Oasis Science and Technology 9

The lower strata of rocks contain fossils of simple
and primitive organisms whereas the upper strata
contain fossils of advanced organisms. A regular
gradation from simple to complex is noted in
the fossils of animals found in those rocks. This
geological succession completely agrees with the
concept of evolution. It is remarkable that fossils of
any one stratum bear a close resemblance to those of
the previous or next stratum. This makes clear that Fig. 20.1 Fossil of Archaeopteryx
there is a relationship between the organisms which
appeared through the successive periods of the geological history. Thus, fossils provide
the evidence that present animals and plants have evolved from the previously existing
ones through the process of continuous evolution.

2. Evidences from comparative morphology and anatomy

Similarities in morphological and anatomical characters among certain groups of plants
and animals are very characteristic from the standpoint of evolution.

Organs similar in structure and origin but different in functions are called homologous
organs. Fore limbs of a man, fore limbs of a horse, patagium of a bat, wings of a bird,
flipper of a whale, etc. are some examples of homologous organs. If their comparative
study is done, we can find similar basic structure with some modifications according to
the adaptation. They contain almost similar type and number of bones, blood vessels,
nerves and muscles arranged in same pattern. However they perform various functions
according to their habit and habitat. It shows that all these organisms evolved from a
common ancestor.

Bat
Bird

Human Cat Bat Porpoise Horse Insect

Fig. 20.2 Homology in the fore limbs Fig. 20.3 Analogy in the wings

Organs having a similar function but different in structure and origin are called
analogous organs, e.g. wings of insects, birds, patagium of a bat, etc. The analogous
organs provide evidence for evolution by telling us that though they are not derived
from common ancestors, they can still evolve to perform similar functions to survive and
flourish under hostile environmental conditions. Actually, the analogous organs provide
the mechanism for evolution.

porpoise /ˈpɜːpəs/ - a sea animal that looks like a large fish with a pointed mouth

BIOLOGY Oasis School Science - 9 343

3. Embryological evidences

Embryology is the study of the nature and

development of embryos. It shows a great

resemblance among certain groups of plants ii ii i i
and animals. For example, the embryos of Fish Salamander Turtle Chicken Rabbit Human

dicots look alike. Similar is the case with other

groups of plants and animals.

The embryos of different vertebrates like fish, ii ii ii ii ii ii
salamander, turtle, chick, rabbit and human
resemble a lot in their early stage of development iii iii iii iii iii iii
and it is very difficult to distinguish one from
another. Later they differ from each other after Fig.20.4 Embryos and young
their growth and development and finally stages of some vertebrates
change into respective animals according to
their parental characters. It indicates that all
these animals have evolved from a common
ancestor.

The biogenetic theory (recapitulation theory)
states that an animal during its development repeats certain ancestral stages of its
evolution. For example, the immature stage in the life cycle of a frog is a fish-like tadpole
having gills and a tail. This shows that frog has evolved from a fish-like ancestor.

Similarly, temporary non-functional teeth in birds' embryos indicate that birds have
evolved from toothed reptiles. In this way, evidences from the study of embryos support
the theory of organic evolution.

4. Evidences from the study of vestigial organs

Vestigial organs are those organs in an organism which are functionless and rudimentary
now but used to function in its ancestors, e.g. coccyx, vermiform appendix, etc.

These organs are actually functionless remnant of the once functioning organs. Tail bone
or coccyx, vermiform appendix, articular muscles of pinna, nictitating membrane, body
hair, segmental muscles of abdomen, etc. are some vestigial organs of human beings.

Ear muscles

Nictitating Body hair
membrane
Segmental Vermiform Coccyx
muscles appendix

344 Oasis School Science - 9 Fig.20.5 Vestigial organs of human body
BIOLOGY

Though the vermiform appendix, ear muscles and tail are functionless in humans they
are quite functional in herbivorous animals like cow, buffalo, etc. In cattle, the vermiform
appendix helps to digest cellulose. The ear muscles are used by these animals to rotate
(move) their ears in the direction of the source of sound. Similarly, nictitating membrane
in the eye is functional in birds, frogs, etc. which provides protection to their eyes but it
is functionless in humans. It proves the animals having vestigial organs and the animals
that still fully use these organs may have evolved from common ancestors. Therefore,
the presence of vestigial organs is a good evidence to support the theory of organic
evolution.

5. Evidences from bridge organisms or connecting links

Organisms having characteristics of two different groups are called bridge organisms
or connecting links. Duck-billed platypus, Archaeopteryx, lung fishes, etc. are some
examples bridge animals. The structure and behaviour of those organisms partly
resemble the lower groups and partly higher groups.

Archaeopteryx Duck-billed platypus

Fig.20.6 Some bridge animals or connecting links

Archaeopteryx, a fossil bird of Jurassic period, serves as a connecting link between the
reptiles and birds. Like reptiles, it shows the presence of teeth in jaws, a long tail with
caudal vertebrae, each finger ending into claw and like birds it has feathers on body,
fore limbs modified into wings, presence of four toes. These characteristics show that
birds have evolved from reptilian ancestors. Similarly, duck-billed Platypus serves as a
connecting link between reptiles and mammals. It is oviparous and cold-blooded like
reptiles and it has mammary glands, hairs and other mammalian characteristics. Certain
fishes having lungs (lungfishes) also serve as the connecting links between fishes and
amphibians. Therefore, the evidences obtained form bridge animals support the theory
of organic evolution.

6. Evidences from distribution of organisms

There are different types of living organisms in different parts of the earth. Organisms
found in one part of the earth may or may not be found in the other parts. It has been
seen that many allied species of plants and animals remain confined to a particular area.
The explanation is that they sprang up from a common ancestor in that region and could
not migrate owing to some barriers like high mountains, seas, deserts, etc. They changed
themselves there according to the new environment. If one region is delinked form the
other for a long time variation also occurs in the organisms and finally new species of
organisms are evolved.

BIOLOGY Oasis School Science - 9 345

20.4 Theories of Evolution

Evidences in favour of evolution testify evolution is real. Several theories have been put
forward from time to time to explain the process of evolution of organisms on the earth.
Historically, three great evolutionary theories have been put forward by three great scientists
to explain the mechanism of evolution. Those theories are as follows:

1. Lamarck's theory of evolution or Lamarckism
2. Darwin's theory of evolution or Darwinism
3. Hugo De Vries theory of mutation

1. Lamark's theory of evolution

The first general theory of evolution was proposed by Jean

Baptiste de Lamarck (1744 – 1829 AD), a French anatomist

and taxonomist. He was the first author to give a general

theory of evolution. His theory was outlined in 1801, and

was published in 1809. He considered that there had been a

progressive development in form and structure. According

to Lamarck, the environment was important not as a direct

cause of evolution but merely as an occasion for evolutionary

changes affecting the shape and organization of animals.

When an animal lives in changed environment, it encounters

certain new needs, which stimulate the animal to satisfy Jean Baptiste de Lamarck

them. The important points of his theory are as follows: Fig. 20.7

i. Environmental effect on organisms

ii. The effect of use and disuse of organs

iii. Inheritance or transmission of acquired characters.

i. Environmental effect on organisms: Due to changed mode of life, certain physical
needs originate in the animal, which are responsible for modification of organs.
This can be illustrated by several examples. A land bird driven by necessity to seek
its food in water gradually assumed characters adapting it to swimming, wading
or to searching food in water.

ii. The effect of use and disuse of organs: Structural variations are due to the
functional needs. When a structure is used, its size increases and failure to use it
results in its disappearance. This is called the theory of use and disuse of organs.
Lamarck illustrated the disuse by the structure of a snake. He explained that in
crawling along the grass the legs of the snake would be stretched repeatedly when
passing through a narrow passage. The legs would interfere with crawling and
hinder the movement of the body. Thus, snakes lost their legs although they are
found in other reptiles.

iii. Inheritance of acquired characteristics: The advantages gained by every organism
due to the structural changes caused by use or disuse are transmitted to the
offspring. Thus, the progression or retrogression of a character is transmitted to
the offspring. This view was explained by the example of giraffe as follows:

346 Oasis School Science - 9 BIOLOGY

The horse like ancestor of the Giraffe came to live in a new and arid environment,
where the food available was only from the taller trees. The animal tried to reach up
to the leaves. Through a conscious effort to reach up to the leaves, neck and limbs
lengthened. The small gain in length made during the life time of an individual
was passed on to the progeny, who gained it more and more. Ultimately the
long-necked giraffe with long legs evolved.

Fig.20.8 Lamarck's idea of evolution of a long-necked giraffe

Objections to Lamarck's theory

There is no reliable evidence for Lamarck's theory and it has little support today. The
main objections to his theory are as follows:

i. The main objection is in the assumption of the inheritance of acquired characters.
The muscles of an athlete increase in strength and bulk with extensive use but
they are never transmitted from father to child.

Similarly, Lamarck's theory of inheritance of acquired characters was strongly
criticized by Weismann. He cut the tails of white mice continuously for 21
generations. However, their progeny did not show any cut tails. Thus, if his
theory was a fact, then tailless mice should have been born, which did not
happen.

ii. The second objection to this theory is the fact that the conscious effort as evident
in giraffe and other animals is hardly to be expected in the plants.

iii. The change in the structure of a body by use and disuse of organs is not manifest
practically.

2. Darwin's theory of evolution

Charles Darwin (1809-1882 AD), a famous English naturalist, put forward the next theory
to solve the problem of evolution. He published his theory in the book "The Origin of
Species by Means of Natural Selection". His theory is popularly known as "Theory of
Natural Selection" or "Darwinism".

Darwin went on a voyage of world exploration, in 1831, on a ship named H.M.S. Beagle
and studied the flora and fauna during his journey. He also studied the population
theory of Malthus and then proposed his theory of natural selection.

BIOLOGY Oasis School Science - 9 347

Darwin's theory can be summarized under the following points:
i. Balance of population growth
ii. Struggle for existence
iii. Variation and heredity
iv. Survival of the fittest or natural selection
v. Origin of new species

i. Balance of population growth

Living organisms have an enormous potential to produce a large number of
offspring but the size of population of any kind of organism remains more or
less constant and they are not found in a large number. For example, the fruit fly,
Drosophilla, completes its life cycle in 10 to 14 days and each female lays about 300
eggs. If all survive and breed there will be about 200000000 Drosophilla in 40 to 50
days during one summer.

Elephant is a slow breeder, Darwin assumed that the elephant matures in 30 years
and lives for 100 years; each female produces about 6 offspring. In 750 years, a
single pair would give rise to about 19 million offspring. Even though all species
produce a large number of offspring, population remains fairly constant due to the
struggle between members of the same species or different species for food, space
and mate.

ii. Struggle for existence

The population of most species remains constant because of the various checks.
According to Darwin, several factors are responsible for keeping animals and plants
more or less in limited numbers. The struggle for existence may be intraspecific,
i.e. among the member of same species and interspecific, i.e. among the members
of different species sharing a common environment. The organisms compete
with one another for food, space and mate. Similarly, the climate also plays an
important role in determining the average number of species due to extreme heat,
cold, heavy rains, or droughts and natural calamities. Thus, struggle for existence
removes many individuals.

iii. Variation and heredity

Since there is everlasting competition to survive, therefore,

there is variation of living beings. Some variations are

suited to the environmental conditions, while others are not.

According to Darwin, these variations are preserved and

transmitted to the offspring, although no cause for these

variations was assigned by him. Darwin knew nothing of

chromosomes and genes, yet he realized that much of the

variation in organisms is hereditary. Those variations which Charles Darwin

are unsuited to the particular condition are eliminated. (1809-1982)
Fig. 20.9

348 Oasis School Science - 9 BIOLOGY

IV. Survival of the fittest or natural selection

Darwin regarded that in the struggle for existence, the individuals which are
provided with favourable variation will lead a more successful life and would
survive and propagate their offspring and the others with unfavourable variations
perish. It is called survival of the fittest. The survivors gradually and steadily
change from one generation to another, and ultimately give rise to new forms.
These new forms are better adapted to their surroundings. Animals which fail
to develop suitable new variation will disappear and the organisms that develop
suitable variation are selected by nature. It is called survival of the fittest or natural
selection. So, the elimination of less progressive organism and selection of more
progressive organism by nature is called natural selection.

V. Origin of new species

Darwin was of the opinion that the adaptation of the survivors to the environment
may result in the formation of new structures, factors or behaviours. These useful
variations when transmitted to the offspring will tend to increase generation after
generation until a new species will develop. Thus, by modification in relation to
changes of environment, it is regarded that the species have reached their present
state of fitness.

Evidences in favour of Darwinism

i) In the past, there existed a large number of animals but due to the scarcity of food,
changed climate and struggle for their habitats only a few survived.

ii) Production of various domestic varieties by artificial selection is evident.

iii) Ancestors of horse were four-toed, from them modern horses have evolved by
reduction of three toes, fibula and ulna.

Critism of Darwinism

Although the theory of Darwin is universally regarded as the chief factor of evolution,
yet there are several drawbacks in or objections to his theory. Some of them are as follows:

i. According to Darwin's theory, only fluctuating variations are the sole cause of the
origin of species. But it is doubtful whether these small variations are of any real
advantage in the struggle for existence so as to bring natural selection into play.

ii. Darwin's theory could not explain how variations arise.

iii. According to Darwin's theory, natural selection is only a factor to bring out
evolution but not the only complete factor for evolution.

iv. According to Darwin's theory, only useful variations are preserved and transmitted
to the offspring. If it is so, there would not be selection of disused parts.

v. Darwin's theory of natural selection does not satisfactorily explain the occurrence
of vestigial organs. According to his theory, vestigial organs are useless.

BIOLOGY Oasis School Science - 9 349

3. Hugo De Vries' theory of mutation

A Dutch botanist Hugo De Vries propounded a theory, in 1901 – 1903 AD, to explain
the cause of evolution. He held that small variations which Darwin regarded as most
important from the standpoint of evolution are only fluctuations around the specific
type. These variations are not inheritable. Hugo De Vries held that large variations
appearing suddenly and spontaneously in the offspring are the causes of evolution. De
Vries called these variations as 'mutations'. His theory is also called 'mutation theory'.

Activity 1

• If possible, select some places in your surroundings like cave, river, etc. Try to
find out fossils or impressions in rocks, sand, soil, etc.

• Observe what kinds of impressions or prints can be found there.

• Prepare a short report and discuss in your class.

SUMMARY

• Evolution is the process of gradual and orderly changes in organisms from a
simple form to a complex one over a long period of time. It is a continuous but
very slow process.

• Organic evolution is a series of related and gradual changes in plants and animals
which occurs due to the continuous variation.

• The doctrine of evolution is supported by many evidences based on palaeontology,
comparative morphology and anatomy, embryology, study of vestigial organs,
connecting links, etc.

• Fossils are the relics of dead plants and animals preserved in rocks over a long
period of time.

• Vestigial organs are the organs present as reduced structure and functionless in
the body, e.g. nictitating membrane, vermiform appendix, ear muscles of human
beings, etc.

• Homologous organs are the organs having similar structure and origin but
different in function.

• The animals which show characters of two different groups of organisms are
called bridge animals or connecting links.

• Jean Baptiste de Lamarck was the first author to give a general theory of evolution.

• According to Lamarck, the favourable variations caused due to use and disuse
after considerably long period of time result in evolution of new species.

• According to Darwin, the struggle eliminates the unfit individuals. The fit
organisms possess some favourable variations and they survive and reproduce.
This is called survival of the fittest.

• The selection of more progressive organism and elimination of less progressive
organism by the nature is called natural selection.

350 Oasis School Science - 9 BIOLOGY

Exercise

Group-A
1. What is organic evolution?
2. List any two evidences of organic evolution.
3. What are fossils? Where are they found?
4. What are bridge animals? Write with examples.
5. What are vestigial organs.
6. What is struggle for existence? Describe on the basis of Darwinism.
7. What are homologous organs? Write with examples.
8. What is meant by natural selection?
9. What do you mean by variation and heredity?
10. Name any two biologists who propounded the theory of organic evolution.

Group-B
1. Fossils are taken as the strongest evidence so far regarding the evolution of organisms.

Justify this statement.
2. Write any two differences between fossils and vestigial organs.
3. Human's fore limbs and fore limbs of a horse are called homologous organs. Why?
4. Differentiate between mutation and variation.
5. Duck-billed platypus is called a bridge animal, why?
6. Differentiate between embryology and palaeontology.
7. Archaeopteryx is considered as the animal developed into bird from a reptile. Give

reason.
8. Differentiate between homologous organs and vestigial organs.
9. Lamarck's theory is not accepted universally. Justify this statement.
10. Differentiate between mutation and heredity.
11. Why are canine teeth of human beings called vestigial organs?

Group-C
1. How do evidence obtained from study of embryos support the theory of organic

evolution? Describe in brief.
2. What are fossils? How do evidences obtained from the study of fossils support the theory

of organic evolution? Describe in brief.

BIOLOGY Oasis School Science - 9 351

3. What is struggle for existence? Describe on the basis of Darwinism.

4. How does population of organisms remain constant in nature? Describe on the basis of
Darwin's theory.

5. What is meant by effect of environment on organisms? Describe on the basis of
Lamarckism.

Group-D
1. Nowadays, scientists do not accept the hypothesis of special creation of god regarding

the evolution of organisms. Why? What would happen if there were no evolution on the
earth?

2. Which organs are shown in the given figure? How do evidences obtained from the study
of these organs support the theory of organic evolution? Describe in brief.

Human Cat Bat Porpoise Horse

3. How are living beings selected naturally? Describe on the basis of Darwinism.
Differentiate between variation and heredity in any two points.

4. Fossils are taken as the major evidences to support the theory of organic evolution,
write? How do, the fossils found in lower strata of rocks differ from the fossils found in
upper strata? Explain.

5. How was the ancestor of long necked giraffe? Describe on the basis of Lamarckism.
Differentiate between embryology and paleontology.

352 Oasis School Science - 9 BIOLOGY

UUNNITIT21 Estimated teaching periods

Theory 8

Practical 2

Nature and

Environment Eugene P. Odum

Objectives

After completing the study of this unit, students will be able to:
• explain the abiotic factors (air, light, temperature, soil and water) and biotic factors

(plants and animals) that affect ecosystem.

• introduce ecosystem with examples.

• explain the interrelationship between plants and animals (autotrophism and
heterotrophism).

• explain the basic needs (food, shelter and cloth) and human dependence on plants
and animals.

• describe ecosystem services and their types.

21.1 Introduction

The earth is inhabited by different species of plants and animals. No organism can live by itself
or without an environment. Various communities of living organisms, i.e. biotic communities
exist in their respective environment, i.e. abiotic environment and there is a constant interaction
between a biotic community and its surrounding environment. Such a system is known as
ecosystem (A. G. Tansley, 1935). The term ecosystem was first proposed by British ecologist
Tansley in 1935 AD but the concept of the ecosystem is older.

Fig. 21.1 An ecosystem Oasis School Science - 9 353
abiotic /ˌeɪbaɪˈɒtɪk/ - non-living things present in an ecosystem

BIOLOGY

An ecosystem is an ecological unit having both structure and function. Thus, ecosystem
can be defined as a selfsustaining structural and functional unit of biosphere consisting of a
community of living organisms and the physical environment.

In an ecosystem, energy and matter are continuously exchanged between non-living and
living components. Ecosystem is an open system and depends on solar energy from outside
as its energy source. Ecosystems are of small size or large size. Between adjoining ecosystems
there is frequent exchange of materials and energy. Thus, they are all interconnected and
hence interrelated. The vast network of all interconnected ecosystems of the earth constitutes
the biosphere.

The biosphere is the life supporting zone, where air, water and land meet, interact and make
life possible. It is made up of living and non-living components on the earth in which each of
the components performs certain functions. The biosphere is the biggest biological unit which
consists of smaller functional units called ecosystems. In the biosphere, there is a constant
interaction between non-living and living components resulting in the transfer of food and
energy.

The ecosystem is regarded to be the basic and functional unit in ecology. It includes organisms
(biotic communities) and abiotic environment. Each of these factors influences the properties
of the other and both are required to maintain life in the biosphere.

Ecology is defined as the branch of science which deals with the study of the structure and
function of nature and the environment. It is the science which studies organisms in relation
to their environment. Ernst Haeckel (1869 AD) coined the word ecology derived from the
Greek words oikos, house and logos, study. He defined ecology as the total relations of the
animal to both its organic and inorganic environments. E. P. Odum (1963 AD) defined ecology
as the study of the structure and function of nature. Thus, ecology is the study of relationship
between organisms and their environment.

An ecosystem can be both natural and artificial. Grassland, pond, river, desert, forest, sea, etc.
are some examples of natural ecosystem whereas aquarium, park, crop-field, etc. are those of
artificial ecosystem.

21.2 Ecological Factors

The external factors that surround and affect the life of organisms in any ways are called
ecological factors or environmental factors. Ecological factors of an ecosystem are classified
into two groups which are as follows:

a. Abiotic factors
b. Biotic factors

a. Abiotic factors
Abiotic factors of an ecosystem are the non-living factors of that ecosystem. Those factors

354 Oasis School Science - 9 BIOLOGY

mainly include physical environment and climatic factors. The physical environment
consists of soil, air, water and various inorganic as well as organic substances. Similarly,
climatic factors include sunlight, temperature, pressure, rainfall, humidity, etc. The
various abiotic factors of an ecosystem are interrelated to each other.

Solar energy

Sun is an ultimate source of energy on the earth. It gives heat and light energy. Green
plants have the ability to capture solar energy to produce their own food by means of
photosynthesis. Green plants cannot manufacture their food in absence of solar energy.

Solar energy also influences the life of plants in many ways. It influences closing and
opening of stomata, flowering, germination of seeds, movements, etc. Solar energy
determines the types of plants and animals in a particular area. Similarly, solar energy
also influences the behaviour of various animals.

Reasonable fact-1

Solar energy plays a significant role to run an ecosystem, why?

Living being depend on solar energy directly or indirectly. Living organism
cannot survive in the absence of solar energy. Green plants require sunlight during
photosynthesis. All the animals depend on the food prepared by plants. Animals get
heat and light from the sun. Some parts of the earth get more sunlight while other
get less sunlight. It affects the environment, climate and biodiversity of that part.
Therefore, solar energy plays a significant role to run an ecosystem.

Air

Air is the mixture of various gases like nitrogen, oxygen, carbon dioxide, etc. Green
plants use carbon dioxide gas to prepare their own food by photosynthesis. During this
process, oxygen gas is given off. Similarly, animals use oxygen gas during respiration
and throw out carbon dioxide. Carbon dioxide is also given off when dead organisms
decay and fossil fuels are burnt.

Nitrogen gas present in the air cannot be used by the plants directly. Nitrogen of air is
converted into nitrates in the soil by microbes and these nitrates are used by plants. Air
also helps in pollination and dispersal of seeds. In this way, the relation between living
beings and air exists in the environment.

Water

Water is the most abundant natural resource on the earth's surface. It is essential for
survival of plants and animals. A cell contains about 90% of water. The oceans cover
about 70% of the earth's surface. Water is also found in rivers, ponds, lakes, etc. Water is
extremely important for living beings since all the chemical reactions which occur in the
body need water as the medium. The amount of water in a geographical region affects the
types of plants and animals. There is a continuous cycling of water from living beings to
the environment, air to land and sea, and back to the atmosphere again through rainfall,
evaporation and transpiration.

BIOLOGY Oasis School Science - 9 355

Soil

Soil is the mixture of humus and tiny bits of mineral particles. It forms the upper part of
the earth's crust. Life on land depends on soil. Terrestrial plants get water and minerals
from the soil. Soil also contains water, air and living organisms like fungi, bacteria,
earthworms, roundworms, etc. Water and air present in the soil are useful for plants and
animals living on it. Soil serves as the habitat for many plants and animals. The quality of
soil differs from place to place which affects the distribution and growth of plants which
in turn affects the animals also.

b. Biotic factors

Biotic factors of an ecosystem are the living organisms present in that ecosystem. On the
basis of nutritional relationship, biotic components of an ecosystem are classified into:

i. Producers ii. Consumers iii. Decomposers

i. Producers

Producers are the chlorophyll Oxygen out
bearing plants which can prepare Light energy
their own food by means of

photosynthesis. Green plants use

carbon dioxide and water in the Carbon dioxide Water and
in minerals
presence of chlorophyll and sunlight Green cells where
to synthesize their food. They food is made
convert solar energy into chemical
energy during photosynthesis. Fig.21.2 Process of making food by green plants
Chemical energy is the source of
food for many organisms. All green
plants, i.e. producers are also called
autotrophs as they synthesize their
own food.

ii. Consumers

Consumers are the heterotrophic animals that depend on green plants, directly or
indirectly for their food. On the basis of nature of food, consumers are divided into
three categories:

Primary Consumers: The consumers that feed directly on green plants or
autotrophs are called primary consumers. They are also called herbivores.
Protozoans, crustaceans, molluscs, zooplanktons, etc. are some examples of
primary consumers of an aquatic ecosystem. Similarly, grasshopper, rabbit, deer,
goat, sheep, cattle, elephant, etc. are some examples of primary consumers of
terrestrial ecosystem.

Secondary Consumers: Secondary consumers are the carnivorous animals that
feed on herbivores. They indirectly depend on green plants for their food and
provide food for tertiary consumers. For example, dog, cat, fox, frog, snake, wild
cat, birds, fishes, etc.

consumer /kənˈsjuːmə/ - the organism that depends on green plants for food

356 Oasis School Science - 9 BIOLOGY

Tertiary Consumers: The consumers that feed on secondary consumers as well
as primary consumers are called tertiary consumers. They also depend on green
plants indirectly for their food. For example, lion, tiger, owl, peacock, whale,
crocodile, etc.

iii. Decomposers

Decomposers are the saprophytic organisms that feed on dead bodies of organisms
and decaying organic matter. They decompose the complex organic compounds
present in the dead organisms into simpler substances. Bacteria and fungi are the
examples of decomposers. They are responsible for regular cycling of materials
in an ecosystem. Through the decomposers, the elements enter the earth again,
which in turn are taken up by the autotrophs.

Role of decomposers in an ecosystem

i. Decomposers break down the dead bodies of plants and animals into simpler forms.

ii. Decomposers help in recycling the materials in the environment.

iii. They help in putting back the nutrients into soil, air and water for reuse by the
producers.

iv. Decomposers maintain the fertility of the soil.

Differences between Autotrophs and Heterotrophs

S.N. Autotrophs S.N. Heterotrophs

1. Autotrophs are the chlorophyll 1. Heterotrophs are the organisms

bearing plants which can pre- which cannot prepare their own

pare their own food by means of food and depend on autotrophs for

photosynthesis. their food.

2. Chlorophyll is present. 2. Chlorophyll is absent.

3. They do not depend on other or- 3. They depend on other organisms for

ganisms for their food. their food.

Examples: All green plants Examples: Cow, deer, tiger, human
being, etc.

Differences between Herbivores and Carnivores

S.N. Herbivores S.N. Carnivores

1. Herbivores are the animals that 1. Carnivores are the animals that feed

feed on autotrophs, i.e. green on flesh.

plants.

BIOLOGY Oasis School Science - 9 357

2. They cannot survive without 2. They directly depend on herbivores

green plants and provide food for for food and indirectly depend on

carnivores. green plants.

Examples: Grasshopper, deer, Examples: Tiger, snake, vulture,
rabbit, cow, etc. lion, etc.

21.3 Types of Ecosystem

On the basis of habitat, there are two types of ecosystem. They are:
i. Aquatic ecosystem and
ii. Terrestrial ecosystem.

Ecosystem

Aquatic ecosystem Terrestrial ecosystem

Freshwater Marine water
ecosystem ecosystem

Pond/Lake ecosystem Grassland ecosystem
River ecosystem Forest ecosystem
Desert ecosystem

i. Aquatic Ecosystem

The ecosystem which exists in water is called aquatic ecosystem. It is mainly of two
types, i.e. freshwater ecosystem and marine water ecosystem. The freshwater ecosystem
can further be sub-divided into pond or lake ecosystem, river ecosystem, etc.

A brief description of a pond ecosystem is given below:

Pond ecosystem
The ecosystem that exists in a pond is called pond ecosystem. A brief description of the

abiotic components and biotic components of a pond ecosystem is given below:

i. Abiotic components

The non-living components present in a pond ecosystem are the abiotic components of
that ecosystem. Water, soil, minerals, air, sunlight, heat, temperature and other inorganic
as well as organic materials are the abiotic components (factors) of a pond ecosystem.

358 Oasis School Science - 9 BIOLOGY

Fig.21.3 Pond ecosystem

ii. Biotic components

All living organisms present in a pond ecosystem are called biotic components of that
ecosystem. The biotic components of a pond ecosystem can be divided into following types:

a. Producers

Producers are the autotrophic plants which can synthesize their own food
by photosynthesis. All aquatic green plants like algae, diatoms, volvox,
phytoplanktons, hydrilla, ranunculus, pistia, lotus, lily, etc. are the producers of a
pond ecosystem.

b. Consumers

Consumers are the heterotrophic organisms that depend on producers directly
or indirectly. Small aquatic animals like amoeba, paramecium, daphnia, cyclops,
zooplanktons, earthworms, insects, etc. are primary consumers of the pond
ecosystem. They feed on producers of that ecosystem.

Small fish, frogs, aquatic insects, molluscs, crustaceans, etc. are the secondary
consumers of the pond ecosystem. Similarly, big fishes, water snakes, carnivorous
aquatic birds (e.g. kingfisher) are the tertiary consumers of the pond ecosystem.

c. Decomposers

The organisms that feed on dead and decaying organic matter are called
decomposers. They decompose all dead bodies of plants and animals and convert
the complex organic matter into simple inorganic matter. Decomposers maintain
the balance in the pond ecosystem. Different kinds of bacteria and fungi are the
decomposers of the pond ecosystem.

Activity 1

To study the abiotic and biotic components of an aquatic ecosystem
• Visit a nearby pond and observe its various components.
• Draw a neat and labelled figure showing the pond ecosystem and prepare a

short report.

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ii. Terrestrial Ecosystem

The ecosystem which exists on land is called a terrestrial ecosystem. This ecosystem can
further be divided into grassland ecosystem, forest ecosystem, desert ecosystem, etc.

A brief description of a grassland ecosystem is given below:

Grassland ecosystem

The ecosystem that exists in the grassland is called a grassland ecosystem. The abiotic
components and biotic components of a grassland ecosystem are as follows:

a. Abiotic components

The abiotic components of a grassland ecosystem are soil, water, air, stone, sunlight,
heat, temperature, humidity, etc. and other decayed materials.

b. Biotic components

The living organisms of a grassland ecosystem
are the biotic components of that ecosystem.
They can be divided into following categories:

i. Producers: All green plants like weeds,
herbs, various types of grasses and other
green plants are the producers of the
grassland ecosystem. They provide food
for the consumers of that ecosystem.

ii. Consumers: Consumers of a grassland

ecosystem are the living organisms that

depend on producers directly or indirectly

for their food. The primary consumers of Fig. 21.4 Terrestrial ecosystem
a grassland ecosystem are animals like

earthworm, insects, rabbit, deer, mouse,

monkey, etc. Carnivorous animals like frogs, birds, wolves, jackals, etc. that feed

on primary consumers are the secondary consumers of that ecosystem. Similarly,

the strong carnivorous animals like leopard, tiger, lion, vulture, hawk, etc. are the

tertiary consumers of that ecosystem.

iii. Decomposers: Various types of bacteria and fungi are the decomposers of a
grassland ecosystem. They act on dead bodies of organisms and decompose the
complex organic matter into simple forms. Then the decomposed matters mix in
the soil, which can be reabsorbed by green plants as nutrients.

Differences between Biotic factors and Abiotic factors

S.N. Biotic factors/components S.N. Abiotic factors/components

1. Biotic factors are all living 1. Abiotic factors are all non-living

organisms present in an ecosystem. things present in an ecosystem.

2. Biotic factors include producers, 2. Abiotic factors include air, solar

consumers and decomposers. energy, soil, water, temperature,

humidity, etc.

360 Oasis School Science - 9 BIOLOGY

Activity 2

To study the abiotic and biotic components of a grassland ecosystem
• Visit a grassland and observe the abiotic and biotic components.
• Draw a neat and labelled figure showing a grassland ecosystem.
• Prepare a short report.

21.4 Interrelation among Producers, Consumers and Decomposers
in an Ecosystem

There is a very close relationship among the plants, animals and abiotic factors of an ecosystem.
They interact continuously among themselves. Therefore, living things and non-living things
are interdependent.

Green plants absorb water and minerals from soil. They take carbon dioxide gas from air and
prepare their food in the presence of sunlight. All animals depend on green plants directly
or indirectly for their food. There are producers, various types of consumers (herbivores,
carnivores and omnivores) and decomposers in an ecosystem. They all live together forming
a community. Herbivorous animals feed on green plants, carnivorous animals feed on
herbivores. Similarly, omnivorous animals feed on both herbivorous as well as carnivorous
animals. When plants and animals die, their body is decomposed by microbes like bacteria
and fungi into simpler inorganic substances which mix in the soil. Producers again absorb
those inorganic substances for their growth and development. In this way, a close relationship
exists among abiotic factors, producers, consumers and decomposers of an ecosystem.

21.5 Food Circulation Process in an Ecosystem

The flow of energy in ecosystem is unidirectional. Foodstuff or biomass is the main source
of energy. Only green plants can prepare their own by means of photosynthesis and they
do not depend on other organisms to obtain their food. Animals cannot produce their own
food. So, they depend on green plants or other animals for their food. Solar energy is the
main source of energy in an ecosystem. Food prepared by green plants circulates through
primary consumers, secondary consumers and tertiary consumers. Decomposers obtain their
food from dead and decaying bodies of plants and animals. In this process of transfer of food
materials, food chain and food web are formed.

21.6 Food Chain

In an ecosystem, a food relationship exists among various living organisms. They interact with
one another for their food preparation and consumption. The food prepared by green plants is
consumed by a series of consumers and finally decomposed by decomposers. Some organisms
consume other organisms and they are in turn consumed by other organisms, thereby forming
a chain. In this chain, transfer of energy takes place. Thus a food chain can be defined as the
transfer of food energy from producers through a series of consumers with repeated eating
and being eaten. It is a sequential process which represents "who eats whom".

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Fig.21.5 Food chain of a forest ecosystem

In a food chain, unidirectional transfer of energy takes place. At each transfer a lot of energy
from food is lost as heat (respiration). Therefore, the number of steps in a food chain is always
limited. The shorter the food chain, the greater is the available energy. An example of food
chain in a grassland ecosystem is as follows:

Grass Rabbit Tiger
(Producer) (Herbivore) (Carnivore)

The given food chain is a three-step food chain of a grassland or forest ecosystem. Here,
grasses produce their own food by photosynthesis and hence they represent producers. The
grass is eaten by rabbit (herbivore) and the rabbit is eaten by tiger (carnivore). The given food
chain shows that grass is the starting point and the tiger is the final point.

Some food chains operating in an ecosystem may contain four-steps or five steps:

A four-step food chain of a pond ecosystem is given below:

Algae Zooplankton Small fish Big fish
(Producer) (Herbivore) (Carnivore I) (Carnivore II)

A five-step food chain of an aquatic ecosystem is given below:

Phytoplankton Zooplankton Fish Squid Seal
(Producer) (Herbivore) (Carnivore I) (Carnivore II) (Top carnivore)

The food chains transfer energy and materials between various living components of an
ecosystem and give dynamism to an ecosystem. The study of food chains helps to understand
food relationships and interactions among various organisms of an ecosystem.

Fig 21.6 Food chain of a grassland ecosystem

21.7 Food Web

The various food chains, operating in an ecosystem cannot function in isolation. Most of the

dynamism /ˈdaɪnəmɪzəm/ - energy to make things succeed

362 Oasis School Science - 9 BIOLOGY

food chains are interconnected under natural conditions. Thus, various food chains form a
network with interconnections and linkages. Hence, a food web can be defined as the network
of various food chains which are interconnected at various trophic levels of an ecosystem.

Hawk Snake

Rabbit Mouse Frog
Bird

Grasshopper

Green plants
Fig.21.7 Food web of a grassland ecosystem

In an ecosystem, one animal based in
its food habit may be linked in more
than one food chain. In a food web, one
organism may occupy position in more
than one food chain. An animal can
obtain its food from different sources
and in turn may be eaten up by various
types of organisms.

The figure above shows a food web of

a grassland ecosystem, which contains

many food chains. In this food web, green

plants may be eaten by grasshopper,

mouse, rabbit, etc. Grasshopper may be

eaten by frog, snake and bird. Similarly,

hawk can obtain its food from rabbit, Fig.21.8 Food web of a terrestrial ecosystem

mouse, bird and snake. The given food

web contains six interconnected food chains. These are as follows:

i. Green plants → Rabbit → Hawk
Hawk
ii. Green plants → Mouse → Bird → Hawk
Snake → Hawk
iii. Green plants → Grasshopper → Frog → Snake

iv. Green plants → Grasshopper →

v. Green plants → Grasshopper → → Hawk

vi. Green plants → Mouse → Snake → Hawk

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21.8 Interrelationship between Plants and Animals

Nutrients are the substances that are required to keep living beings alive. Nutrition is the
process by which living organisms receive the food necessary to grow and be healthy. On the
basis of nutritional relationship, biotic factors of an ecosystem can be divided into two groups,
viz. a. autotrophs and b. heterotrophs. The mode of nutrition of autotrophs is called autotrophic
nutrition whereas the mode of nutrition of heterotrophs is called heterotrophic nutrition.

a. Autotrophs: Autotrophs are the organisms that can prepare their own food by
photosynthesis. All the green plants are autotrophs and their mode of nutrition is called
autotrophic nutrition or autotrophism. Photosynthesis is the process by which green
plants produce their own food by using carbon dioxide and water in the presence of
sunlight. Green plants use solar energy and synthesize organic food stuff by using
inorganic matter.

b. Heterotrophs: Heterotrophs are the living organisms which cannot prepare their own
food and their mode of nutrition is called heterotrophic nutrition. Animals derive their
food from green plants directly or indirectly. This process is called heterotrophism. All
animals and non-green plants show heterotrophic nutrition.

On the basis of mode of nutrition, heterotrophs are of following types:

i. Parasites ii. Saprophytes and iii. Holozoic organisms

i. Parasites: Parasites are the living organisms that derive their food and shelter
from their hosts. For example, mosquito, roundworm, liver fluke, tapeworm,
amoeba, leech, etc. Hosts are the living organisms that provide food and shelter to
the parasites. Some non-flowering plants like rust (Puccinia), smut (Ustilago), etc.
are the examples of parasitic plants.

ii. Saprophytes: Saprophytes are the organisms that derive their food from dead
and decaying organic matters. Fungi and bacteria are the common examples of
saprophytes. They act on the dead body of plants and animals and decompose
them into simple inorganic forms.

iii. Holozoic organisms: The organisms that feed on the whole body of plants or animals
or both are called holozoic organisms and their mode of nutrition is called holozoic
nutrition. Most of the animals except parasites and saprophytes show such mode
of nutrition. Holozoic nutrition includes four different processes, viz. ingestion,
digestion, assimilation and egestion. Human beings, tiger, vulture, snake, deer,
butterfly, fish, frog, paramecium, etc. are some examples of holozoic organisms.

21.9 Basic Needs

Human beings depend on other animals and plants to obtain their food and shelter. Food,
shelter and cloth are three basic needs of human beings. They fulfill their needs from plants
and animals.

a. Food: Food is essential for the survival of living organisms. No organism can survive
without taking food. Human beings obtain their food from various plants and animals.

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Human beings cultivate cereals, pulses, fruits and vegetables to obtain their food.
Similarly, human beings also feed on flesh of animals and animal products like milk,
egg, honey, etc.

b. Shelter: Human beings live on land. They construct houses, buildings, huts, camps, etc.
to obtain shelter. They use stone, cement, bricks, straw, iron rods, wood, etc. to construct
their shelter.

c. Cloth: Human beings use various types of clothes to cover their bodies. Clothes are worn
to prevent the body from heat and cold. Human beings use various types of plant fibres,
animal fibres and synthetic fibres for making clothes. Cotton, jute, hemp, etc. are plant
fibres. Wool and silk are animal fibres whereas nylon, polyster, terylene, etc. are some
examples of synthetic fibres. Those fibres are used for making various types of clothes.

21.10 Ecosystem Services

The benefits which are obtained by human beings from the environment are called
ecosystem services. The service of ecosystem are mentioned below:

1. Provisioning services
The products obtained from an ecosystem are called provisioning services. They include

following things.

(a) Foods and fibres
The foods and fibres required for human beings are obtained from ecosystem. Food,

timbre, jute, firewood, hemp, etc. are obtained from plants and meat, silk, wool, leather,
etc. are obtained from animals.

(b) Fuel

Human beings need fuel to cook food, run automobiles, operate machines, etc. We use
petrol, diesel, coal, firewood, biogas and other organic substances as fuel. These fuels are
obtained from ecosystem.

(c) Ornamental resource

Human beings use a variety of ornaments. They use shell, bone, leather, etc. to make
ornaments which are obtained from ecosystem.

2. Regulating services

The benefits obtained by human beings due to the balance in ecological system are called
regulating services. They include (a) climate regulation and (b) water purification.

(a) Climate regulation

Ecosystem affects local and global climate. Forest helps to regulate rain cycle and
temperature in local level. Similarly, release of carbon dioxide and other industrial gases
affects the climate of a place.

(b) Water purification

Ecosystem helps in water purification directly or indirectly. It filters impure substances
present in water and decomposes biological waste products. Similarly, the change in
ecosystem affects the pollination, regulation of human diseases, soil erosion, etc.

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3. Cultural services
Ecosystem affects natural beauty, peaceful/joyful environment, culture, behaviour, etc.

Ecosystem also affects religious thoughts and values. Similarly, ecosystem increases the
values of social relation, cultural heritage, etc. Balanced ecosytem helps to increase clean
environment, attractive scene, natural beauty, etc. It helps to attract tourists.
4. Supporting services
They include services like nutrient recycling, primary production, soil formation, etc.
These services provide food regulation, water purification, etc.

SUMMARY

• Ecosystem is defined as the structural, functional and self-sustaining unit of biosphere.

• Biosphere is the largest unit of biological system in which many ecosystems can operate
together.

• An ecosystem contains two factors. They are – abiotic factors and biotic factors.

• Abiotic factors of an ecosystem are the non-living factors of that ecosystem. They
include sunlight, air, water, soil, temperature, rainfall, etc.

• Biotic factors of an ecosystem are the living factors of that ecosystem.

• Biotic factors are mainly of three types, viz. producers, consumers and decomposers.

• Solar energy is the main source of energy for an ecosystem.

• Producers are the living organisms which can prepare their own food by photosynthesis.

• Consumers are the animals that depend on green plants directly or indirectly for their
food.

• Consumers are mainly of three types, viz. primary consumers, secondary consumers
and tertiary consumers.

• Decomposers are the saprophytic organisms that decompose complex bodies of plants
and animals into simple inorganic forms.

• Food chain is defined as the transfer of food energy from producers through a series of
consumers with repeated eating and being eaten.

• A food web is the network of various interconnected food chains.

• Autotrophs are the green plants which can prepare their own food by means of
photosynthesis and the process is called autotrophism.

• Heterotrophs are the organisms which depend on autotrophs directly or indirectly for
their food and the process is called heterotrophism.

• Heterotrophs are of three types, viz. parasites, saprophytes and holozoic organisms.

• Food, shelter and cloth are the three basic needs of human beings.

• The benefits which are obtained by human beings from the environment are called
ecosystem services.

• The products obtained from an ecosystem are called provisioning services.

• The food and fibres required for human beings are obtained from the ecosystem.

366 Oasis School Science - 9 BIOLOGY

Exercise

Group-A
1. What is ecosystem?
2. What is meant by ecology?
3. Define abiotic factors and biotic factors.
4. List the various abiotic factors of an ecosystem.
5. List the various biotic factors of an ecosystem.
6. What are producers?
7. What is community? What type of organisms are found in community?
8. What are biotic components? Give any two examples.
9. What are abiotic components? Give any two examples.
10. Define primary consumers with any two examples.
11. What is a food chain?
12. What is a food web?
13. Define tertiary consumers and give any two examples.
14. What is photosynthesis?
15. What are the raw materials essential for photosynthesis?
16. What type of organisms are called heterotrophs?
17. Define parasites and omnivores with any two examples of each.
18. Name any two carnivorous animals.
19. What do you mean by trophic level? Write with an example.
20. List the abiotic and biotic factors of a pond ecosystem.
21. Which ecological process is shown below.

Oasis School Science - 9 367
22. What are four basic needs of human beings?
23. What is meant by ecosystem services?
24. What are provisioning services in an ecosystem?
25. What is meant by regulating services in an ecosystem?
26. What is meant by cultural services in an ecosystem?

BIOLOGY

Group-B
1. Air and water are called biotic factors and living beings are called biotic factors. Give

reason.
2. Differentiate between a biotic factors and biotic factors.
3. Green plants are called producers and animals are called consumers, why?
4. Differentiate between producers and consumers.
5. Cow is called primary consumer and vulture is called tertiary consumer, why?
6. Differentiate between food chain and food web.
7. Differentiate between herbivores and carnivores.
8. The number of producers is always more than that of the consumers in nature. Give

reason.
9. Green plants are called autotrophs and animals are called heterotrophs. Give reason.
10. Identify producers, primary consumers, secondary consumers and tertiary consumers

from the given food chain.

Group-C
1. Describe in brief the role of the sun to run an ecosystem.
2. What is a food web? How is it operating in nature?

3. Hawk Snake
Mouse
Rabbit Frog
Bird

Grasshopper

Green plants

368 Oasis School Science - 9 BIOLOGY

i) Name the producers and secondary consumers in the above given food chain.

ii) What would be the effect on the food chain if all the snakes were killed?

4. What is the relationship between plants and animals in an ecosystem? Explain in brief.

5. Write a short note on supportory services in an ecosystem. What would happen if there
were no abiotic factors in nature?

Group-D

1. Describe the role of producers to operate an ecosystem. Write any two differences
between consumer and decomposer.

2. Draw a neat diagram showing the food web of a grassland ecosystem. Differentiate
between food chain and food web.

3. Identify the given factors in the terms of abiotic factors, producers, consumers and
decomposers:

– Solary energy – Grass ` – Air

– Snake – Mouse – Water

– Fungi – Soil

4. Draw a neat figure showing the food web of a pond ecosystem. Differentiate between
herbivores and carnivores in two points.

5. Described in brief the importance of food and cloth for human beings.

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Compulsory Science

Part 4 : Astronomy and Geology
Scope and sequence of the subject matter

Area Unit Syllabus
Earth and Geographic 1. Natural Hazard
Phenomena • Introduction to natural and man-made hazard
• Glacier flood, glacier lake outburst and cyclone
• Causes, effects and mitigating measures

The Universe 2. Greenhouse • Introduction to greenhouse and its effects
• Artificial greenhouse and its uses
3. The Earth in the • Climate change
Universe • Introduction
• Causes and effects
• Mitigating measures
• Rotation of the earth
• Revolution of the earth
• Phases of the moon
• Position of the sun, earth and moon
• Formation of umbra and penumbra
• Lunar eclipse and solar eclipse

370 Oasis School Science - 9 ASTRONOMY AND GEOLOGY

UNIT 22 Estimated teaching periods

Theory 4

Practical 1

Natural Hazard Cyclone

Objectives

After completing the study of this unit, students will be able to:
• introduce natural hazards and man-made hazards and describe the management

of hazards.

• explain the causes, effects and protective measures of natural hazards, viz.
glacier flood, glacier lake outburst and cyclone.

22.1 Introduction

Environment can degrade naturally or through human activities. Those disasters which are
caused by natural processes suddenly and unfortunately are called natural disasters. Flood,
landslide, earthquake, volcano, etc. are the most destructive and devastating calamities which
cause a variety of environmental hazards. The above mentioned disasters occur frequently in
different parts of the earth's surface. All the countries are affected by environmental hazards
but the damage caused by them may be more or less. The occurrence of natural disasters and
their effects depend upon geographical and meteorological factors. Scientific technology and
public awareness are helpful to minimize the effects of these calamities.

(a) Earthquake (b) Glacier flood (c) Landslide (d) Volcanic eruption

Fig. 22.1

A natural hazard is a naturally occurring dangerous event that might have a negative effect
on people or the environment. Natural hazards can be grouped into two broad categories, viz.
(i) Geophysical hazards, and (ii) Biological hazards. Geophysical hazards include geological
and meteorological phenomena such as earthquake, soil erosion, volcanic eruption, cyclone,
etc. Similarly, biological hazards include a diverse array of disease and infestation. Other
natural hazards such as floods and wildfires can result from a combination of geological,
hydrological and climatic factors. Some natural hazards may occur periodically while others
occur suddenly. For example, flood and landslide occur every year in rainy season whereas
earthquake, volcanic eruption may occur suddenly.

hazard / ˈhæzəd/ - a thing that can be dangerous or cause damage

ASTRONOMY AND GEOLOGY Oasis School Science - 9 371

Natural hazards that occur in a country depend on geological structure. For example, flood
and landside occur frequently in Nepal, earthquake occurs frequently in Japan and cyclone
or hurricane occurs frequently in coastal regions. In this unit, we will study natural and
man-made hazards and their management. Similarly, we will study the causes, effects and
protective measures of glacier flood, glacier lake outburst and cyclone.

22.2 Hazard

A hazard is a natural or man-made situation that poses a level of threat to life, health, property
or environment. Most hazards are dormant or potential, with only a risk of harm, however
once a hazard becomes active, it can create an emergency. A hazardous situation that has come
to pass is called an incident, e.g. occurrence of earthquake, landslide, flood, etc. Hazards may
be both natural and man-made. Similarly, hazards may be physical, chemical, biological, etc.

Physical hazards are conditions or situations that can cause the body physical harm or intense
stress. Physical hazards can be natural or man-made, e.g. earthquake, landslide, explosion of a
bomb, collapsing of a building, road accident, etc. Chemical hazards are chemical substances
that can cause harm or damage to the body, property or environment. They may be of both
natural and man-made origin, e.g. harmful gases, acids, insecticides, etc. Biological hazards
are the biological agents that can cause harm to human body. These biological agents can be
viruses, bacteria, fungi and foreign toxins. However, hazards are broadly classified into two
types, viz.

i) Natural hazards, and

ii) Man-made hazards

i) Natural hazards

The hazards which occur on the earth by natural processes are called natural hazards.
Earthquake, flood, landslide, glacier lake outburst, volcano eruption, cyclone, etc. are
some examples of natural hazards. Some of the natural hazards occur periodically while
other occur suddenly in different parts of the earth. Natural hazards are more destructive
and devastating than man-made hazards.

ii) Man-made hazards

The hazards that occur as a result of human activities are called man-made hazards.
Epidemics, road accident, bomb explosion, collapsing of buildings, outburst of dams,
aeroplane crash, desertification, etc. are some examples of man-made disasters.

(a) (b) (c)

372 Oasis School Science - 9 Fig. 22.2

ASTRONOMY AND GEOLOGY

22.3 Management of Natural Hazards

Hazards are caused by various factors. Human beings cannot stop these hazards. But
the possibility of damage can be minimized. Therefore, proper management of hazards
and their mitigating measures should be designed on the basis of types and causes of
disasters. Following activities help in the management of natural hazards.

i) Development of public awareness

ii) Rescue of the affected people

iii) Mobilization of help in proper way

iv) Help, rehabilitation and relief to the affected people

v) Follow precautions of hazards

22.4 Management of Man-made Hazards

Following activities help in the management of man-made hazards.

i) Develop public awareness
ii) Spread awareness about epidemics
iii) Keep your surroundings clean
iv) Conduct afforestation programmes
v) Keep water sources free from pollution
vi) Follow traffic rules
vii) Maintain vehicles periodically
viii) Conduct sanitation programmes
ix) Maintain balance in fertility of soil
x) Pay attention to personal hygiene
xi) Manage fire brigade and check household wiring system
xii) Extinguish fire properly
xiii) Arrange treatment for victims
xiv) Stop unhealthy competition among human beings
xv) Broadcast various information regarding hazards
xvi) Conduct land utility plan
xvii) Conserve forests and wildlife

22.5 Disaster Risk Management Fig. 22.3

Disaster is a sudden unfortunate or adverse event which causes
great damage to human beings as well as plants and animals.
Disasters occur rapidly, instantaneously and indiscriminately.
These extreme events, either natural or man-induced, exceed
the tolerable magnitude within or beyond certain time limits,
make adjustment difficult, result in loss of property and life.

disaster /dɪˈzɑːstə(r)/ - an unexpected event, such as earthquake, flood, etc.

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Disaster risk management includes sum total of all activities, programmes and measures
which can be taken up before, during and after a disaster with the purpose to avoid a disaster,
reduce its impact or recover from losses. The three key stages of activities that are taken up
within disaster risk management are as follows.
1. Before a disaster (pre-disaster)
Pre-disaster activities include those activities which are carried out to reduce human

and property losses caused by a potential hazard. For example, carrying out awareness
campaigns, strengthening the existing weak structures, preparation of the disaster
management plans at household and community level, etc. Such risk reduction measures
taken under this stage are termed as mitigation and preparedness activities.

2. During a disaster (disaster occurrence)

These activities include initiates taken to ensure that the needs and provisions of victims
are met and suffering is minimized. Activities taken under this stage are called emergency
response activities.

3. After a disaster (post-disaster)
The initiatives taken in response to a disaster with a purpose to achieve early recovery

and rehabilitation of affected communities, immediately after a disaster strikes are called
response and recovery activities.



(a) (b)
Fig. 22.4

22.6 Disaster Risk Management Cycle

The disaster risk management cycle consists of four phases. (i) Prevention/ Mitigation (ii)
Preparedness (iii) Response (iv) Rehabilitation or Reconstruction in post-disaster stages.
In the "prevention/mitigation' phase, efforts are made to prevent or mitigate damage, (e.g.
construction of dikes and dams against flood). Activities and measures for ensuring an
effective response of the impact of hazards are classified as "preparedness', (e.g. emergency
drills and awareness). Response includes such activities as rescue efforts, first aid, fire fighting
and evacuation. In the rehabilitation/ reconstruction phase, considerations of disaster risk
reduction should form the foundations for all activities. Some examples of measures taken in
each phase are listed in the given table.

374 Oasis School Science - 9 ASTRONOMY AND GEOLOGY

Disaster Earthquake Flood Storm, Cyclone, Landslide
Typhoon,
Phase - Seismic design - Construction of Hurricane -Construction of
dikes erosion control
1.Prevention/ - Retrofitting - Construction of dams
Mitigation of vulnerable -Building of dam tide wall
buildings - Construction of
- Afforestation - Establishment of retaining walls
- Installation of forests to protect
seismic isolation, - Construction against storms - Construction
seismic response of flood control and operation of
control system construction - Construction of meteorological
reservoirs shelter observation system
- Construction
and operation - Construction - Construction
of earthquake and operation of and operation of
observation system meteorological meteorological
observation system observation system

2. Preparedness (i) Preparation of hazard maps
(ii) Food and materials stockpiling
(iii) Emergency drills
(iv) Construction of early warning system
(v) Preparation of emergency kits

3. Response (i) Rescue efforts
(ii) First aid treatment
(iii) Fire fighting
(iv) Monitoring of secondary disaster
(v) Construction of temporary housing
(vi) Establishment of tent villages

4. Rehabilitation/ (i) Disaster resistant construction
Reconstruction (ii) Appropriate land use plans
(iii) Livelihood support
(iv) Industrial rehabilitation planning

Taking appropriate measures based on the concept of disaster risk management in each phase
of the disaster risk management cycle can reduce the overall disaster risk.

22.7 Glacier Flood

Glacier and glacial lakes in the Hindu-Kush-Himalayas are essential natural resources. They
are the source of rivers that provide fresh-water to about one-third of the world's population.
In the Himalayas of Nepal, as in many other parts of the world, glaciers are receding and
glacial lakes are forming as a result of current global warming. Besides being a significant
natural resource, glacial lakes have a potential to be the source of a natural disaster. If the
moraine dams of a glacial lake fail, the water can burst out, leading to massive floods and debris
flows with potentially extensive damage downstream, including loss of life, livelihoods, and
infrastructure. There are many examples in Nepal in which loss of lives and property have
occurred as a result of glacial lake outburst floods (GLOFs). In Nepal, there are many rivers

glacial /ˈɡleɪsiəl/ - caused or made by glaciers or formed by snow

ASTRONOMY AND GEOLOGY Oasis School Science - 9 375

like Arun, Trishuli, Dudhkoshi, etc. that originate from Tibet. Downstream of those rivers are
at the risk of glacial lake outburst flood. There are about 3252 glaciers and 2323 glacial lakes
in Nepal. Among them 20 glacial lakes in Nepal are potentially dangerous. In August 1985,
a sudden outburst flood from the Dig Tsho glacial lake in Nepal destroyed 14 bridges and a
hydropower plant at Namchebazar.

(a) Fig. 22.5 (b)

Causes of glacier flood

The major causes of glacier flood are as follows:

i) Melting of snow
ii) Change in climate
iii) Geographic energy
iv) Global warming
v) Glacial lakes outburst
vi) Tectonic shocks

vii) Human encroachment

Effects of glacier flood

The speed of the flood, its duration and amount of the
debris present in the flood determine its effect. The major
effects of flood are given below:

i) A glacier flood destroys land structures, natural and
cultural heritages.

ii) It destroys life and property.

iii) It damages the fertile land by depositing soil and Fig. 22.6
sand over it.

iv) It causes excessive landslide and soil erosion.
v) It makes habitat of wildlife unsuitable.

vi) It damages the constructed structures like buildings, dams, roads, bridges, water supply
systems, etc.

vii) It causes lack of food and induces the outbreak of diseases.

viii) It impedes the economic development of the country.

376 Oasis School Science - 9 ASTRONOMY AND GEOLOGY

Protective measures of glacier flood
i) Field investigation and mapping of glacial lakes should be done.
ii) Identification and ranking of critical (potentially dangerous) glacial lakes should be

done.
iii) Dykes should be constructed parallel to the rivers to reduce the force of water flow.
iv) Deforestation should be stopped and trees should be planted on the bare land.
v) Reservoirs should be constructed to store the flood water to reduce the flow of water

downward.
vi) Flood measuring stations should be set up in the flood prone areas to predict the flood.
vii) Watersheds like river, pond, lake, etc. should not be destroyed.
viii) Flood hazard map should be prepared for proper management of flood-prone areas.

Tsho Rolpa Glacier
Fig. 22.7

22.8 Glacial Lake Outburst Flood

A glacial lake outburst flood (GLOF) is a type of

outburst flood that occurs when the dam containing

a glacial lake fails. The dam consists of glacier, ice

or a terminal moraine. Failure of a glacial lake can

happen due to erosion, a build up of water pressure,

an avalanche of rock or heavy snow, an earthquake,

volcanic eruption under the ice or if a large enough

portion of a glacier breaks off and massively displaces

the water in a glacial lake.

The volume of glacial lakes varies but may hold Fig. 22.8

millions to hundreds of millions of cubic meters of

water. Catastrophic failure of the containing ice or glacial sediment can release this water over

periods of minutes or days. Glacial lake outburst floods are often compounded by a massive

river bed erosion in the steep moraine villages.

There are a number of imminent deadly GLOFs situation that have been identified worldwide.
The Tsho Rolpa glacier lake is located in the Rolwaling valley, about 110km north east of
Kathmandu valley. The lake is dammed by a 150 m high unconsolidated terminal moraine

ASTRONOMY AND GEOLOGY Oasis School Science - 9 377

dam. The lake is growing larger every year due to the melting and retreat of the Trakarding
glacier, and has become the largest and most dangerous glacier lake in Nepal with 90 to 100
million cubic meters of water stored.

Even though GLOF events have been occurring in Nepal for many decades, the Dig Cho glacial
lake outburst, which took place in 1985, has triggered detailed study of this phenomenon. In
1996, the water and energy commission secretariat of Nepal reported that five lakes of Nepal
were potentially dangerous. These glacial lakes are Dig Tsho, Imja, Lower Barun, Tsho Rolpa
and Thulagi, all lying above 4100m. A study done by ICIMOD and UNEP (2001) reported
20 potentially dangerous lakes in Nepal. In ten of them GLOP events have occurred in the
past few years and some have been regenerating after the event. Additional dangerous glacial
lakes may exist in parts of Tibet that are drained by streams crossing into Nepal, raising the
possibility of outburst incident in Tibet causing downstream damage in Nepal.

Impacts of glacial lake outburst flood Fact File-1
i) It destroys life and property.
ii) It destroys land structures. The flood occurred due to outburst of
iii) It damages fertile land and crops. glacier lakes in the Himalayan region is
called glacier lake outburst flood.

iv) It causes soil erosion.

v) It destroys human settlement, roads, bridges, etc. downstreams.

22.9 Cyclone

A cyclone is an area of closed, circular fluid motion
rotating in the same direction as the earth. It is usually
characterised by inward spiralling wind that rotates
anticlockwise in the northern hemisphere and clockwise
in the southern hemisphere. Most large scale cyclonic
circulations are centred in areas of low atmospheric
pressure.

A tropical cyclone is a rapidly rotating storm system Fig. 22.9 Cyclone or typhoon

characterized by a low pressure centre, strong winds and

a spiral arrangement of thunderstorms that produce heavy rain. Depending on its location and

strength, a tropical cyclone is called hurricane, typhoon, tropical storm, and simply cyclone.

It is one of the natural disasters that can partially or completely damage the settlements, life

and property near the sea or ocean. It damages lots of life, property and infrastructure every

year in India, Bangladesh, Japan, Mexico, Philippins, USA, etc. But Nepal cannot be affected

directly by cyclone as it is a landlocked country.

Every cyclone is known by its specific name. Meteorologists give the name of cyclone like that
of human beings, birds, etc. e.g. Katrina, Bhola, Gorki, Mitch, etc. A cyclone named 'Bhola'
killed 4 lakh people in Bangladesh in 1970 AD and a cyclone named Gorki killed 14,0000
people in 1991 AD in the same country. Similarly, in 2005 a cyclone named Katrina killed 1800
people and damaged the property worth millions in the USA.

hurricane /ˈhʌrɪkən/ - a violent storm with very strong winds

378 Oasis School Science - 9 ASTRONOMY AND GEOLOGY

Causes of cyclone

The temperature of sea water in the upper 50m should be at least 26.50C or more for the
development of cyclone. A cyclone develops with a low pressure zone within 50 to 250
north and south latitude. Water vapour with warm air rises up when the air concentrates
in low pressure zone which organizes cluster of thunderstorm with weak surface winds.
It is called tropical disturbance. As this process continues, the surface winds strengthen
and flow forcefully around and into the centre of the growing storm. But the atmospheric
pressure decreases. As a result, the storm becomes larger and stronger. When the speed
of rotating storm is more than 119 km/h., it changes into cyclone. The speed of cyclone
may reach upto 200km/h. The water vapour flowing upwards cools down fast and
releases heat which is the main source of energy for a cyclone or typhoon.

The core of the cyclone has higher temperature than that in its surroundings. So the
water vapour rises up and condenses, then the hot air from the central part of the cyclone
gets down which generates the regular activation of cyclone. The central spiral windy
mass of cyclone is called eye. The eye is circular in shape. The pressure of air in the core
of eye is less than its outer parts. The diameter of eye ranges from 30–60 km. The rate of
change in the shape of eye indicates the powerful or weak cyclone. The shape of eye
becoming small indicates more powerful cyclone.

When the cyclone reaches the land, the heat Fig. 22.10 Eye of cyclone
energy provided by the ocean is lost. The strength
of cyclone decreases gradually and finally ends.
The cyclone developed above the sea may be weak
and ends if there is no continuous circulation of
energy source. On the basis of the wind speed
of the cyclone and damages caused by it in the
Atlantic ocean and North pacific ocean, the cyclone
can be divided into five categories, according to
Saffir-Simpson scale. The cyclone belonging to
category 1 and category 2 have low wind speed
resulting in minimal to moderate damages.
Similarly, 3, 4 and 5 categories have extreme
damages because of its high wind speed. The
wind speed of category 5 is more than 250 km/h.

The water level of the ocean rises up more than seven metres high during the movement
of cyclone. It causes flood in the coastal area. The process of rising of water level due to
cyclone is called sea surge or storm surge. It may destroy life and property.

Effects of cyclone
1. Cyclone destroys life and property on coastal areas.

2. The heavy rainfall induced due to the cyclone causes other disasters like flood and
landslide.

3. Cyclone causes soil erosion and destruction of crops.

4. Cyclone deposits silt in fertile lands and reduces the fertility of the soil.

5. Cyclone causes disturbances in the activities like fishing, shipping, boating, etc.



ASTRONOMY AND GEOLOGY Oasis School Science - 9 379

Safety measures of cyclone

Cyclone is very destructive in coastal regions as it is quite unpredictable. However,
meteorologists forecast the probability, direction and speed of cyclone with the help of satellites.
It helps people to take precautions. Some safety measures against a cyclone are as follows:

1. The government should collect information and give early warning to the people
in the coastal regions or in the sea.

2. The buildings in the coastal regions should be made strong by adopting cyclone
resistant technology.

3. We should construct emergency shelters or houses for the victims of cyclone.

4. Necessary preparation should be made to rescue the victims of cyclone.

5. Public awareness should be provided to the people of coastal regions.

6. People should remain informed of the warnings and instructions given by
government and they should act accordingly.

SUMMARY

• A natural hazard is a naturally occurring dangerous event that might have a negative
effect on people or the environment.

• A hazard is a natural or man-made situation that poses a level of threat to life, health
property or environment.

• Hazards may be both natural and man-made; similarly, hazards may be physical,
chemical, biological, etc.

• Disaster is a sudden unfortunate or adverse event which causes great damage to
human beings as well as plants and animals. Disasters occur rapidly, instantaneously
and indiscriminately.

• Disaster risk management includes sum total of all activities, programmes and
measures which can be take up before, during and after a disaster with the purpose
to avoid a disaster, reduce its impact or recover from losses.

• The disaster risk management cycle consists of four phases. (i) Prevention/ Mitigation
(ii) Preparedness (iii) Response (iv) Rehabilitation or Reconstruction in post-disaster
stages.

• A glacial lake outburst flood (GLOF) is a type of outburst flood that occurs when the
dam containing a glacial lake fails.

• The volume of glacial lakes varies but may hold millions to hundreds of millions
cubic meters of water.

• A cyclone is an area of closed, circular fluid motion rotating in the same direction
as the earth. It is usually characterised by inward spiralling wind that rotates
anticlockwise in the northern hemisphere and clockwise in the southern hemisphere.

380 Oasis School Science - 9 ASTRONOMY AND GEOLOGY

Exercise

Group-A
1. What is hazard? What are its types?
2. How many types of natural hazard are there? Name them.
3. Define manmade hazard with examples.
4. What is glacier flood?
5. In which places of Nepal there is possibility of glacier flood?
6. What is glacier lake outburst?
7. What is meant by GLOF?
8. What is cyclone? Why is it called a natural hazard?
9. What is meant by sea surge and tsunami? Write.

10. Name the hazards shown in the given figures.
i) ii)

Group-B
1. Differentiate between natural hazard and man-made hazard.
2. Flood, landslide and earthquake are called natural hazards. Why?
3. Differentiate between glacier flood and glacier lake outburst.
4. Road accident and aircraft accident are called man-made hazards. Why?
5. Write any two differences between tropical storm and typhoon.
6. Glacier flood occurs frequently in Nepal, why?
7. Cyclone cannot affect Nepal directly. Give reason.
8. Differentiate between glacier flood and cyclone.

Group-D
1. List the major effects of glacier flood.
2. Write down the major causes of cyclone.
3. Write down the major effects of cyclone.
4. Write down the effects of glacier lake outburst.
5. What are the protective measures of glacier flood? Write.
6. How is management of natural hazard done? Write any four points.
7. Write down the phases of disaster management cycle. Explain any two of them.
8. Write a short note on glacier lake outburst in Nepal.
9. Write any four protective measures of cyclone. Write any two differences between

natural hazard and man-made hazard.

ASTRONOMY AND GEOLOGY Oasis School Science - 9 381

UNIT 23 Estimated teaching periods

Theory 3

Practical 0

Greenhouse Greenhouse

Objectives

After completing the study of this unit, students will be able to:
• introduce greenhouse in natural environment and explain its effects.

• explain the importance and utilities of artificial greenhouse.

• introduce climate change and describe causes, effects and mitigating measures
of climate change.

23.1 Introduction

A greenhouse is a structure with walls and roofs made chiefly of transparent materials such
as glass or plastics in which plants requiring regulated climatic conditions are grown. A
greenhouse is also called a glasshouse or a hothouse. The size of greenhouses ranges from
small sheds to industrial-sized building. A miniature greenhouse is known as cold frame. The
interior of a greenhouse exposed to sunlight becomes significantly warmer than the external
ambient temperature protecting its contents in cold weather.

Fact File-1

The house made artificially
by glass or plastic in botanical
gardens or agricultural fields
is called artificial greenhouse.

Fig. 23.1 Artificial Greenhouse

Greenhouses are used extensively by botanists, commercial plant growers, and gardeners.
Particularly in cool climates, greenhouses are useful for growing and propagating plants
because they both allow sunlight to enter and prevent heat from escaping.

In this unit, we will study greenhouse in natural environment, greenhouse effect, adverse

ambient /'aembiənt/ - relating to the surrounding area; on all sides

382 Oasis School Science - 9 ASTRONOMY AND GEOLOGY

consequences of greenhouse effect, artificial greenhouse, its importance and utilities, climate
change, causes and effects of climate change, and measures of climate change management.

23.2 Greenhouse Effect

Different types of gases like carbon dioxide,

chlorofluorocarbon, methane, oxides of nitrogen,

water vapour, etc. are present in the troposphere

of the atmosphere. These gases cover the earth's

surface making dense canopy similar to the glass

frame of an artificial greenhouse. The dense

canopy of different gases allows the solar

radiations to enter the earth surface but does not

allow it to escape out after reflection. As a result,

these solar radiations are absorbed in the Fig. 23.2
atmosphere, increasing temperature of the earth.

The phenomenon of increasing the temperature Reasonable fact-1

of the earth as in artificial greenhouse is called greenhouse effect. The gases which are
The roof of artificial greenhouse is made
responsible for the greenhouse effect are called slanted, why?

greenhouse gases. Environmental scientists Ans: The slanted roof of greenhouse occupies
estimated that carbon dioxide had 57% impact more area. So, the roof of artificial greenhouse is
on greenhouse effect, chlorofluorocarbon had made slanted to allow more sunlight to enter.

25%, methane had 12% and that of oxides of

nitrogen was 6%. The temperature of the earth is increasing gradually due to greenhouse

effect. This process is called global warming. A large mass of ice in the polar caps melts due to

global warming which increases the level of the sea. It affects the lives of people in coastal

areas. Similarly, the temperature of higher regions is increasing more as compared to the

lower regions due to the drying of the water resources and reduction in the amount of ice in

the Himalayan region.

The sources of greenhouse gases

The greenhouse gases are released from different human activities as well as by some natural
processes. Some of them are listed below:

1. Carbon dioxide gas (CO2) is produced by burning of fossil fuels like coal, oil, natural
gases, etc.

2. Methane (CH4) is produced from the decomposition of domestic wastes and sewage.

3. Chlorofluorocarbon (CFC) is released from refrigerators, air conditioners, aerosol spray
cans, etc.

4. Water vapour (H2O) is released from the oxidation of organic compounds as well as
vaporization of water from water sources.

ASTRONOMY AND GEOLOGY Oasis School Science - 9 383

Importance of greenhouse effect

If there were no greenhouse gases in the atmosphere, all the solar radiation entering the
earth surface would escape into the space. As a result, heat would not be stored on the earth.
Consequently, the temperature of the earth would be less by 39 0C than today's temperature.
Ice would cover the earth and there would not be any organism on the earth. So, greenhouse
effect is very important for the existence of lives on the earth.

Adverse impacts of greenhouse effect

Due to various human activities, the concentration of greenhouse gases is increasing day by
day. It increases the temperature of the earth. The adverse consequences of greenhouse effect
are given below:

1. Effects on animals
i. It helps to spread different types of diseases like malaria, filariasis, cholera,
diarrhoea, etc.

ii. It helps to increase the number of pathogenic insects.

2. Effects on plants
i. It affects water cycle, soil moisture and soil composition. As a result, there is a
change in the cultivation and harvesting periods of crops.

ii. Due to the effect of global warming, tropical plants are seen at the temperate region.

iii. It helps in breeding, growth and development of disease causing insects.

3. Effects on climate
i. It increases the temperature of the earth.

ii. It brings melting of ice in the polar region, which increases the sea level. As a
result, low land areas of the earth may submerge.

iii. It changes the pattern of rain fall and weather condition.

Ways of controlling greenhouse effect

Greenhouse effect can be controlled by following methods:

i. It can be controlled by decreasing deforestation and increasing afforestation.

ii. It can be controlled by reducing the use of fossil fuels like petrol, diesel, kerosene,
coal, etc.

iii. It can be controlled by banning the production and use of CFCs.

iv. It can be controlled by using solar energy, wind energy, biogas, etc.

23.3 Artificial Greenhouse

The houses which are made artificially by glasses or plastics in botanical gardens or agricultural
fields are called artificial greenhouses. These houses allow the micro waves of sunlight to
enter but do not allow them to escape out after reflection. As a result, they convert solar energy

384 Oasis School Science - 9 ASTRONOMY AND GEOLOGY

into heat energy and the energy is stored inside the greenhouse. Ultimately, the temperature
inside the greenhouse increases. The roof of artificial greenhouse is slanted to allow more
sunlight to enter.

Fig. 24.3 Artificial greenhouse

Importance and utilities of artificial greenhouse

Greenhouses have more temperature than in their surroundings. So, different plants like
flowers, fruits, vegetables, etc. can be grown in off-season. It helps to earn money, greenhouses
help prevent the extinction of some plants due to global warming. Similarly, the plants that
grow in hot places can be grown in cold places inside greenhouses. The importance and
utilities of greenhouses are as follows.

i) Some species of plants can be grown throughout the year inside greenhouses.

ii) Fruits, vegetables, flowers, etc. can be grown in off-season.

iii) In cold countries, crops and other plants can be grown inside greenhouses.

iv) The plants that grow in summer season can be grown in winter season inside artificial
greenhouses.

v) The plants grown inside artificial greenhouses help to control environment pollution.

23.4 Climate Change

Climate is the atmospheric phenomenon over
a long period of time. Climate change refers to
the variation in the earth's global climate or in
regional climate over time. Human beings are
responsible for change in the climate of a region.
The main factor for climate change is increase in
level of carbon dioxide in the atmosphere. Over
use of fossil fuels, deforestation, burning of
firewood, forest fire, etc. increase concentration
of carbon dioxide in the atmosphere.

Climate change is a change in the statistical Fig. 23.4

ASTRONOMY AND GEOLOGY Oasis School Science - 9 385

distribution of weather patterns when that change lasts for an extended period of time, i.e
decades to millions of year. It may refer to a change in average weather conditions or in the
time variation of weather around longer-term average condition. Nepal has different climatic
conditions due to variation in geographical structures. Nepal is extended form 60 m to 8848m.
Nepal has been divided into Terai, Hilly and Himalayan region. The climate of Nepal ranges
from extreme hot to extreme cold. So, Nepal is a sensitive country in terms of climate change
and change in climate is a burning issue for Nepal.

Causes of Climate Change

Climate change is caused by various factors such as biotic processes, variations in solar
radiations received by the earth, tectonic movements, volcanic eruptions, etc. Certain human
activities like deforestation, industrialization, excessive use of chemical fertilizers, etc. play a
significant role in climate change. The major causes of climate change are given below.

1. Increase in temperature

Different parts of the earth receive different amount of solar radiation due to geographical
variation. The parts of the earth that receive more solar radiation become hotter than the
parts that receive less solar radiation. The increase in temperature is one the causes of
change.

2. Release of greenhouse gases

Different types of greenhouse gases like carbon dioxide, chlorofluorocarbons, methane,
nitrous oxide, ozone, etc. are released in atmosphere due to various human activities.
These greenhouse gases are responsible for climate change.

3. Deforestation

Forests help to maintain balance in amount of carbon dioxide and oxygen in atmosphere
as green plants use carbons dioxide gas for photosynthesis. The amount of carbon
dioxide gas in atmosphere increases due to deforestation which results in increase in
temperature and climate change.

4. Excessive use of chemical fertilizers

Greenhouse gases are released due to excessive use of chemical fertilizers. Similarly,
overuse of chemical fertilizers makes the land dry. As a result, temperature of the earth
increases and change in climate takes place.

5. Industrialization

Various types of gases like carbon dioxide, sulphur-dioxide, etc. are released in
atmosphere while running industries. There gases contribute to greenhouse effect which
results in change in climate.

6. Volcanic eruption

Dust particles and compounds of sulphur are released during volcanic eruption. These
substances accumulate in stratosphere and block the solar radiation which results in
climate change.

386 Oasis School Science - 9 ASTRONOMY AND GEOLOGY

Effects of Climate Change

(i) It causes loss of biodiversity.
(ii) It decreases agricultural production and changes the crop pattern.
(iii) It melts snow in polar region and the Himalayan region.
(iv) It increases the level of sea, due to the melting of ice in the polar region.
(v) It decreases the amount of fresh water.
(vi) It affects the global water cycle.
(vii) It changes wind circulation and affects the pattern of rainfall of a particular place.
(viii) It causes improper distribution of rainfall.

Measures of climate change management

1. Deforestation should be discouraged and afforestation should be encouraged.
2. Plantation should be done on bare parts of land.
3. The resources of water should be conserved and managed.
4. Overuse of fossil fuels should be reduced.
5. Alternative sources of energy should be developed and used.
6. Environment pollution should be minimized.
7. Release of greenhouse gases should be stopped.
8. Use of chlorofluorocarbons should be banned.
9. Proper management of waste materials should be done.
10. Natural environment should be conserved.
11. Agriculture system should be improved.
12. Unmanaged development works should be controlled.
13. Proper use and management of automobiles should be ensured.
14. Over use of chemical fertilizers should be discouraged.
15. Public awareness should be generated.
Activity 1

• Prepare an artificial greenhouse nearby your house by using plastics.
• Note down the change in temperature inside and outside the greenhouse.
• What can you conclude from this activity?

Activity 2

• Study the adverse effects of climate change in your locality.
• Find out the causes of climate change in your locality.
• Suggest the measures of climate change management.
• Prepare a short report and submit to your science teacher.

ASTRONOMY AND GEOLOGY Oasis School Science - 9 387

SUMMARY

• A greenhouse is a structure with walls and roofs made chiefly of transparent
materials such as glass or plastic in which plants requiring regulated climatic
conditions are grown.

• Greenhouses are used extensively by botanists, commercial plant growers, and
gardeners.

• The houses which are made artificially by glasses or plastics in botanical gardens
or agricultural fields are called artificial greenhouses.

• Greenhouses have more temperature than in their surroundings. So, different
plants like flowers, fruits, vegetables, etc. can be grown in off-season.

• Climate is the atmospheric phenomenon over a long period of time. Climate
change refers to the variation in the earth's global climate or in regional climate
over time.

• Climate change is a change in the statistical distribution of weather patterns when
that change lasts for an extended period of time, i.e decades to millions of years.

• Climate change is caused by various factors such as biotic processes, variations in
solar radiations received by the earth, tectonic movements, volcanic eruptions.

• Increase in temperature, release of greenhouse gases, deforestation, excessive
use of chemical fertilizers, industrialization, volcanic eruption, etc are the major
causes of climate change.

Exercise

Group-A
1. Define greenhouse.
2. What is meant by greenhouse effect?
3. What are greenhouse gases? Name any two greenhouse gases.
4. Write any two causes of greenhouse effect on the earth.
5. What is an artificial greenhouse?
6. What is climate change?
7. What are the main causes of climate change in Nepal?
8. Write down the major effects of climate change.
9. What is the effect of climate change on human health?

388 Oasis School Science - 9 ASTRONOMY AND GEOLOGY

Group-B
1. Differentiate between natural greenhouse and artificial greenhouse.
2. Natural greenhouse effect is very essential on the earth, why?
3. Artificial greenhouse gases are very essential for human beings, why?
4. The roof of artificial greenhouse is made slanted, why?
5. Increase in release of various greenhouse gases is the main cause of climate change.

Justify this statement.
6. Deforestation and industrialization cause climate change. Justify this statement.

Group-D
1. Write down the utilities of artificial greenhouse.

2. What is the effect of climate change on human health? Write any four effects.

3. Climate change invites energy crisis, how? Justify this statement.

4. How does climate change occur due to increase in release of greenhouse gases?

5. How does climate change occur due to deforestation? Write in brief. Differentiate
between greenhouse and greenhouse effect.

6. How does climate change occur due to industrialization? Differentiate between and
natural greenhouse and artificial greenhouse.

7. Write in brief about the effect of climate change in agriculture and water resources.
Differentiate between greenhouse and cold frame.

8. Write in brief about the impact on human settlement and physical facilities due to climate
change.

ASTRONOMY AND GEOLOGY Oasis School Science - 9 389

UNIT 24 Estimated teaching periods

Theory 4

Practical 1

The Earth in the

Universe Yuri Gagarin

Objectives

After completing the study of this unit, students will be able to:
• explain rotation and revolution of the earth.
• describe the phases of the moon.
• explain the relationship among the sun, earth and moon in terms of their position.
• define umbra and penumbra with figures.
• explain solar eclipse and lunar eclipse with labelled figures.
• introduce satellites with their types.

24.1 Introduction

Universe is the vast surrounding space that includes everything around us like the earth,
solar system, stars, galaxies, etc. The earth receives heat and light from the sun. The sun is a
medium sized star. It is about 1.5 × 108 km away from the earth. Planets revolve round the sun
in their elliptical orbits almost in the same plane. Our solar system is present in the Milkyway
galaxy which can be observed with the help of a powerful telescope.

The Milkyway is the spiral shaped galaxy which includes solar system along with other
planets, stars, constellations, etc. In constellation, the Milkyway is at the center. The sun lies in
the two-thirds of the Milkyway galaxy.

24.2 Light Year

The distance between the celestial bodies is extremely large. Therefore, it is difficult to measure
the distance between them in kilometre. Hence, we express such distance in light year.

Light travels 3 × 108 m in one second in vacuum and hence 9.46 × 1015m in one year.

One light year = speed of light × 1 year

= 3×108 m/s × 1 year

= 3×108 m/s × 365 × 24 × 60 × 60s

= 9.46×1015m

∴ One light year = 9.46 × 1015m


390 Oasis School Science - 9 ASTRONOMY AND GEOLOGY

This distance 9.46 ×1015m is called 1 light year. Thus, 1 light year is defined as the distance
travelled by light in one year in vacuum.

Light takes 8 minutes and 20 seconds to reach the earth from the sun. So the distance between
the earth and the sun is 8 light minutes. The nearest star, Proxima Centauri, is about 4.3 light
years away from the solar system. It means that light takes 4.3 years to reach the solar system
from the star. The length of our galaxy (Milky way) is 100,000 light years and its diameter is about
800 light years. The nearest galaxy, Andromeda, is about 130,000 light years away from the earth.

24.3 Solar System

The family of the sun containing eight planets and their satellites, asteroids, comets, etc. is
called solar system. Our solar system consists of eight planets, satellites, asteroids, comets, etc.
They are all moving in the space along with the sun. The sun is a medium sized star having the
surface temperature of about 5400°C. It is located at the centre of the solar system. The source
of heat of the sun is the thermonuclear fusion reaction. It is the reaction in which two or more
light nuclei combine to form a single heavy nucleus. In the sun, hydrogen gas is converted into
helium gas and a vast amount of energy is produced.

The earth is the only planet where the living beings exist due to favourable conditions like
suitable temperature, presence of life supporting gases and water.

Fig. 24.1 Solar system

The planets revolve around the sun in their elliptical orbits. During their motion, they are
at different distances at different times from the sun and their speed is also different. The
nearest planet Mercury has one surface very hot and the other very cold. It is due to this
reason that during its rotation around its axis, the same side faces towards the sun. Mercury
has no atmosphere. Venus is very hot and has small amount of oxygen in its atmosphere.
Mars has a small amount of water. It has a small amount of oxygen in its atmosphere. Though
the environment of the Mars is similar to that of the Earth, no life is found to exist there. The
planets from Jupiter to Neptune are very cold so there is no possibility of life in these planets.
The International Astronomy Union, in 2006 AD, has decided to displace the Pluto from the
status of planet to dwarf planet because Pluto is very small as compared to the average size of
other planets. Similarly, the orbit of the Pluto coincides with the orbit of Neptune.

satellite /ˈsætəlaɪt/ - a heavenly body that revolves around a planet

ASTRONOMY AND GEOLOGY Oasis School Science - 9 391

392 Oasis School Science - 9 Table 25.1 Comparative study of planets Some information about the eight planets of the solar system is given in the following table:

Planet Avg. Least dis- Period Avg. Diameter Period of Surface Gravity Gases in the atmp- Mass Density Density No. of
Distance tance from of rev- Orbital (km) rotation temperature (earth =1) sphere (possible) (earth=1) (gm/cc) (earth=1) satellites
Mercury from the earth olution velocity known
Venus the sun (x106km) (days/or (km/s) (0F) 0.055 5.42 1
Earth (x107km) years) 0.815 5.25 0.97 0
57.6 1 5.52 1 0
891.7 87.97 47.89 4851.2 58.65 days 333 0.386 Not present 3.99 0.73 1
10.72 day 243.02 days 465 1.33 0.25 2
23 h 56 m 45 0.69 0.13
ASTRONOMY AND GEOLOGY 14.88 41.4 224.7 35.63 12035.2 0.871 CO2, H2O, O2 1.27 0.23 63
days 1 N2, O2, CO2, H2O 1.64 0.30
60
- 365.25 29.79 12672 27
days 13

Mars 22.56 55.7 686.98 24.13 6742.4 24 h 37 m -80 0.38 CO2, N2, Ar, O2, 0.107
days 22s CO, Ne, Kr, Xe, H2O

Jupiter 76.8 628.76 12 13.06 1139040 9 h 55 m -160 2.53 H2, He, CH2, NH3, H2O 317.892

years

30 s

Saturn 144 1277.4 29.5 9.64 115811.2 10 h 30m -220 1.07 H2, He, CH4, NH3 95.16

years

Uranus 288 2587 84 6.81 50441.6 17 h 14m -323 0.91 H2, He, CH4, NH3, H2O 14.54

years 24 s

Neptune 448 4310 164 5.43 48972.8 16 h 6m 36s -330 1.14 CH4 17.15

years

Source: World Almanac, 2007