
lie at the higher position. An example of food chain of grassland
ecosystem is as follows:

373 Times' Crucial Science Book - 9

In this food chain, foods are prepared by grass (producers). The
grass is eaten by grasshopper (primary consumer). The grasshopper
is eaten by frog (secondary consumer). The frog is eaten by snake
(tertiary consumer). In this food chain, four organisms are involved.
Therefore, it is called 4-step food chain.
Food web
A food chain cannot function in an isolation. Various food chains
operate with interconnection and linkage in an ecosystem forming
a network. Such network is called food web. Thus, food web can
be defined as a network of food chains in an ecosystem which are
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Food web
In a food web of a grassland ecosystem, many food chains are
interlinked by various organisms. In the above food web, rabbit
may be eaten by fox or tiger. Similarly, grasshopper may be eaten
by hawk or sparrow or frog.
The food web provides alternative pathways of food availability.
Interrelationship between plants and animals
Animals and plants are interconnected with each other for
nutrition. Plants manufacture foods using inorganic substances by
photosynthesis. Animals get their foods from plants. When animals
die they get decomposed and provide nutrients to the plants. On
the basis of nutrition, organisms are divided into two groups:

i. autotrophs ii. heterotrophs
a. Autotrophs
Autotrophs are the organisms that can prepare their foods
themselves. All green plants are autotrophs. They are also called

Times' Crucial Science Book - 9 374

producers of an ecosystem. They use carbon dioxide, water and
minerals as raw materials for the preparation of food. Green
plants use solar energy to prepare the organic foods.

b. Heterotrophs

7KH RUJDQLVPV ZKLFK FDQQRW SUHSDUH WKHLU IRRGV WKHPVHOYHV DUH
FDOOHG KHWHURWURSKV They get their foods from plants and other
animals. All animals and non-green plants fall in this category.
Heterotrophic organisms are also divided into three groups:

a. Parasite

The organisms which get
their foods directly from
other organisms in the
form of liquid are called
SDUDVLWHV The organisms
which provide foods directly
to the parasites are called
hosts. Mosquito, liverfluke,
lice, round-worm, amoeba, Roundworm

plasmodium, etc are some parasitic animals. Similarly, non-green
plants like rust, smut, etc are some parasitic plants.

Fact Reason

Why is roundworm called parasite?
Roundworm is called parasite because it sucks the blood of other
organisms and completely depends on other organisms for food.

b. Saprophytes
The organisms which get their foods from dead and decayed organic
PDWWHUV DUH FDOOHG VDSURSK\WHV Fungi and bacteria are examples
of saprophytes. They are also called decomposers. They decompose
complex organic molecules into smaller molecules.
c. Holozoic organisms
The organisms which feed on solid organic substances obtained
IURP SODQWV RU DQLPDOV RU ERWK DUH FDOOHG KROR]RLF RUJDQLVPV Most
of the animals and human beings are holozoic organisms. Holozoic
nutrition includes four different life processes. They are ingestion,
digestion, absorption and excretion. Human beings, tiger, cow,
snake, deer, fish, frog, etc are holozoic organisms.

375 Times' Crucial Science Book - 9

Ecosystem services
The benefit that human beings get from the ecosystem is called
HFRV\VWHP VHUYLFH It includes the following services:
1. Provisioning services
7KH SURGXFWV WKDW DUH REWDLQHG IURP WKH HQYLURQPHQW DUH FDOOHG
SURYLVLRQLQJ VHUYLFHV The provisioning services include food and
fibres, fuel, ornamental resources, etc.
a. Food and fibres: Human beings obtain a number of products

from the ecosystem. They obtain main food, fruits, vegetables,
etc from the ecosystem. They also obtain the fibres such as
jute, silk, cotton, etc from the ecosystem.
b. Fuel: Human beings use wood, firewood, dry dung, straw and
other dry things. These things are obtained from the ecosystem.
c. Ornamental resources: People from different societies use skin,
shell, bones, etc of animals as ornaments. These are obtained
from the ecosystem. Similarly, the ornamental metals such as
gold, silver, etc are also obtained from the ecosystem. Flowers
are also used for ornamental purposes.
2. Regulating services
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LQ QDWXUDO HFRV\VWHP DUH FDOOHG UHJXODWLQJ VHUYLFHV It includes the
following services:
a. Water purification: The ecosystem helps in the purification of
water directly or indirectly. It helps to decompose the organic
impurities present in water and purify it. The evaporation of
even polluted and dirty water produces pure water vapour
which falls down as rain which is pure water.
b. Climate regulation: Ecosystem also helps in climate regulation
in local level as well as in the global context. The green forest
helps in the regular rainfall and maintaining temperature at
the local level. In the global context, it can consume carbon
dioxide released due to human causes and lessens the risk of
climate change.
3. Cultural services
Ecosystem affects the natural beauty, comfortable environment,
norms and values of human beings, etc. The change in ecosystem
also affects religious beliefs, social traditions and culture, etc. A
balanced and beautiful ecosystem attracts tourists whereby people

Times' Crucial Science Book - 9 376

of different places get opportunity to understand cultures and
traditions of one another.

4. Supporting services

Supporting services in an ecosystem include the food production by
the producers, decomposition of dead bodies of plants and animals
and soil formation, recycle of nutrients, etc. It also includes food
regulation service.

Learn and Write

1. Plants are called producers of an ecosystem. Why?
Plants prepare their foods themselves from carbon dioxide,
water and minerals in the presence of sunlight during
photosynthesis. The foods prepared by the plants are not
for the plants only but for the animals also. All the animals
directly or indirectly depend upon the foods prepared by the
plants. Therefore, plants are called producers of an ecosystem.

2. A mushroom is called saprophyte. Why?
A mushroom cannot prepare its food itself. It gets its food from
dead and decaying organic matter. Therefore, mushroom is
called saprophyte.

3. Many food chains get interlinked in an ecosystem. Justify.
A food chain shows the nutritional relation of organisms of
an ecosystem in a linear form. But one organism does not
depend upon only one food chain. It depends upon many food
chains and becomes member of many of them. Thus, many
food chains are interlinked in an ecosystem.

Glossary

Interdependent : dependent upon each other
Substratum : an underlying layer of rock or soil beneath the surface of
the ground
Humus : organic component of soil which is formed from decaying
organic material
Vascular system : relating to blood vessels or conduction of materials in plants
Microbes : microscopic organisms
Rust : a plant disease caused by pathogenic fungi

Smut : a plant disease caused by fungi

Main points to remember

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LQ D SDUWLFXODU SODFH LV FDOOHG ELRORJLFDO FRPPXQLW\

(FRV\VWHP LV GHÀQHG DV WKH LQWHJUDWLRQ RI ELRORJLFDO FRPPXQLW\ DQG
WKHLU SK\VLFDO HQYLURQPHQW

377 Times' Crucial Science Book - 9

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$OO SODQWV DQLPDOV DQG PLFUREHV PDNH ELRWLF IDFWRUV RI DQ HFRV\VWHP
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SURGXFHUV
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FRQVXPHUV
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Exercise

1. Answer these questions
a. What is a biological community ?
b. What is an ecosystem? What are its main components?
c. What are abiotic factors of an ecosystem? Explain them briefly.
d. What are biotic factors of an ecosystem? Explain them briefly.
e. What are producers? Why are green plants called producers
of an ecosystem?
f. How are producers, consumers and decomposers related?
g. What is food chain? Draw a food chain of a grassland ecosystem.
h. What is food web? Draw a food web of a grassland ecosystem.
i. What is autotroph?
2. Define following terms with examples.
i) Primary consumers ii) Secondary consumers
iii) Decomposers iv) Tertiary consumers

Project Work

Observe the grassland or pond ecosystem whatever is easier or accessible for
you. Observe the different components, draw their diagram and explain in brief.

Times' Crucial Science Book - 9 378

Chapter 1DWXUDO

22 +D]DUGV Charles Francis Richter

He is famous for Richter magnitude
scale. The magnitude of earthquake is
measured in the unit of Richter Scale

ƐƟŵĂƚĞĚ WĞƌŝŽĚƐ ͗ ϲ

Objectives

ƚ ƚŚĞ ĞŶĚ ŽĨ ƚŚĞ ůĞƐƐŽŶ͕ ƐƚƵĚĞŶƚƐ ǁŝůů ďĞ ĂďůĞ ƚŽ͗

• GHÀQH WKH PHDQLQJ RI QDWXUDO GLVDVWHUV
• explain the causes, effects and preventive measures of natural disasters (earthquake,

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Mind Openers

• Do you know what natural disasters mean?
• What natural disasters have you observed or experienced? How was it? Discuss.

Natural hazards
The natural activities which cause the damage of natural
resources, man made constructions and lives of animals are
called natural disasters. (DUWKTXDNH ÁRRG ÀUH ODQGVOLGH
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the hazard
2. Providing physical as well as economic support to the

victims of hazard
3. Making arrangements for the fast rescue and rehabilitation

of the victims
4. Mobilizing the organizations related to rescue of victims

for helping the victims

379 Times' Crucial Science Book - 9

Management of man-made hazards
1. Fixing a particular age and academic qualification for

getting driving licence
2. The use of nuclear reactors, weapons, fatal chemicals, etc

should be minimized or stopped
3. Creating public awareness and observing the principles of

personal hygiene
4. Conserving forest and conducting afforestation programmes

in bare hills and naked areas
5. Assuring proper earthing while constructing residential

house or commercial building to prevent thunderstorm
6. Constructing embankments and check walls in fast flowing

rivers and streams
7. Maintaining the fertility of soil through the use of compost

fertilizers and green manures
Disaster management cycle
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Times' Crucial Science Book - 9 380

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381 Times' Crucial Science Book - 9

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1. It causes glacial flood.
2. It destroys human settlement and results in the loss of life

and property.
3. It can destroy the infrastructures of development such as

road, bridge,hydroelectricity project, communication system,
etc.
4. It can cause deforestation.
Preventive measures of snowslides
1. It is necessary to identify snowslide prone areas and to take
steps in advance.
2. Residential areas should be away from snowslide prone
areas.
3. The human activities such as skies, use of explosives, etc
minimized.
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Times' Crucial Science Book - 9 382

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1. Erosion of rocks damming the glacial lakes
2. Avalanche of rocks or heavy snowmass in a glacial lake
3. Earthquake that damages the walls or support of the

glacial lake
4. Pressure due to the large mass of snowy water contained

in a glacial lake
5. Volcanic eruption under the ice. However, this cause has

not affected Nepal ever since.

383 Times' Crucial Science Book - 9

(IIHFWV RI JODFLDO ODNH RXWEXUVW ÁRRG
1. It causes flood in the draining rivers.
2. It can cause heavy loss of life and property.
3. It destroys human settlement and cultivable land.
4. It can destroy wildlife.
5. It can destroy the infrastructures of development
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1. A regular monitoring is necessary to identify dangerous

glacial lakes.
2. Gradual outlet of water of the lake should be managed for

risky lakes.
3. Human settlement and grazing of cattle should be avoided

near bigger glacial lakes.
Cyclone
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Times' Crucial Science Book - 9 384

Causes of cyclone
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Effects of cyclone
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D Sea-surge or storm surge causes the loss of life and property

of coastal region.

385 Times' Crucial Science Book - 9

E 7KH F\FORQH DIIHFWHG UHJLRQV UHFHLYH UDLQIDOO WKDW FDXVHV WKH
disasters like flood, landslide, soil erosion, etc.

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in the ocean during cyclone is dangerous.

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causes the destruction of crops and damage of fertile land.

Safety measures against cyclone
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measures against cyclones.
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should be proided to the people of coastal regions.
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given by the government in different media.
Learn and Write

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Times' Crucial Science Book - 9 386

/DQG VOLGH DOVR FDXVHV IORRG +RZ"
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Main points to remember

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which occur naturally are called natural disasters.

2. Flood is the inundation of normally dry land due to
RYHUÁRZLQJ RI ZDWHU VRXUFHV

3. Landslide is the sliding of land, soil or rocks, etc from a
sloppy land.

4. Landslide is caused by deforestation, volcanic eruption,
HDUWKTXDNH DQG ÁRRG

5. Shaking or vibration of the earth’s surface is called
earthquake.

6. Earthquake is caused by tectonic activities, volcanic
activities and local activities.

7. Earthquake is of two types: horizontal earthquake and
vertical earthquake. Horizontal earthquakes is more
devastating than vertical earthquake.

8. Volcano is an opening in the earth’s surface through which
hot lava, and gases come out to the surface of the earth.

9. Cyclone is a special and powerful storm which originates
over big seas or oceans near the equator and spreads
forcefully to a longer distance in a rotating motion

387 Times' Crucial Science Book - 9

Exercise

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Chapter

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Times' Crucial Science Book - 9 390

1. Combustion of fuels in factories, industries, vehicles and
other machines produces carbon dioxide and water vapour.

2. The incomplete combustion of fuels releases methane and
other hydrocarbons into the atmosphere.

3. Forest fire and burning of solid wastes releases a large
amount of carbon dioxide into the atmosphere.

4. The decaying of solid wastes releases methane into the
atmosphere.

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releases a lot of harmful gases into the atmosphere.

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into the atmosphere.

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1. The greenhouse effect causes global warming.

391 Times' Crucial Science Book - 9

2. It causes climate change.
3. It badly affects the natural water cycle.
4. It can favour the over population of harmful insects. such

insects can destroy the crops or spread diseases.
5. It can disturb the natural ecosystems.
6. The increase in earth temperature can lead to the spread of

fatal diseases.
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Times' Crucial Science Book - 9 392

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1. Unusual melting of snow from the high Himalayas can

result in the drying of rivers in the future. As the snow of
the high Himalayas is the origin of many rivers of Nepal,
climate change can badly affect our country.

393 Times' Crucial Science Book - 9

2. The problems of heavy rainfall in some places and drought
in other places are being observed. These problems are due
to the climate change.

3. There is gradual decrease in the crop production.
4. The level of seawater is increasing rapidly. It can result in

sinking of islands and flooding in the coastal countries.
5. There is gradual degradation in the biodiversity due to

climate change.
6. Unusual rainfall has caused scarce rainfall in rainy season

and unwanted rainfall in other seasons.
7. Since the climate change can dry up the large sources of

water, it can hamper the hydro-electricity production. Thus,
we may face energy crisis due to climate change.
8. Severe weather events and droughts can render landscapes
more susceptible to wildfires.

Measures of climate change management

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1. The afforestation programme should be made widespread

as a global campaign.
2. The release of greenhouse gases in to the atmosphere should

be minimized as far a possible. It can be achieved through
the use of hydro-electricity, solar energy, etc.
3. The use of fossil fuels should be replaced by alternative
sources of energy.
4. Public awareness programmes should be conducted.
5. The running of old vehicles should be discouraged so that the
release of greenhouse gases in the atmosphere is minimized.
6. Emphasis should be given in sustainable development.
7. The sources of water resources should be conserved and
managed.
8. The unplanned urbanization should be controlled.
9. The roads and bridges should be constructed causing
minimum damage to the environment.
10. Crops of improved and disease resistant varieties should be
developed to cope with the changed climate.

Times' Crucial Science Book - 9 394

Glossary

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Main points to remember

1. A framework of house with glass or plastic roof and the walls
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2. The gases which cause greenhouse effect are called greenhouse
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warming.

5. The change in climatic conditions for a long period of time
due to human activities or natural instability is called
climate change.

6. If the number of trees is decreased due to deforestation, much
amount of carbon dioxide gets collected in the atmosphere
and it causes global warming and climate change

Exercise

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Times' Crucial Science Book - 9 396