4. Natural selection
According to Drawin's theory, organisms which compete for a place in the world, only
those having advantageous variations survive and reproduce. And those who do not
have advantageous variations will disappear. Nature selects those organisms which are
able to compete with other organisms.
The organisms which are fit to compete will survive and reproduce. This process is called
natural selection.
5. Origin of new species
Living organisms develop new characteristics during struggle for existence. The
advantageous characteristics of parents are transmitted to their offspring. When this
process continues for several generations, the newly formed organism look different from
their ancestors. As a result, new species of organisms are evolved form the same ancestors.
Criticisms on Darwinism
The major criticisms on Darwinism are given below:
1. Darwin could not explain the evolution of organisms from variation clearly.
2. Natural selection is only a minor cause of origin of new species. But it is not a main
cause of origin of new species because mutation also results in the formation of new
species.
3. According to Darwinism, only useful variations are transmitted from one generation
to another. But both useful and useless characteristics transmit equally from one
generation to another.
4. Darwin's theory does not explain about the existence of vestigial organs in organisms.
Key Concepts
1. The word evolution has been derived from the Latin word evolvere which mean to
unroll.
2. The sequence of gradual changes in primitive organisms over millions of years
which forms a new species is called evolution.
3. Scientists believe that life originated on the earth about 600 millions years ago in the
form of primitive and unicellular organism.
4. Charles Darwin proposed the term evolution for the first time. He says that the
present complex life has been evolved from an earlier simple form of life by gradual
changes over a long period of time.
5. The dead remains or impressions of plants and animals left in sedimentary rocks
are called fossils.
6. An embryo is the very early stage of an organism. It develops from a zygote due to
cell division.
7. The evidences obtained from the study of homologous and analogous organs also
provide evidence in favour of evolution.
GREEN Science (Biology) Book-9 351
8. Homologous organs are those which are different in functions but similar in
structure and origin. Fore limb of human being, fore limb of a horse, fore limb of a
cow, patagium of a bat, flipper of a whale, etc.
9. Those animals which show the characteristics of two different groups are called
bridge animals. For example, Archaeopteryx (a fossil bird of Jurassic period, duck-
billed platypus, echidna, lung fishes, etc.
10. According to Lamarck, when an organ is used, its size increases and when an organ
is not used for a long time, its size decreases gradually and disappears.
11. Those characteristics which are obtained by an organism during its life time are
called acquired characteristics.
12. According to Lamarck, new characteristics develop in the organisms according to
wish and need of organisms which is totally incorrect.
13. According to Darwin's theory, organisms which complete for a place in the world,
only those having advantageous variations survive and reproduce. And those who
do not have advantages variations will disappear.
14. According to Darwinism, only useful variations are transmitted from one generation
to another. But both useful and useless characteristics transmit equally from one
generation to another.
Sequential General Exercise 1
1. Choose the best answer from the given alternatives.
a. Who propounded the theory of evolution for the first time?
Lamarck Charles Darwin
Hugo de Vries Alfred Russel
b. When did Lamarck publish his theory of evolution?
In 1809 B.S. In 1809 A.D.
In 1908 AD In 1859 AD
c. Which one of the given evidences is taken as the most reliable evidence in favour
of organic evolution?
Evidences from bridge animals
Evidences from distribution of organisms
Evidences from fossils
Evidences from embryology
352 GREEN Science (Biology) Book-9
d. Which of the following organs is the vestigial organ?
vermiform appendix heart
liver kidney
e. When did Charles Darwin published his book "Origin of Species"?
In 1860AD In 1959 AD
In 1559 AD In 2059 B.S.
2. Answer the following questions.
a. What is meant by evolution?
b. Define organic evolution.
c. Write any three evidences that support the theory of organic evolution.
d. What is palaeontology?
e. How do evidences obtained from study of fossils support theory of organic
evolution? Explain.
f. Where are fossils found?
g. How are fossils formed in nature? Describe.
h. What is embryology? How do evidences obtained from study of embryos support
the theory of organic evolution? Describe in brief.
i. What are bridge animals? Give any two examples.
j. How do evidences obtained from the study of bridge animals support the theory
of organic evolution? Describe in brief.
k. How do evidences obtained from vestigial organs support the theory of organic
evolution? Explain.
3. Write any two differences between homologous organs and analogous organs.
4. Write any two theories of evolution.
5. State and explain Lamarck's theory of evolution.
6. Write any three drawbacks of Lamarck's theory.
7. What is meant by use and discuss of organs?
8. Write a short note on Darwinism.
9. What is meant by struggle for existence?
10. What is natural selection? Describe in brief in context of Darwinism.
11. Write any two drawbacks of Darwin's theory.
GREEN Science (Biology) Book-9 353
Grid-based Exercise 2 (1 Mark Each)
Group ‘A’ (Knowledge Type Questions)
1. What is organic evolution?
2. What are fossils?
3. What are homologous organs?
4. What are vestigial organs?
5. Which types of organs are shown in the given figure?
Human Cat Whale Bat
6. What is struggle for existence?
7. What are bridge animals?
8. What is natural selection ?
9. Define variation and heredity.
10. How was the ancestor of long necked giraffe?
11. Name any two biologists who propounded the theory of organic evolution.
12. What is palaeontology?
13. What are shown in the given figure?
For Group ’B’ (Understanding Type Questions) (2 Marks Each)
14. Why are fossils taken as the strongest evidence obtained so far regarding the evolution
of organisms? Give reason.
15. Why are vermiform appendix and canine teeth of human beings called vestigial
organs? Give reason.
16. Lung fishes and duck-billed platypus are called bridge animals. Give reason.
17. Write any two differences between Lamarckism and Darwinism.
18. Archaeopteryx is considered as the animal developed into bird from a reptile. Why?
19. Darwin's theory is also not accepted universally. Give any two reason.
20. Write any two differences between mutation and variation.
354 GREEN Science (Biology) Book-9
For Group ‘C’ (Application Type Questions) (3 Marks Each)
21. What is struggle for existence? Describe on the basis of Darwinism.
22. How do evidences obtained from study of embryos support the theory of organic
evolution? Describe in brief.
23. What are fossils? How do evidences obtained from the study of fossils support the
theory of organic evolution? Describe in brief.
24. What is meant by "effect of environment on organisms"? Describe on the basis of
Lamarckism.
25. How does population of organisms remains constant in nature? Describe on the basis
of Darwin's theory.
For Group ‘D’ (Higher Abilities Type Questions) (4 Marks Each)
26. How are living beings selected naturally? Describe on the basis of Darwinism.
27. Which types of organs are shown in the given figure? How do evidences obtained
from the study of these organs support the theory of organic evolution? Describe in
brief.
28. Nowadays, scientists do not accept the hypothesis of special creation of god regarding
the evolution of organisms. Why? What would happen if there were no evolution on
the earth?
29. Explain Lamarck's theory of evolution in brief.
30. Explain Darwin's theory of evolution in brief.
GREEN Science (Biology) Book-9 355
UNIT Nature and
21 Environment
Weighting Distribution Theory : 9 Practical: 2
Before You Begin
The surface of the earth is formed by soil, stone, rivers, lakes, pond, ocean,
etc. The earth is surrounded by a thick layer of atmosphere. The physical
nature of earth consists of various components like soil, water, rocks, air,
etc. The physical components of the earth have direct or indirect impacts
on life style of various living organisms. Thus, there is a close relationship
between the components of physical environment and living organisms
in the earth. All living beings get food, water, oxygen, carbon dioxide,
minerals, etc. form the physical environment.
Different types of animals and plants live on the earth. All living beings
(i.e. animals and plants) require favourable environment for their
existence. Various communities of living organisms exist in their respective
environment. Thus there is a constant interaction between communities of
organisms and their surrounding environment. Such a interaction between
living organisms (i.e. biotic components) and surrounding environment (i.e
abiotic components) is called ecosystem. The concept of ecosystem is older,
but the terms was first proposed by a British ecologist A.G. Tansley in 1935
AD. The ecosystem contains biotic components like producer, consumer,
decomposer, etc. and abiotic components like air, water, light, temperature,
soil, rock, etc. In this unit, the brief description of factors influencing the
animals and plants, ecosystem, food chain, interrelationship between
animals and plants, and ecosystem services is presented.
Learning Objectives Syllabus
After completing the study of this unit, students will be able to: • Ecological factors
i. introduce environment and its components. • Ecosystem
ii. describe the abiotic factors and biotic factors that
• Food circulation process in
affect ecosystem. ecosystem
iii. introduce ecosystem with examples.
iv. describe the interrelationship between plants and • Food chain and food web
animals. • Interrelationship between
v. explain the basic needs and human dependence on animals and plants
plants and animals. • Ecosystem services
vi. explain ecosystem services and their types.
Glossary: A dictionary of scientific/technical terms
ecosystem : a self-sustaining structural and functional unit of biosphere
abiotic : non-living things present in an ecosystem
biotic : living things present in an ecosystem
ecology : the branch of science which deals with ecosystem
autotrophs : the green plants which can synthesize their own food by photosynthesis
356 GREEN Science (Biology) Book-9
Ecological factors: Factors influencing in the animals and plants
The totality of our surrounding consists of various living organisms and non-living
things like light, heat, soil, air, temperature, water, etc. These various types of external
factors that affect life of organisms are called ecological or environmental factors. The
continuous interaction and interrelationship between/among various living components
and components of physical environment create ecosystem in the environment. The
environmental or ecological factors are classified into abiotic factors and biotic factors.
The brief description of these factors is presented below.
Abiotic Factors
The non-living factors of ecosystem that include physical environment and climate
factors are called abiotic factors. The physical environment includes air, water, soil and
other various organic and inorganic substances. The climatic factors include temperature,
pressure, rainfall, sunlight, weather, humidity, etc. These various abiotic factors of an
ecosystem are interrelated to each other. The brief description of some of the abiotic
factors of an ecosystem is presented below.
Air
The mixture of various gases such as nitrogen, oxygen, carbon dioxide, helium, argon,
neon, etc. is called air. The layer of air that surrounds the earth is called atmosphere.
Besides various gases, air contains molecules of water and water vapour. Air helps in
pollination of plants. Living beings inhale oxygen and release carbon dioxide during
respiration. Green plants requires carbon dioxide for photosynthesis. Green plants take
carbon dioxide during photosynthesis and oxygen is produced as byproduct.
Water
Water is an essential natural resource required for the life processes of animals and plants.
Water plays vital role in the growth and development of living being. Living beings cannot
exist in the absence of water on the earth. Green plants need water for photosynthesis. All
animals including human beings use water from rivers, lakes, ponds, wells, oceans, etc.
for various purposes mainly for drinking to remain alive.
Soil
Soil is formed from humus, minute rock particles and minerals. The structure of soil
varies from place to place. The colour of the soil is also different due to the presence
of minerals in it. The quality of the soil gets improved due to mixing the decomposed
biodegradable materials in it.
Solar energy
The sun is the major source of energy. It gives solar energy in the form of heat and
light. Solar energy is essential for living beings. Green plants prepare their own food by
GREEN Science (Biology) Book-9 357
photosynthesis in the presence of sunlight. The accessibility of solar energy varies from
place of solar energy varied from place to place due to the geographical situation. The
variation in the solar energy determines variation in climate, rain fall, food production,
etc. As a result, biodiversity in different places is possible.
Biotic Factors
The living organisms of an ecosystem are called biotic factors. Various organisms in
environment are interrelated and interdependent. Biotic factors refer to community of
organisms. On the basis of the nutritional relationship, biotic factors are classified into:
producers, consumers and decomposers.
a. Producers
The living beings that can prepare their food on their own are called producers. The
chlorophyll bearing plants are producers. They produce their own food by photosynthesis.
The green plants that can prepare their own food are also called autotrophs since they
synthesize their own food other living beings in ecosystem take food from producers.
B. Consumers
The living beings which depend on producers for their food directly or indirectly are
called consumers. On the basis of nature of the food they take, consumers are classified
into: primary consumer, secondary consumer and tertiary consumer.
i. Primary consumers
The living beings which directly depend on plants for their food are called primary
consumers. Primary consumers are called herbivores since they feed on plants. The
examples of primary consumers are cow, buffalo, goat, sheep, rabbit, etc.
ii. Secondary consumers
The living beings which depend on primary consumers directly for their food are called
secondary consumers. These are carnivorous animals since they feed on flesh of herbivores.
Secondary consumers indirectly depend on green plants for their food. Some examples of
secondary consumers are dog, fox, frog, snake, birds, etc. Secondary consumers provide
food for tertiary consumers.
iii. Tertiary consumers
The living beings which depend on primary consumers and secondary consumers for
their food are called tertiary consumers. Tertiary consumers also indirectly depend on
green plants for their food. Some examples of tertiary consumers are lion, tiger, crocodile,
whale, owl, peacock, hawk, shark, crocodile, vulture, etc.
358 GREEN Science (Biology) Book-9
Fig.C. Decomposers
The organisms that decompose dead bodies of organisms by decaying them are called
decomposers. In other words, decomposers are saprophytic organisms that feed on
decaying organic matter or dead bodies of organisms. Decomposers decompose the
complex organic compounds present in the dead bodies of the organisms or organic
matter into simpler substances. Such soluble minute particles are mixed in the soil and
roots of the plants absorb them. In other words, plants get required nutrients from the
decomposed materials. The examples of decomposers are bacteria and fungi. They play
a vital role in maintaining balance in ecosystem by providing required materials for the
growth of plants in the environment.
Ecosystem
The self-sustaining, structural and functional unit of biosphere that includes both biotic
communities and abiotic environment is called ecosystem. It is considered as a basic
unit of ecology. Both biotic and abiotic components of the ecosystem are essential to
maintain life in the biosphere. Also, each of the factors of ecosystem influence the other
by interconnecting and interrelating to each other. On the basis of habitat, ecosystem is
broadly divided into: terrestrial ecosystem and aquatic ecosystem.
Terrestrial Ecosystem
Terrestrial ecosystem refers to the ecosystem which exists on land. It is further divided
into grassland ecosystem, forest ecosystem, desert ecosystem, etc.
21.1
Terrestrial Ecosystem
The ecosystem which exists in the grassland is called grassland ecosystem. There are
various biotic and abiotic components in the grassland ecosystem. Soil, air, water, rocks,
sunlight, heat, temperature, humidity and other decayed materials are abiotic components
of grassland ecosystem. Similarly, various living organisms are the biotic components
of grassland ecosystem. Biotic components of grassland ecosystem are classified into
producers, consumers and decomposers.
GREEN Science (Biology) Book-9 359
Producers are all green plants that can prepare their own food. All kinds of green plants
like plants, shrubs, herbs, weeds, grasses, etc. are the examples of producers. Producers
provide food to various types of consumers that exist in grassland ecosystem.
Similarly, the living organisms that depend on producers for their food are called
consumers of grassland ecosystem. Consumers are further divided into primary, secondary
and tertiary. The primary consumers are the living organisms that directly depend on
producers for their food. For example, rabbit, goat, monkey, insects, earthworm, mouse,
etc. The carnivorous animals that directly depend on the primary consumers for their
food are called secondary consumers. For example, birds, frog, wolf, jackal, cat, dog, etc.
Similarly, the strong carnivores such as tiger, leopard, vulture, hawk, lion, etc. are tertiary
consumers of grassland ecosystem. The decomposers of the grassland ecosystem are
various types of bacteria and fungi.
Decomposers act dead bodies of organisms and decompose their complex organic matter
into simple substances. The minute particles of decomposed materials are the nutrients
for green plants.
Aquatic Ecosystem
The ecosystem which exists in water is called aquatic ecosystem. Aquatic ecosystem is
further classified into freshwater ecosystem and marine water ecosystem. The freshwater
ecosystem is further divided into pond or lake ecosystem, river ecosystem, etc.
Pond or lake ecosystem refers to the ecosystem that exists in a pond or lake. There are biotic
and abiotic components in pond ecosystem. The biotic components of pond ecosystem
are classified into producers, consumers and decomposers.
sun light
mackerel
small fish
one-celled life shrimplike creatures
(magnified) (magnified)
Fig. tuna
21.2 large shark
Aquatic ecosystem
360 GREEN Science (Biology) Book-9
All living organisms that can synthesize their own food by photosynthesis are called
autotrophic plants. The examples of producers in pond ecosystem are all aquatic plants
like algae, hydrilla, pistia, lotus, lily, diatoms, volvox, phytoplanktons, etc. They all
provide food to consumers of pond ecosystem.
The heterotoophic organisms that depend directly or indirectly on producers of pond
ecosystem are called consumers. The consumers of pond ecosystem are further classified
into primary, secondary and tertiary. The aquatic animals that feed on producers are
called primary consumers of pond ecosystem. Some examples of primary consumers of
pond ecosystem are small aquatic animals like amoeba, paramecium, cyclops, daphnia,
earthworms, insects, zooplanktons, etc. Similarly, small fish, frog, aquatic insects,
crustaceans, molluscs, etc. are secondary consumers of pond ecosystem. Likewise, big
fishes, carnivorous aquatic birds, water snakes, etc. are the tertiary consumers of pond
ecosystem.
The organisms of pond ecosystem that feed on dead organic matter are called decomposers.
Decomposers act on dead plants and animals and convert complex organic matter of
decomposing substances into simple inorganic matter. The examples of decomposers in
pond ecosystem are different types of bacteria and fungi. They maintain balance in the
pond ecosystem.
Ecosystem
Terrestrial Ecosystem Aquatic Ecosystem
Grassland Ecosystem
Fresh water Maine water
Forest Ecosystem Ecosystem Ecosystem
Desert Ecosystem
Pond/lake Ecosystem
River Ecosystem
Food Circulation Process in an Ecosystem
Energy is essential for continuation of life processes of any living organism. The major
source of energy is food stuff or biomass. Green plants can prepare their food by
photosynthesis. They are producers in ecosystem and they provide food to consumers.
The plants like yeast, mucor, mushroom, etc. are saprophytes since they get their food
from dead organisms. Similarly, animals cannot prepare their food and hence they
depend on plants directly for their food. Thus, food prepared by green plants circulates
through primary consumers, secondary consumers and tertiary consumers. Similarly,
decomposers obtain their food from dead and decaying bodies of animals and plants. In
ecosystem, each living organism obtains food from dead and decaying bodies of animals
and plants indirectly. In ecosystem, each living organism obtain food from other source
in different forms for their livelihood. Therefore, the process of transfer of food materials
from an organism to another creates food chain and food web in ecosystem.
GREEN Science (Biology) Book-9 361
Food Chain
In an ecosystem, there is a food relationship among various living organisms to continue
their life processes. There is a continuous interrelationship between produces and
consumers in an ecosystem for their food. As a result, a food chain exists in an ecosystem
for food preparation and food consumption. Producers provide food to consumers
and decomposers get food from decomposing materials like dead bodies of animals or
decaying plants.
Fig.21.3
Fig.
Food chain in grassland ecosystem
Some animals consume other animals and they are animals consumer other animals and
they are in furn consumed by other organisms in an ecosystem. As a result, a chain of food
is formed in which transform of energy takes place. The transform of consumers with
repeated eating and being eaten is called food chain, thus, a food chain is a sequential
process which is created among various living organisms by eating and being eaten. In
forest ecosystem, deer eats grass and deer is eaten by tiger.
Grass/plants Deer Tiger
(Producer) (Herbivore) (Carnivore)
Food web
21.4 Food web
362 GREEN Science (Biology) Book-9
Various food chains that exist in different ecosystems cannot function in isolation. The
various food chains create a network with interconnections and linkages under natural
conditions. Thus, the network of various food chains with the interconnection at various
trophic levels of an ecosystem is called a food web. It is a complex network of food chains
in an ecosystem.
Differences between Food chain and Food web
Food chain Food web
1. It is a sequential process which 1. It is a network of various food chains
represents who eats who. which are interconnected at various
trophic levels.
2. It is formed by various levels of an 2. It is formed by the interconnection of
ecosystem. various food chains.
3. There are many food chains in an 3. There is one food web in an ecosystem.
ecosystem.
Activity 1
Make a visit to a grassland nearby your school or home in different groups of the
classmates. Observe the producers, primary consumers, secondary consumers, tertiary,
consumers, and prepare a short report on it. Also, discuss it in your classroom.
Interrelationship between Animals and Plants
In an ecosystem, animals and plants are interrelated for their food. Green plants prepare
complex organic matter by using simple organic matter.All living organisms need nutrients
to be alive, grow and develop. The substances that are required to keep living organism
alive are called nutrients. Similarly, nutrition is the process by which living organisms
obtain food to continue their life processes. On the basis of nutritional relationship, biotic
factors of an ecosystem are categorized into autotrophs and heterotrophs.
Autotrophs
The organism that can prepare their own food by photosynthesis are called autotrophs
and the mode of nutrition of autotrophs is called autotrophic nutrition. All green plants
are autotrophs and their mode of nutrition is autotrophic nutrition or autotrophism.
Autotrophs are producers. All green plants are produces since they can prepare then own
food by using water, carbon dioxide and sunlight with the help of chlorophyll. All the
producers synthesize organic food material by using inorganic matter in the presence of
sunlight.
Heterotrophs
The living organisms that cannot prepare their own food and depend on producers
directly or indirectly for their food are called heterotrophs or heterotrophic organisms.
The mode of nutrition of heterotrophs is called heterotrophic nutrition or heterophism.
GREEN Science (Biology) Book-9 363
All animals and non-green plants are heterotrophs and their mode of nutrition is called
heterotrophism. On the basis of mode of nutrition, heterotrophs are classified into
parasites, saprophytes and holozoic organisms.
Differences between Autotrophs and Heterotrophs
Autotrophs Heterotrophs
1. They can synthesize their own food. 1. They cannot synthesize their own
2. Chlorophyll is present. food.
3. Most of them are plants. 2. Chlorophyll is absent.
3. Most of them are animals.
Parasites
The living organisms that get their food and shelter from their hosts are called parasites.
Hosts are the living organisms that provide food and shelter to the parasites. The examples
of parasitic organisms are leech, mosquito, amoeba, liverfluke, roundworm, tapeworm,
etc. Similarly, some examples of parastitic plants are rust (Puccinia) smut (Ustilago), etc.
Saprophytes
The organisms that obtain their food from dead and decaying organic matters by acting
upon them are called saprophytes. Saprophytes decompose dead bodies of animals and
parts of decaying plants and change them into simple inorganic matters. The common
examples of saprophytes are bacteria and fungi.
Holozoic organisms
Holozoics organisms refer to the organisms that feed on the whole body of plants or
animals or both. The mode of nutrition of holozoics is called holozoic nutrition. Most
of the animals except parasites and saprophytes have holozoic mode of nutrition. Some
examples of holozoics are human beings, dog, frog, tiger, vulture, fish, snake, butterfly,
paramecium, etc. Holozoic nutrition includes four different processes. They are ingestion,
digestion, assimilation and egestion.
Ecosystem services
The benefits that human beings obtain from the ecosystem are called ecosystem services.
Some of the ecosystem services are mentioned below with brief description.
Provisioning services
Provisioning services of an ecosystem refer to the products that human beings obtain
from an ecosystem. They are foods and fibres, fuel, and ornamental resources.
Human beings get foods and fibres from ecosystem. the foods and fibres that can be
obtained from plants are food, timber, jute, firewood, etc. Similarly, milk, meat, wool,
leather, etc. are obtained from animals.
364 GREEN Science (Biology) Book-9
Similarly, human beings need fuel to cook food, operate machines and automobiles, The
energy can be derived from petrol, diesel, kerosene, coal, firewood, biogas and other
substances as fuel. These all materials are obtained from ecosystem.
Likewise, different types of ornaments that human being use are obtained from the
ornamental resources in the environment. Different types of materials like shell, bone,
leather, etc. are used to make ornaments.
Regulating services
Regulating services refer to benefits obtained by human beings due to the balance in
ecological factors. Regulating services include climate regulation and water purification.
Ecosystem affects climate in local and global level. Balance in ecosystem regulates climate.
For example, forest helps regulate temperature and water cycle. Similarly, carbon dioxide
and other industrial gases affects the climate of the locality.
Similarly, balanced ecosystem helps in water purification directly or indirectly. In balanced
ecosystem, impure substances of water get filtered. The biological waste products are
decomposed and get mixed in soil. Ecosystem regulates human diseases and natural
diseases by various ways.
Cultural services
Ecosystem affects cultural norms and values including religious thoughts, behaviour,
etc. It also affects natural beauty and habitat of living organisms. Also, ecosystem helps
maintain social and biological relationship among various living beings. It helps preserve
cultural heritages. Moreover, balanced ecosystem helps increase fresh environment and
conserve natural resources. It also helps attract tourists by conserving tourists destinations.
Supportory services
Supportory services included nutrient recycling, soil formation, primary production,
food regulation, water purification, etc.
Key Concepts
1. The continuous interaction and interrelationship between/among various living
components and components of physical environment create ecosystem in the
environment.
2. The non-living factors of ecosystem that mainly include physical environment and
climate factors are called abiotic factors.
3. The mixture of various gases such as nitrogen, oxygen, carbon dioxide, helium,
argon, neon, etc. is called air.
4. Air is very important abiotic factor for living beings.
5. Water is an essential natural resource required for the life processes of animals and
plants.
6. The sun is the major source of energy. It gives solar energy in the form of heat and
light.
GREEN Science (Biology) Book-9 365
7. The living organisms of an ecosystem are called biotic factors. Various organisms in
environment are interrelated and inter-dependent.
8. The living beings that can prepare their food on their own are called producers.
9. The living beings which depend on producers for their food directly or indirectly
are called consumers.
10. The living beings which directly depend on plants for their food are called primary
consumers.
11. The living beings which depend on primary consumers directly for their food are
called secondary consumers.
12. The living beings which depend on primary consumers and secondary consumers
for their food are called tertiary consumers.
13. The organisms that decompose dead bodies of organisms by decaying them are
called decomposers.
14. The self-sustaining structural and functional unit of biosphere that includes both
biotic communities and abiotic environment is called ecosystem.
15. Terrestrial ecosystem refers to the ecosystem which exists on land. It is further
divided into grassland ecosystem, forest ecosystem, desert ecosystem, etc.
16. The ecosystem which exists in water is called aquatic ecosystem. Aquatic ecosystem
is further classified into freshwater ecosystem and marine water ecosystem.
17. The transform of consumers with repeated eating and being eaten is called food
chain. Thus, a food chain is a sequential process which is created among various
living organisms by eating and being eaten.
18. The network of various food chains with the interconnection at various trophic
levels of an ecosystem is called a food web.
19. The organism that can prepare their own food by photosynthesis are called
autotrophs and the mode of nutrition of autotrophs is called autotrophic nutrition.
20. The living organisms that cannot prepare their own food and depend on producers
directly or indirectly for their food are called heterotrophs or heterotrophic
organisms.
21. The living organisms that get their food and shelter from their hosts are called
parasites.
22. The organisms that obtain their food from dead and decaying organic matters by
acting upon them are called saprophytes.
23. Provisioning services of ecosystem refer to the products that human beings obtain
from an ecosystem. They are foods and fibres, fuel, and ornamental resources.
24. Provisioning services of ecosystem refer to the products that human beings obtain
from an ecosystem.
25. Regulating services refer to benefits obtained by human beings due to the balance
in ecological factors.
366 GREEN Science (Biology) Book-9
Sequential General Exercise 1
1. Choose the best answer from the given alternatives.
a. What is called the group of organisms that exists in common environment and
organisms have interrelationship for flow of energy?
Biotic components Community
Parasites Abiotic components
b. Which one is decomposer among the following?
Snake Green plant
Mushroom Caterpillar
c. Which one is the producer among the following in a lake ecosystem?
Fish Bacteria
Hydrilla Paramecium
d. What is called the network of food chains that exists in an ecosystem?
Food chain Community
Food web All of the above
e. Which one is not a holozoic among the following?
fish paramecium
fungi butterfly
2. Answer the following questions.
a. What is ecosystem? What does it contain?
b. Define ecological factors. Name any four biotic components of an ecosystem.
c. What are biotic factors and abiotic factors. Give two examples of each.
d. Define decomposers. Explain the importance of decomposers in an ecosystem.
e. Define the forest ecosystem with examples. Explain the role of producers in a
grassland ecosystem.
f. What is aquatic ecosystem? Define autotrophic plants of pond ecosystem with
examples.
GREEN Science (Biology) Book-9 367
g. Explain food circulation process in an ecosystem with examples.
h. Define food chain. Present an example of food chain in a forest ecosystem.
i. What does food web mean? Explain with example.
j. How do animals and plants interrelate in an ecosystem? Explain with examples.
k. What do you mean by ecosystem services? Name any four ecosystem services
and explain any one of them.
3. Differentiate between:
a. Producers and consumers
b. Secondary consumers and tertiary consumers.
c. Food chain and food web
d. Autotrophs and heterotrophs
e. Parasites and saprophytes
4. Give reason:
a. Green plants are called producers.
b. Bacteria are called decomposers.
c. Mushroom is a saprophyte.
d. Human being is a holozoic organism.
e. All green plants are autotrophs.
f. Leech is a parasitic organism.
g. Non-green plants are heterotrophs.
5. Classify the following living beings under the topics of producer, consumer
decomposer, parasite and saprophyte
Green plants, mushroom, algae, lion, frog, bacteria, fungi, leech, mosquito
6. Study the given figure and answer the following questions.
a. What is the name of ecosystem shown in the figure.
b. Name primary consumer and tertiary consumer in the figure.
c. The grass shown in the figure is producer, why?
368 GREEN Science (Biology) Book-9
7. Draw a well labeled diagram of pond ecosystem including producers, consumers
and decomposers in it.
8. "The proper balance among producers, consumers and decomposers is the result of
balanced ecosystem in nature". Justify this statement with appropriate examples.
Project work
Make a visit to a nearby pond, lake, stream or river and observe producers, primary
consumers and secondary consumers in selected water body. Identify and enlist them
in proper category. Present it in your classroom for discussion.
Grid-based Exercise 2
Group ‘A’ (Knowledge Type Questions) (1 Mark Each)
1. What is ecosystem?
2. What is ecology?
3. What are producers?
4. What are biotic components?
5. What are abiotic components?
6. Define primary consumers.
7. What is a food chain?
8. What type of organisms are called autotrophs?
9. What is photosynthesis?
10. What are four basic needs of human beings?
11. What are ecosystem services ?
12. What are cultural services in an ecosystem ?
For Group ’B’ (Understanding Type Questions) (2 Marks Each)
13. Why are green plants called producers and animals are called consumers? Give
reason.
14. Consumers cannot survive in the absence of producers, why?
15. Write any two differences between food chain and food web.
16. Describe in brief the role of decomposers to operate an ecosystem.
17. An ecosystem cannot operate in the absence of the sun. Give reason.
18. Write any two differences between producers and consumers.
19. Write any two differences between herbivores and carnivores.
For Group ‘C’ (Application Type Questions) (3 Marks Each)
20. What is the relationship between plants and animals in an ecosystem? Explain in
brief.
GREEN Science (Biology) Book-9 369
21. Write a short note on supportory services in an ecosystem. What would happen if
there were no abiotic factors in nature?
22. Describe in brief the role of the sun to run an ecosystem.
23. What is a food web? How is it operating in nature? Explain with figure.
24. Study the given food chain and answer the following questions.
Grass Grasshopper Frog
Snake
i. Name the producer and secondary consumer in the above food chain.
ii. What would be the effect on the food chain if all the snakes were killed?
For Group ‘D’ (Higher Abilities Type Questions) (4 Marks Each)
25. Identify the given factors in the terms of abiotic factors, producers, consumers and
decomposers:
Solar energy Grass Air
Snake Mouse Water
Fungi Soil
26. Draw a neat figure showing the food web of a pond ecosystem. Differentiate between
herbivores and carnivores in two points.
27. Describe in brief the importance of food and cloth for human beings. 2+2
28. Describe the role of producers to operate an ecosystem. Write any two differences
between consumer and decomposer.
29. Draw a neat diagram showing the food web of a grassland ecosystem. Differentiate
between food chain and food web.
370 GREEN Science (Biology) Book-9
Geology and Astronomy
UNIT Natural Hazard
22
Weighting Distribution Theory : 4 Practical: 1
Before You Begin
Various types of disasters occur in nature due to degradation of environment
naturally or through human activities. The major cause of occurring such
disasters is imbalance in environment. The disasters that occur suddenly
by natural processes are called natural disasters. The most destructive and
devastating natural disasters are earthquake, variety of environmental
hazards. The natural disasters occur frequently in different parts of the
world, but their occurrence and effects depend upon geographical and
meteorological factors of the place.
The occurrence of natural hazards and their impact on environment
depends on geological structure of the land. Also, climatic factors are
responsible for many natural hazards. Landslides and floods frequently
occur in Nepal due to its geographical structure. Earthquake frequently
occurs in Japan and cyclone or hurricane occurs frequently and gravity of
natural hazards is determined by geographical structure, climatic factors
and land structure of the particular area. In this unit, introduction to
various natural hazards, description of management of natural hazards,
causes, effects and preventive measures of glacier, outburst of glacier lake
and cyclone is presented.
Learning Objectives Syllabus
After completing the study of this unit, students will be able to: • Introduction to natural
i. introduce natural hazards and man-made hazards. hazards
ii. describe the methods of management of hazards. • Types of natural hazards
iii. explain the causes, effects and protective measures • Management of hazards
of natural hazards, viz. glacier flood, glacier lake
outburst flood and cyclone. • Disaster risk management
• Glacier flood, glacial lake
out-burst food and cyclone:
causes, effects and mitigating
measures
Glossary: A dictionary of scientific/technical terms
hazard : a natural or man-made situation which adversely affects life and property
disaster : an unexpected event like earthquake, flood, landslide, etc.
glacial : formed by snow or glaciers
hurricane : a violent storm with very strong winds
GREEN Science (Geology and Astronomy) Book-9 371
Hazard
A natural or man-made situation that possesses threat to lives and properties in
environment is called a hazard. A hazardous situation that has come to pass is called an
incident. Most hazards in nature are dormant or potential. When the hazards come to
their extremity, they become active and show their dangerous and devastating nature by
claiming lives and properties.
Hazards may be both natural and man-made in environment. Similarly, some hazards may
be physical, biological, chemical, etc. Some examples of natural hazards are earthquake,
volcano, landslide, etc.
The conditions or situations that can cause the body physical harm or inverse stress
are called physical hazards. Physical hazards may occur naturally or through human
activities. Some examples of natural hazards are earthquake, volcano, etc. The man-made
hazards occur more due to the human activities. For example, landslide, flood, road
accident, explosion of bomb, etc.
The chemical substances that create threat in environment and harm lives, properties and
environment are called chemical hazards. Chemical hazards may be both natural and
man-made. For example, insecticides, harmful gases, acids, etc. The biological agents that
can cause risk in living beings are called biological hazards. Such hazards are bacteria,
viruses, fungi, foreign toxin, etc. They have adverse impacts in the lives of living beings.
Although, there are many types of hazards, broadly the hazards that occur in nature are
categorized into natural hazards and man-made hazards. The brief description of these
hazards is presented below.
Natural Hazards Fig.
Various natural processes are Earthquake
responsible for occurring different types
of destructive and devastating hazards
in nature. The hazards which occur
in nature due to the natural processes
are called natural hazards. They occur
automatically in nature periodically or
all of a sudden and out of human control.
Some examples of natural hazards are
earthquake, volcanic eruption, landslide,
glacier, flood, cyclone, etc. In comparison 22.1
to man-made hazards, natural hazards
are more dangerous and devastating.
Man-made Hazards
Some hazards in nature are caused due to adverse impact of various human activities
in nature. The hazards which occur as a result of human activities are called man-made
hazards. Some examples of man-made hazards are road occident, collapsing of buildings,
372 GREEN Science (Geology and Astronomy) Book-9
bomb explosion, epidemics, outburst of dams, aeroplane crash, desertification, etc. In
comparison of natural hazards, man-made hazards are less destructive and in the control
of human being to a large extent.
Fig.
22.2 Collapsing building
Bomb explosion
Management of Natural Hazards
Various natural factors are responsible for occurring natural hazards. Thus, human beings
cannot stop natural disasters from occurring. But, there is the possibility of minimizing
the damage and loss that may occur by natural disaster. Therefore, it is necessary to
design plan for management of natural disasters by identifying their types of causes of
their occurrence. Adoption of the following activities may be helpful in the management
of natural hazards.
i. Generating public awareness to stay alert to natural disasters.
ii. Conducting immediate rescue activities for the disaster affected people.
iii. Managing physical and financial support for affected people.
iv. Mobilization of various welfare organizations to provide support to the affected
people.
v. Following various precautions and preventive measures for natural hazards.
Management of Man-made Hazards
In comparison to natural hazards, man-made hazards are in the control of human beings.
Man-made hazards can be controlled to a large extent by adopting the following activities.
i. Generating public awareness against man-made hazards
ii. Maintaining environmental sanitation
iii. Spreading awareness regarding epidemics
iv. Conducting afforestation programmes and discouraging deforestation
v. Keeping natural resources pollution free
vi. Following traffic rules to minimize road accidents
GREEN Science (Geology and Astronomy) Book-9 373
vii. Maintaining vehicles periodically
viii. Adopting scientific way for agricultural Do You Know
activities
• Hazard is a condition/event that has
ix. Paying much attention to personal potential for causing injury or loss
hygiene of life or damage to property and
environment.
x. Discouraging forest fire
• Disaster is an event that occurs
xi. Maintaining wiring system of electricity suddenly/unexpectedly in most
supply cases. It disrupts the normal course
of life in affected area. It results in
xii. Arranging proper treatment for loss or damage to life, property and
victimized and disease affected people environment.
xiii. Broadcasting various informative
programmes regarding hazards
xiv. Conservation and preservation of green forests and wildlife.
xv. Stopping unhealthy competition among human beings in different sectors.
Disaster management cycle
Various activities that are conducted before a disaster, during a disaster and after a
disaster form a cycle. It consists of four phases: Prevention/ mitigation, preparedness,
response and rehabilitation or reconstruction. The various activities that are adopted in
disaster risk management cycle are presented below.
Activities before a Disaster or Pre-disaster Activities
The activities that are carried out to minimize the loss of lives and properties are called
pre-disaster activities. It includes generating awareness through campaigns and other
activities, preparation of the disaster management plans at various levels, strengthening
the existing weak structures, etc. These activities are called preventing or mitigating
activities adopted to minimize risk of disasters.
Activities during a disaster or Disaster occurrence activities
The emergency response activities that are taken to ensure needs and provisions for the
victims during disaster are called activities during a disaster. Taking precautions, assisting
ans supporting victims, etc. are the activities that are conducted during a disaster.
Activities after a Disaster or Post-disaster Activities
The activities that include recovery and rehabilitation, of affected communities
immediately after the disaster occurred are called post-disaster activities. These
activities include rescue of victims, treatment of affected people, distributing food
to needy and affected people, management of shelter, clothing, etc. Also, analysis of
damaged structures, compensation to needy people, management of basic needs, flow
of social services to the affected people, etc. are the activities that need to be conducted
in post-disaster period.
374 GREEN Science (Geology and Astronomy) Book-9
Glacier Flood
Glaciers are essential natural resources
and source of river that provide fresh-
water in the Himalayan region of Nepal.
Glaciers are receding and glacial lakes
are forming due to global warming.
These glacial lakes are the sources of
natural disasters also. The outburst of Fig.
such lakes lead to floods that may claim
lives and properties. In Nepal, there are
many examples of glacial lake outburst 22.3
floods. There are about 3252 glaciers and Glacier flood
2323 glacial lakes in Nepal. Few glacial lakes have been outburst so far. Among 2323
glacial lakes in Nepal, 20 are potentially dangerous. In Nepal, there are many rivers like
Arun, Trishuli, Dudhkoshi, etc. that originate from Tibet. Downstream of these rivers are
at the risk of glacial lake outburst flood. A study has shown that the floods in these rivers
has claimed lives and properties at different times.
Causes of Glacier Flood
There are many causes of glacier flood. The major causes of glacier flood are given below:
i. Global warming
ii. Melting of snow
iii. Glacial lake outburst
iv. Geographic energy
v. Change in climate
vi. Tectonic shocks
vii. Human encroachment
Effects of Glacier Flood
The effects of glacier flood depend on speed of flood, amount of debris in the flood and
duration of the flood. The major effects of glacier flood are given below.
i. Destruction of land structures, natural resources, physical structures and cultural
heritages
ii. Destruction of fertile land
iii. Destruction of lives and properties
iv. Occurrence of landslides and soil erosion
v. Destruction of habitat of the living beings
vi. Destruction of agricultural products that may invite starvation
vii. Outbreak of epidemics and other various diseases
viii. Slow down the economic development of the country
GREEN Science (Geology and Astronomy) Book-9 375
Preventive measures of Glacier Flood
Glacier flood can be prevented by various ways. Some of the protective measures of
glacier flood are mentioned below.
i. Mapping of glacial lakes by field investigation
ii. Construction of dykes parallel to the rivers to slow down the current of water flow
iii. Identification and ranking of glacial lakes on the basis of their potential danger
iv. Encouraging afforestation and discouraging deforestation
v. Construction of reservoirs to store the flood water
vi. Establishment of flood measuring stations in the flood prone areas
vii. Preparation of flood hazard map in flood-prone areas
viii. Adopting precautions in glacier flood-prone areas
ix. Generating public awareness against glacier flood
Glacier lake outburst flood (GLOF)
A type of outbrust flood that occurs due
to filling of the dam containing a glacial
lake is called glacial lake outburst flood.
The dam of the glacial lake consists
of glacier, ice or a terminal moraine.
Failure of glacial lake dam occurs due
to erosion, water pressure, avalanche,
earthquake, volcanic eruption, etc. As a
result, a large amount of glacier breaks Fig.
off and displaces the water in a glacial
lake massively. Catastrophic failure of 22.4 Glacier Lake outburst
the containing ice or glacial sediment can
release the water of the lake by glacier
lake outburst. Glacier lake outburst floods are often compounded by a large amount of
river bed erosion in the steep moraine villages. The volume of glacial lakes varies, but
may hold millions to hundred millions of cubic meters of water.
There are many deadly glacial lake outburst floods identified worldwide. In Nepal, the
Tsho Rolpa glacier lake is situated in the Rolwaling valley. The lake is dammed by a 150
m high unconsolidated terminal moraine dam. This lake is growing larger every year due
to the melting and retreat of the trakarding glacier. It has become most dangerous glacier
lake in Nepal storing 90 to 100 million cubic meters water.
Effects of glacier lake outburst
The major effect of glacier lake outburst flood are given below.
i. Destruction of lives and properties
ii. Destruction of land structures
376 GREEN Science (Geology and Astronomy) Book-9
iii. Sources of floods, soil erosion and landslides
iv. Destruction of fertile land and agricultural products
v. Destruction of physical infrastructures like human settlements, roads, bridges, etc. in
downstream
Cyclone
A circular fluid motion that rotates in Fig.
as closed area in the same direction
as the earth is called a cyclone. A
cyclone is an inward spiraling wind
that rotates clockwise in the southern
hemisphere and anticlockwise in the
northern hemisphere. Generally, large
scale cyclones are centered in the low
atmospheric pressure areas.
A rapidly rotating storm system
characterized by strong winds, low 22.5
pressure center and a spiral arrangement Cyclone
of thunderstorms is called a tropical
cyclone. It produces heavy rain. It is a natural disaster which causes loss in lives and
properties depending upon its strength. Cyclone has adverse effects in different parts
of the world every year. It claims lives and properties in Bangladesh, India, Japan,
Philippines, Mexico, America etc. Nepal cannot be affected by cyclone directly since its
landlocked geographical location.
Meteorologists give different names to cyclones. The names of some cyclones are Bhola,
Katrina, Gorki, Mitch, etc. In Bangladesh, a cyclone named 'Bhola' claimed 4 lakh people in
1970 AD and 'Gorki' killed 14,000 people in 1991AD. Similarly, a cyclone named 'Katrina'
claimed 1800 people and millions worth property in 2005 AD in America.
Cause of Cyclone
The process of developing a cyclone starts when the temperature of sea water in 50m
depth from the surface of the sea is 26.5°C. In this process, water vapour with warm
air rises up when the air concentrates in low pressure zone which organizes cluster of
thunderstorms with weak surface winds. This process is called tropical disturbance.
The continuation of tropical disturbance results in strengthening of surface winds and
blowing forcefully around and into the centre of the growing storm. The storm becomes
stronger and larger when the atmospheric pressure decreases. The strong storm changes
into cyclone when the speed of rotating storm is more than 119km/h and may reach up
to 200km/h. In cyclone, the water vapour flowing upwards cools down fast and releases
heat. It is the main source of energy for a cyclone.
GREEN Science (Geology and Astronomy) Book-9 377
Effects of Cyclone
When cyclone develops, wind blows in terrifying speed. The wind blowing in extremely
high speed sweeps and damaged human settlements and other structures. It also claims
lives of people and other animals. During storm surge of cyclone, human settlements of
the sea beach may be submerged due to raise in water level. The major effects of cyclone
are mentioned below.
i. Destruction of lives and properties in coastal regions
ii. Source of other disasters like flood, soil erosion, landslide due to heavy rain fall
induced by cyclone
iii. Destruction of land structure, fertile land and agricultural products
iv. Reduction in fertility of the fertile land due to deposit of silt due to cyclone
v. Disturbances in water related activities like boating, fishing, shipping etc.
Protective Measures of Cyclone
Cyclone is a quite unpredictable natural disaster that occurs in coastal regions. It is
destructive and devastating in coastal regions since it claims lives and properties
violently in a short period of time. Meteorologists can forecast only the probability,
direction and speed of cyclone with the help of satellites. Such forecast may be helpful
to adopt precautions. Some protective measures that can be adopted against cyclone are
mentioned below.
i. Collecting information regarding cyclone and warning people of the coastal regions
ii. Adopting cyclone resistant technologist to build houses in the coastal regions
iii. Constructing emergency shelters for victims of cyclone
iv. Rescuing cyclone affected people in the short period
v. Generating public awareness against cyclone among the people of coastal regions
vi. Updating to the information regarding cyclone by the people of coastal regions
Key Concepts
1. A natural or man-made situation that possesses threat to lives and properties in
environment is called a hazard.
2. When the hazards come to their extremity, they become active and show their
dangerous and devastating nature by claiming lives and properties.
3. The conditions or situations that can cause the body physical harm or inverse stress
are called physical hazards.
4. The chemical substances that create threat in environment and harm lives, properties
and environment are called chemical hazards
5. The biological agents that can cause risk in living beings are called biological
hazards. Such hazards are bacteria, viruses, fungi, foreign toxin, etc.
6. The hazards which occur in nature due to the natural processes are called natural
hazards.
378 GREEN Science (Geology and Astronomy) Book-9
7. The hazards which occur as a result of human activities are called man-made
hazards.
8. Human beings cannot stop natural disasters from occurring. But, there is the
possibility of minimizing the damage and loss that may occur by natural disasters.
9. Various activities that are conducted before a disaster, during a disaster and
after a disaster form a cycle. It consists of four phases: Prevention/ mitigation,
preparedness, response and rehabilitation or reconstruction.
10. The activities that are carried out to minimize the loss of lives and properties are
called pre-disaster activities.
11. The emergency response activities that are taken to ensure needs and provisions for
the victims during disaster are called activities during a disaster.
12. The activities that include recovery and rehabilitation of affected communities
immediately after the disaster occurred are called post-disaster activities.
13. A type of outburst flood that occurs due to filling of the dam containing a glacial
lake is called glacial lake outburst flood.
14. A circular fluid motion that rotates in as closed area in the same direction as the
earth is called a cyclone.
Sequential General Exercise 1
1. Choose the best answer from the given alternatives.
a. What is responsible for natural hazards in nature?
Chemical energy Geographical energy
Geological energy Physical energy
b. How many glacial lakes are there in Nepal?
3252 2323
2423 2523
c. Which one is the cause of glacier flood? Global warming
Soil erosion
Air pollution Water pollution
d. What is the cause of failure of glacial lake dam?
Soil erosion Avalanche
Land structure Water pollution
GREEN Science (Geology and Astronomy) Book-9 379
e. What is the name of the cyclone that occurred in 1970 AD in Bangladesh?
Katrina Gorki
Bhola Mitch
2. Answer the following questions.
a. What does a hazard mean? Mention different types of hazards.
b. Define natural disasters. Differentiate between natural hazards and man-made
hazards.
c. What do you mean by management of natural hazards? Explain briefly.
d. Mention any 10 ways of controlling man-made hazards.
e. What does disaster management cycle mean? Make a list of pre-disaster activities.
f. Why are post-disaster activities important?
g. What is glacier flood? Mention any five causes of glacier flood.
h. What are the effects of glacier flood? Mention any six effects of glacier flood.
i. How can the effects of glacier flood be minimized? Explain briefly.
j. What do you mean by glacier lake outburst? Mention any five effects of glacial
lake outburst.
k. Define cyclone. Cyclone is a natural disaster of coastal region, why?
l. Explain the causes of cyclone.
m. Mention any four effects and four protective measures of cyclone.
Project work
Make a study of any one natural hazard that occurred in your area and prepare a
short report on it in the following format.
a. Introduction b. Causes
c. Effects d. Preventive measures
e. Conclusion
Present the report in your classroom.
380 GREEN Science (Geology and Astronomy) Book-9
Grid-based Exercise 2
Group ‘A’ (Knowledge Type Questions) (1 Mark Each)
1. What is a natural hazard?
2. How many types of natural hazard are there? Name them.
3. What is meteorology?
4. Define man-made hazard with one examples.
5. What is glacier flood ?
6. In which places of Nepal there is possibility of glacier flood? Write.
7. What is glacier lake outburst?
8. What is cyclone?
9. What is meant by GLOF?
10. Define tropical disturbance.
11. What is tropical storm and cyclone?
12. What do you mean by the eye of a cyclone?
13. Write down the major effects of cyclone.
For Group ’B’ (Understanding Type Questions) (2 Marks Each)
14. Write any two differences between natural hazard and man-made hazard.
15. Write any two differences between glacier flood and cyclone.
16. Flood and earthquake are called natural hazards. Give reason.
17. Glacier flood occurs frequently in Nepal. Give any two reasons. .
18. Road accident is called man-made hazard whereas landslide is called natural hazard,
why ?
19. Cyclone cannot affect Nepal directly, why ?
20. List the major effects of glacier flood.
21. What are the main causes of cyclone?
22. Write down the major effects of cyclone.
23. What are the protective measures of glacier flood? Write.
24. Write down the effects of glacier lake outburst.
25. Describe in brief the importance of study of meteorology in the context of Nepal.
For Group ‘D’ (Higher Abilities Type Questions) (4 Marks Each)
26. Mention the steps of disaster management cycle. Explain any one of them.
27. How is management of natural hazards done? Write any four points.
28. Write a short note on glacier lake outburst in Nepal.
29. Mention any four effects and four protective measures of cycle.
30. Write a short note on glacier flood.
GREEN Science (Geology and Astronomy) Book-9 381
UNIT Greenhouse
23
Weighting Distribution Theory : 4 Practical: 0
Before You Begin
A structure with walls and roofs made by transparent materials is called
a greenhouse. Generally, the materials like glass or plastics are used to
make greenhouse. The plants that require regulated climatic conditions
are grown in greenhouse. You might have heard about greenhouse. It is
also called hot-house or glasshouse. The interior of a greenhouse becomes
significantly warmer than the surrounding temperature. Greenhouses
are constructed in different sizes according to need. Some greenhouse
are small sheds, whereas some are industrial-sized building.
Greenhouses are used for maintaining botanical gardens, growing
commercial plants, vegetable farming, etc. Generally, greenhouses are
used for growing and propagating plants in cold climates. Greenhouses
allow sunlight to enter and prevent heat from escaping from their
interior. Greenhouse has an important role in our daily life. In this unit,
introduction to natural greenhouse and its effects, importance of artificial
greenhouse and use, and climate change are presented.
Learning Objectives Syllabus
After completing the study of this unit, students will be able to:
i. introduce greenhouse in natural environment and • Introduction to greenhouse
and its effects
explain its effects.
• Artificial greenhouse and its
ii. describe the importance of greenhouse. utility
iii. describe the utilities of artificial greenhouse. • Climate change
- Introduction
iv. introduce climate change. - Causes
- Effects
v. describe causes, effects and mitigating measures of - Mitigating measures
climate change.
Glossary: A dictionary of scientific/technical terms
greenhouse : the glasshouse made to regulate climatic conditions
climate : the average atomspheric condition of a place over a long period of time
deforestation : the process of cleaning forests
382 GREEN Science (Geology and Astronomy) Book-9
Greenhouse Effect
There are different gases in the troposphere of the atmosphere. Such gases are carbon
dioxide, chlorofluoracarbon, methane, oxides of nitrogen, water vapour, etc. Along with
the gases, dust particles are also present in the atmosphere. The layer of gases and dust
particles cover the surface of the earth making dense canopy. Such canopy allows solar
radiations to enter the earth but does not allow to escape after reflection. As a result, the
temperature of the earth increases due to the effect of solar radiation. Thus, it works as an
artificial greenhouse. The phenomenon of increasing the temperature of the earth due to
the canopy of greenhouse gases that works like glass or plastic in an artificial greenhouse
is called greenhouse effect in nature. The greenhouse gases are carbon dioxide, methane,
chlorofluorocarbon, oxides of nitrogen, water vapour, etc.
It is estimated that carbon dioxide has the greatest impact on greenhouse effect. The impact
of carbon dioxide is 57%, chlorofluorocarbon has 25%, methane has 12% and oxides of
nitrogen has 6%. Due to the effect of greenhouse, the temperature of the earth increases
gradually. The process of increasing the temperature of the earth due to the greenhouse
effect is called global warming. Global warming is responsible for melting snow capes
resulting in increment of level of sea. Similarly, the temperature of the higher regions
increases due to melting of ice and drying of water resources. It has adverse impacts on
all living organisms including human beings.
Cause of Greenhouse in the Earth
Various greenhouse gases are released from different human activities and by some natural
processes. One of the important greenhouse gases, carbon dioxide is produced by burning
fossil fuels. Similarly, methane is produced from decomposition of biodegradable wastes.
Likewise, chlorofluorocarbon is released from air conditioners, refrigerators, aerosol
spray cans, etc. Water vapour is produced from the oxidation of organic compounds and
vaporization of water from different water resources like lakes, streams, rivers, seas, etc.
These all gases form canopy around the earth's surface and greenhouse is formed.
Importance of Greenhouse Effect
The earth absorbs solar radiations due to the greenhouse effect. The solar radiations
that enter the earth cannot escape after reflection due to the greenhouse in the earth.
In the absence of greenhouse, heat cannot be stored on the earth and consequently the
temperature of the earth would be less by 39°C than today's temperature. As a result, ice
may cover the earth and there is no possibility of any living organism on the earth due
to extreme cold and presence of ice everywhere. Thus, greenhouse plays a vital role in
maintaining favourable temperature for the existence of living beings on the earth.
Adverse Impacts of Greenhouse Effect
Although, greenhouse plays a vital role for the existence of different living beings on the
earth, it has many adverse impacts too. Some of the adverse impacts of greenhouse effect
on the earth are mentioned below.
i. It increases temperature in atmosphere.
GREEN Science (Geology and Astronomy) Book-9 383
ii. It brings changes in water cycle.
iii. It brings hazards in the health of living organisms including human beings.
iv. It reduces agricultural productivity and production.
v. It helps in melting of snow in the polar regions and drying water resources.
vi. It helps in increasing sea level due to the melting of snow. The increase in the sea level
adversely affects human settlement in coastal regions.
vii. It brings negative impacts in biodiversity.
viii. It creates desertification.
ix. It imbalances ecosystem in nature.
x. It changes pattern of weather condition.
Artificial Greenhouse
The structures with walls and roofs that Fig.
are made by glasses or plastics are called
artificial greenhouses. Artificial
greenhouses are used in agricultural
farms, botanical gardens, etc. to maintain
favourable temperature for the plants
that are grown inside them.
Artificial greenhouse allows to enter 23.1
solar radiation but does not all it to
escape after reflection. As a result, interior of
the greenhouse becomes hot due to changing Do You Know
of solar light energy into heat energy inside
them. The heat energy preserved inside A small artificial greenhouse is called cold
the artificial greenhouses increases the frame.
temperature inside them. The slanted roofs
of artificial greenhouses allow more sunlight
to enter inside the greenhouse. The required
amount of temperature for the plants inside the greenhouses helps them to grow and
develop well.
Importance and Utility of Artificial Greenhouse
The importance and utility of artificial greenhouse is mentioned below.
i. Off-seasonal vegetable can be grown by maintaining favourable temperature inside
the greenhouse.
ii. Various plants that may die in cold temperature can be conserved.
iii. Special types of plants can be grown throughout the year.
384 GREEN Science (Geology and Astronomy) Book-9
iv. Agricultural products can be produced in the countries having extremely cold
temperature/climate.
v. Different types of types of flowers, vegetables, fruits, etc. can be grown throughout
the year.
vi. Environmental pollution can be controlled by growing plants inside greenhouses.
Climate Change
Climate is an abiotic component of atmosphere. It is an atmospheric phenomenon over a
long period of time. It has been observed that it varies over time due to various reasons.
The variation in the climate in global or regional level over time in called climate change.
More over climate change is a change in the statistical distribution of weather patterns.
Such type of change lasts for a long period of time. Various human activities are mainly
responsible for changing climate. Increase the level of carbon dioxide in the atmosphere,
over use of fossil fuels, burning of firewood, deforestation, etc. are the major causes of
climate change.
Nepal has variation in climate conditions due to its geographical diversity. The highest
peak of the world, i.e. Mt. Everest, lies in Nepal. Similarly, Nepal is divided into three
geographical regions: Mountain, Hill and Terai. Thus, climate of Nepal ranges from
extremely cold to extremely hot due to its geographical structure. Therefore climate
change has become a burning issue for Nepal in present days.
Causes of Climate Change
Various human activities as well as natural processes are responsible for climate change.
The cause of various movements, volcanic eruption, variation in solar radiation on the
earth, etc. play vital role in changing climate. Similarly, human activities like deforestation,
industrialization, excessive use of chemical fertilizers and pesticides, etc. also have a
major role in climate change. The factors that play vital in climate change are described
below briefly.
i. Increase in temperature
The temperature of the earth varies due to the variation in geographical structures. Some
parts of the earth receive more solar radiation, while other parts do less. The parts of the
earth receiving more solar radiations have more temperature and less solar radiation
receiving parts have less temperature. Thus, increase in temperature causes climate change.
ii. Greenhouse effect
Various human activities are responsible for producing greenhouse gases like carbon
dioxide, chlorofluorocarbon, methane, etc. These gases create greenhouse effect on the
earth which is responsible for climate change.
GREEN Science (Geology and Astronomy) Book-9 385
iii. Deforestation
Green plants balance the amount of carbon dioxide and oxygen in the atmosphere.
Deforestation causes destruction of green plants of the forest and hence amount of
carbon dioxide increases in the atmosphere. The more amount of carbon dioxide in the
atmosphere causes climate change.
iv. Industrialization
Industrialization is the major source of producing greenhouse gases like carbon dioxide,
sulphur dioxide, methane, etc. These gases are responsible for greenhouse effect which
results in climate change.
v. Excessive use of chemical fertilizers
Various greenhouse gases are produced due to excessive use of chemical fertilizers. Also,
use of chemical fertilizers makes the soil dry. Greenhouse effect and rise in temperature
result in climate change.
vi. Volcanic Eruption
Volcanic eruption is the source of dust particles and compounds of sulphur in environment.
Dust particles and compounds of sulphur block the solar radiation by accumulating in
strastosphere of the atmosphere. It ultimately results in climate change on the earth.
Effects of Climate Change
Climate change has many adverse effects on plants and animals including human beings.
The major effects of climate change are give below.
a. Impact on ecosystem and biodiversity
Many species of animals and plants cannot adapt themselves in the changing environment.
So, they are in the verge of extinction due to global climate change.
b. Increase in temperature
Due to climate change, the average temperature on the surface of the earth is increasing
day by day. When the average temperature from 2001 to 2010 AD was compared with
the temperature of 1980 AD, it was found that the temperature of 1980 AD was less. The
statistical data from 1976 to 2005 AD shows that the average temperature of Nepal is
increasing at the rate of 0.04°C per year. It shows that climate change is responsible for
increasing global temperature.
c. Impact on human settlement
The settlement of human beings in Himalayan region, hilly region, near the rivers, near
the sea and coastial region is being affected by climate change. The flood in Koshi river,
and the flood in Sunkoshi river destroyed life and property and displaced many people
from their settlement.
386 GREEN Science (Geology and Astronomy) Book-9
d. Impact on human health
Human beings suffer from various diseases due to climate change. The efficiency of
human beings decreases and animals suffer from different types of diseases due to climate
change.
e. Negative impact in water resources
Water resources are adversely affected by climate change. The rate of snowfall and
deposition in Himalayas is decreasing year by year. The ice on Himalayas melts very fast.
It affects the flow of water in rivers. When the temperature increases, the ice of Himalayas
melts and result in floods and landslides. Climate change also affects the pattern of rainfall
and water cycle.
f. Impact on agriculture
Greenhouse effect, acid rain, heavy rainfall, drought, hailstones, etc. are caused due to
climate change. Climate change also brings changes on the surface of the earth due to flood
and landslides. These phenomena has negative impact on agriculture and productivity
of crops.
g. Impact on physical facilities
The physical infrastructure like buildings, roads, bridges, water reservoirs, etc. many
be damaged due to effect of climate change.
h. Disaster caused due to climate change
Climate change is the major cause of the disasters like flood, landslide, GLOF,
drought, heavy rainfall, etc.
i. Energy crisis
Running water resource is the major source to generate hydroelectricity. The decrease
in amount of water in rivers is the decrease in production of hydroelectricity. It results
in energy crisis in near future due to effect of climate change.
Measures of Climate Change Management
1. We should minimize the overuse of fossil fuels.
2. We should stop unmanaged urbanization.
3. We should develop and use alternative sources of energy.
4. Public awareness should be generated.
5. We should improve our agricultural system.
6. We should dispose wastes properly.
7. We should control the pollution caused by fossil fuels in factories and industries.
8. We should conserve natural environment.
GREEN Science (Geology and Astronomy) Book-9 387
9. We should minimize the production and emission of greenhouse gases.
10. We should reduce the use of fossil fuels.
11. We should develop diseases free species of plants and animals.
12. We should manage the means of transportation properly.
13. We should minimize the use of insecticides, pesticides and chemical fertilizes.
14. Development works should be sustainable.
15. We should plant trees on bare parts of land.
16. Environmental pollution should be controlled.
17. We should encourage afforestation and discourage deforestation.
18. We should conserve water resources.
Key Concepts
1. The phenomenon of increasing the temperature of the earth due to the canopy of
greenhouse gases that works like glass or plastic in an artificial greenhouse is called
greenhouse effect in nature.
2. The process of increasing the temperature of the earth due to the greenhouse effect
in called global warming. Global warming is responsible for melting snow capes
resulting in increment of level of sea.
3. Greenhouse plays a vital role in maintaining favourable temperature for the
existence of living beings on the earth.
4. The structures with walls and roofs that are made by glasses or plastics are called artificial
greenhouses. Artificial greenhouses are used in agricultural farms, botanical gardens, etc.
to maintain favorable temperature for the plants that are grown inside them.
5. The variation in the climate in global or regional level over time in called climate
change.
6. Various human activities as well as natural processes are responsible for climate
change. The cause of various movements, volcanic eruption, variation in solar
radiation on the earth, etc. play vital role in changing climate. Similarly, human
activities like deforestation, industrialization, excessive use of chemical fertilizers
and pesticides, etc. also have a major role in climate change.
7. Due to climate change, the average temperature on the surface of the earth is
increasing day by day.
8. The settlement of human beings in Himalayan region, hilly region, near the rivers,
near the sea and coastal region is being affected by climate change.
9. Climate change also brings changes on the surface of the earth due to flood and
landslides. These phenomena has negative impact on agriculture and productivity
of crops.
388 GREEN Science (Geology and Astronomy) Book-9
Sequential General Exercise 1
1. Choose the best answer from the given alternatives.
a. Which of the given gas is not a greenhouse gas?
oxygen chlorofluorocarbon
methane carbon dioxide
b. Which of the following is the main cause of climate change?
deforestation
increase in temperature
increased release of greenhouse gases
volcanic eruption
c. Artificial greenhouse stores .................
heat energy light energy
sound energy electrical energy
d. What type of climate is found in terai region of Nepal?
very hot moderate
cold very cold
e. What is artificial greenhouse made of?
glass metal
glass and plastic plastic
2. Answer the following questions.
a. Define greenhouse and write its types.
b. What is meant by greenhouse effect?
c. Write any four harmful effects of greenhouse effect.
GREEN Science (Geology and Astronomy) Book-9 389
e. What is artificial greenhouse made of? Write its utility.
f. Write down the importance of cold frame.
g. Write down the utility of artificial greenhouse.
h. What do you man by climate change?
3. Write any five major causes of climate change and describe any two of them.
4. Industrialization and deforestation play a great role for climate change. Justify
this statement.
5. Write any six effects of climate change and describe any two of them.
6. Write any five measures of climate change management.
7. How does climate change affects human settlement ? Explain with examples.
8. Write any two differences between natural greenhouse and artificial greenhouse.
9. Analyze the causes of climate change in the context of Nepal.
10. Why is the roof of artificial greenhouse made slanted? Give reason.
Grid-based Exercise 2
Group ‘A’ (Knowledge Type Questions) (1 Mark Each)
1. Define greenhouse.
2. What is greenhouse effect ?
3. What are greenhouse gases ?
4. What is artificial greenhouse made of?
5. What is an artificial greenhouse ?
6. What is climate change ?
7. Name any four greenhouse gases.
8. What happens due to absence of greenhouse effect on the earth?
9. What are the main causes of climate change in Nepal ?
10. What is the effect of climate change on human health ?
11. What is cold frame ?
12. Write any two causative factors of climate change.
13. What is the effect of climate change in atmospheric temperature ?
390 GREEN Science (Geology and Astronomy) Book-9
For Group ’B’ (Understanding Type Questions) (2 Marks Each)
14. Write any two utilities of artificial greenhouse. ;
15. The roof of artificial greenhouse is made slanted. Give reason.
16. Artificial greenhouses are very useful for human beings, why ?
17. Climate change affects agricultural system adversely. Justify this statement.
18. Climate change invites energy crisis. Justify this statement with examples.
19. List the major effects of glacier flood.
20. Write down the major effects of cyclone.
21. What is the effect of climate change on human health? Write any two effects.
22. Write any two measures of climate change management.
23. Increase in release of various greenhouse gases is the main cause of climate change.
Give reason.
24. Write down the cause of being more temperature inside the greenhouse than that of
its surroundings.
For Group ‘D’ (Higher Abilities Type Questions) (4 Marks Each)
25. How does climate change occur due to industrialization? Write in brief.
26. Write in brief about the impact on human settlement and physical facilities due to
climate change.
27. How does climate change occur due to increase in release of greenhouse gases? Write
in brief.
28. How does climate change occur due to deforestation? Explain.
29. Explain the effect of climate change in agriculture and water resources.
GREEN Science (Geology and Astronomy) Book-9 391
UNIT The Earth in the
24 Universe
Weighting Distribution Theory : 4 Practical: 1
Before You Begin
The vast surrounding space around us is called universe. It includes
solar system, stars, galaxies, constellations, planets, satellites, etc. The
earth is a planet that lies in the solar system. The sun in the solar
system is the medium-sized star and one of the important members
of solar system. It is about 1.5 × 108 km away from the earth. The
earth revolves around the sun. Similarly, other planets also revolve
around the sun in their elliptical orbits. The solar system is situated
in the milky-way galaxy. It can be observed with the help of powerful
telescope from the earth. The spiral shaped galaxy that consists of
solar system and other stars, planets, constellations, galaxies, etc.
is the milky-way galaxy. The milky-way galaxy contains about 1011
stars. In the universe, the milky-way is at the center and the sun lies
in the two-thirds of the milky-way galaxy.
Learning Objectives Syllabus
After completing the study of this unit, students will be able to:
i. describe rotation and revolution of the earth. • Units related to Astronomical
distance
ii. introduce and describe the phases of the moon.
• The solar system
iii. explain the relationship among the sun, earth and • Motions of the earth
moon in terms of their position. • Phases of the moon
• Positions of the sun, the earth
iv. introduce eclipse and state its types.
and the moon
v. describe solar eclipse and lunar eclipse with labelled • Sidereal month and synodic
figures.
month
vi. define satellites and explain their types with examples. • Umbra and Penumbra
• Eclipse (solar eclipse and lunar
eclipse)
Glossary: A dictionary of scientific/technical terms
universe : the vast surrounding space that includes everything like galaxy, solar
system, etc.
light year
satellite : the total distance covered by light in one year through a vacuum
eclipse : the heavenly body revolves around the planet
: the phenomenon of casting a shadow on the earth or the moon
392 GREEN Science (Geology and Astronomy) Book-9
Units Related to Astronomical Distance
The solar system consists of 8 planets and other 173 satellites. The earth is only suitable
for existence of living beings among eight planets. The earth revolves around the sun in
an elliptical orbit. The motion of the earth in this pattern is called on orbital motion or
revolution. Also, the earth moves in its own axis. It is called rotation of the earth. The days
and nights occur due to the rotation of the earth, whereas change in seasons occurs due
to the revolution of the earth.
The distance between astronomical bodies is called astronomical distance. Astronomical
distance cannot be measured in units like meter or kilometer since the astronomical bodies
are very far from each other. The following units are used to measure the astronomical
distance.
1. Light year ii. Astronomical unit iii. Par sec
Light year
One light year is defined as the distance travelled by light in one year in vacuum. It is the
unit used for measuring the distance between celestial bodies.
Facts about light year
The speed of light in vacuum = 3 × 108 m/s
Hence the light travels in one year = 9.46 × 1015m/s
∴ One light year = speed of light × 1 year
= 3 × 108m/s × 1 year
= 3 × 108m/s × 365 × 24 × 60 × 60s
= 9.46 × 1015m
∴ One light year = 9.46 × 1015m
Therefore, the distance 9.46 × 1015m is called 1 light year.
Astronomical Unit
The average distance between the sun and the earth is called astronomical unit. Its value
is 1.5 × 1011m, i.e 1 Astronomical unit = 1.5 × 1011m.
Par sec
Par sec is the unit of measuring the distance between celestial bodies. It is greater than
light year. 1 par sec = 3.26 light years.
The distance between the earth and the sun is 8 light minutes. Light takes 8 minutes
and 20 seconds to reach the earth from the sun. The nearest star from the solar system is
Proxima centauri. It is about 4.3 light year away from the solar system. The nearest galaxy
from the earth is Andromeda. The distance between Andromeda and the earth is 130, 000
light year. The length of Milky-way galaxy is 100, 000 light year and its diameter is about
200 light years.
GREEN Science (Geology and Astronomy) Book-9 393
The Solar System
The family of the sun which consists of
eight planets, their satellites, asteroids,
comets, etc is called solar system. The sun
is the medium-sized star around which all
planets, their satellites, asteroids, comets,
etc. revolve in their orbits. The sun lies
at the center of solar system. The surface
temperature of the sun is about 5400°C.
The nuclear fusion reaction is the source Fig.
of heat of the sun. In this reaction, a single
heavy nucleus is formed by combining 24.1
two or more light nuclei. Similarly, a vast
Solar System
amount of energy is produced in the sun
by the conversion of hydrogen gas into helium gas.
All planets revolve around the sun in their elliptical orbits. The earth is the only planet
having suitable conditions for the existence of living beings. Moreover, the earth has
suitable temperature, water and supporting gases required for the existence of living
beings.
Motion of the Earth
There are two types of motions of the earth. They are diurnal motion and annual motion.
The earth takes 1 day (i.e. 23 hour 56 minutes 4 seconds) to complete one rotation around
its axis. It is called diurnal motion. The motion of the earth in which it rotates around its
own axis is called diurnal motion. The axis of the earth tilted at an angle of 66.5° with its
orbital plane. The earth rotates from west to east in its axis. The rotation of the earth
causes day and night on the surface of the earth.
The earth revolves around the sun in its own Do You Know
elliptical orbit. It takes 365 days, 5 hours,
48 minutes and 46 seconds to complete one There are 365 days in a year. But every
revolution around the sun. This revolution of fourth year has one more day. The
the earth is called annual or orbital motion. particular year which have 366 days is
called a leap year. The extra day in a leap
Seasons on the Earth year is added in February. Thus, February
has 29 days in the leap year.
The revolution of the earth causes the change
of seasons on the earth. It occurs due to the
following reasons.
i. Revolution of the earth around the sun.
ii. Spherical shape of the earth
iii. Tilted axis of the earth
iv. Elliptical orbit of the earth.
394 GREEN Science (Geology and Astronomy) Book-9
Change of Seasons on the Earth
The earth completes one revolution around the sun in 365 days. The earth revolves around
the sun in an elliptical orbit and the axis of rotation of the earth is tilted at an angle of
66.5°. Due to these reasons, the earth is not always at the same distance from the sun
which results in the change in seasons on the earth. The duration of one year, i.e. 365 days
is divided into four seasons. They are:
i. Summer season ii. Autumn season
iii. Winter season iv. Spring season
The tilted axis of rotation of the earth always lies in the same direction. Due to this, the
position of the northern and southern hemispheres of the earth towards the sun keeps on
changing throughout the year. When the northern hemisphere is tilted towards the sun,
we experience summer and the people in the southern hemisphere experience winter.
Spring and autumn seasons occur when the earth lies in between these two extreme
positions in its orbit.
Spring
March 21/22
Fig. Summer Sun
June 20/21
Winter
December 21/22
24.2 Autumn, September 22/23
Formation of seasons on the earth
On June 21, i.e. 8th of Asar, the earth lies the farthest from the sun in the southern
hemisphere, but the nearest from it in the northern hemisphere. So, the northern
hemisphere experiences the longest day and the southern hemisphere experiences the
shortest day on June 21. At this time, the summer season occurs in the northern hemisphere
and the winter season occurs in the southern hemisphere.
On December 22, i.e. Poush 7, the northern hemisphere has the shortest day and the southern
hemisphere has the longest day. At this time, the winter season occurs in the northern
hemisphere and the summer season occurs in the southern hemisphere.
On March 21, i.e. Chaitra 8, the sun lies above the equator and the days and nights are
equal in all parts of the earth. At this time, the spring season occurs in the northern
hemisphere and the autumn season occurs in the southern hemisphere.
On September 23, i.e. Asoj 7, the rays of the sun fall perpendicularly on the equator. So,
day and night are equal in both hemispheres. At this time, the autumn season occurs in
the northern hemisphere and the summer season occurs in the southern hemisphere.
GREEN Science (Geology and Astronomy) Book-9 395
Phases of the Moon
Different shapes of moon can be seen every day when viewed from the earth. What is the
reason behind this fact? Have you seen different shapes of the moon or not?
The planets and satellites do not have their own source of light for shining. They shine by
reflecting the light from the sun. The moon is the natural satellite of the earth. It does not
have its own source of light. The moon always presents its same face towards the earth.
When the reflected light of the moon reaches the earth, the moon becomes visible. We see
only that part of the moon which reflects the sunlight towards the earth.
Third quarter
Waning crescent Waning Gibbous
New moon Full moon
Waxing crescent Waxing Gibbous
Fig. Fig.
24.3Fig. First quarter
Phases of moon
When the moon lies in between the sun and
the earth, the reflected light from the moon
does not reach the earth and the moon is not
visible. This day is called the new moon day.
The dark side of the moon faces the earth on
the new moon day.
On the night just after the new moon day, a 24.4
crescent moon can be seen. The other part of
the moon is only faintly visible. The crescent New moon
goes on increasing till the 15th day from the Full moon
new moon day when the full bright face of
the moon is visible. The day is called the full
moon day.
The gradual increase in the bright disc of the 24.5
moon is called waxing of the moon. The
bright disc of the moon increases for 15 days
after the new moon day. This duration is
called the bright half. After the full moon, the
bright face of the moon goes on decreasing
every day for 15 days. This duration is called
the dark half. The gradual decrease in the
bright disc of the moon is called waning of
396 GREEN Science (Geology and Astronomy) Book-9
the moon. So, the waxing and waning of the disc of the moon, as the moon revolves
around the earth, is called the phases of the moon.
On the full moon day, the moon rises in the Do You Know
eastern sky and it rises 50 minutes later the When the earth lies between the moon and
next day. The moon revolves around the the sun, the full bright face of the moon is
earth in its own orbit. The moon completes seen from the earth. This day is called the
one revolution around the earth in 2731 d ays. full moon day.
This duration is called the sidereal month. 1
2
Similarly, the duration between two consecutive new moons or full moons is 29 days.
This duration is called the synodic month.
Differences between Synodic month and Sidereal month.
Synodic month Sidereal month
1. This is the time period between two 1. This is the time taken by the moon to
new moons or two full moons. complete one revolution around the
earth.
2. Its duration is 2921 days. 2. Its duration is 2713 days.
Positions of the Sun, the Earth and the Moon
The sun is the nearest star from the earth. It is a medium-sized star consisting of masses
of hot gas. More then 70% hydrogen gas is present in the sun. The sun revolves around
the galaxy and it also revolves around its own orbit. The earth revolves around the sun in
its elliptical orbit. Thus, in the course of revolution, the earth reaches far from the sun and
comes near to the sun due to its elliptical orbit around the sun. The moon is the natural
satellite of the earth. It revolves around the earth in its elliptical orbit. In the course of
revolution of the earth and the moon, sometimes the moon the earth and the sun lies in
the same straight line. Sometimes, the moon lies between the earth and the sun. Similarly,
sometimes the earth lies between the sun the moon. In the course of revolving around the
earth, the moon also revolves around the sun.
Umbra and Penumbra Penumbra Earth’s
Umbra orbit
When an opaque object
blocks the light coming
from the source, shadow
is formed on the screen.
When an opaque object,
large than the light source, Moon
is placed between the light Fig. Sun Total eclipse Earth
Partial eclipse Moon’s
source and the screen, two orbit
portions of shadow are 24.6
formed. They are inner
Process of shadow formation
GREEN Science (Geology and Astronomy) Book-9 397
portion and outer portion. The completely dark inner portion of the shadow that does
not receive light at all is called umbra. Similarly, the outer lighter portion of shadow
that receives some light from the source is called penumbra. In the process of shadow
formation, umbra and penumbra can be observed. Source of light, opaque object and
screen are essential for shadow formation.
Activity 1
Place a ball between a cardboard and a torch light on a table in a straight line. Focus the
light of torch light and observe it. Study it and explain the process of shadow formation
with figure.
Eclipse
The sun is a luminous body with its own source of light. The earth and the moon are
non-luminous and opaque bodies. They do not have their own source of light. They shine
by reflecting the light coming from the sun. We know that the earth revolves around the
sun and the moon revolves around the earth in their fixed elliptical orbits. In the course
of revolution, sometimes the sun, the earth and the moon come to lie in a straight line.
In such situation, the body which lies in between casts a shadow and causes an ellipse.
Hence an eclipse is the phenomenon of casting shadow on the earth or on the moon in
course of the revolution of the earth and the moon in their orbits.
The causes of eclipse are given below.
i. Light travels in a straight line.
ii. The earth revolves around the sun and the moon revolves around the earth.
iii. The sun, the earth and the moon come to lie in a straight line with the earth or the
moon in between.
iv. The earth casts shadow on the moon or the moon casts shadow on the earth.
Types of Eclipse
There are two types of eclipse. They are lunar eclipse and solar eclipse.
Lunar Eclipse
When the sun, the earth and the moon come to lie, in a straight line with the earth is in
between, the earth casts shadow on the moon causing the lunar eclipse. Lunar eclipse
the phenomenon of casting shadow by the earth on the moon. The conditions of causing
lunar eclipse are :
i. The sun, the earth and the moon come to lie in a straight line in the course of revolution
of the earth and the moon.
ii. The earth lies in between the sun and the moon.
The orbital plane of the moon makes on angle of 5.15° with the orbital plane of the earth.
Thus, the orbits of the earth and that of the moon intersect at two points. These two points
398 GREEN Science (Geology and Astronomy) Book-9
Fig.are called Rahu and Ketu. On the full moon night, the moon lies at this point and the sun,
the earth and the moon come to lie in a straight line. The earth casts its shadow on the
moon since the earth lies between the sun and the moon. Therefore, a lunar eclipse can
occur only on a full moon day.
24.7
Lunar Eclipse
But at every full moon day there is no lunar eclipse since the moon does not lie at Rahu
and Ketu and the sun, the earth and the moon do not come to lie in a straight line at every
full moon day.
Total Lunar Eclipse and Partial Lunar Eclipse
The moon passes through the different areas of shadow when it moves round the earth.
The moon is a non-luminous body and hence it is not visible itself. Thus, the moon is
invisible when it comes to lie in the umbra cone of the earth. In this situation, it does
not receive any light from the sun and hence does not reflect any light. This condition is
called total lunar eclipse. Similarly, the moon comes slightly out of the line in the course of
revolution. In this condition, the moon is not be completely in the umbra cone of the earth
and hence it receives some light from the sun and reflects it. Thus, the moon is partially
visible from the earth. The situation of lunar eclipse in which the moon is partially visible
is called partial lunar eclipse.
Solar Eclipse
Solar eclipse is the condition of casting shadow on the earth by the moon. When the sun,
the earth and the moon come to lie in a straight line in the course of revolution with the
moon in the middle, the moon casts its shadow on the earth. This condition is called solar
eclipse. Thus, the phenomenon in which the moon casts shadow on the earth during the
revolution of the earth and the moon is called solar eclipse. The causes of solar eclipse are :
i. The sun, the earth and the moon come to lie in a same straight line in the course of
revolution of the earth and the moon.
ii. The moon lies between the earth and the sun.
iii. The moon casts its shadow on the earth.
GREEN Science (Geology and Astronomy) Book-9 399
A solar eclipse occurs only on a new moon day since the dark side of the moon faces the
earth on new moon day only. But on every new moon day, the sun, the earth and the
moon do not come to lie in a straight line and hence there is no lunar eclipse on every
new moon day. The orbital plane of the earth is at an angle of 5.15° with the orbital plane
of the moon.
Fig.
Fig.
24.8
Solar Eclipse
Total Solar Eclipse and Partial Solar Eclipse
In the course of revolution, the portion of the earth completely falls in the umbra region.
This condition of solar eclipse is called total solar eclipse. In total solar eclipse, the sun
appears as a black circular disk with ring of light. The duration of total solar eclipse is
very short (i.e. 8 minutes). Similarly, the condition of solar eclipse in which the portion of
the earth falls in the penumbra is called partial solar eclipse.
Sometimes the distance between the earth
and the moon in increased during the solar
eclipse. In this situation, the sun is appeared
as a ring-like structure since the central part
of the sun is blocked. The situation of solar 24.9 Total eclipse Annular eclipse Partial eclipse
eclipse is called an annular solar eclipse. In
Different types of solar eclipse
every 1000 years, an annular solar eclipse
occurs in a particular place of the earth. It is harmful to view solar eclipse with naked eyes
because it can damage our eye sight permanently. Solar eclipse can be viewed through safety
glasses or forming an image of the sun on a screen by different methods.
Differences between Lunar eclipse and Solar eclipse.
Lunar eclipse Solar eclipse
1. In lunar eclipse, the earth lies in the 1. In solar eclipse, the moon lies in
between the sun and the moon in a between the sun and the earth in a
straight line. straight line.
2. It occurs in full moon day. 2. It occurs in new moon day.
3. In lunar eclipse, the shadow of the 3. In solar eclipse, the shadow of the
earth falls on the moon. moon falls on the earth.
400 GREEN Science (Geology and Astronomy) Book-9
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Green Science 9 Final PDF (2076)
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