Blooming Science-9-2077 final final for press

3. Modern Concept of Origin of Life

Modern concept was suggested by Operin in 1930 AD. According to this theory, the first
living cell arose from simple elements. Micro-molecules like carbon, hydrogen, oxygen, nitrogen
etc. united to produce macro-molecules interacted to produce the first living cell by a process
called abiogenesis. Abiogenesis means development of a living thing from a non-living matter.
These cells gradually became more complex to the present day form, by the process of organic
evolution.

Evidences of Organic Evolution

The study of living organism of the past and the present shows that there has been a very slow
and gradual changes in the organism. This has led to the evolution of new forms. The process of
evolution is a continuous process which will continue forever. Some of the evidences are:

(a) Evidence from classification.

(b) Evidence from palaeontology.

(c) Evidence form comparative morphology and anatomy.

(d) Evidence from vestigial organs.

(e) Evidence from embryology.

(f) Evidence from geographical distribution.

(g) Evidence from bridge animals. (Connecting link)

(a) Evidence from Classification:

We have already studied the classification of plants and animals. We find that there is a
gradual link from the simpler forms to the complex forms. Classification gives the idea that the
simple form might have given rise to the complex forms. The resemblance of fish to amphibian,
amphibian to reptiles and reptiles to aves and mammals give an indication of the process of
evolution.

(b) Evidence from Palaeontology:

The remains of animals or plants (usually the hard part like bones or shells) which have
been buried in rocks for millions of years and have gradually turned into stone are called fossils.
Palaeontology is the study of fossils which are of great significance particular as evidences in
favour of organic evolution.

Fossils are found in sedimentary rocks. During the flow of water from various sources, it
carries soil, wood, dead bodies, etc. into the ocean these substances settle at the bed of the ocean,
make layers one above other and finally form sedimentary rock. The dead bodies of animals
decay inside the rocks but bones remain intact and leave impressions inside the rocks after a long
time.
In these rocks, the fossil of the most primitive and the simplest form of organisms remain in
the lowermost strata and the fossils of higher forms of organisms remain on the uppermost strata.
From the study of fossils of different organisms it becomes clear that the complex form of
organism originated gradually from the simple form. Therefore the evidences from fossils have
been given high priority.

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The first fossils found were of marine plants and animals, latter the fish, amphibians and
reptiles developed. A time came when giant reptiles came into existence on the earth. These
giant reptiles were the dinosaurs which have now been disappeared from the earth. Mammals
and specially man are of recent origin. The organisms which existed in the past and were formed
earlier are called primitive. The organisms that evolved from the earlier forms and came into
existence later are called advanced.

Pleistocene Carpals

2 × 106 years

Equus

1.6 m

Pliocene Hoof
42
7 × 106 years

Pliohippus

1.0 m 3

Miocene Merychippus

26 × 106 years

1.0 m 42
3

Oligocene Mesohippus

38 × 106 years

Eocene 0.6 m 42
3
54 × 106 years Hyracotherum
0.4 m 52
43
Fig: Evolution of Horse
Metacarpals

Most convincing evidence in support of organic evolution came from fossils. Figure given
shows how the present day horse has evolved from the earlier horse which was a very small

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animal in comparison to the modern horse. The present day horse not only has longer legs but
also has a walk on a single toe. This has increased the swiftness and speed of the animal.

The age of a fossil is determined with the help of carbon dating and its radioactivity.

(c) Evidence from Comparative Morphology (External) and Anatomy (Internal structure):

1. Homologous Organs: The basic structural plan of the organs in different groups of animals
remains the same. This shows that simpler animals have given rise to the complex ones by
developing variations. The bones in the fore limbs of a man, the legs of a horse, the wings of
a bat, the wings of a bird and the flippers of a seal have the same structural plan. It is modified
differently in each animal according to its requirement of work. The organs that have the same
structural plans and origin but differ in functions are called homologous organs. This is the proof
of the fact that the vertebrates have a common ancestor.

Whale Bird Bat Ox Horse Man

2. Analogous Organs: The organs that have different structural plan and origin but similar in
function are called analogous organs. The wings of bird and insects are analogous organs. This is
the proof of these two groups were not evolved from the same ancestor.

Fig: Wings of bird Fig: Wings of butterfly

(d) Evidence from Vestigial Organs:

Vestigial organs are the undeveloped and non-functional organs in some organism. The same
organs in other organism are found well developed and functional. The vermiform appendix,
tailbones, ear muscles, conjunctive, wisdom tooth, segmented muscles in abdomen are some
examples of vestigial organs of man. The presence of these organs in the body shows that they
were present in the ancestral form and were used to function in them. However, in some form,
they lost their utility and become non-functional. For examples, vermiform appendix is used
for digestion of cellulose in some herbivores, conjunctiva is used to protect the eye in aquatic
vertebrates, etc.

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Canine Nipple Nictitating
Ear muscles membrane

Body hair

Coccyx

Fig: Vestigeal organs of man

(e) Evidence from Embryology:
The embryos of all vertebrates are so similar in shape and structure in their early stages that
it is difficult to distinguish them apart. Embryos of mammals and reptiles resemble more than
mammals and fishes. The similarity in vertebrates is a proof of evolution and it indicates that
these forms have evolved from common ancestor.

Fish Tortoise Chicken Rabbit Human

(f) Evidence from Geographical Distribution:

Geographical distribution of the organism on the major land mass of the earth furnishes
the evidences of evolution for the present day. The present distribution can be explained by
past distribution of the evolution. Certain zones have their own characteristic animals. However,
place with same climatic condition in different regions of the earth do not have the same animals.

For example, the elephants are found in Africa and Asia but not in other places like America.
Although the common climates of these places are alike, yet the common animals found are
diverse in nature.

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(g) Evidence from Bridge Animals: (Connecting Links)

There are some similarities between lower animals and higher animals developed from
lower animals. There are few intermediate forms connecting the two groups. This intermediate
forms connecting the two groups of animals are called connecting links. The archaeopteryx, a
fossil bird in Jurassic period serves as a connecting link between the reptiles and birds. This bird
consisted of wings and feathers as well teeth and a long tail.

Similarly, the duck-billed platypus, a living animal found only in Australia, serves as a
connecting link between the reptiles and mammals. The platypus is a mammal because it has
hairs, mammary glands and other mammalian features. On the other hand, unlike mammals, it is
oviparous and cold blooded.

Archaeopteryx Platypus

Theories of Evolution

Evidences in favour of evolution shows that the present day life upon the earth has evolved from
the past life through a series of changes. Scientists have made attempts to explain the mechanism
of evolution. The most prominent ones were Jean Baptiste de Lamarck, Charles Darwin, Alfred
Russel Wallace and Hugo de Vries. The important theories are:

1. Lamarck’s theory of inheritance of acquired characters.

2. Darwin’s theory of natural selection.

3. Hugo de Vries theory of mutation.

1. Lamarck’s Theory: Lamarck (1809AD) states that environment has a great influence in
shaping animals. The change in environment would result in the need for new habits in the
animal. The new habits may involve modification in the structure of the body to adjust with the
new environment, and this results in evolution. Lamarck’s theory of evolution is the inheritance
of acquired characters which can be summed up as:

(i) Effects of Environment: The environment in which living organism exists influences them
and this influence lead to change in their habits. The change in habits results in unusual activity
of an organ of structure of organism. The people living in himalayan region has red checks and
partially opened eye which is different than people of other places. Similarly, animals in cold
region and hot region have different features. These all are due to effect of environment.

(ii) Use and Disuse of Organs: According to Lamarck, the development of an organ depends on
its use and disuse. The continuously use of an organ enhances its efficiency and size and leads to
its better development. However those organs which are not used, leads to its reduced efficiency,
size and ultimately disappeared.

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(iii) Inheritance of Acquired Characters: All the characters that have been acquired in
an organism during its life time are inherited and passed on from one generation to another
generations. After certain generations the off-springs produced become entirely different from
the ancestor. The organisms with new characteristics, therefore, form a new species.
Lamarck explained that the earlier giraffes probably had short necks which were subjected to
frequent stretching to enable them to reach the leaves on trees. This gradually brought about the
elongation of the neck. Thus, the giraffe of today has a very long neck. The other examples are the
eyes of cave animals whose sight became functionless and have ever disappeared. Carnivorous
animals possess claws etc.

Fig: Evolution of giraffe
Criticism of Lamarck’s Theory: Lamarck’s theory has not been found satisfactory to explain the
mechanism of evolution. Following are the criticism of Lamarckism.
a. Use and disuse of organs do not change the shape and size of the body practically.
b. New organs result from new needs of organism have been found untrue.
c. An iron smith’s son does not take birth with strong arm muscles through the trade is
practiced in the family generations.
d. A tail of rat was cut for many generations (around 21 generations by Wiseman wise
man) but size of tail of rat wasn’t decreased.
2. Drawin’s Theory of Natural Selection
Charles Darwin (1809AD-1882AD) was an eminent naturalists who propounded the theory
of natural selection. He published his opinion in his book ‘Origin of species by natural selection’.
Darwin made a wide collection of variations and studied them in detail. He suggested that a new
species came into existence through a process of natural selection.
The main features of Darwin’s theory are:
(a) Enormous fertility: The fertility rate among the living organisms is very high and every
organism has an innate desire to reproduce.
For example; an elephant, the slowest breeder, reproduces at least 6 young ones in its life
time. If we presume that all the progeny survive, then, in a period of 750 years, there will be
about 19,000,000 elephants descended from a single pair.

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The great fertility of animal is compensated by great destruction so that the total number of

individuals of any species remains constant. A pair of housefly can give birth ?DO
to 1 trillion of offspring in its life.
(b) StruggleforExistence:Thelargenumber But very few of them survive. You
of organisms produced compete with each Know
other for food and shelter. That is, they
struggle for existence. The struggle is not

only between members of the same species, but also between different species. They also struggle

against the physical environment, heat, rain, cold, fire, flood, etc.

(c) Variation and Heredity: No two off-springs derived from the same parents are alike. They
show minute differences. This is known as variation. Variation may arise due to genetic reasons
or due to change in the environment. Variations give rise to new characters and heredity and
pass them to the next generation. The variations are one of the most important factors of organic
evolution.

(d) Natural Selection: Nature controls the environment and selects the individuals which can
best survive in it. This is known as natural selection.

(e) Survival of theFittest: In the struggle for existence, various organisms compete with each
other. Only those which have favourable variation survive and reproduce. The other having no
favourable variation are automatically perished. Organisms which survive are the fittest because
they are able to adapt to the environmental changes. This is known as survival of the fittest.

(f) Origin of Species: According to Darwin, if a group of individual belongings to the same
species survives, the condition of life continues varying in different direction and natural
selection. Then, each variation after many generations will be so different from its parent and
ancestors that it will be developed as new species.

Criticism of Darwinism

(a) New species arise suddenly at a single step due to mutation and not due to
accumulation of small variation generation after generation.

(b) Darwin’s theory does not explain the origin of variations.

(c) It does not distinguish between heritable and non heritable variations.

d ) It is not always the case that useful variations are selected.

3. Hugo de Varies Theory of Mutation

Mutation theory was given by a Dutch Biologist named Hugo De Vries, in 1901AD. Mutation
is defined as sudden chromosomal change by which discontinuous variation takes place. Mutation
occurs by radiation and some chemicals called mutagens. An organism affected by mutation is
called mutant. The mutagens interfere with the coding system in the DNA to cause mutation.
The majority of mutations are harmful, but a very small proportion of them may be useful for an
organism. It is one main factors of evolution to mankind. Black patch on body, disability by birth,
cut a lip, six fingered limbs etc are its examples.

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Let’s Learn

1. Platypus is considered as a bridge animal between birds and mammals. It is because it is
oviparous and has beak like in birds, has fur and mammary glands like in mammals.

2. Dinosaurs get extinct in Mesozoic era. It is because they were too large to hibernate in dens
and they had no fur or feathers to be protected from the extreme cold. In this era the earth’s
climate was too cold. Similarly, they could not compete with mammals for their existence.

3. A good athlete is acquired character because this character need not be transmitted to the
newly born off springs.

Main Points to Remember

1. Evolution is the process of gradual change in living beings from simpler form to complex
form.

2. Complex organisms are assumed to evolve from simple organism over a period of millions
of years. It is called organic evolution.

3. The theory of organic evolution is supported by various evidences collected from different
branch of science. They are fossils, embryology, morphology, taxonomy, vestigial organs,
geographical distributions, etc.

4. Fossils are the impressions or remains of animals and plants preserved from the geological
past, buried in mud or sand, which later hardened into rocks.

5. Organs which are similar in structural plan and origin but differ in functions are known as
homologous organs.

6. Organs which are functional in one organism but functionless in other and are present in very
much reduced condition are called vestigial organs.

7. Lamarck’s theory of “Inheritance of acquired characters” states that modifications which
organisms acquire in adaptation to the environment to meet during its life time are
automatically handed down to its descendents and so become part of the heredity.

8. Darwin’s theory of “Natural selection” states that the tremendously produced off-springs of
an organism struggle with each other for their survival. Only those organism which are
able to produce suitable variations survive other will destroy. On a long run, the organism
with suitable variations will be so different from its parents and ancestors that it will be
graced as new species.

9. Hugo de Vries theory of mutation states that new species arise from sudden and unpredictable
changes but not gradual accumulation of small variation in the organisms.

PRO J ECTWORK

1. Make a list of some of the vestigial organs found in human body and discuss why are they
present in this form.

2. If possible visit to Natural Historical Museum, Swayambhu, Kathmandu to observe

fossils, preserved animals and plants. Prepare a report about your visit.

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Exercise

1. Choose the correct answer from the given alternatives.

i. Theory of special creation is related to...............................

a. science b. human c. god d. all of above

ii. Canine teeth is ...............................

a. homologous organ b. vestigial organ c. analogous organ d. none of above

iii. ................................ is sudden chromosomal change by which variation occures in
organisms.

a. Enormous fertility b. Mutation c. connecting links d. none of above

iv. Origin of ....................... is point of Darwinism.

a. species b. disase c. variation d. character

v. The process of gradual and orderly change in organisms from one form to another is
called.......................

a. evolution b. organic evolution c. mutation d. all of above

2. Answer the following questions.

a. Write the theories put forward about evolution of life on the earth.

b. What is organic evolution?

c. What are vestigial organs? Name some vestigial organs in human.

d. Differentiate between:

i. Homologous organs and analogous organs

ii. Struggle for existence and survival of fittest.

e. How does study of fossil give the evidence of organic evolution? Explain.

f. Write the evidences in support of organic evolution.

g. Define mutation.

h. State the three fundamental views included in Lamarck’s theory.

i. Why does a population of a species not increase although the number of offspring produced
from a single parent is always more?

j. What is natural selection? What kinds of animals survive in nature?

k. According to Lamarck’s theory of evolution, what is the reason behind the disappearance of
human tail?

l. What types of animals are called bridge animals? What evidences are obtained from such
animals in support of the organic evolution.

m. Findings from the study of fossils found in the sedimentary rocks have been used as the
evidences for organic evolution. How do the fossils found in the lower strata of sedimentary
rocks differ from the fossils found in the upper strata?

n. Describe how the findings from the embryological study have supported the theory of organic
evolution.

p. How are fossils formed?

q. Mention the major points of Darwinism.

r. What function could the vermiform appendix have performed in the ancestral forms?

s. What is variation? Classify it.

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Chapter NATURE AND ENVIRONMENT

21

Learning Outcomes Estimated Periods: 9+2

On the completion of this unit, the students will be able to:
• describe the effects of biotic factors and abiotic factors (air, light, temerature, soil,

water and organisms) on plants and animals.
• introduce and explain ecosystem service with examples.
• describe the interrelation of producers, consumers and decomposers.
• describe interrelationship of plants and animals interms of nutrition.
• describe the dependance of human beings on other animals and plants for basic needs

like food, shelter and clothing.

On the surface of the earth, there are soil, stone, rocks, rivers, lakes, ponds, sea etc. The crust
of the earth is enveloped with atmosphere. The physical world of the earth is composed of such
substances or components. They have direct or indirect effects on the plants, human and other
living beings in the surrounding. There is a close relationship between the substances of the
physical environment and the living beings. The organisms receive necessary substances such as
food, water, oxygen, carbon-dioxide, minerals etc from the physical environment. If the quality
or composition of the materials like air, light, temperature, soil, water etc is degraded the effect
will be on plants and animals.

Composition of Ecosystem

The ecosystem is important in the environment. It includes biotic and abiotic factors and different
aspects related to it. The study of its composition and conduction processes helps us to know
about the environment.

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Introduction of Ecosystem

There is a close relationship between organism and different physical aspects. The inter-
relationship between them is called ecosystem. The branch of science that studies about the
ecosystem is called Ecology. The Ecology is one of the branch of science that deals with plants,
animals, different ecological factors and interrelationship among them. In short, the ecosystem
is the combined form of animals, plants and various aspects of the environment of a place. The
definition coined by different environmentalists are different. The British environment Mr. A.G.
Tansley developed the concept of environment for the first time in 1935AD. As he proposed
ecosystem as the science that studies all aspects of man and environment. So, the ecosystem is
the basic functional unit of various aspects of environment which are inter-dependent and
inter-related and the reaction between their units is a continuous process.

Structure of Ecosystem

The ecosystem are different types. The biotic factors and abiotic factors are the main components
of the ecosystem. They are also known as living and non-living causative factors that affect the
environment. The plants, human being, animal, birds, microbes etc are different kind of living beings
included into biotic factor which is also known as organism community. Abiotic factor includes non-
living things such as soil, light, air, etc. and they are physical factors.

There is a continuous exchange of energy and other materials between biotic and abiotic factors
of an ecosystem. Due to this type of energy flow phenomenon there has been balance in the
nature.

(a) Biotic Factor: (The living factor)

All organisms in an environment including plants, animals and micro-organisms are
biotic factors. They are inter-related and inter-dependent. One organism will be getting some
assistance from another organism, Human beings, animals, insects, parasites, organism in soil
and microscopic organisms all come under biotic factors. Deer, sheep, cow, ox, goat etc are
grazing animals. They live on green plants. Over grazing destroys plants, herbs and makes the
soil loose & weak. It makes the land barren. The biotic factor indicates living community, which
includes producers, consumers and decomposers. On the basis of energy flow in the ecosystem,
the community is classified as follows.

(i) Producer: In the living community, the producer has special importance. The green plants are
the producers. The planktons, tiny floating plants or plants with roots, algae, herbs and other
plants are producers. Producers are living being and they make their own food. They do not
depend upon other for food. So the producers are autotrophs. Other organisms in the ecosystem
receive food and energy from these producers.

(ii) Consumer: The organisms in this group depend upon other animals and plants. On the basis
of food, the consumers are divided into three groups.

• Primary consumer • Secondary consumer
• Tertiary consumer

The organisms that depend upon plants for food are primary consumer. The animals in this
group are herbivores. Cow, goat, rabbit, deer etc are primary consumers. The animals that depend
on primary consumers for food are secondary consumers. Animals in this group may be both
herbivores and carnivores. Cats, Snakes, Jackal, frog etc are secondary consumers. Generally the

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animals in tertiary consumer group are physically strong. They depend upon primary consumers
and secondary consumers for food. Leopard, tiger, big fishes, crocodile, python, etc are tertiary
consumer in the ecosystem. Some animals are carnivores and some are omnivores.

Herbivores

Organisms which mainly feed on green plants are herbivores. For example; Cow, deer,
goat, etc

Carnivores

Organisms which mainly feed on flesh are carnivores. For example; Tiger, lion, leopard, etc.

Omnivores

Organisms which mainly feed on both plants and flesh are omnivores. For example; Human, Cat,
Dog, etc.

The green plants prepare their food. Herbivores depend upon green plants for food.
Carnivores and omnivores feed on the herbivores. At the end, animals die and microbes decay
the dead body and decompose it into simpler substance which are mixed up with the soil. The
green plants reuse these substances for their growth and development. The relationship among
organisms are continuous processes in the environment.

Grass Grasshopper Bird

(iii) Decomposer

Microbes like bacteria, fungi etc are decomposers. These microbes are the cause of
decaying of body of dead animals get mixed in the soil. Plants get nutrients from them.
This helps to maintain balance in the nature.

(b) Abiotic Factors (The non-living factor)

The abiotic factor includes the non-living components of the environment like air, solar
energy, temperature, soil, water etc. The different factors in the environment are inter-
dependent and inter-related. The biotic factors in the environment influence the abiotic
factor and vice versa. It is briefly explained below.



312 Blooming Science Book 9

(i) Air

The air is one of the important factor among abiotic factors. The air around the earth
is called atmosphere. It is composed of various gases like nitrogen, oxygen, carbon
dioxide, neon, helium, and others. It also has water particles and water vapour. Plants
take carbon dioxide gas in and give oxygen gas out during photosynthesis. All animals
including human breathe in oxygen gas and breath out carbon dioxide gas. In this way,
inter relationship between the plants and animals in an environment is being maintained.
The air helps in pollination and dispersal of seeds of the plants.

(ii) Solar Energy

The solar energy plays an important role on the life of the plants, animals and other
organisms. The sun is the main source of energy. It gives light and heat which are very
important for living beings. The plants prepare their food through photosynthesis in the
presence of solar energy. Due to geographic reasons some place get more sunlight while
some get less. Because of this reason, the weather, rainfall, agricultural production of
different places are variable. As a result, distribution of plants, animals and other organism
in different places is also different.

(iii) Soil

The soil is the other important factor of the environment. It is composed of rock particles,
minerals etc. But the composition of the soil from different place is different. The colour
of the soil differs according to minerals and organic matter present in it. The quality of the
soil will be improved if humus (matter made by decay or decomposition of organic
matters) is mixed in the soil.

Soil has minerals, organic matter, microbes and many chemical elements like nitrogen,
phosphorus and potassium which are essential for plants. Water and mineral are absorbed
by the plants from the soil. They are necessary for plants to grow. Plants produce grains,
fruits, vegetables and other substances needed for the animals. People construct their
homes, sheds etc on the land. If there is disturbance in the condition and composition
of the soil, the plants and animals will be directly affected. So, plants of different places
are different.

(iv) Water

Water is necessary for the life processes of plants and animals. The body of human
being, plants and other organisms is made of a lot of water. Water is important requirement
for photosynthesis. Human beings use water from river, lakes, ponds, springs, waterfalls,
seas etc for their life. The water has been important factor for the plants and animals to run
their life in different ways.

Differences between Biotic Component and Abiotic Component

Biotic Component Abiotic Component

1. It is the living component of an ecosystem. 1. It is the non-living component of the ecosystem.

2. It comprises producers, consumers and 2. It comprises physical environment such

decomposers. Eg. Plants, animals, micro- as soil, water, air and climatic factors like

organisms etc. light, temperature, pressure, humidity etc.

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Inter Relation between Plants and Animals

In an ecosystem, the plants and the animals are inter-related. The plants prepare complete organic
matter from simple inorganic matter. Animals receive food needed for them from the plants. The
organisms are classified as autotrophs and heterotrophs on the basis of the ways they receive their food.

(a) Autotrophs

The organisms that prepare their own food are called autotrophs. The green plants belong to
this group. They can prepare their own food because they have chlorophyll. They prepare
their food from carbon dioxide and water by photosynthesis in presence of sunlight. So
they do not need to depend upon others for food. Such organisms are autotrophs.

(b) Heterotrophs

The organisms that depend upon other organisms for their food are called heterotrophs.
Animals, parasites, mould and microbes belong to this group. They are further classified
as consumer and decomposers. They depends upon plants and other animals for their food.
The undigested part of the food is egested by animals and is used by the plants in suitable
condition.

Parasites

Parasites are organisms that obtain their food directly from other living organisms called hosts.
Tapeworm, roundworm, mosquito, flea, bedbug and the plants without chlorophyll are some
example of parasites.

Saprophytes

Saprophytes feed on dissolved organic and inorganic substances produced by dead and decaying
plants and animals. For example, fungi, mushroom and bacteria.

Holozoic

The organisms feed on both plants and animals are called holozoic. Such nutrition is more
common. Almost all animals including human being follow this nutrition system. This nutrition
system includes ingestion, digestion, absorption and excretion.

Differences between Phytoplanktons and Zooplanktons

Phytoplanktons Zooplanktons

1. These are microscopic plants which float 1. These are microscopic aquatic animals
freely on the surface of water in a pond, which freely float on the surface of water
lake, river or oceans. in a pond, lake, river or oceans.

2. They are autotrophs i.e. they are producers 2. They are consumers of first order.
of aquatic food chain.

3. Example: Algae 3. Example: Protozoa, very small fish etc.

Food Circulation Process in Ecosystem

Energy is necessary in order to carry out the life processes. Foodstuff is the main sources of
energy. Plants can prepare their food themselves. Some plants are parasitic in nature. Animals
are not able to prepare their food materials themselves. Therefore they obtain their food from
plants or other animals. Birds feed on insects. Similarly fish feed on small insects as well as other
planktonic organisms. Fish is eaten by man and other animals like snake, egrets, etc. According
to ecosystem animals will get their food materials from different sources in order to survive.

314 Blooming Science Book 9

Thus, relationship between autotrophs and heterotrophs will be maintained in the process of
fulfilling their nutritional requirements. In the process of interchanging food materials, the food
chain and food web will be formed.

Food Chain (The process of eating and being eaten up)

The community of living organisms and physical factors have a intimete relationship. The ecosystem
function with their mutual relationship. We can be cleared about the ecosystem analyzing its factors.

Food chain starts from producers i.e. from green plants. The food prepared by green plants
is used by consumers for the energy they need to live. Energy is passed in the form of chain
from porducers to primary consumers and from them to secondary consumers and so on. The
decomposers feed and convert dead bodies of producers and consumers into simple inorganic
substance which can again be used by producers to make food.

Grass (Producer) Grasshoppers (Primary consumer) Frogs (Secondary consumer) Snakes (Tertiary consumer)

Nitrogen, Carbon dioxide Bacteria and fungi Excretory wastes and
and other simple substances (Decomposers) remains after death

The transfer of energy from producers through a series of organisms (herbivores, carnivores,
decomposers) with repeated eating and being eaten is called food chain.

In above figure, grass is eaten by grass hoppers which are in turn eaten by frogs. The frogs are
then eaten by snakes and snakes by hawk. In a food chain, each link is called a tropic level.
Generally maximum energy is available at the first trophic level. Each step of food chain is called
tropic level.

Trophic Level

The producer, consumer arrangement is known as trophic structure and the position that an
organism occupies in a food chain is called trophic level.

The green plants like phytoplankton, herbs, shrub or trees derive their energy from sun are called
producers. The producers belong to first trophic level. All the herbivores or primary consumers
derive their energy from the producers belong to second trophic level. The secondary consumers
which feed on primary consumers consistute the third trophic level. The tertiary consumers that
feed on the secondary consumers represents the fourth trophic level.

In a grassland ecosystem there are four trophic levels which are shown in the figure. From the
trophic level we can say that the transfer of energy and materials takes place from one trophic
level to another trophic level through food chain.

Fourth trophic level Tertiary consumers

Third trophic level Secondary consumers

Second trophic level Primary consumers

First trophic level Producers

Trophic level

Blooming Science Book 9 315

Food Web

In an ecosystem, an organism does not depend fully on another for its survival. Herbivores feed
on varieties of plants. Plants are not only eaten by rabbits but also by goat, mice etc. Carnivores
eat different types of herbivores, omnivores eat different kinds of plants and animals.

Food web is a inner connected series of food chains that establishes a network of relationship
among various organisms. For example, the various food chains operating in the food web are:

Deer Lion

Grass Zebra Lion

Grass Zebra Vulture Lion
Grass Deer Vulture Gazelle

In above food web, plants are at the first tropic level, grass Zebra Vulture
hoppers are at second trophic level, mice are also at second Grass
trophic level as they are herbivores too. Lizard is at third
trophic level, hawks are at fourth trophic level when they
feed upon lizards and third trophic level when they feed
upon mice.

Each food chain in a food web constitutes a single pathway. Alternate pathways in a web help to
maintain the stability of living community.

Food web provides a concise description of feeding patterns which determine the flow of energy
and matter through a community. So any alternation in the food web of a community may have
far reaching consequences. Hence, food webs can be used to predict and explain the effects of
changes within the community.

Differences between Food Chain and Food Web

Food Chain Food Web

1. It is a series organisms through which food 1. It is formed by a whole community of

energy flows in an ecosystem. interlinked living things and is made of

several food chains.

2. It has only one path way for flow of energy. 2. It has several alternative pathwayss for the
flow of energy.

3. It does not give a complete picture of 3. It gives a complete picture of the inter

the interrelationship amongst the various relationship amongst the various organisms

organisms of an ecosystem. of an ecosystem.

4. Example 4. Example: Snake Hawk

Grass → Insects → Frog Mice Rabbit

Plant

316 Blooming Science Book 9

Types of Ecosystem

There are many types of ecosystem in the earth. According to the geographical conditions of the
earth, producers and consumers are different. The main type of ecosystems are goven below:

Ecosystem

Terrestrial ecosystem Aquatic ecosystem

Forest Grasiland Desert Sea/oceans Fresh water
ecosystem ecosystem ecosystem
ecosystem ecosystem

River Pond Water shed
ecosystem ecosystem ecosystem

Here, we will discuss about forest ecosystem and pond ecosystem only .

a) Forest ecosystem: In the forest, grasses and trees are the main producers. The consum-
ers like deer, zebra, wild buffalo, fox, jackel, tiger, lion, etc. directly or indirectly depends on
producers. The process of transfer of food in between producers and consumers is shown in
diagram.

Forest ecosystem

Blooming Science Book 9 317

b. Pond Ecosystem: The small mass
of still water formed either naturally or
artificially which is smaller than lake is called
pond. In the pond aquatic plants are produc-
ers. the zooplanktons small fishes, larva of
insects, big fishes, etc are the consumers.
The following diagram explains clearly the
exchange of energy between producers and
consumers.

Ecosystem services Pond ecosystem

The benefit which are obtained from ecosystem are called as ecosystem services. The fol-
lowing are the ecosystem services.

1. Provisioning services: The products that are obtained from the ecosystem are called
provisioning services. It includes following products:

a) Food and fibres: Human beings obtain various products from the ecosystem. Food, fruits,
vegetables etc are main food products obtained from ecosystem. We get fibres like silk, cot
ton, jute, etc from ecosystem.

b) Fuel: Firewood, straw, wood, dry dung can be used as fuel which can be obtained from
ecosystem.

c) Oranamental resources: Animals skin, bones, shells etc are used by human beings as
ornaments. Similarly, ornamental metals like gold, silver, copper are also obtained from
ecosystem.

2. Regulating Services: The ecosystem services which are obtained from ecosystem due to
balance in ecosystem are called regulating services. It includes :

a) Climate regulation: The ecosystem effects the local as well as global climate. The green
forest helps in regular rainfall and maintaining temperature at the local level. In global con
text, it can consume carbondioxide released due to human activites and decreases the risky
of climate change.

b) Water purification: The ecosystem directly or indirectly affects the water purification phe
nomenon in nature. It helps to decompose the organic impurities present in water and purify
it.

3. Cultural services: Natural beauty, pleasant environment, human’s culture and
activitiesareaffectedbyecosystem.Thechangeinecosystemalsoaffectsreligiousbeliefs,social
traditions and culture etc. A balanced and beautiful ecosystem attracts tourists which in
crease the living standard of people. the ecosystem also provides oppertunities to learn the
culture of various people.

4) Supporting services: These include services such as nutrient recycling, primary
production and soil formation. these services make it possible for the ecosystems to provide
services such as food supply, flood regulation and water purification.

318 Blooming Science Book 9

Basic requirements

Man has been trying to control his environment since the early days of civilization. There are
three basic requirements of human beings. They are food, shelter and clothes, which are obtained
from different plants and animals.

1. Food: Food is one of the most important basic requirements for the survival of organisms.
Human beings cultivate cereals (wheat, corn, rice, etc.) and other plants in the fields.
Human beings use cereals, pulses, vegetables and fruits as their proper healthy diet.
Likewise, human beings depend on animals for eggs, meat, fish, etc. for their daily
food. Since ancient times, plant and animals from the sea and forest have been used as a
source of food. In different countries, different types of marine animals are consumed as
food. From nutritive point of view, marine plants and animals constitute a rich source of
carbohydrates, proteins, minerals, salts and vitamins.

2. Shelter: The second most important basic requirement for survival is shelter. Human beings
make buildings, houses, huts, etc. for their own shelter of for their domestic animals. The
raw material that is used for making a shelter is mainly derived from natural resources.
Wood is the most important jungle product and it is used for the construction of buildings,
doors, windows, etc.

3. Cloth: The third basic requirement of human beings is cloth. The raw material to make
cloth is mainly derived from different plants and animals. Leather, wool and silk are
derived from animals. Likewise, cotton, simal, etc. provide thread which is used for
weaving.

Let’s Learn

1. The producers are also called transducers because they are able to change light energy into
chemical energy.

2. Producers belong to the first trophic level because they are capable of producing their own
food with the help of sunlight.

3. Human beings play a vital role to maintain a balance in nature. It is because human beings
can help in balance of nature in the following ways:
a. By controlling the over population.
b. By proper management of the waste product of cities.
c. By establishing industries at suitable places in safe ways.
d. By aforestation and conserving the natural resources.

Main Points to Remember

1. Ecosystem is the functional unit of ecology. It deals with the study of interrelationship
between living being and non-living objects.

2. Ecosystem is composed of biotic and abiotic factors. Aboitic factors are air, soil, water,
sunlight, etc whereas biotic actors are producers, consumers and decomposers. Consumers
are of three types-primary, secondary and tertiary.

3. Herbivores feed on the plants. Carnivores feed upon herbivores. Some animals feed on
plants and animals. They are called omnivores.

Blooming Science Book 9 319

4. Green plants are autotrophs because they can manufacture their food by themselves.

5. Animals are heterotrophs. They can not prepare their own food.

6. Decomposers help to decompose the dead bodies of plants and animals and mix them to
the soil. Bacteria and fungi are decomposers.

7. The basic requirements of human beings are food, cloths and shelter.

8. Food chain is the transfer of energy from producers through a series of organisms with
repeated eating and being eaten.

9. Food web is a interconnected series of food chains that establishes a network of relationship
among various organisms.

10. Each step of food chain is referred to as tropic level.

11. A community is a group of interdependent organisms sharing a particular environment.

12. The benefits obtained from ecosystem are called ecosystem services.

13. The category of ecosystem services are provisioning services, regulating services, cultural
services and supporting services.

PRO J ECTWORK

1. Prepare a chart to show inter-relation between biotic and abiotic factors.

2. Observe the water bodies like pond, lake, etc. or land of your surrounding and prepare
a report.

Exercise

1. Choose the correct answer from the given alternatives.

i. which class of biotic factor is also called as saprophytic oraganism.

a. Producer b. consumer c. tertiary consumer d. decomposer

ii. The process of eating and being eaten in ecosystem is called................

a. food chain b. trophic level c. food web a. all of them

iii. “Water purification” comes under which service of ecosystem?

a. supporting b. regulating c. provisioning d. non of them

iv. Many food chains get interlinked in ecosystem to form

a. ecosystem terrices b. ecosystem c. food web d. food chain

v. In pond ecosystem, zooplanktons belongs to.................

a. producers b. P. consumers c. S. consumers d. decomposers

2. Answer the following questions.
a. Define ecosystem? What are the two major components of ecosystem ?
b. Mention four abiotic factors that affect the ecosystem.
c. How do bacteria and fungi act as decomposers ?

320 Blooming Science Book 9

d. Shown below is a part of food chain.

Grass Rabbit Jackal

Tiger

i) Identify the producer and primary consumer in above food chain.

ii) Give two reasons why the population of jackals would increase if all the tigers were
killed.

e. When you eat meat, what level of consumer are you?

f. How do decomposers help to make soil fertile ? Explain in brief.

g. Why are producers regarded as the biotic food source in the environment ? How do they
produce their food?

h. What will happen in ecosystem if all micro-organisms die?

i. Given below is a food chain found in a National Park.

Grass Deer Tiger Micro-organisms

Identify the decomposers in the above food chain. Suggest two ways on the basis of above
food chain by which the population of deer can be increased.

j. State whether the following are producer, primary consumer, secondary consumer
decomposer and abiotic factor

Rabbit, Grass, Fish, Fungi, Tiger, Yeast, Light, Whale

k. Explain the types of ecosystem services.

l. Why is the number of producers larger than consumers in nature ?

m. Biotic factors of an ecosystem are classified in three major groups. Name them.

n. Which one biotic factor should be largest in number in order to balance the ecosystem ?

o. Differentiate between

i) Producer and consumer ii) Carnivores and omnivores

iii) Food chain and food web iv) Autotrophs and heterotrophs

p. Write Short Notes on: .

a) Pond Ecosystem b) Forest Ecosystem c) Tropic level

Q. Arrange them in a food chain.

a) Rats, Snakes, Plants, Hawks (Eagle)

b) Duck, Pondweed, Water snail, Large water beetle

c) Man, Goat, Plant d) Birds, Frogs, Insects, Grass

e) Caterpillar, Cabbage, Hawk

Blooming Science Book 9 321

Chapter NATURAL DISASTERS

22

Learning Outcomes Estimated Periods: 4+1

On the completion of this unit, the students will be able to:

• introduce natural disasters and their management.

• describe their causes, effects and preventive measures of some natural disasters like
snow slide, glaciers lake outburst and hurricane.

Introduction

Disaster is a sudden event that is very unfortunate consequence for us and badly affected by
it. Disaster involves large-scale loss of life and property. It also reduces cultivable lands and
destroys forests. Those disasters, which are mainly caused by nature, are called natural disasters.
Mainly natural disasters are caused by two reasons. They are geographical and meteorological.
Earthquake and volcanic eruption are caused by geographical regions but snowslide, glof and
hurricanes are caused by meteorological reasons. They have usually been more destructive of life
and property than have accidentally resulting from human action. Deforestation and urbanization
like human activities also support some natural disasters to occur. Natural disasters are as old
as the earth itself. All the countries of the world are affected by natural disasters but their nature
may vary in different countries. Such disasters affect the surface of the earth and its inhabitants.
Some natural disasters like volcanic eruption and earthquake are out of our control. We can take
some steps to minimize their effects. Some of the disasters can be controlled to some extent by
our activities. In this unit we will study about reasons, effects and preventive methods of some
natural disasters like snowslide, glof and hurricane.

Hazard

A hazard is any agent that can cause harm or damage to humans, property or the envi-
ronment. In other word, it is agent which has the potential to cause harm to a vulnerable target.
Hazards may be classified as natural hazard and anthropogenic hazard.

a) Natural hazards: It is a natural phenomenon that might have a negative effect on humans
or the environment. Natural hazard may be caused due to geophysical and biological factors.
Earthquake, volcanic eruptions, wildfires, cyclonic storms, flood, droughts and landslides are
caused due to geophysical factor. Whereas epidimic of diseases, infections are caused due to
biological factor.

b) Man made(Anthropogenic): Man made disasters are hazards caused by human
action or inaction. Man made disasters may adversely affect humans, other oraganisms and
biomes and ecosystem. Accidents, desertifications, riots, fuel crisis, nuclear weapons are some
anthropogenic hazards. The hazards whatever, natural or man made must be managed properly
as to reduce risk of possible harm caused by them.

322 Blooming Science Book 9

Management of natural hazard

Natural hazards can’t be stopped but it can be managed to reduce effects in people and environ-
ment. We can do following activities to reduce the effects of natural hazards:

1) Public awarness can help people to prepare for possible hazards.

2) The institutions to co-operate the victims must be deloyed as quick as possible.

3) Providing physical as well as economical support to the victims of hazards.

Management of man hazards

a) Proper age and qualification must be fixed for getting driving licence.
b) Proper safety measures must be enforced in the use of nuclear reactions, weapons,
chemicals etc.
c) Conserving forest and conducting afforestation programmes in bare hills and naked
areas.
d) Maintaining the fertility of soil by increasing the use of organic fertilizers.
e) Creating the clean environment and observing the principles of personal hygiene.
f) Developing the healthy competitions in between humans.
g) Local radio and Tv’s must telecast programmes related to public awarness.
h) Houses must be properly earthed.

Disaster management cycle

The man made hazards as natural hazards may harm the people. When hazard takes life
of people or harm them in anyway it is called disaster. In the time of disaster, it is very important
to manage it properly in order to reduce the loss caused by it. The steps involved in the manage-
ment of disaster are called as disaster management cycle. They are:

1. Preparedness: This is the step done before the disaster. We must be prepared for any
type of disasters. Pre-planning to face disaster, managing recent materials, storing necessary
foods, managing sound communication, etc come under their step.

2. Response(During disaster): We must be calm and cool during disaster. We should
manage ourselves and help weak and helpless people.

3) Recovery (After dister): After disaster is gone, we should focus ourselves in rescuing
the victims. Security forces like police, army can be used for this propose. In the other hand,
red-cross society, scouts, NGO’s, INGO’s and general people also play important roles in rescue
operation. The victims must be provided with water , food and shelters, those who are injured
must be taken hospitals immediately. After the rescue operation is finished, we must focused to
rehabilate the victims. Government can provide aids, loans for them to construct the houses and
so on. Those who have lost their family members must be councelled.

4) Mitigation: All the activities done in order to decreases the risky of disaster come in
this step. some of mitigating measure are as follows:

a) People living in vulnerable places must be shifted to safe place.

b) Disaster prone zone must be identified and safety measures must be implemented
accordingly.

Blooming Science Book 9 323

c) In cities, building codes should be forcefully implemented.
d) The awareness programme must be conducted.
e) Bridges, waterpipe system, roads, public places must be monitered timely.

Snow Slide

Our mountain is covered with heavy snow, according to altitude, the thickness of snow in moun-
tain may vary. The temperature of mountain when increases the snow melts and slide down-
wards. This phenomenon is called snow slide (or av ralanche). There is high risk of snow slide
in various region of himalaya. In 2012 AD snowslide in Mt. Annapurna caused seti river to flood
which killed 20 people in pokhara.
Cause of snow slide
a. Climate change
b. Earthquake
c. Glacial lake outbrust
d. Use of explosives
e. Human activities(lie construction of roads, bridges, houses)
f. Volcanic eruption under snow
Effects of snow slide
a. It causes flood in rivers
b. Loss of lives and property
c. Destruction in development infrastructure
d. Destroy the crops, vegetation and wildlife
Preventative measures of snow slide
a. The snowslide prone zone must be identified.
b. The residents living near the prone zone must be swifted to safe place.
c. Taking proper action to decrease the global warming or climate change.
d. Public awareness should be given to public living near by prone zone.
e. Snow slide forecasting system or predicting should be developed.
f. The human activities such as skies, use of explosives must be minimized.
g. Afforestation can be done in possible area.

Glacier lake outbrust flood (Glof)

The lakes situated in mountains are called glacier lake. Usually these lakes are formed by melt-
ing of snow in mountains. Some of these lakes are found in frozen state while others can be in
liquid state. These lakes donot have strong walls and bottom to support the large mass of water.
In Nepal there are large number of glacier lakes. The global climate change has effected the gla-
cier lake. the temperature of mountain is increasing, this increase in temperature has resulted the

324 Blooming Science Book 9

melting of large mass of snow. The size of glacier lake increases slowly due to climate change
and sometime the weak walls of glacier lake may brust resulting the flood in lower level which
is called as glacier lake outbrust(glof).

In 1968 due to GLOF, river Budhi gandaki was flooded heavely while in 1985 Dickcho glacier
lake in sagarmatha region brusted and the flood destroyed the hydropower project near by it.

Tscho-Rolpa glacier lake was also in the risk of brusting in the past but now it is safe. Such type
of various lakes in mountain region are in danger zone, they may brust out at any time. They re-
lease large mass of water in nearby river which causes massive flood. Such a flood can take lives
and destroy the property. Some potentially dangerous lakes are Imja, Lower Barun, Thulagi, etc.

Causes of glacial lake outbrust

a. Erosion of rocks that dammed the lake

b. Snow slide in glacial lake

c. Melting of snow due to climate change

d. Shock waves during earthquakes, explosion etc.

e. Sometimes heavy snow fall can increase the mass of snow over glacial lake and chance
of brusting increases.

Effect of glacial lake outbrust

a. Flood in the river

b. Loss of lives and property

c. Destruction of infrastrutures like roads, bridges, communication system, hydropower
projects, etc.

d. Destroy the cultivable land, wildlife and vegetation.

Preventive measures of Golf

a. A regular monitoring is necessary to identify dangerous glacial lakes.

b. Gradual outlet of water of the lake should be managed for danger ous lakes.

c. Human settlement should be shifted way from risky glacier lakes.

Hurricane

Hurricane is also a natural disaster. In different regions
of the world it is known by different names. It is known
as typhoon in North Western Pacific ocean, Cyclone in
South Indian ocean region and as Willi in southern Pacific
ocean region. The teen hurricane is common in Northern
Atlantic Ocean and Eastern Pacific ocean region. The
hurricane is migratory tropical cyclone that originates
over ocean in certain regions, near the equator. It forms
in between the region of 5° to 25° north and south latitude from equator. The region is termed as
doldrums. Hurricanes arise in the western Indian region including the Caribbean Sea and Gulf of
Mexico. Thus India, Bangladesh, China, Philippines, Japan, Mexico, United States of America
and maximum countries of Caribbean Sea are highly influenced by it.

Nepal is safe by direct influence of hurricanes. Hurricane is destructive. They destroy life and
property in a very large scale every year.

Blooming Science Book 9 325

A hurricane has the highest pressure at its margin lowest pressure at its centre. Few kilometer of
area in region of a hurricane is called as eye of the storm. Eye in central round oval. The radius
of eye is about 15 to 30 km, average diameter is about 24 km.

The size of the eye of a hurricane indicates the strength of the storms. The decreasing size of the
eye of a hurricane show its increasing strength. The size of hurricane is measured by distance
between the eye and its marginal region which is called the radius of the hurricane. The radius of
the smallest hurricane is about 200 km and that of a largest hurricane is about 900 km or more.

As hurricane is migratory it may come over land also name of hurricanes is given after the name of
person. Gilbert, Andrew, Agnes and Hugo are some big hurricanes of 19th century. Some examples
of recent hurricanes are Charley, France, Jeanne, Ivan, Katrina, Bhola, Mich, Sandy etc.

The strength of a hurricane is measured in Sandy - simpson scale which ranges between 1-5.
The mildest category 1 has winds of 120km/hr and the strongest category 5 exceeds 250 km/hr.
Hurricanes having magnitude l and 2 do not loss more life and property but having magnitude 3
or more loss life and property in a large scale.

Causes of Hurricanes

Hurricanes are occurred in oceans of equatorial regions. We know that equator of the earth
receives the highest strength sun rays, which support to be heated the ocean water. When the ocean
water at any region gains the temperature of 26.5° to the depth about 50 metres, it reduces the
atmospheric pressure of that region. It is the beginning of the hurricane. Due to the development
of low pressure center, when the warm saturated air prevalent in the doldrums is under run and
forced upwards by denser cooler air. The atmospheric pressure drops sharply from the edge of the
stone towards its center and the wind velocity rises. The wind attains maximum force close to the
point of lowest pressure. It is about 724 ton = about 724 mmHg. The wind becomes hurricane,
only when it gains speed of 120 km/hr. The temperature of central region is found greater than
that in marginal region. This situation forms a convectional current that helps to conduct the
regular movement of air, the hurricane. Hurricanes are occurred in between August and October
but their frequency is maximum in September.

Effects of Hurricanes

Hurricane has enormous energy in it which is very devastating. Due to a hurricane the sea level
may increase up to 7 m high. The increasing sea level due to a hurricane is called as storm- surge
or sea-surge. The adverse effects of a hurricane are the following:
1. Storm-surge or sea-surge storm causes flood which sweeps life and property.
2. As the ocean is violent during hurricane any mean of transportation in ocean is not suitable
during it. It can sink a strong ship also.
3. The wave formed by hurricane losses the property in coastal region.
4. Sometimes it becomes the cause of a heavy rain also.
5. It causes also landslide and destroys the development structures.
6. It becomes the cause of the death of number of sea animals which imbalances the sea-
ecosystem.
7. It deposits debris in fertile lands and turns them into unfertile.
Some losses of life and property by hurricane century and onwards are given below for the
expansion of your knowledge.

326 Blooming Science Book 9

Safety Measures of Hurricane

Now a-days Radar, weather-satellites and other devices supply data to hurricane monitoring
centers. The weather satellites Okean (USSR), Almazl 1 (USSR) and MSG I (Europe)
are doing the same job.

The following activities are the some major safety measures of a hurricane.

1. The government should predict the time, direction and magnitude of hurricanes by the help
of hurricane monitoring centers.

2. The structures made in coastal regions and in oceans must be strong to safe from the energy
of hurricanes.

3. Emergency shelters should be constructed near ocean to save the life of the people.

4. Public awareness should be provided of the people, of the country who are facing hurricane.

5. Alertness should be maintained by all the stakeholders like health team, volunteers etc.

6. The person of particular regions always should follow the instruction strictly given through
the different media.

Let’s learn

1. Snow slide causes Glof. The large mass of snow sometimes deposites over the glacial
lake due to snow slide. The pressure of heavy snow may brust the walls of glacial
lake resulting the flood in the lower level.

2. Climate change is one of the cause of snow slide and glof. It is because the temperature
of mountain is increasing due to climate change. The snow melts and slide down as
snow slide which may also help in Golf.

3. Hurricane doesn’t occur in Nepal it is because we are not connected with sea or oceans.

Main Points to Remember

1. A hazard is the situation which brings threat to human life property and environment.

2. Hazard caused by natural force is called natural hazard.

3. Man-made hazard is called as anthropogenic hazard.

4. Preparedness response, recovery and mitigation are the steps of disaster management
cycle.

5. Nepal has large number of glacial lakes which are at risky of brusting.

6. Snowslide is caused by melting of snow.

7. Afforestation can prevent snowslide.

8. Glacial lakes brust due to erosion of rock that dammed the lake.

9. Settlement near the glacial lake should be Shifted to the safe place.

10. Earthquake can cause both snowslide and golf.
11. Hurricane is a destructive disaster. It is a migratory tropical cyclone that originates over

ocean in certain region near the equator.
Blooming Science Book 9 327

PRO J ECTWORK

If you have ever experienced the management of natural disasters affected people in your
locality, make a short report on it.

Exercise

1. Choose the correct answer from the given alternatives.

i. Those phenomena which bring threat to human and are mainly caused by natural
are called ..................................

a. Natural disaster b. Anthropogenic disaater

c. Natural hazards d. Both a and c

ii. Flood, cyclone is a .................................disaster.

a. Natural b. Anthropogenic c. Artificial d. Both a and c

iii. Both avalanche and GLOF are caused by:-

a. Earthquake b. Cyclone c. Drought d. All of the above

iv. .................................. is one of the steps of disaster management cycle.

a. Hurriedness b. Mitigation c. Migration d. Both b and c

v. Glof is called caused by:-

a. Landslide b. Earthquake c. Avalanche d. All of the above

2. Answer the following questions.

a. What is hazard? Expalin its types.

b. How can you manage natural hazard? Write in the points.

c. How can you manage anthropogenic hazard? List the points.

d. Write the steps of disaster management cycle and explain any two of the steps.

e. What jobs are done during response and recovery steps of disaster management cycle?

f. What is snow slide? Write its causes, effects and preventive measures.

h. Define GOLF? Write its causes, effects and preventive measures.

i. What is hurricane? Write two preventive measures.

3. Differentiate between:

328 Blooming Science Book 9

a. Hazard and disaster

b. Snows slide and Glof

c. Man-made and natural hazard

4. Give reasons:

a. Nepal is at high risk of Glof.

b. Afforestation can minimize the effects of snow slide.

c. Hurricane occurs in doldrum regions.

d. Glacier lakes can brust due to heavy snowslide.

e. Earthquake can cause both snowslide and Golf.
f. Humans are responsible for every types of disasters.

5. Study the diagram and answer the questions: B APreparedness
i. Name ‘B’ and ‘D’ Recovery
ii. Write the jobs done in ‘B’
iii. Write the differences between ‘C’ and ‘D’ CD

Disaster Management cycle

Blooming Science Book 9 329

Chapter GREEN HOUSE

23

Learning Outcomes Estimated Periods: 4

On the completion of this unit, the students will be able to:

• introduce green house effect in natural environment with its effects and
describe importance and uses of artificial green house.

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

The Earth is a Natural Green House

Earth’s atmosphere acts like the glass of a greenhouse. Different gases such as nitrogen, oxygen,
carbon dioxide, methane, nitrous oxide etc. are present in the atmosphere. Nitrogen and oxygen do not
trap sun’s radiation. Carbon-dioxide gas and methane are the greenhouse gases. They trap the sun’s
radiation. Heat that is normally re-radiated back into space by the earth is absorbed by these gases
and heat the troposphere. Greenhouse effect received its name because the earth’s atmosphere acts
much like the glass of the greenhouse. The sunlight enters a greenhouse through the glass and heats
the interior. The roof and walls block the escape of the heat.

Greenhouse effect is warming of the earth’s surface that occurs due to the trapping of the sun’s heat
by the earth’s atmosphere. This effect raises the temperature of the earth and also changes weather
and climate over green house effect is not good for the living organism. Without this effect, the
average surface temperature of the earth would be less than the present normal temperature which

killed the possibilities of life on the earth surface as well.

In the passed 100 year the earth’s temperature is increased by 0.74°. In this way from 1977 AD
to 1994 AD the temperature of the earth is increased at the rate of 0.06°C per year in average. It
is causing global warming. It is found that the temperature of the polar region is increasing more
than that of the equatorial region. Similarly temperature of high peaks of mountain is increasing
by more than in Terai and mid mountainous regions. It is reducing the water resources of river
by melting the snow faster. The following precautions should be taken to face the adverse effects
of green house effects.

1. Our dependence on fossil fuel energy should be reduced by using alternative energy
sources. It helps to produce less green house gases.

2. Reforestation should be conducted as mission all over the world as plants absorb CO2
elements from the atmosphere.

3. Population growth should be checked.

330 Blooming Science Book 9

Greenhouse

Greenhouse is a building in which plants can be grown throughout the year. Its roof and walls
are made of green glass or plastic. So greenhouses are sometimes called glasshouses. It provides
heat, light and moisture essential for the growth of the plants.

Sun

Incident heat Transparent glasses
from the sun

Heat reflected by the
surface of green house

Plant

Fig: A Green House (Artificial)

A green house is a form of controlled environment for the agriculture because the light, moisture,
temperature and other essentials for the plant growth is regulated there.
The sun’s heat passes easily through the glass and retains much of the heat inside. The glass keeps
the greenhouse warm by trapping heat from the sun. The temperature inside the greenhouse is
more than outside.

Importance of artificial green houses

1) Different ornamental plants and vegetables such as cucumber, lettuce, tomatoes are
grown in green houses.
2) These plants can be grown out of their normal growing seasons in greenhouses. In other
words, summer plants can be grown in winter.
3) Countries with cold climate can grow fruits and vegetables inside green house.

Effects of the over Green House Effect

1. Global warming is caused by thee green house effect. It influences forests directly. The
plants found at tropical regions are also seen in the temperate region gradually. The global
warming may cause the melting of snow at polar region. It may increase sea level by
which many islands may be disappeared in ocean.

2. Agriculture system is badly affected by the over green house effect.
3. Water cycle is also affected by the over green house effect.

4. Due to the change in temperature on the earth, many diseases of skin and eye will be caused.

Blooming Science Book 9 331

5. It is causing adverse effects on ecosystem.

6. Different types of diseases are caused among human being like skin cancer, eye diseases,
etc.

Climate Change

Climate change is a significant and lasting change in the statistical distribution of weather
patterns over periods ranging from decades to millions of years. It may be a change in average
weather conditions. Climate change may be limited to a specific region or may occur across the
whole Earth.

The most general definition of climate change is a change in the statistical properties of the
climate system when considered over long periods of time, regardless of cause. Accordingly,
fluctuations over periods shorter than a few decades, , do not represent climate change.

The term sometimes is used to refer specifically to climate change caused by human activity,
as opposed to changes in climate that may have resulted as part of Earth’s natural processes.In
this latter sense, used especially in the context of environmental policy, the term climate change
today is synonymous with anthropogenic global warming. Global warming refers to surface
temperature increases, while climate change includes global warming and everything else that
increasing greenhouse gas amounts will affect.

Causes of climate change

a. Increase in temperature: The temperature of earth is increased due to the various reasons
like pollution, population growth, etc. The record of last 3 decades shows that temperature
on earth has increased a lot. Climate change occurs due to increase in temperature of earth
too.

b. Release of greenhouse gases: Our dependence of fossil fuel has not decreased. The burning
of these fuels produce green house gases like CO2, CO, NO2 , SO2 , etc. This causes climate
change.

c. Deforestation: Due to industrialisation, urbanisation and population growth, area of forest
is decreasing day by day. Trees absorb CO2 for photosynthesis, which help in balancing CO2
amount is atmosphere. But due to deforestation, the numbers of trees are decreasing which
helps to increase CO2 in atmosphere and causes climate change.

d. Increase in the use of chemical fertilizers: The use of different chemical fertilizers like Urea,
Potash, etc. help in climate change. These fertilizers when used produce green house gases
like CO2 , No2, etc. which absorb solar radiation more than necessary to increase temperature
of earth. They also pollute the soil and water source.

e. Industrialisation: The industry uses fossil fuelas source of energy. When fuels are burnt
GHG’S like CO2, SO2, NO2, CO, NO3, etc. are released. They help to increase the temperature
of earth by absorbing more and more solar radiation which ultimately brings climate change.
Gases released from industry also cause acid rain.

f. Volcanic eruption: Due to volcanic eruption, our atmosphere gets contaminated with dust,
clouds and harmful gases. Sometimes these particles block the solar radiations entering to
earth. Due to lack of sufficient solar energy, earth may cool down which cause climate
change.

332 Blooming Science Book 9

Effects of climate change

a. Change in temperature: The temperature of earth is increasing due to climate change. From
decades of 70s to 2005, the temperature of earth has increased to about 1.40oF. The data
shows that temperature of our country is also increasing on average of 0.04oC every year.
This increase in temperature is due to climate change.

b. Impact on biodiversity and ecosystem: The climate change on earth has adversly effected
the plants and animals. The plants and animals which can’t adopt climate change are either
decreasing from earth or are in verge of extinction. The ecosystem of land and water both
are affected by climate change.

c. Impact on human health: Human beings are badly affected by climate change. We are
affected by various diseases. New virus like ebola, zika are giving threat to human kind. The
pathogens like bacteria, protozoans are also being stronger than in past. Our efficiency in
work is also decreasing due to climate change.

d. Impact on agriculture: Due to climate change the weather pattern of different places are
changing. Somtimes we experience heavy rain, while sometimes no rain which effect
the agriculture. The hills suffer from landslides, in terai, flood problems are increasing these
all phenomenon decrease the productivity of soil which directly effect the agriculture. Due
to drought, the productive land is transforming into desert.

e. Disasters: Many disters like flood, landslides, snowslides Glof, hurricanes, scarcity of water,
etc are seen in earth and are increasing too which are due to climate change.

f. Impact on water resources: The climate change has effected the water cycle. The different
sources of water like pond, lake, stream drying. The excessive melting of snow and glacier
are decreasing the sources of water in long term.

g. Impact on human settlement: Sea-level is increasing due to climate change. The polar caps
are melting faster than we expect. The low level islands are in danger of being drowned. Due
to scarcity of water, desertification, human settlement is affected.

h. Energy crisis: Due to decrease in sources of water, hydropower projects are badly affected.
In context of our country, during raining season’ if raining is less then hydro electricity
production decreases which can cause load shedding. This may lead to shortage of energy in
future.

i. Impact on natural heritages: Green house gases also cause acid rain, which fades the colours
of monuments, building and sculptures. Such natural heritages are eroded gradually by acid
rain.

Measures of climate changes management

a. Reforestation programme should be conducted.

b. Awarness programm about harmful effect of climate change should be conducted.

c. Reducing the emission of green house gasses(GHG’s).

d. Promoting the alternative sources of energy.

e. Reducing the use of fossil fuels.

f. Controlling the pollution caused by industries and factories by using filters in chimneys.

g. Promoting public vehicles more than private vehicles.

i. Minimizing the use of chemical fertilizers, instead promoting the use of organic manure

j. Conserving and managing sources of water.

Blooming Science Book 9 333

Let’s Learn

1. Green house effect is advantageous because it maintains the suitable temperature of the
earth at days and nights. In the presence of suitable temperature only the living things can
survive.

2. Over green house effect is disadvantageous. It may affect the water cycle system badly. It
may spread many types of diseases and increases harmful insects. It reduces crop yielding
and changes the climatic pattern.

3. There is warm inside a greenhouse. It is because the glass used in the construction of green
house allows passing short waves only through it. When the short waves of the sun strike
on the earth surface, they change into infrared radiation or long waves and they cannot
escape out easily through the glass. It makes warm inside the glass house.

Main Points to Remember

1. Greenhouse effect is warming of the earth’s surface that occurs due to the trapping of the
sun’s heat by the earth’s atmosphere.

2. Climate change is a significant and lasting change in the statistical distribution of weather
patterns over periods ranging from decades to millions of years.

3. In green houses the temperature is changed after the entry of solar radiation which is
stored there.

4. Chlorofluorocarbon (CFC), sulphur dioxide, carbon dioxide, carbon monoxide, nitrous
oxide and methane are mainly responsible for ozone layer depletion.

5. Green house effect is caused by increased CO2 and other gases present in the atmosphere.
These gases make the earth warm. But excess of green house gases may increase the
global temperature which is called global warming.

6. The air pollutants like the oxides of sulphur, oxides of nitrogen and halogens are released
into the atmosphere where they react with water vapour to form acids. These acids mix
with rain and fall as acid rain.

7. Increase in temperature, release of GHG’s, deforestatyion, use of chemical fertilizers,
volcanic eruption,etc are some causes of climate changes.

8. By doing some measures we can controll climate changes.

PRO J ECTWORK

Construct a small green house near your house/school in winter season and measure the
inside temperature by using maximum-minimum thermometer and compare this
with outside temperature. Discuss the difference in your class.

334 Blooming Science Book 9

Exercise
1. Choose the correct answer from the given alternatives.

a. Which of the following is not an example of a green house gases?

a. CO2 b. O3 c. N2O d. H2
b. Anthropogenic cause of climate change is ..................................

a. Solar output b. Agrirculture and factory wastes

c. Increase in CO2 concentration d. Both b and d
c. The roof of an artificial green house is made up of ..................................

a. woods b. glasses c. bricks d. both b and c

d. Few components of the atmosphere that have the capacity of absorbing solar heat
and emit the radiation within the thermal infrared range are known
as ...........................

a. noble gases b. green house gases c. inert gases d. halogen

e. Climate change is similar to:-

i. Global warmimg ii. Green house effect

iii. Season change iv. Weather change

2. Answer the following questions.
a. What is greenhouse effect? Write its advantages.
b. In artificial green house summer vegetables can be grown even in winter, why?
c. What is an acid rain? How does it affect us?
d. Green house effect is both advantageous and disadvantageous to us. Justify your answer.
e. What is climate change? Mention its any 4 causes effects and preventive measures.
f. How does climate changes affect
a) human health
b) Agriculture
c) Natural Disaster
3. Give reasons:
a) Roof of a green house is made slanted.
b) Green house is warm inside.
c) Earth is a natural green house.
4. Draw a neat sketch to show artificial green house.

Blooming Science Book 9 335

Chapter THE UNIVERSE

24

Learning Outcomes Estimated Periods: 4+1

On the completion of this unit, the students will be able to:
• explain diurnal and annual motion of the earth.
• explain the phases of the moon, sidereal and synodic month.
• determine the relation of position of the moon, the earth and the sun.
• explain umbra and penumbra with diagram.
• explain lunar and solar eclipses with diagrams.

The Universe

The vast region that includes everything in the whole creation is called universe. It contains sun,
star, planets, satellites, comets, meteors, meteorites etc. Stars are the larger and twinkling bodies
situated very far away from us. There are billions of stars in the universe. The cool stars appear
red and orange. The hot stars appear bluish white. The temperature of the star is estimated by
observing its colour. The sun is the nearest star about 1.5 × 108 km from us. A group of billions
of stars form galaxy. Our solar system lies in Milky way galaxy.

The branch of science which deals with the study about stars, planets and all other objects in the
space that make universe is called astronomy.

The universe has unlimited size and unknown shape. All the existing things including different
galaxies, constellations, planets, satellites, comets, meteors, meteorites, asteroids etc constitute
it. Our earth is a planet, which is a member of the solar system. The solar system is situated in
a galaxy called milky way. The milky way is a medium sized galaxy, which consists of about
150 billion of stars. Astronomers believe that there are about 1012 such galaxies in the universe.
Now you can imagine that how huge the universe is? Because of its so huge and unlimited size
the distance between two heavenly bodies is inconvenient to measure in meters and kilometers.

Units used to Measure Distance in the Universe

The universe is so vast that it is not convenient to measure the distance in meter or kilometer;
Hence, astronomical unit, light year and parsec are used to measure the distance in the universe.

Astronomical Unit: It is defined as the distance between the sun and the earth and its value is
about 1.5 × 1011 m. This unit is suitable for measuring the distance of the planets and satellites
in solar system.

1AU = 1.5 × 1011 m

336 Blooming Science Book 9

Light year: It is defined as the distance travelled by light in one year. Its value is about

9.5 × 1012 km.

Note: Velocity of light = About 3 × 108 m/s

[1 year = About 365 days, 1 day = 24 hour, 1 hour = 60 min and 1 minute = 60 seconds.]

Now, The distance covered by light in one year = 365 × 24 × 60 × 60 × 3 × 105m

= 9.46 × 1015m or about 9.5 × 1015 m.

∴ 1 light year = 9.5 × 1012 km = 63240 AU 1’’ arc

Parsec: The term parsec comes from the words parallax and Earth Earth’s orbit
second. It is defined as the distance at which the mean radius 1AU Sun
of the earth’s orbit subtends an angle of one second of arc. It is
equal to 3.26 light years.

1 Parsec = 3.26 light years = about 3.1 × 1015 m = 206265 AU

Some distances in the universe are mentioned below:

1. Proxima centauri Light year Parsec
2. Sirius 4.3 1.31
3. Vega 8.6 2.63
4. Length of Milky Way 26.5 8.12
5. Thickness of Milky Way 105 3.06 × 104
6. Distance between the sun and the galactic centre 8 × 104 2.45 × 104
7. Distance between the Milky Way and the Andromeda 2.5 × 104 7.6 × 103
2 × 106 6.1 × 105

Galaxy

Billions of stars make a galaxy. In the universe, it has been estimated that 10,000 crore galaxies
are existing. Some galaxies are spiral in shape and some are elliptical, some are long bands and
may be some are even in circular form. Among these galaxies, Milky Way is one which has
nearly 1,500,000,000,000 stars (15 Arab). The sun is a star in this galaxy. Solar system lies in
this galaxy. Another nearest galaxy is Andromeda, which is 20 lakhs light years away from us.

Milky Way Galaxy

Sun and about 100 billion stars are in this galaxy. The centre of galaxy is called galactic centre.
Milky Way galaxy is spiral in shape. It takes nearly 100,000 years for light to reach from one
edge to the other edge of Milky Way Galaxy across the diameter.

The sun is at a distance of 33 thousand light years from galactic centre. Sun is revolving round

the galactic centre and it takes about 250 lakh years (25 million years) for sun to make a

complete revolution round the galactic centre. The time taken to make one complete revolution

round the galactic centre by the sun is known as Cosmic year.

Blooming Science Book 9 337

Note: Size of Milky Way: 100,000 light years across
Thickness near the sun: 500 light years thick in the disc
Central bulge: 20,000 light years across, 3000 light years thick
Contains: 100 billion stars

The Moon; A Natural Satellite of the Earth

The moon is the nearest celestial object to the earth. The equatorial
diameter of the moon is 3476 km. The moon is the only satellite
of the earth which has about 30 plains, 30,000 craters and several
mountains on it. The mean distance between the earth and the
moon is about 3,85,000 km and its surface area is about 37,940,000
km2. There is no oxygen and water on the moon due to which,
possibility of life is nil there. Its temperature varies in a very high
range in twenty-four hours (-125oC to 130oC). Its gravity is one
sixth of that of the earth.

An American astronaut, Neil Armstrong was the first person to Fig: Moon
step on the moon on 20 July 1969 A.D. He was accompanied by

Edwin Aldrin and Michael Collins. Neil Armstrong and Edwin Aldrin landed on the moon by

using Eagle Lunar Module. They collected the sample of rock, did simple experiments and took

photographs of the surface of the moon. Then they returned safely on the earth.

Phases of the Moon

When we observe the sky daily for some days, we find that the moon changes its shape everyday.
It is called phases of the moon.

m3
m4 m2

m1
m5

m6 m8

338 Blooming Science Book 9 m7

The moon changes its shape daily because of the following reasons: ?Did
i. The moon is non-luminous body and In the full moon night, although
You
reflects the sunlight. moon is supposed to be seen full Know

but only 50% seen, other part is
ii. The moon is revolving around the earth in hidden by its own shadow.

its elliptical orbit.

Because of the above two reasons, on different days, different bright parts of the moon is facing
towards the earth. Hence, the moon changes its shape daily and phases of the moon occur.

When the moon is forming an angle of 0o from the plane of earth’s orbit, the whole dark part of

the moon is faced towards the earth and hence any part of the moon is not seen. We say that it

is a new moon (m1). After 24 hours when the moon forms an angle of 12o from the plane of the
orbit, a little bright part of the moon faces towards the earth and a minimum part of the moon

is seen bright. It is called waxing crescent (m2). In this way bright part of the moon increases
everyday. When the moon forms an angle of 90o, the bright part of the moon is seen in the form

of hemisphere, which is called first quarter (m3). The moon moves toward in the same direction
by increasing its bright region. When it forms an angle of 168o, very little part of the moon

remains dark and it is called waxing gibbous (m4). When it reaches at m5 condition i.e., it forms
an angle of 180o from the planet, the moon is seen completely round, which is called full moon.

The period of a month in which the moon increases its bright part is called bright half or waxing

moon. It is the first half of a lunar month.

After full moon condition; when it forms an angle of 192o, very little part of the moon is covered

bNy odtaer:kness and it is called waning gibbous (m6). In this way the dark part of the moon increases
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7. The moon rises fifty minutes before the sun setting on waxing gibbous.

Sidereal Month and Synodic Month

We know that the earth revolves around the sun and the moon revolves around the earth in their
own orbits in anticlockwise direction. We have studied in this unit about the revolution and the
period of revolution of the earth also. Now we will study some much more about revolution of
the moon.

The moon completes one revolution around the earth in about 27.33 days [27 days, 7hr, 43 min
and 11.5 sec]. This period is called a sidereal month, which is widely used in palmistry. In the
given illustration the time taken by the moon to move from ‘m1’ to ‘m2’ condition is one sidereal
month.

When the moon is in ‘m1’ condition, it is new moon but in ‘m2’ condition new moon does not
occur. For the next new moon (m3) the moon takes 2 days, 5hr and 51.5 sec more. The time taken

Blooming Science Book 9 339

by the moon to come from m1 to m3 condition is called a synodic month or a lunar month. Thus,
the duration between two consecutive new moons is called synodic month. Its duration is 29
days, 12 hours, 44 minutes and 3 seconds i.e. about 29.5 days.

Sun

Sidereal month (27d, 7hr, 13m, 11.5s or about 2713d)
Synodic month (29d, 12hr, 44m, 3s or about 2913d)

New moon New moon 2d, 5hr,
m1 51.5s
Moon’s orbit around
the earth m2
m3

The distance is about 30o A
A

Earth’s orbit around the sun

Differences between Sidereal and Synodic Month

Sidereal Month Synodic Month

1. It is the single revolution of moon around 1. It is the moon’s revolution around the earth

the earth. with respect to the sun.

2. It is about 27 days, 7 hours, 43 minutes and 2. It is about 29 days, 12 hours, 44 minutes

11 seconds. and 3 seconds.

3. This is the time period to revolve once 3. This is the time period between one new

around the earth. moon and next new moon.

Artificial Satellites

An artificial satellite is made on the earth and moves continuously around the earth.
The orbit of artificial satellite is elliptical and characterized by three parameters
apogee, perigee and inclination. There are basically five types of satellites for
different purposes.

Weather Satellites: They are designed to study overall weather patterns of the
earth.

Communication Satellites: They are improved for the quality and speed of mass
communication.

Navigation Satellites: They are designed to know the exact position of navigators
in the air or in the oceans in any weather.

Scientific Satellites: They gather all kinds of information about the universe. Fig: Rocket

Military Satellite: They are used to observe troop movements, spy on military bases, or detect
the testing of nuclear weapons in space.

340 Blooming Science Book 9

Diurnal and Annual Motion of the Earth

The earth moves round on its axis as well as in its orbit around the sun. The motion of the earth

on its axis is called diurnal motion and a complete round on its axis is called a rotation. The earth

takes about 24 hours [23hr, 56 min and 4.09s] to complete one rotation. The motion of the earth

in its orbit is called annual motion and a complete round around the sun is called a revolution.

The revolution of the earth has a direct concern with the change in seasons and varying length of

day and night. The rotation of the earth causes day and night on the earth. The earth takes about

365 days [365d, 6 hr, 9 min and 9.54 s] to complete one revolution. North Pole

Rotation

2312o Tropic Arctic circle
6612o Equator cancer
of

66 1o 6612o
2 2312o
0o
Plane of ecliptic 2321o

Plane of ecliptic Antarctic Tropic
circle
of capricorn

Equator

Axis 66 1o
2

The axis of the earth is inclined to plane of the ecliptic at an angle of 66.5o, it causes different
seasons and varying lengths of day and night. If the axis were perpendicular to this plane, all
parts of the earth would have equal days and nights at all times of the year.

Day and Night; an effect of the Rotation of the Earth

Day and night on the earth occurs due to
its rotation. When the earth rotates on its
axis, only one portion of its surface faces
the rays of the sun and experiences day.
The other portion which is away from the
sun’s rays will be in darkness experiences
night.

To understand better about the cause of
day and night, place a globe or ball as the
earth in a dark room and use a flash of light
or a table lamp representing the sun. Do you see all the parts facing light?

The earth rotates eastwards, every part of the earth’s surface will be exposed to the sun at some
time or the other. The part of the earth’s surface that emerges from darkness into the sun’s rays
experiences sunrise. Later, when it is gradually obscured from the sun’s rays, it experiences sunset.

Blooming Science Book 9 341

The Revolution of the Earth and its Effects E4
E2
When the earth revolves around

the sun, it moves in an elliptical

orbit and a complete revolution

takes about 365.25 days or a year.

A normal year is taken to be 365 E3
days and an extra day added every E1

four year as a leap year. We know June
that, the axis of the earth is inclined

to the plane of the ecliptic. It causes

the different seasons and varying

lengths of day and night.

In E1 condition of the earth in the given diagram June 21, when the Scan for practical experiment
northern hemisphere is tilted towards the sun. It is called summer

solstice. In this condition the northern hemisphere has the longest day

and the shortest night. But the southern hemisphere has the shortest

day and the longest night. In this condition the northern hemisphere

receives the stronger, direct rays of the sun for a longer time. It makes

the region warmer i.e., summer. In that period the southern hemisphere

has winter. visit: csp.codes/c09e24

IanwEay3 cfornodmititohne on 22 December when the northern hemisphere is tilted northern hemisphere has
sun, it is called winter solstice. In this condition the
the shortest day and the longest night but the southern hemisphere has the longest day and the
shortest night. In winter solstice, the northern hemisphere receives the weaker and slanted rays
of the sun, for a shorter time. It makes the northern hemisphere much colder i.e., winter. On that
day the southern hemisphere has summer.

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world has equal days and equal nights. The 22 march is called spring equinox and 23 September
is called autumn equinox.

Beyond the Arctic circle and the Antarctic circle, the darkness lasts for 6 months and day light is
continued for the remaining half of the year. It is extreme cold in this region and the sun is never
high in the sky.

Eclipse Eclipse occurs
M2
The revolution of the earth around
the sun and the moon around the E2
earth, causes these three bodies
to fall in a straight line at some M1 Eclipse doesn’t occur
time. In this condition, either the
shadow of the moon casts on the Plane of the Sun M1
earth or the shadow of the earth earth’s orbit E1
casts on the moon and eclipse
occurs. M2
An eclipse is darkening of a
heavenly body as it passes Plane of the
through the shadow of another moon’s orbit
body in space.

342 Blooming Science Book 9

Eclipses occur on new moon and full moon only because only on these days, there is the
possibility of all the three bodies (the sun, the moon and the earth) lying in a straight line.

Causes of Eclipse

The main causes of eclipse are:
1. Only the sun of the solar system is luminous body and the moon and the earth are non-

luminous body.
2. While revolving the earth around the sun and the moon around the earth, sometimes all the

three masses lie in a straight line.
3. The moon and the earth are opaque, non transparent.

Umbra and Penumbra

Penumbra Umbra

Pencil

Light from window White paper

Take the blank page of your exercise book as a screen facing towards the pane of window.
Now place a pencil or pen in between the screen and the window in such a way that it casts
shadow. You will get a dark shadow called the umbra and light shadow around the umbra called
penumbra. If penumbra is not clear, increase the distance slightly between the screen and the
pencil. The umbra and penumbra play a vital role for the eclipse to be occurred.

Usually the umbra causes total eclipse in which the whole heavenly body is obstructed and
penumbra causes partial eclipse in which only a part of the body is obstructed.

Solar Eclipse

When the moon passes directly between the earth and the sun, it obscures the sun. It casts a

shadow on the earth. From the region of shadow some or total part of the sun is not seen. It is

called solar eclipse. Orbit of the earth

west west A

moon

B
Sun C

Penumbra Earth

East Revolving moon from East
west to east in its orbit

Fig: Solar Eclipse

Blooming Science Book 9 343

When an observer is in A i.e. in Umbra region of the earth, he/she experiences total solar eclipse.
If the observer is in B or C he/she experiences partial eclipse. Usually partial solar eclipse occurs
frequently and total solar eclipse repeats after 360 years at any particular place. Total solar eclipse
stays maximum for 8 minutes only. Total solar eclipse is very important for scientists because
they can study about corona of the sun in this condition.

Solar eclipse occurs on new moon. It begins from western part and escapes from the eastern part
of the sun. Solar eclipse stays for short period because during it the moon and the earth are in
opposite motion and area of the moon’s shadow is less. (Moon is smaller than earth so it takes
less time to obstruct the rays coming from the sun.)

The sun is seen like a ring

Sun’s ray Opposite cones of umbra

Moon

Earth

Fig: Annular Eclipse

If the moon is at apogee (The farthest from the earth) in its orbit, the umbra form an opposite
cone and the bright part of the sun is seen as a ring called annular eclipse. It is very rare and
repeats after a thousand year only.

Lunar Eclipse

When the earth passes directly between the sun and the moon, it obstructs light of the sun. The
earth casts its shadow on the moon and the moon darkens partially or completely. It is called
lunar eclipse.

m3Earth

m2

Sun

Earth’s orbits m1

Moons orbits

Fig: Lunar Eclipse

If the whole moon is in penumbral region a Penumbral eclipse is occurred in which whole the
moon is seen fainter. When it is partially in umbra, partial lunar eclipse is occurred and when
completely covered with umbra, total lunar eclipse is occurred. In above diagram lunar eclipse
begins from ‘m1’ condition which is penumbral. In ‘m1’ and ‘m3’ condition partial lunar eclipse
occurs and total lunar eclipse is experienced in ‘m2’ condition only. The moon escapes from

344 Blooming Science Book 9

eclipse after ‘m3’ condition. Total lunar stays for 1 hour and 40 minutes. During total lunar
eclipse, the moon does not darken completely, it is because the atmosphere of the earth through
which the rays of the sun refract towards the moon and the moon appears coppery red. Annular
lunar eclipse never occurs.

Lunar eclipse occurs on full moon only and it begins from the eastern region of the moon. The
illustration shows that the eastern region of the moon enters first in the shadow of the earth.
(As the moon revolves eastward). Lunar eclipse stays longer than solar eclipse because in this
condition the moon and the earth are moving in the same direction and the shadow of the earth
has more area than that of the moon.

The Nodes; Rahu and Ketu

Rahu
Line of node

Moon
Ketu
When we study the above diagram, we find that the plane of the moon’s orbit cuts the plane of the
earth’s orbit at two points called nodes (Rahu and Ketu). The imaginary line which connects these
two nodes is called line of nodes. For eclipse to occur, the moon must be at or closer to the nodes
and the line of nodes must coincide or nearly coincide with the line joining to the sun and the earth.

Why do eclipses not occur every full moon and new moon?

Eclipse occurs
M2

M3 E2 M1 Eclipse
E1 doesn’t occur
Eclipse Plane of the
doesn’t occur
E3 earth’s orbit Sun

E4 M1
Plane of the

moon’s orbit

M4 Eclipse occurs

On every new moon and full moon, eclipses do not occur because of the inclination of the planes
of the moon’s orbit and the earth’s orbit. The inclination is of 5.15o to 5.5o. Due to it in most of
the new moons and full moons the position of moon is found little bit high or low from the plane
of the earth’s orbit as shown in E1 and E3 conditions of the figure. In this condition shadow of any
heavenly mass does not cast on the other. But sometimes when the planes of the moon’s orbit
and the earth’s orbit coincide, shadow of one mass casts on the other causing eclipse [condition
E2 and E4 in the above illustration]. The sun is eclipsed when the moon comes between it and the
earth. The moon is eclipsed when it passes into the shadow cast by the earth.

Blooming Science Book 9 345

Differences between the Solar and Lunar Eclipses

Solar Eclipse Lunar Eclipse

1. It occurs when the moon comes between 1. It occurs when shadow of the earth falls on

sun and earth. moon.

2. It occurs only on new moon day. 2. It occurs only on full moon day.

3. A small part of the earth falls in the umbra 3. Being larger than moon, earth casts a larger

of moon’s shadow and a large part falls shadow. The entire moon often falls within

in the penumbra where the sun is only the umbra of earth’s shadow and total lunar

partially blocked. eclipse occurs.

Let’s Learn

1. Lunar eclipse is never annular. It is because annular lunar eclipse occurs only when the
earth forms inverted cones in between it and the moon. Because the earth is bigger than
the moon and it is impossible to form of such double opposite cones in between them so
annular lunar eclipse is never occurred.

2 Lunar eclipse stays longer than solar eclipse because of the following reasons:

i. During lunar eclipse the moon and the earth both move in the same direction but
during solar eclipse, they move in opposite directions.

ii. Area of the earth’s shadow is more than that of the moon’s shadow.

Because of the above reasons the moon has to remain for longer time in the earth’s shadow
comparatively the earth remains in the moon’s shadow, thus the lunar eclipse stays longer
than solar eclipse.

3. Partial eclipse stays longer than total eclipse. It is because usually partial eclipse is caused
by penumbra and total eclipse is caused by umbra. The area of penumbra is more than the
area of umbra thus partial eclipse stays longer than total eclipse.

4. There is no possibility of the survival of organism on the Mercury and Neptune. It is
because the Mercury is the closest planet to the sun and it is very hot. But Neptune is the
farthest planet from the sun thus it is the coldest planet. Similarly they do not have the
essential things for life like O2, N2, water etc. on them.

5. Moon rising occurs about fifty minutes later daily. It is because ,to repeat a moon rising at
the same place, the earth has to complete one rotation, for which it needs about 24 hours.
In this duration, in the direction of the earth motion, the moon also forms an angle of 12o.
To cover the extra distance the earth needs about 50 minutes later daily.

6. Solar eclipse begins from western region because in it the moon obstructs the sun light,
and it revolves around the earth eastward. In this way the moon obstructs the western
region of the sun at first, during the solar eclipse.

7. Total solar eclipse is rare at a particular place because it is caused by the umbra of the
moon, which has a very less area. There is a very less possibility of casting the umbra
again at the same place where the total solar eclipse was occurred once. It needs 360 years
to repeat a total solar eclipse at the same pace.

8. Total solar eclipse is very important for scientists. It is because during the total solar
eclipse the corona of the sun can be studied. Scientist can know many new things about
the sun and the solar system by studying it.

346 Blooming Science Book 9

Main Points to Remember

1. All the aggregates of all existing things or the whole certain embracing all celestial bodies
and all of the space are called the universe.

2. Planets revolve around the sun in their own orbits.
3. The planets surrounded with asteroid belts are called inner planets and those, which are

beyond the belt, are called outer planets.
4. Meteors burn up in the atmosphere but meteorites reach on the earth surface.
5. The time taken by the moon to complete one revolution around the earth is called sidereal

month. Its value is about 27.33 days.
6. The time taken by the moon to form next new moon is called synodic month or lunar

month. Its value is about 29.5 days.
7. In partial eclipse some part of the moon or the sun is not seen but in total eclipse the whole

mass becomes invisible.
8. Annular eclipse occurs on the sun in which the bright part of the sun is seen in the form of a ring.
9. Lunar eclipse occurs on the full moon and solar eclipse occurs on the new moon.
10. The distance between the heavenly bodies is measured in light year, astronomical unit and

parsec.
1 parsec = 3.26 LY = 206265 AU
11. When the nuclei of hydrogen change into nuclei of helium, energy releases in the form of

solar energy.
12. The motion of the earth on its axis is diurnal motion and on its orbit is annual motion.
13. Annual motion causes change in season and year etc.

PRO J ECTWORK

Observe the formation of umbra and penumbra by using a torch light and a ball or candle,
matches and cardboard. Draw the diagram of your observation.

Exercise

1. Choose the correct answer from the given alternatives.

i. The hottest planet in our solar system is ..................................

a. Earth b. Neptune c. Mercury d. Venus

ii. The distance in space is measured in :

a. Astronomical Unit b. Light year c. Parsec d. All of above

iii. The motion of the earth on its axis is called ..................................

a. diurnal motion b. annual motion c. synodic month d. all of above
Blooming Science Book 9 347

iv. The duration of sideral month is about .................................. days.

a. 29.5 b. 27.3 c. 28 d.31

v. Lunar eclipse occurs on the ..................................day.

a. Full moon b. New moon c. Half moon d. Both a and b

2. Answer the following questions.

a. Define light year and AU.

b. Write a short note on the sun. How does the sun provide energy continuously?

c. Study the diagram and answer the following questions:

i. What is the duration called between m1 and m3? Sun M2 M3
ii. What is the duration called between m1 and m2? E2
iii. What angle is formed by the earth between E1 and E2. M1
iv. In which condition of the moon new moon does not E1

occur?

v. What time is taken by the moon to come from m2 to m3
condition.

d. What are diurnal and annual motion of the earth? How do day and night occur?

e. What is the main factor causing years and change in season? Show by diagram how does
season changes in the northern hemisphere of the earth.

f. What are the phases of the moon? How are they caused?

g. What are new moon and full moon? Define crescent (waxing crescent).

h. What is eclipse? Write down the causes of solar eclipse and lunar eclipse.

i. What is natural satellite? Name the planets which have no satellites.

3. Write are the differences between:

a. Galaxy and constellation b. lunar and solar eclipse

c. Star and planet d. partial and total eclipse

e. The Earth and Neptune f. bright half and dark half

4. Give reasons:

a. Planets do not twinkle but stars do.

b. Colour of Mars is red.

c. Possibility of life is nil on the Mercury and the Pluto.

d. Eclipse occur only on new moon and full moon.

348 Blooming Science Book 9

5. Answer the following questions after studying the diagram: b
SM E

a. What eclipse is occurred in this condition?
b. From which region is the eclipse started?
c. How long does the total eclipse of that type stay?
d. What type of eclipse partial or total is seen from ‘b’?
e. What type of eclipse can be seen from the moon in this condition?

6. Study the given diagram and answer the following questions:

S EM

a. What eclipse is occurred in this condition?

b. From which region the eclipse is started?

c. What type of eclipse is seen from the moon in the condition?

d. If the eclipse is total, how long will it stay?

e. Will the eclipse occur on new moon or full moon?

7. Write short notes on:

(i) first and last quarter (ii) umbra and penumbra

(iv) sidereal month (iv) dwarf planet

8. Give reasons:

a. Partial eclipse stays longer than total eclipse.

b. Total solar eclipse cannot be experienced from every part of the earth at the same time.

c. Solar eclipse begins from the western region.

d. Lunar eclipse stays longer than solar eclipse.

e. Eclipses do not occur on every new moon and full moon.

f. Northern hemisphere has the longest day on 21 June.

Blooming Science Book 9 349

9. Draw the diagram of:

(i) lunar eclipse (ii) solar eclipse

(iii) sidereal and synodic month (iv) the phases of the moon

10. What are artificial satellites? What are the purposes of establishing artificial satellites?

11. The moon does not stay at the same distance from the earth. Why? What will happen when
the earth is not tilting at the angle of 66.5o?

12. Study the diagram and answer the following questions:

E4

E1 N Sun E3 Sun
S

E2

a. On which condition of the earth it has equal days and nights?
b. On which condition does northern hemisphere have the longest night and why?
c. On which condition does Nepal have the longest day and why?
d. What is the cause of more cold weather in the southern hemisphere in E1 condition?

350 Blooming Science Book 9