Some words concerning Mendelism
Unit character
A particular character of an individual is called unit character. Each
organism has its own unit character. For example, a pea plant has
own type of pods, stem, leaves or flowers.
Allele or allelomorph
An allele is one of the two or more forms of genes controlling a pair of
contrasting characters. For example, tallness and dwarfness are a pair
of contrasting character. Gene for tallness 'T' and gene for dwarfness
't' are alleles for each other.
Homozygous or pure organism
An organism which consists of two similar genes for a particular
character is called homozygous or pure organism. For example, TT is
pure tall and tt is pure dwarf.
Heterozygous or hybrid organism
An organism which consists of both alleles for a pair of contrasting
characters is called heterozygous or hybrid organism. Heterozygous
organism contains one dominant and another recessive allele. For
example, an organism having genes Tt is a heterozygous organism.
Dominant character
The character which gets expressed in heterozygous form is called
dominant character. Gene for dominant character is represented by
capital letter. For example, when there is a cross between pure tall
and pure dwarf organisms, tallness will be expressed in the offspring
even though both genes are present. Therefore, tallness is dominant
character.
Recessive character
The character which cannot express in heterozygous form and remains
hidden is called recessive character.
Gene for recessive character is represented by small letter. For example,
dwarfness is recessive character. Thus, it does not get expressed in the
next generation when there is cross between tall and dwarf plants.
Phenotype and genotype
The external appearance of an organism is called phenotype.
Genetic make-up of an organism for a particular character is called
genotype. For example, a pea plant having gene Tt and another pea
plant having genes TT are similar in phenotype but different in
genotype. It is because both plants are tall in external appearance but
the composition of genes for the character tallness is different in these
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two plants.
F1 generation: The generation which is obtained by crossing different
parents is called F1 generation.
F2 generation: The generation which is obtained by crossing two
organisms of F1 generation is called F2 generation.
Monohybrid cross: The cross involving only one pair of contrasting
characters at a time is called monohybrid cross. For example, cross
between a tall plant and a dwarf plant.
Dihybrid cross: The cross involving two pairs of contrasting characters
at a time is called dihybrid cross. For example, cross between red
flowered tall plant and white flowered dwarf plant.
Mendel's laws or Mendelism
On the basis of the experiments conducted on pea plants with
contrasting characters, he formulated the following laws.
i) Law of dominance
ii) Law of purity of gametes or law of segregation
iii) Law of independent assortment
Law of dominance
The law of dominance states that when there is a cross between a
pair of contrasting characters, only one of them will get expressed
phenotypically while other gets hidden in the F1 generation. The
character which expresses itself is dominant character and other
which can not express is called recessive character.
It can be clarified with the help of following example:
Phenotype of parents Pure tall Pure dwarf
Genotype of parents TT
Crossing tt
Gamete formation TT tt
Fertilization
F1 generation Tt Tt Tt Tt
All hybrid tall
When a cross is made between pure tall (TT) and pure dwarf (tt) plants,
all plants are found tall (Tt) in F1 generation. In the plants of F1
generation, genes for both tallness (T) and dwarfness (t) are present.
But only tallness gets expressed. It is because tallness dominates over
dwarfness.
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Fact &Reason
All the offspring were black in F1 generation after mating black and white dog,
why?
All the offspring were black in F1 generation after mating black and white dog
because black is the dominant character.
Law of purity of gametes or law of segregation
Law of segregation states that two members of a pair of alleles remain
together in the hybrids of F1 generation but they segregate or separate
during formation of gametes. Thus, each gamete receives only one type
of allele and a gamete is always pure.
It can be clarified with the following example.
In Mendel's experiment, the offspring obtained in F1 generation are
hybrid tall. It means both the genes for tallness (T) and dwarfness
(t) are remaining together. When gametes are formed from them, the
genes separate, so that one gamete receives either gene for tallness (T)
or gene for dwarfness (t). Thus, a gamete is pure tall or pure dwarf.
Due to the above reasons, the offspring of F2 generation are found in
the ratio of 3 tall and 1 dwarf. Even though phenotypic ratio is 3:1 (3
tall and 1 dwarf), the genotypic ratio is 1:2:1 (one pure tall, two hybrid
tall and one pure dwarf).
Phenotype of parents Hybrid tall (Male) Hybrid tall (Female)
Genotype of parents Tt Tt
Selfing
Gamete formation Tt Tt
Fertilization
TT Tt Tt tt
Pure dwarf
F2 generation Pure tall
Hybrid tall
Phenotypic ratio = 3:1 (3 tall and 1 dwarf)
Genotypic ratio = 1:2:1 (1 pure tall : 2 hybrid tall: 1 pure dwarf)
Some monohybrid crosses done by scientists in animals are given below:
Monohybrid cross in guinea pigs
When pure black guinea pig is crossed with pure white guinea pig, all
the guinea pigs of F1 generation are found black. Here, both types of
genes, i.e. gene for blackness and gene for whiteness are present but
only blackness gets expressed because it is dominant character. When
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the guinea pigs of F1 generation are crossed together, 75% guinea pigs
are found black and 25% guinea pigs are white. It was found that the
law of dominance and law of purity of gametes were true for animals
also.
Parents cross
Gametes fertilization
First Sperms Selfing Eggs All black
phenotypically
Filial
Generation Ratio:
Gametes 3 black to 1 white
phenotypically
Second
Filial
Generation
Monohybrid cross in drosophila
T.H. Morgan performed a monohybrid cross on drosophila, a type of
fruitfly. He selected a long winged and a short winged drosophila and
crossed them. He found that all the drosophila of F1 generation, were
long winged. Again, he crossed the drosophila of F1 generation. Then
he found that 75% of the drosophila were long winged and 25% of
the drosophila were short winged. The results obtained in F1 and F2
generation were in accordance with Mendel's law of dominance and
the law of purity of gametes.
parents LL ll
long winged (LL) short winged (ll)
F1 generation Ll Ll
self crossing long winged (Ll) long winged (Ll)
F2 generation
pure long hybrid long winged (Ll) pure short
winged (LL) winged (ll)
long winged
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Some hereditary characters in human beings.
In human beings, various types of dominant and recessive characters
are present. Each character works as unit character. Some of the
characters are as follows:
Rolling Folding can't roll/ Clubbed Hitch No hitch
of tongue of tongue fold tongue thumb hiker's hiker's
(dominant) (dominant) (recessive) (dominant) thumb thumb
(recessive) (dominant)
Dominant character Recessive character
1. Curly hair 1. Straight hair
2. Free earlobe 2. Joined earlobe
3. Straight thumb 3. Back turned thumb
4. Dimpled cheek 4. Non-dimpled cheek
5. Rolling tongue 5. Non-rolling tongue
6. Folding of tongue 6. Non-folding of tongue
Certain hereditary characters found in human beings depend upon sex.
Due to this, certain diseases are seen only in males while others are seen
only in females. Such diseases are called sex-linked diseases. For example,
haemophilia, baldness, etc are found in males only. Breast cancer is found
in females only.
Fact &Reason
What difficulties Mendel would have faced if he had carried out his experiment
on human?
Human has long life span, less contrasting characters and some social norms in
practical life due to which it would be impossible to carry out the experiment on
human.
Activity21 .1 Try to find out the above six hereditary characters in the
students of your class. Compare such characters of own family members. Why
are the characters of your family member different?
Variation
No any two individuals in the world are exactly similar. Even
the offspring from the same parents have some differences. Even
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though the twins seem similar, they are not exactly similar in all
respects. They may be different in terms of height, colour of hair,
colour of skin, structure of body, etc. Thus, every organism has its
own unique individuality so that it will be different from others. It is
called variation. Thus, variation may be defined as the structural or
physiological difference due to the genetic or environmental reason.
Fact &Reason
Why is variation so important in genetics?
Variation is the basis of heredity and source of evolution of new organisms. It
provides individuality to each member of the species. It also enables organisms to
adapt in changing environment. So, variation is so important in genetics.
The variation may be classified into two types:
Hereditary variation
When we look at the newly born organisms, they are different from
each other even though they are produced from the same species.
This variation is due to difference in the structure and function of
genes inherited from the parents. Crossing over takes place during
the formation of gametes by meiosis cell division. This causes the
variation in the characters of offspring from their parents. Such
variation is called hereditary variation. Thus, hereditary variation is
a type of variation which is inherited from one generation to another
generation through genes.
Fact &Reason
Why are the offspring obtained from same parents are not exactly similar?
The offspring obtained from same parents may have some similarities but are not
exactly similar due to variation and mutation that occurs during the formation
of gametes.
Environmental variation
The organisms having similar genotype also differ from each other in
phenotype due to environmental factors like food, light, temperature,
humidity, etc. Such differences are called environmental variation.
These variations are not inheritable to the next generations. Thus,
the variation among the organisms due to the environmental factors is
known as environmental variation.
The above variations may be continuous or discontinuous. The
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variation which gets transmitted from one generation to another is
called continuous variation. For example, difference in height, colour,
facial appearance, etc. Sometimes, a sudden or drastic change occurs
in the characters of organisms. It is called discontinuous variation.
For example, extra toes of limbs of an individual, cut at lip by birth,
disability of babies by the birth, etc. It is also called mutation.
Mutation
Sometimes, a sudden change occurs in the structure of the genes due
to some factors like uv radiations, x–rays, etc. This causes the drastic
change in the characters of organisms. It is called mutation.
Thus, mutation is defined as a drastic change in the organisms due
to change in gene caused by the factors like u-v rays, x-rays, different
chemicals, etc.
Birth of a baby without limb, extra toes of limbs of an individual, one
horned ship, four legged chicken, etc are examples of mutation.
Differences between variation and mutation:
Variation Mutation
1. It is a physiological or 1. It is the sudden change in genetic
morphological difference that gives composition of an organism.
individuality to an organism.
2. It can be caused by heredity and 2. It can be caused by the chemical
environment. and physical factors such as UV-
ray, X-rays, different chemicals, etc.
3. Variation may be a continuous or
discontinuous. 3. Mutation is always a discontinuous
variation.
Learn and Write
1. Mendel could not be successful in his experiment if he
used frog instead of pea plants. Why?
Frog does not have many pairs of contrasting characters as in pea. The
frog reproduces only by cross-fertilization. But, the pea reproduces by
self and cross pollination. The frog needs special climatic condition to
survive and reproduce. Therefore, he would not be successful in his
experiment, if he used frog instead of pea plants.
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2. Red colour in the flower is dominant character whereas
white colour is recessive character. Why?
When there is a cross between pea plants with pure red coloured
flower and a pure white coloured flower, the offspring in F1
generation are the plants with red coloured flower. Although, the
offspring have the genes for both red colour and white colour,
only the red colour gets expressed in the heterozygous form.
Therefore, red colour is dominant over white colour.
3. White coloured guinea pigs may be born from black
coloured guinea pigs. How ?
If the parents are hybrid black, they contain the genes for both black
and white colour. White being a recessive character cannot express.
But, it gets expressed in the next generation when two genes for
white colour remain together in the offspring. Thus, black coloured
guinea pigs give birth to white coloured guinea pigs.
Main points to remember
1 The process of transfer of characters from parents to offspring is
called heredity.
2 The characters which get transferred from parents to offspring
are called hereditary characters.
3 The branch of biology which deals with the study of heredity is
called genetics.
4 The character which expresses itself in heterozygous form is called
dominant character.
5 The character which cannot express in heterozygous form is called
recessive character.
6 External or morphological appearance of an organism is called
phenotype.
7 Genetic makeup of an organism for a particular character is
called genotype.
8 The organism which contains a pair of alleles for a pair of
contrasting characters is called hybrid.
9. The law of dominance states that when there is a cross between a
pair of contrasting characters, only one of them will get expressed
phenotypically while other gets hidden in the F1 generation.
10. The law of segregation states that two members of a pair of alleles
remain together in the hybrids of F1 generation but they segregate
or separate during formation of gametes.
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11. The variation which is inherited from one generation to another
through genes is called hereditary variation.
12. The variation among the organisms due to the environmental
factors is called environmental variation.
13. The drastic or sudden change in the organisms due to change in
the gene by the environmental factors like u-v radiation, x-rays,
chemicals, etc is called mutation.
Exercise
A. Very short answer questions (1 mark )
1. What is heredity or inheritance?
2. What are genes?
3. What are hybrids ?
4. What is genetic variation ?
5. Write the full forms of DNA and RNA.
6. What is phenotype?
7. What are sex-linked diseases ? Give an example.
8. Name any two sex-linked diseases found only in females.
9. Name any two sex-linked diseases found only in males.
10. State Mendel's Law of Dominance.
11. Write any two dominant and recessive characteristics of
human beings.
12. What are hereditary characteristics?
13. What are recessive characteristics? Give one example.
14. What are dominant characteristics? Give one example.
15. State Mendel's second law.
16. What is monohybrid cross?
17. What is variation?
18. What is continuous variation? Give one example.
19. Define mutation or discontinuous variation with examples.
B. Short answer questions (2 mark)
1. What is gene? Where is it located?
2. Differentiate between mutation and variation.
3. State any two difficulties Mendel would have faced if he had
carried his experiment on frog instead of pea plant.
4. Offspring obtained from same parents show some similarities
but they are not exactly similar to each other. Why?
5. Write any two differences between phenotype and genotype.
6. Why did Mendel select pea plants for his study? Give any four
reasons.
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7. When a pure pea plant with red flower is crossed with pure
pea plant with white flower, what will be the characteristics of
offspring in first filial generation ? Explain with chart.
8. Why is Mendel called the father of genetics ?
9. Write any two differences between dominant characteristic
and recessive characteristics.
10. Differentiate between continuous and discontinuous variation.
11. What are the factors for mutation?
12. In a cross between long winged housefly with short winged
housefly, only long winged houseflies were seen in F1
generation, why?
13. Write any two symptoms of Hemophilia.
14. Write two importance of variation.
15. A woman has got four daughters but not son. Does it mean
that the husband does not produce 'Y chromosome bearing
sperm? Explain with chart.
16. Give reasons:
i) Blue eyed offspring may be formed from brown eyed
parents.
ii) When black and brown dogs are crossed, all offspring will
be black.
iii) Mendel did not select human for his experiment.
C. Long question (3 mark)
1. Pea with round seed and wrinkled seed are cross fertilized
and result is shown in the table. Answer the following
questions on the basis of the table.
Gametes R r
R RR Rr
r Rr rr
i) Write phenotype and genotype ratio of round pea
and wrinkled pea in that generation.
ii) Both law of dominance and law of segregation hold
on that result, how?
2. How are the new species produced due to variation? Explain.
3. Does Mendel's law apply to human beings too? State any two
difficulties Mendel would have faced if he had carried his
experiment on human beings instead of pea plants.
4. Pea plants with red flower (RR) and white flower (rr) are cross
pollinated first and then self pollinated. What will be the
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colour of flower of the offspring of the first and the second filial
generation? Why? Write with with necessary chart.
5. Draw a chart to show the first generation and second
generation resulted due to the cross of long winged housefly
(LL) and short-winged housefly (ll). Justify the law of purity of
gamete on the basis of your chart.
6. After the mating of a black dog with a white dog, all the
offspring in the F1 generation were black. Why are white dogs
not seen in the offspring? Justify with the help of a chart.
D. Very long answer questions (4 marks)
1. Show the result of cross between wrinkled seeded pea
plant and round seeded plant till F2 -generation. Write the
genotypic and phenotypic ratio of offspring in both F1 and F2
generations.
2. Explain Mendel’s second law. Show the genotype and
phenotype of offspring produced by crossing a rat with long
tail and a rat with short tail up to second filial generation.
Project Work
Take two varieties of pea seed and sow them in the field. Remove
all male parts from the flowers of one of the plants and female
parts from the other before the flowers gain maturity. Then
cross-pollinate them. Let the seeds mature. Then sow the new
seeds in the soil. What kinds of will be observed?
Glossary
• Inheritable : characters that can transfer from one generation
to another
• Segregation : separation
• Assortment : collection
• Wrinkled : having small messy folds, having irregular
surface
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Chapter
20 Environmental
pollution and its
Management John Muir
John Muir also known as "John of the Mountains", was an influential
Scottish-American naturalist, author, environmental philosopher,
glaciologist and early advocate for the preservation of wilderness.
Estimated Periods: 9 (6T+3P)
Objectives
At the end of the lesson, students will be able to:
• define environmental pollution and explain the causes, effects and mitigating
measures of air, water and soil pollution.
• Explain the conservation and management strategies of forest and water
sources.
The unwanted change in the natural quality of environment due to the
addition of harmful substances or the loss of some useful components
is called environmental pollution. The environmental pollution can be
categorized into four types – air pollution, water pollution, land
pollution and sound pollution.
Air pollution
The addition of smoke, dust, bad smell
and poisonous gases in the air decreases
the natural quality of air. This makes
the air dirty and unfit for breathing.
The dirty air can carry the germs of
diseases and harmful chemicals. Such
air is harmful to us. The decrease in
the natural quality and amount of air
due to the addition of smoke, dust and
poisonous gases in it is known as air
pollution.
Sources of air pollution
1. Natural sources: The sources which cause air pollution from natural
phenomena are called natural sources. Volcanic eruption, forest
fire, soil erosion, decay of dead organisms, wind, storm, etc are the
natural sources of pollution.
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2. Artificial sources: The man-made sources of pollution are called
artificial sources. Burning of fuels and solid wastes, industries,
vehicles, nuclear power plants and weapons, agricultural wastes,
etc are some artificial sources of pollution. The harmful gases such
as CO, CO2, NO, NO2, SO2, Cl2, NH3, etc are produced from the
artificial sources.
Effects of air pollution
1. Adverse effects in human health: The atmosphere provides oxygen
for the respiration of human beings. A healthy adult human respires
about 22,000 times in a day. If the air is polluted, it causes several
diseases such as tuberculosis, bronchitis, asthma, heart diseases,
nose problems, eye irritation, etc. The polluted air also causes the
loss of sleep, tiredness, etc.
2. Inhibition of biological growth of plants: The increase in the
concentration of air pollutants in the atmosphere reduces the
amount of solar radiations available for the plants. Then the stomata
present in the leaves of plants do not open properly. This results in
poor intake of CO2 from the atmosphere and less production of
food by photosynthesis. It hampers the growth and development
of plants.
3. Reduction in visibility: The excess of dust and smoke in the
atmosphere reduces the visibility. In such condition, we cannot see
the things lying at far distances. This creates difficulty in viewing
scenes, driving vehicles, flying aeroplanes, etc.
4. Reduction in solar radiation: The pollutants such as dust and
smoke present in the atmosphere absorb the solar radiations
themselves. Some pollutants scatter the radiations. Such effect
heats up the atmosphere but the earth cannot get required amount
of solar radiations.
5. Greenhouse effect: The increase in the concentration of greenhouse
gases such as carbon dioxide, methane, nitrous oxide, sulphur
dioxide, water vapour, etc in the environment traps more amount
of solar heat in the atmosphere. Such effect is called greenhouse
effect. The greenhouse effect increases the surface temperature
of the earth and causes global warming. The global warming has
caused the melting of polar ice caps and increase in the level of seas.
The global warming has several other dangerous effects.
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6. Depletion of ozone layer: A number of pollutants such as
chlorofluoro carbons (CFCs), methyl chloroform, carbon
tetrachloride, methyl bromide, etc are being accumulated in
the atmosphere from different sources. If such gases reach the
stratosphere, they decompose by absorbing UV radiations from
the sun and produce nascent chlorine or bromine. These nascent
halogens cause the destruction of large number of ozone molecules.
7. Acid rain: Some acidic oxides such as sulphur dioxide, nitrogen
dioxide, sulphur trioxide, hydrogen chloride, etc are released into
the atmosphere from industries and vehicles. If these gases get
mixed with drops of water, they form acid and fall down as acid
rain.
8. Destruction of historical monuments: Metallic and limestone
structures are badly affected by acid rain. The acid rain is degrading
the historical monuments and buildings.
9. Climate change: The change in climatic conditions for a long period
of time due to human activities or natural instability is called climate
change. In fact, the disturbance in the normal periodic occurrence
of natural phenomena such as water cycle, change in seasons, etc is
called climate change. There can be extreme cold in winter, extreme
hot in summer, drought, excessive rainfall, etc due to climate
change.
The climate change has several harmful effects in the environment.
Unusual melting of snow from the high Himalayas due to climate
change can result in the drying of rivers in the future. On the other
hand, the level of sea water is increasing rapidly. It can result in
sinking of islands and flooding in the coastal countries.
Prevention of air pollution
The pollution of air can be prevented in the following ways:
1. The old vehicles produce a lot of harmful gases and smoke so the
running of old vehicles should be strictly prohibited.
2. The smoke released from the factories and industries should be
turned into harmless forms before they are released into the air.
3. The use of improved oven in the village areas is the best way to
minimize smoke production.
4. The use of biogas, solar energy and electricity as the source of
energy instead of petroleum and coal is helpful to prevent air
pollution.
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5. The roads of the cities should be kept clean so that the running
of vehicles on the road does not blow up dust.
6. Defecation or urination at the open places releases germs into the
atmosphere. So, people must defecate or urinate in the toilet only.
Water pollution
Several human activities are
responsible for adding harmful
materials and chemicals in water.
Throwing human and animal excreta
and other waste materials in the water
sources pollutes the water. Industrial
effluents, pesticides and chemical
fertilizers used in agriculture, sewage, Water pollution
etc badly pollute the water sources. The dirtiness of water due to the
addition of unwanted and harmful materials into it is known as water
pollution.
Even the water from natural sources such as lake, spring, well, river,
underground water, rainfall, etc may not be safe for our household use.
Water from these sources may contain living and non-living impurities.
Bacteria, algae, round worm, water fleas, tiny insects, eggs of mosquito,
etc are the living impurities whereas dust, soil, dissolved salts, poisonous
metal ions, etc are the non living impurities present in water.
Do you know?
About 71 per cent of the earth surface is covered with water. Out of
total water, 97 per cent is occupied by the sea water. Only 3% water is
available in the other sources.
Causes of water pollution
Water can be polluted in the following ways:
1. Mixing of sewage and garbage into the source of water.
2. Decay of dead plant parts and dead animals in the source of water.
3. Mixing of industrial effluents and other wastes with the sources of water.
4. Use of pesticides (DDT, BHC, Aldrin, Dialdrin, etc) and chemical
fertilizers in agricultural field. These chemicals are washed away
by moving water and are mixed with low-lying water sources.
5. Allowingdomesticanimalsdrinkwaterandhavingbathatthesourcesofwater.
6. Washing clothes, cleaning household utensils and having bath at
the sources of water.
Effects of water pollution
Polluted water can transmit the germs of dangerous diseases such as
diarrhoea, dysentery, cholera, typhoid and jaundice. If these diseases
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are not treated on time, they can take the life of people. So, the polluted
water is severely harmful to us. The main effects of water pollution
are as follows:
1. Polluted water transmits the germs of diseases such as diarrhoea,
cholera, dysentery, typhoid and jaundice in human beings.
2. Polluted water is a cause of harmful worm infestation in human beings.
3. Bad smell spreads around from polluted water.
4. Mercury, lead and arsenic present in water are severely harmful
to our health.
5. Harmful chemicals may cause adverse effect on cattle or other
animals that drink water from the polluted sources.
6. It also affects the life of aquatic animals.
7. Polluted water cannot be used for domestic as well as industrial
purpose.
Measures to control water pollution
Control measure of water pollution are as follows:
1. Bathing and cleaning clothes and utensils near the source of
water should be avoided
2. The chemicals and wastes produced from factories and industries
should be treated and refined before mixing to the river, lakes or
oceans.
3. The domestic dirt and filths should not be thrown nearby the
source of water.
4. Mixing of sewage and garbage to the source of water should be
avoided.
5. The soil erosion, floods and landslides should be controlled so
that sources of water will not be polluted.
6. People should be made aware about the bad impacts of water
pollution.
7. Excessive use of insecticides and chemical fertilizers should be
avoided
Soil pollution
The undesirable change in the quality of soil is called soil pollution.
Soil is polluted by different wastes
produced by the human beings. The
household wastes such as garbage,
dust, rags, filth, paper, broken glass,
plastics, etc thrown carelessly on the
land cause land pollution. Soil pollution
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Causes of soil pollution
Soil can be polluted in the following ways:
1. Throwing of garbage and other wastes on the open land.
2. Decay of dead plant parts and dead animals in the land. It also
causes air and water pollution.
3. Throwing the non-biodegradable wastes such as plastics, glass,
metal parts, etc into the soil.
4. Dumping of wastes from laboratories, hospital, factories, etc into
the open land.
5. Using pesticides and chemical fertilizers in the fields.
Effects of soil pollution
1. The polluted land attracts flies, rats and other animals which harm
human beings.
2. It kills the useful animals inhabiting in soil such as earthworm and microbes.
3. It can spread many air borne and water borne diseases.
4. It spreads foul and harmful smell in the environment.
5. The polluted land makes the whole environment ugly in appearance.
6. Soil pollution reduces the fertility of soil. Crops give low yield in
polluted land.
Measures to control land pollution are as follows:
1. Insecticides and chemical fertilizers should be used properly.
2. Non-biodegradable things like plastic, rubber, metal, glass bottles,
etc should be reused.
3. Bio-degradable things like excess food, peels of fruits and vegetables,
cattle dung, etc should be used to prepare compost manure.
4. Chemicals and wastes from factories and industries should be
turned into harmless forms before mixing on the land.
5. Non-biodegradable goods should be recycled and reused.
Conservation and Management of Forest and Water Resource
Water resources are very important natural resources. They are
essential for the survival of all living beings. Some of the measures for
the conservation of the forest and water resource are explained below:
1. Enhancing public awareness and participation
The efforts of a single individual cannot do anything for the
conservation of the environment. Even the efforts of government only
are insufficient to make environment clean, green and attractive.
There is major role of people for conserving the water resource and
forest. For this, the people should be made aware about their roles and
responsibilities. The awareness programme can be conducted through
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formal education, public notice, campaigns, seminars, trainings, etc.
The conservation and promotion of the forest and water sources needs
active participation of the people. People should have collective efforts
for keeping their locality, neighbourhood or town clean and healthy.
2. Afforestation
The process of planting the saplings of trees in bare or open lands and
restoring the forest is called afforestation. We should grow saplings of
trees in the naked plains, hills and slopes. The plants absorb the rain
water and increase the level of ground water as well as reduce flood.
The roots of plants hold the soil firmly and minimize the risk of flood
and soil erosion. This helps in the conservation of environment.
3. Conservation of water sources
We obtain water from river, lake, well, spring, stream, melting of
snow, etc. The protection of such sources is the conservation of water
resources. The programs such as afforestation, protection from flood
and landslides, avoiding the grazing of cattle in the forest, avoiding
forest fire, etc help to conserve water resources. The protection of the
lakes, ponds, wells, etc from getting filled with sand, silt and other
things is also necessary to conserve water resources.
4. Conservation of land
The land in hilly and sloppy area can be protected through avoiding the
cattle grazing or rotational grazing in pasturelands, terrace farming,
retaining walls, embankments, etc. The fertile soil of plain land can be
conserved by protecting from flood and by limiting the use of chemical
fertilizers and pesticides. The soil should be conserved to continue the
natural quality of soil and maintain its fertility. The conservation of
soil helps to conserve the environment.
5. Pollution control
The pollution spoils the environment and makes it unfit for the
survival of living beings. Pollution hampers the growth and spread
of plants. This in turn badly affects water sources. So, the pollution
control is very important for the conservation of the environment.
6. Environmental cleanliness
Throwing of wastes carelessly in the village, town or neighbourhood
mixes harmful chemicals and wastes in to the sources of water. It can
transmit the germs of diseases in human beings, animals and birds. So,
all the people should make efforts for the cleanliness of environment.
The decaying solid wastes should be turned into compost manure and
the non-decaying solid wastes should be destroyed properly.
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Measures of climate change management
We can reduce the risk of climate change or manage its harmful effects
in the following ways:
1. Tree plantation is the best way to conserve nature and reduce the
effects of human-caused or natural disasters.
2. There should be significant reduction in the production of green
house gases.
3. The consumption of fossil fuel should be replaced by alternative
sources of energy as far as possible.
4. There should be adequate measures for the control of pollution.
5. The natural components of environment should be conserved.
6. Much emphasis should be given in following the principles of
the sustainable development while carrying out development
activities.
Learn and Write
1. Define pollution Management.
- Process of controlling, minimizing and preventing cause of
environmental pollution is known as pollution management.
2. What are primary air pollutants ?
- The pollutants that directly mix to the atmospheric air after being
emitted from various sources like industry, lab etc. are known as
primary pollutants.
3. Differentiate between natural and artificial source of air
pollution.
- Differences between natural and artificial sources of air pollution
are as follows.
Natural sources of air pollution Artificial sources of air pollutions
1. The sources which cause air 1. The sources which causes are
pollution from natural phenomena pollution through human activities
are natural sources of air pollution. are known as artificial sources of
air pollution.
2. Forest fire, volcanic eruption, 2. Burning of fuels and solid wastes,
transpiration, soil erosion, pollen emissions from industries, vehicle
dispersal, decay of organisms etc. emissions, agricultural wastes,
are natural sources of air pollution. nuclear wastes etc. are artificial
sources of air pollution.
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Main points to remember
1. The unwanted change in the natural quality of environment due to the
addition of harmful substances or the loss of some useful components is
called environmental pollution.
2. The environmental pollution can be categorized into four types – air
pollution, water pollution, land pollution and sound pollution
3. The decrease in the natural quality and amount of air due to the addition of
smoke, dust and poisonous gases in it is known as air pollution.
4. The dirtiness of water due to the addition of unwanted and harmful
materials into it is known as water pollution.
5. The household wastes such as garbage, dust, rags, filth, paper, broken glass,
plastics, etc thrown carelessly on the land cause land pollution.
6. Running of heavy vehicles in the road, horns of vehicles, crowd of
people, factories, industries, etc produce loud sound.
7. The process of planting the saplings of trees in bare or open lands and
restoring the forest is called afforestation.
Exercise
A. Very short answer questions (1 mark)
1. What is environment?
2. What do you mean by environmental degradation?
3. What is environmental pollution?
4. What is air pollution?
5. Write two causes of air pollution.
6. Mention any two effects of air pollution.
7. What is water pollution?
8. Write two causes of water pollution.
9. Mention any two effects of water pollution.
10. What are natural sources of air pollution? Write with
examples.
B. Short answer questions (2 marks)
1. Write two roles played by plant in controlling air pollution.
2. Why does the river flowing nearby cities become polluted?
3. What are artificial sources of air pollution ? Write with
examples.
4. List four major sources of soil pollution.
5. List four major sources of water pollution.
6. List four major anthropogenic causes of soil pollution.
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7. “The main cause of climate change is air pollution.”Justify this
statement.
C. Long question (3 marks)
1. How does air pollution inhibit biological growth of plants?
Explain.
2. Write any six suggestions that can help to reduce soil
pollution.
3. Write down the methods of conservation and management of
forests.
4. Identity any three ways for the management of domestic
wastage.
5. Write down the measures to control water pollution.
6. Write down the measures to control air pollution
7. Write any three applications of forest in our daily life.
D. Very long answer questions (4 marks)
1. Mention some measures of conservation and management of
forest and water resource.
Project Work
Observe the condition of environment of your locality. Find out
whether there is any kind of pollution. Prepare a brief report
explaining causes, effects and preventive measures of the
pollution.
Glossary
• Prohibited : banned, not allowed
• Mine : a hole in the ground for obtaining minerals
• Risk : danger
• Threatened : likely to become extinct
• Extinction : having no members of the species or family in
existence, complete disappearance
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Chapter
21 History of
The Earth
Immanuel Kant
Immanuel Kant was a German philosopher
who is considered a central figure in
modern philosophy.
Estimated Periods: 5 (4T+1P)
Objectives
At the end of the lesson, students will be able to:
• explain the history of the earth by the study of the rocks and fossils;
• explain the evolution of life through evidence from fossils;
• interpret the mechanism of fossilization and formation of fossil fuel;
• explain the importance of fossil fuel.
The earth is the planet where life is possible. It has been believed that
the earth was evolved along with other planets of the solar system.
Many scientists have put forward their opinions about the evolution
of the earth. But there is no uniformity in their theories. Some of the
important hypotheses about the origin of the earth are as follows:
Planetesimal hypothesis
A French scientist George Wofan, put forward the theory of evolution
of the earth in 1749 AD. According to this hypothesis, the earth along
with other planets and satellites, was formed when a comet moving
around the universe stroke the sun millions of years ago.
Nebular hypothesis
A German philosopher, Immanual Kant, put forward nebular
hypothesis in 1755 A.D. It was later improved by Laplace in 1796
AD. According to this hypothesis, there was a gaseous mass called
nebula revolving in the sky. The nebula is composed of clouds, gases,
dust particles, etc. When the nebula cooled down, it grew smaller and
started to rotate faster. As the surface of the cloud cooled, a ring of
matter was formed at the equatorial region. The ring escaped out from
the surface of the main mass. The escaped mass changed into planets
and the central mass into the sun.
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Tidal hypothesis
The English astronomers James Jeans and Harold Jeffrey proposed
the tidal hypothesis in 1917 AD. According to this hypothesis, a big
star orbiting around the sun exerted a tidal pull when approached to
the sun. Due to the tidal pull, a long filament of fragmented matter
was drawn from the sun. The fragmented tidal matter cooled and got
separated. Thus, planets and satellites were formed.
Hence, the earth was also formed along with the other planets.
The evolution of the earth, its age, its structure, etc has been
discovered on the basis Estimated age 4.6×109 years
of different scientific 5,09,700,000km2
investigations. The age Total surface area
of the earth has been Area of lithosphere 14,8 4,00,000 km2
estimated on the basis of Area of hydrosphere 36,13,00,000 km2
study of rocks and fossils.
Diameter 12,756.3 km
According to "The world Average density 5.7g/cc
Mass 6×1024 kg
Book Encyclopedia",
some of the facts about
the earth are given in the Number of satellite 1
table below. Average temperature 20°C
Geological time scale
The age of the earth has been estimated about 4.6 billion years. The
earth was not as the present form at the time of its origin. It has
passed through different stages from the time of origin to the present
form.
A time scale that covers the earth's history from its origin to the
present is called geological time scale. The history of the earth can
be divided into four different divisions. They are eon, era, period and
epoch. Eon is the largest unit. It is divided into two divisions. They
are: cryptozoic and phanerozoic eon. An era is a very long interval of
time which contains one or more periods.
Cryptozoic eon
This eon extended from 4500 to 570 million years ago. In this eon,
invertebrates and cryptogams were evolved. It is further divided into
proterozoic era.
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Proterozoic era
This era began 4.5 billion years ago and ended 570 million years ago.
During this era, the igneous rocks like iron and gold mixed gneiss,
granite, etc were formed. Very simple and unicellular organisms were
evolved at the end of this era.
Phanerozoic eon
This eon started from 570 million years and is still running at present.
In this eon, vertebrates and phanerogams were evolved. The eon is
further divided into following eras:
a. Paleozoic era b. Mesozoic era c. Cenozoic era
Paleozoic era
This era began 570 million
years ago and ended at 250
million years ago. During
this era, invertebrate and
vertebrate animals were
developed in the ocean and
on the land. Fast growing
bushes and giant fern plants
(coal plants) were developed.
Fossils of plants and animals
of this era proved that there Organisms in paleozoic era
were abundant number of amphibian plants and animals. Therefore,
this era is called the era of amphibians.
It was supposed that there was a change in the weather and
atmosphere. Paleozoic era is further divided into seven periods. They
are Permian, Pennsylvanian, Mississippian, Devonian, Silurian,
Ordovician and Cambrian. Mississippian and Pennsylvanian periods
are jointly called Carboniferous periods.
Mesozoic era
This era began 250 million
years ago and ended 65.5
million years ago. From the
study of rocks and fossils,
it was found that different
types of hills and mountains
were formed during this era.
Mesozoic era is further divided
Organisms in Mesozoic era
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into three periods. They are- Triassic, Jurassic and Cretaceous.
Dinosaurs, the most famous organisms of this era, were evolved in
Triassic period. They become abundant and dominant in Jurassic
period and became extinct in Cretaceous period. Conifers appeared in
this era. The earliest angiosperms had appeared in the middle of the
cretaceous periods.
This era is often called the age of reptiles because the reptiles were
abundant and dominant organisms of this era.
Cenozoic era
This era began from 65.5 million years ago and is still running
at present. The processes like rock breaking, volcanic eruption,
formation of different types of mountains, etc took place in this era.
Mountains were supposed to form at Eocene epoch in this era. A
continuous change occurred in the atmospheric condition as a result
of temperature change. Ice started to form due to very cold weather.
Due to the change in the weather and atmospheric condition, ancient
organisms became extinct and new organisms developed. This era was
divided into seven periods. They are Paleocene, Eocene, Oligocene,
Miocene, Pliocene, Pleistocene, and Holocene (Recent).
Fact &Reason
Why did dinosaurs evolve earlier than human?
Dinosaurs were simpler than human as dinosaurs are reptiles and humans
are mammals. Evolution always occurs from simpler form to complex form. So,
dinosaurs evolved earlier than human.
Evolution of life
About 570 million years ago, there was no favourable environment
for the evolution of organisms on the earth's surface. After continuous
change in the climatic condition, faurable environment developed for
the evolution of life in the water. During the course of evolution of
life, various kinds of organisms were evolved on the earth. Some of
them continued to survive and some of them became extinct. These
organisms have left many evidences of their survival, development
and disappearance. The parts of skeleton, hard parts of plants and
animals, etc were found embedded in the rocks, land surfaces, stones,
etc. They left impressions in such rocks. They are called fossils.
Scientists studied and analyzed these fossils and discovered the
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process of evolution of life.
Upto Archean era of cryptozoic eon, there were no sedimentary rocks
which contained fossils. This indicates that evolution of life did not
take place. In Proterozoic era, there was a rainfall due to changes
in water, land and weather. This made a favourable condition for
the evolution and development of the organisms. Then primitive
aquatic organisms were evolved in this era. The climatic conditions
become favourable in the Paleozoic era, then, aquatic and terrestrial
invertebrates and vertebrates evolved in this era. In the same period,
the evolution of aquatic and terrestrial plants occurred. In Mesozoic
era, evolution of aquatic and terrestrial life continued. Different types
of plants including gymnosperms (conifers) were evolved. During this
era, tortoise, dinosaurs, etc were also evolved. It was believed that
the dinosaurs became extinct in the same era. At the end of this era,
mammals began to evolve. Because of the abundance of large number
of reptiles, Mesozoic era is called the age of reptiles.
Fact &Reason
Mesozoic era is called age of creepers, why?
In Mesozoic era large sized reptiles like dinosaurs dominated the world. Due to
which, mesozoic era is called age of creepers.
In Cenozoic era, different geological revolutions like change in
atmosphere, fragmentation of rocks, etc occurred due to the decrease of
temperature of the earth. As a result of this, many organisms became
extinct and new organisms like aves and mammals were evolved and
developed. The earliest men were evolved about 2 million years ago.
Human dominance began to increase in this era.
Fact &Reason
Cenozoic era is called era of mammals?
Cenozoic era is dominated by mammals. Therefore, Cenozoic era is called era of
mammals.
A short description on different eras, epochs, periods and the main
events have been summarised in the table below:
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Eon Era Period Epoch Duration Evolution of life
(in MY age)
Cryptozoic or From 4500 to 2500 Origin of Earth
Pre-cambrian
Proterozoic Archean From 2500 to 540 Evolution of unicellular origanism
and development of multicellular organisms
Mesozoic (From Palaeozoic (from Cambrian From 540 to 490 Development of few sea organisms
250 to 65.5 MY) 540 to 250 MY) Ordovician From 490 to 440
Silurian From 440 to 420 Development of vertebrate animals in the sea
Evolution of land life, green vegetation and development
Devonian From 420 to 360 of fishes.
Evolution of wing bearing insect, development of fishes
Carboniferous From 360 to 300 and plants.
Permian From 300 to 250 Evolution of reptiles and amphibians, development of fern
Triassic From 250 to 200 plants.
Jurassic From 200 to 150
Extinction of many vertebrate and in vertebrate animals
Cretaceous From 150 to 65.5 and development of first reptiles.
From 65.5 to 55.8 Evolution of dinosaur, bird, reptile and coniferous plants
Phanerozoic Tertiary Paleocene From 55.8 to 33.9 Dominance of reptiles, well developed dinosaur, birds
Neogene Paleogene Eocene and other lives.
From 33.9 to 23 Evolution of flowering plants and different insects.
Oligocene From 23 to 5.33 Extinction of dinosaur and other larger reptiles.
Miocene Evolution of mammal
Development of mammals, (e.g. elephant, whale), owl
etc.
Development of sharp toothed animals like cats and
monkeys.
Development of grasses.
Cenozoic (From Pliocene From 5.33 to 1.8 Evolution and development of human beings.
65.5 MY ago to present)
Pleistocene From 1.8 to 0.012 Development of stone age human and giant hairy
elephant.
Quaternary
Holocene or From 0.012 to Dominance of modern man and other mammals.
Recent present
* 1 MY (Million Year) = 10,00,000 (Ten lakh years)
Fossil
Fossils are the impressions or hardened
remains of the plants or animals that
existed thousands or millions of years
ago. Generally fossils are found in
sedimentary rocks.
Fact &Reason
What is the evidence of presence of dinosaurs in the past?
Fossils of dinosaurs have been found preserved inside the crust of the earth which
act as the evidence of presence of dinosaurs in the past.
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Identification of fossils
Different types of fossils can be generally identified from the
impressions of body organs of the organisms. Some of the ways of
identification of fossils are as follows.
a. Impressions of whole or a part of organs of dead bodies remains
in sedimentary rocks. The fossils are identified by studying
such impressions.
b. A part of skeletal system or the whole skeleton of animals is
preserved in sedimentary rocks as fossil.
c. Hard parts of organisms like skeleton, teeth, shoot, bones,
leaves, shells, etc are preserved in the sedimentary rocks as
fossils.
Process of fossil formation
Fossils are formed by different processes. The process by which a
fossil is formed is called fossilization. It is not compulsory that all
the organisms form fossils after their death. Fossils are formed under
favorable conditions only. A number of factors affect fossilization. But,
the two factors given below play important role in this process.
a. The organism's body should have hard parts.
b. The dead bodies of organisms should be covered by protective
materials.
Some of the methods of fossilization are as follows:-
i. When dead bodies of organisms are carried by water and get
settled at the bottom of the sea, they are covered by sediments
like sand, mud and gravel. The soft parts of the body get decayed
but hard parts like teeth, bone, leaves, etc get preserved in the
original form in the rocks.
ii. During natural disasters like volcanic eruption, earthquake,
landslide, flood, etc the dead bodies of organisms sink into seas
or remain under the earth surface. The soft parts of their bodies
decay while the hard parts remain pressed down in the ground.
The external structure of such hard parts are formed in the soil,
sand, stones, etc and fossils are formed.
Similarly, when entire body of plants and animals are buried under the
earth, their soft parts decay and vacant space is formed. The vacant
space gets filled with other objects. Thus, figures of the organs of bird,
branches of plants, organs of animals, etc remain in hard objects in
the form of impressions.
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Importance of fossils
Importance of fossils can be explained in the following points.
a. They provide evidence of evolution of organisms.
b. They help to get idea about the origin of life on the earth.
c. They help to know about the extinct animals and plants.
d. They help to know about different strata of sedimentary rocks.
e. They help to study the ancient geography and climate of a
country.
f. Fossil fuels like coal and petroleum are the main sources of energy.
Fossil fuels
The fuels which are obtained from the remains of dead plants and
animals of millions of years ago are called fossil fuels. Coal, petrol,
diesel, kerosene, natural gases, etc are the examples of fossil fuels.
Coal
Coal is a fossil fuel which is black or brown carboneous deposit formed
from plants buried under the earth millions of years ago.
It is found in the form of layers in the mines. Mainly, there are
four types of coal. They are: (i) peat (ii) lignite (iii) bituminous (iv)
anthracite.
Peat: It is a coal of low quality. It is soft and looks like soil. It is
formed from decaying vegetation. It burns with little heat and more
smoke.
Lignite: It is a dark brown coal. It burns more easily than peat.
Bituminous: It is a black and hard coal. It is mostly used for domestic
purpose. It burns with more heat and little smoke.
Anthracite: It is the coal of the best quality. It contains high
percentage of carbon. It is shining. It burns slowly without smoke.
Fact &Reason
Why is coal called fossil fuel?
Coal is formed due to the action of high pressure and temperature on the remains
of plants buried under the crust of the earth millions of years ago. So, coal is
called fossil fuel.
Formation of coal
It is believed that coal was formed from the fossils of plants. In
carboniferous period, there were forests of fast growing bushes and
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fern plants in the swamps of the earth. Those plants were buried under
the earth due to some natural processes like earthquake, landslide,
flood, etc. They were covered by sediments of soil and sand along with
water and were protected from decaying. Due to high temperature and
pressure, chemical changes occured in the dead bodies of the plants.
As a result, some gases escaped out and a black residue containing
carbon hydrogen and oxygen left in the form of layers. Due to high
pressure from the overlying mud and sand, liquid part squeezed out
leaving the solid coal. Thus coal is formed.
Coal is found in Dang district of Nepal.
Fact &Reason
What is carbonization?
The process of formation of coal from the parts of plants due to high temperature
and pressure inside the crust of the earth is called carbonization.
Importance of coal
Importance of coal can be discussed in following points.
a. It is used in industries, houses and other places as a source of heat.
b. If coal is insufficient amount, it can be used to generate electricity.
c. It is used as a fuel in factories like brick factory, iron factory, etc.
d. It is used to make various organic compounds like benzene, phenol, etc.
e. It is a source of national income of some countries.
Mineral oil
Mineral oil is the mixture of Pipes to take out
oil and gas
hydrocarbons (90- 95%) and
petroleum. Mineral oil is also
called rock oil because it is found
between the layers of rocks under
the earth's surface. Paraffin, Hard rock
lubricating oil, petrol, kerosene, Gas
Oil
grease, wax, asphalt and other Water
many products can be obtained Mineral oil
from mineral oil.
Formation of mineral oil
It is believed that mineral oils were formed from the decomposition
of parts of plants and animals. When the dead bodies of plants and
animals were buried under the soil, sand, etc, they could not decay due
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to lack of oxygen. Under high pressure of sedimentary rocks, scarcity
of oxygen, moderate temperature and the action of bacteria, the dead
bodies were converted into a dark semi-liquid substance. It is called
crude oil. It remains trapped between two rocks. The rocks present at
the bottom is called bed rock and that present at the top is called cap
rock. Following products can be obtained from crude mineral oil:
Petroleum products Uses
Natural gas As a fuel
Peotroleum ether As a solvent, for cleaning purpose
Diesel Vehicle fuel
Kerosene As a fuel
Lubricating oil or grease Lubrication
Vaseline Medicine
Paraffin wax Making candles and matches
Petroleum cake Fuel, construction of roads
Importance of mineral oil
1. Mineral oil is used to run vehicles. It is widely used for cooking
purposes.
2. It is used as lubricants.
3. It is used in many industries as fuels.
4. It is used for making various types of chemicals like plastics,
fertilizers, dyes, insecticides, etc.
5. Coal tar, a product of petroleum is used for the construction of roads.
Learn and Write
a. The earth and human beings were not originated at the
same time. Why?
At the time of origin of the earth, there was no favourable
environment for the survival of living things. The suitable
environment for the survival of the human being was developed
after about 4 billions years of the origin of the earth. It is
estimated that the earth was originated about 4.6 billion years
ago but the human was originated about 2 million years ago.
Thus, the earth and the human beings were not originated at
the same time.
b. Fossils were found in the sedimentary rocks. Why?
Fossils were formed when dead bodies of plants and animals were
covered by soil, mud, sand, etc. The mud, soil and sand which
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remained above the dead bodies of plants and animals changed
into sedimentary rocks after long time. Therefore, fossils were
found in sedimentary rocks.
c. Fossil is important for human beings. Why?
Fossils of ancient organisms are used as fossil fuel. Fossils like
petroleum, coal, etc are used as fossil fuel. Fossils can be used to
study about the evolution of the earth and the evolution of life on
the earth. Thus, fossil is very important to human beings.
Main points to remember
1. Hypotheses like planetesimal hypothesis, nebular hypothesis, tidal
hypothesis, etc are the main hypotheses about the origin of the earth.
2. The estimated age of the earth is 4.6×109 years.
3. A time scale that covers the earth's history from its origin to the
present is called geological time scale.
4. Geological time scale is divided into cryptozoic and phanerozoic eons.
5. Proterozoic, Paleozoic, Mesozoic and Cenozoic era are the eras of the
earth's history.
6. Origin of the life began from Proterozoic era.
7. Paleozic era began 540 million years ago and ended at 250
million years ago.
8. Mesozoic era began 250 million years ago and ended at 65.5
million years ago.
9. Cenozoic era began from 65.5 million years ago and is still running.
10. Fossils are the impressions or hardened remains of the plants or
animals that existed thousands or million years ago.
11. Fossils help to provide the evidence of evolution, to know about
extinct animals, to know strata of various layers of the rocks, etc.
12. Coal is a fossil fuel which is black or brown carboneous deposit
formed from plants buried under the earth millions of years ago.
13. Peat, lignite, bituminous and anthracite are various types of coals.
14. Mineral oil is the mixture of hydrocarbons and petroleum.
Exercise
A. Very short answer questions (1 mark)
1. Write the estimated age of the earth.
2. What is geological time scale?
3. In which eras did owl and flowering plants evolve?
4. In which era did dinosaurs evolve and in which era did they
become extinct?
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5. What is carbonization?
6. What is crude oil?
7. What is the evidence that there were dinosaurs on the earth
in the past history?
8. In which era did the evolution and development of mammals
take place?
9. Name the eon and era in which there is dominance of human
beings?
10. What are fossils?'
11. What are the two conditions required to form mineral oil
inside the earth's crust?
12. How is the information about ancient living being taken?
13. Define paleontology.
14. Name the coal of superior quality.
15. How many types of coal are there?
16. What are fossil fuels?
17. Why are fossils not found in igneous rocks?
18. Mention the name of the periods and eras in which following
changes occurred:
i) Evolution of unicellular animals ii) Evolution of dinosaurs
iii) Evolution of human beings iv) Evolution of fishes
v) Extinction of dinosaurs
B. Short answer questions (2 marks)
1. Why is coal called a fossil fuel?
2. Write any two importance of mineral oil.
3. How is coal formed ? Explain in brief.
4. Write any three differences between Palaeozoic era and
Mesozoic era.
5. Why did dinosaurs evolve earlier than humans?
6. State the tidal hypothesis about the origin of the solar
system. Who propounded it?
7. State the nebular hypothesis about the origin of the solar
system. Who propounded it?
8. State the planetesimal hypothesis about the origin of the
solar system. Who propounded it?
9. Which era is called the era of creepers, why?
10. Why is Mesozoic era called golden age of reptiles?
11. Why is Cenozoic era called the era of mammals?
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C. Long answer questions (3 marks)
1. List any three major events of Mesozoic era.
2. List any three events of Cenozoic era.
3. List any three events of Paleozoic era.
4. Write any three differences between Mesozoic era and
Cenozoic era.
5. Differentiate between anthracite and bituminous coal.
6. Differentiate between mineral oil and coal.
7. Explain the main steps of fossil formation.
8. The study of fossils is important for human beings. Justify
this statement.
D. Very long answer questions (4 marks)
1. Explain the process of formation of mineral oil with diagram.
Give reasons to minimize the consumption of mineral oil in
the countries like Nepal.
2. Explain evolution of life in cenozoic era.
3. Explain the evolution of life in palaeozoic era.
4. Explain the evolution of life in mesozoic era.
Glossary
• Hypothesis : assumption, a statement that is assumed to
be true for the sake of argument
• Evolution : gradual development and advancement of an
organism
• Planetesimal : a small rocky astronomical object thought
to have orbited the Sun in the early stages
of the solar system before coalescing with
others to form the planets
• Conifers : any tree that has thin leaves needles and
produces cones. Many types are evergreen.
Pines, firs, junipers, larches, spruces, and
yews are conifers
• Impermeable : not permitting the passage of liquid, gas, or
other fluid
• Nebula : a cloud in the space
• Era : a lot of time smaller than eon and greater
than period
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Chapter
22 Climate change and
Atmosphere Joesph Farman
In 1984 British Antarctic Survey scientists, Joesph Farman
, Brian Gardiner, and Jonathan Shanklin, discovered a
recurring springtime Antarctic ozone hole.
Estimated Periods: 3 (3T+0P)
Objectives
At the end of the lesson, students will be able to:
• explain the efforts of national and international bodies to minimize climate
change.
• explain different layers (including ozone layer) of the atmosphere;
• explain the effects of chlorofluorocarbon on ozone layer;
• explain the uses and importance of artificial green house;
• explain the impacts of green house gases on the environment;
• explain the bad impacts of industrial gases on the environment.
The earth and its surrounding is divided into three parts. They are:
i. lithosphere ii. hydrosphere iii. atmosphere
Lithosphere: It is the land part of the earth.
Hydrosphere: It is the mass of the water present on the earth.
Atmosphere: It is a thick layer of mixture of various gases which
surrounds the earth.
In this unit, we shall discuss about the atmosphere.
Our earth is surrounded by a thick layer of air containing different
gases. It is called atmosphere. The gravity of the earth holds the
atmosphere around it. Atmosphere contains mixture of various gases,
water vapour, smoke and dust particles. It mainly consists of nitrogen
(78%), oxygen (21%) and carbon dioxide (0.03%). Other gases present
in the atmosphere are hydrogen, helium, argon, ozone, etc.
The atmosphere holds heat on the earth. It prevents the entry of
ultraviolet rays to the earth surface. Thus, it protects the life on
the earth. Therefore, the atmosphere is called the canopy of the air
around the earth.
Climate Change
The atmosphere has a significant role in the climate of a place. The
change in the temperature and humidity brings unfavourable effects
in the organisms. Hence, it is necessary to minimize the factors that
cause climate change.
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National and International efforts to minimize climate change
The climate change has imparted negative effects in human beings,
other animals and plants. Its effects are increasing worldwide.
It has turned to be a global problem. Several studies have shown
that the increasing trend of climate change is increasing threats to
the existence of organisms on the earth. Therefore, it is necessary
to combat climate change across the globe. The United Nations
Organization has taken the issue seriously and forwarded some steps
for solving the problem. Including the contents of climate change in
the curriculum of school, college and university is also an important
effort for increasing awareness to control climate change. Different
attempts for the minimization of climate change and improvement in
environment are described below:
Attempts made in national level
The attempts that have been made in Nepal for minimizing the effects
of climate change are called national level efforts. A short introduction
of such attempts is included here.
1. National Communication Report
2. Strategic Programmes to Combat Climate Change
3. National Climate Change Adjustment Programmes
4. Climate Change Policy, 2067 BS
5. Local Level Adjustment Programmes against Climate Change
6. Other programmes
1. National Communication Report
Nepal has prepared a detailed report in climatic changes and
submitted its national communication report to the fund of the
United Nations Convention on climate change. The effects of
climate change in Nepal and its mitigating measures and capability
building to combat climate change and necessary policy, rules and
planning are emphasized in the report. It has also pointed out
the sectors that are prone to the effects of climate change. Those
sectors include agriculture, transportation, industries, forest,
health, waste management, etc. It has also stressed on the need
of establishing a scientific research centre to explore and study
such issues.
2. Strategic Programmes to Combat Climate Change
The Climate Investment Fund has invited Nepal to participate
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in the Global Programme to combat climate change in 2009. The
Global Climate Model Programme supports the poor nations to
combat climate change by providing financial aid. The ‘Strategic
Programmes to Combat Climate Change’ of Nepal has been
divided into five areas and is taken as the long-term program to
combat climate change. The five different areas are:
a. Climatic adjustment of watersheds that lie in the hilly
ecosystem catchment areas
b. Mainstreaming of the risk management of climate change in
development projects
c. Increasing the climatic adaptation of endangered species
d. Mitigating the risks developed due to climate change
e. Construction of a skilled community for the management of
climate change through active participation of private sector
3. National Climate Change Adjustment Programmes
This programme A.D. was commenced by the government of
Nepal in December, 2010. The main objective of this program
is to evaluate climate change and its risks. It is operating 250
programmes under nine integrated programmes.
4. Climate Change Policy, 2067 BS
The increase in atmospheric temperature due to climate change
imparts negative effects in agriculture, biodiversity, public
health, forest, socio-economic aspects, etc in Nepal. Hence, it is
essential to conduct public awareness against climate change. It
is necessary to emphasize minimizing, controlling and managing
the effects of climate change. To address such issues, The Climate
Change Policy (2067 BS) with specific objectives and policies has
been brought into action.
5. Local Level Adjustment Programmes against Climate
Change
It adopts four main principles, namely inclusive, readiness,
progressive and flexible while selecting the process of adjusting
and mitigating the climate change effects. It also performs the
role of making plans, implementing and coordinating in local and
national level programmes. These programmes also aim to provide
assistance to the people of very poor and needy community, area
or family. This programme is being operated in the local and
community level.
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6. Other programmes
A number of other efforts are in practice for reducing the amount
of carbon dioxide into the atmosphere. Such programmes include
Improved Oven and Biogas Plant, Rainwater Harvesting,
Improved Brick Factory, Pre-information System about Natural
Disasters, etc.
Efforts made in the international level
The efforts that are made outside Nepal to minimize the harmful
effects of climate change are called international efforts. The efforts
made in the international level are as follows:
1. United Nations Convention about climate change
2. Conference of the Concerned and the Recognized Countries
about Climate Change
3. Agenda 21
4. Kyoto Protocol
5. Intergovernmental Forum
6. Methods of minimizing the emission of green house gases
according to Kyoto Protocol
7. Minimizing the carbon emission resulted due to deforestation
1. United Nations Convention about climate change
The international community started to combat against climate
change since June 1992 in Rio de Janerio, Brazil, at the Earth
Summit. There was the participation of 154 nations of the world
in that convention. The conference had addressed the issues of
Increasing Environmental Pollution, Sustainable Development,
Hazardous Effects of Climate Change, etc. As the climate change
cannot be brought under control completely, it is necessary we
adapt ourselves according to the changed climate. Nepal signed
the convention in June 12, 1992. The parliament of Nepal approved
the convention in 1994 and its provisions were implemented in
Nepal.
2. Conference of the Concerned and the Recognized Countries
about Climate Change
According to the UN Convention signed in 1992, the signing
countries must inform the member countries about the progress
made in their nation regarding the climate change. The concerned
countries have attended the conferences about climate change for
19 times untill 2013. The conference of 2014 was held in Peru.
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Nepal has prepared and implemented the Climate Change Policy
in 2011.
3. Agenda 21
The work plan ‘Think Globally and Act Locally’ was brought in
practice to address the issues of climate change and sustainable
development in the 21st century. This work plan is called Agenda
21. This work plan prioritizes the balance between environment,
development and society for carrying out sustainable development.
4. Kyoto Protocol
The Kyoto Protocol is the international carbon emission reduction
agreement. This international emission reduction agreement
was signed on December 11, 1997, at the third Conference of the
Parties, in Kyoto, Japan. The main objective of this protocol is
to reduce the emission of green house gases and to control the
rise in temperature. Until 2008, 36 developed and 137 developing
countries of the world have approved the protocol. Nepal had
signed the Kyoto protocol in 16 September 2005. According to this
Protocol, the countries had to reduce emissions of six greenhouse
gases by 5.25% between 2008 and 2012, based on 1990 levels. This
duration is called first commitment period. Some amendments
were made to this protocol by the convention of 8 December 2012
held in Doha, Qatar. According to the amendments, the developed
nations should declare the second commitment of the 8 years
between the years 2012 to 2020 to reduce the green house gas
emission.
5. Intergovernmental Forum
The intergovernmental forum has been formed for the study and
research about climate change. The forum was established in
1988 through the joint efforts of World Weather Organization and
United Nations Environment Programme. It prepares evaluation
reports about climate change through scientific studies, research
and exploration.
6. Methods of minimizing the emission of green house gases
according to Kyoto Protocol
The developed countries are strengthening their economy
through the establishment of industries. The burning of fossil
fuels in such industries releases a lot of green house gases into
the atmosphere. Thus, the developed countries are responsible
for the release of largest amount of green house gases. And, it
is difficult to stop this. Hence, the Kyoto protocol has simplified
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this problem through the provision of international emission
trade between the developed and developing countries, collective
implementation and clean development process.
7. Minimizing the carbon emission resulted due to deforestation
Carbon emitted as carbon dioxide is the main factor of climate
change. The forest is the prominent agent for the absorption and
storage of such carbon. Hence, the developed countries should
play a significant role to control deforestation. The developing
and underdeveloped countries get compensation from the
developed countries to control deforestation. The developing
and underdeveloped countries have also agreed this provision
theoretically.
Layers of atmosphere
On the basis of height and temperature, the atmosphere is divided
into five distinct layers. They are:
i. Troposphere ii. Stratosphere iii. Mesosphere
iv. Thermosphere v. Exosphere
Troposphere
It is the lowermost layer of the 720 km
atmosphere. The thickness of this layer
varies from place to place. Its thickness
is about 8-10km at the poles and about
16km from the equator.
This layer consists of mainly carbon 80 km
dioxide, water vapour, nitrogen, oxygen,
argon and dust particles. It is estimated 50 km
that 95% of the total atmosphere is in 16 km
this layer. The upper boundary of the
troposphere is called tropopause. The air
closer to the earth surface is warmer due
to reflection of heat by the earth surface.
The temperature gradually decreases
with increase in height at the rate of
about 6.5° per kilometer. The temperature at the boundary varies
from –80°C to –55°C.
Different climatic activities like rainfall, cloud formation, frost,
hailstorm, fog, tornado, thunderstruck, lightning, etc occur in this
layer. Scientists forecast weather by studying these activities. Human
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activities like the production of different gases from industries, dust
from industries, smoke from burning fuels, etc affect this layer.
Fact &Reason
Why is troposphere important for meteorologists?
All the meteorological activities like cloud formation, lightning, rain, frost,
hailstorms etc. occur in troposphere. So, troposphere is very important for
meteorologists to forecast the weather.
Stratosphere
It is the layer which lies above the troposphere. It is extended from
16km to 50km above the earth's surface. The upper boundary of this
layer is called stratopause. There is negligible amount of humidity, as
a result of which there is thin cloud. The temperature rises gradually
with increase in height. It has the temperature of -55°C to -75°C at
the lower layer and -2°C at the upper layer.
This layer contains ozone. Hence, it is called ozonosphere. Ozone is
a special type of oxygen containing three atoms in one molecule. It
absorbs about 99% of the uv rays of solar radiation and protects the
life on the earth from harmful effects of uv radiations. Therefore, it is
called protective layer. This layer is clear and cloudless. So, often jet
planes fly in this layer.
Fact &Reason
Why is stratosphere called protective layer?
Stratosphere consists of ozone layer at the top which absorbs harmful solar
radiation preventing it to come to the surface of the earth. Thus, it protect us
from dangerous diseases like skin cancer, cataract etc. Therefore, stratosphere is
called protective layer.
Mesosphere
It is the layer which lies just above the stratosphere. It extends from
the altitude of 50km to 80km above the earth's surface. The upper
boundary of this layer is called mesopause. The temperature of this
layer decreases with increase in altitude. This is the coldest layer of
the atmosphere. Its upper surface has the temperature of - 110°C.
It has very less ozone to absorb ultraviolet rays. Trails of hot gases
released from the meteors are seen in this layer. Strong winds blow in
eastward during winter and westward during spring season.
Thermosphere
It is the layer of atmosphere which lies just above the mesosphere. It
extends from 80km to 720km above the earth's surface. In this layer,
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the density of the air is low and gases are present in small amount.
This layer comprises 0.01 percent of total volume of atmosphere. Its
upper surface has hydrogen and helium and the lower surface has
nitrogen and oxygen.
Fact &Reason
Which layer of the atmosphere is called ionosphere, why?
Thermosphere is called ionosphere because the gases present in this layer are in
the ionic form due to the effect of ultraviolet radiation.
This layer is directly affected by solar radiations. The solar radiations
ionize the molecules of nitrogen and oxygen into ions. These ions are
present in the upper layer of thermosphere. Therefore, upper layer
of thermosphere is also called ionosphere. The charged particles
released from the sun hit the ions in the ionosphere making them
glow in different colours. Such coloured light is called aurora. This
layer is responsible for the communication of radio waves.
Fact &Reason
Why is thermosphere important for communication purpose?
The gases in thermosphere are present in ionic form which bounces back
the signals that help in communication. So, thermosphere is important for
communication purpose.
Exosphere
The layer of the atmosphere which lies above the thermosphere is
called exosphere. It extends beyond 720km above the earth's surface
and reaches upto the space. It is the topmost layer of the atmosphere
and is also called fringe region.
In this layer, the gravity of the earth is weak. Therefore, few atoms or
molecules of gases are present. There are mainly the light gases like
hydrogen and helium. These molecules and atoms move with high
speed without colliding with each other. The temperature of this layer
varies from 1200°C. to 6000°C.
Ozone layer
Ozone is a pale blue gas found is stratosphere. It is made up of three
atoms of oxygen and is highly poisonous. Its molecular formula is O3.
When atmospheric oxygen is exposed to uv rays of solar radiation, it
dissociates into nascent oxygen. This nascent oxygen then combines
with other oxygen molecule and forms ozone molecule.
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O2 U-V radiation O + O (Nascent oxygen)
O + O2 → O3
The ozone layer is spread from 16km to 50km from the earth's surface.
Importance of ozone layer
The ozone layer protects the earth from the effect of harmful radiations
coming from the sun. Ozone layer absorbs 99% of the uv radiations.
It acts as a curtain to preserve aquatic and terrestrial ecosystems on
the earth. It prevents us from dangerous diseases like cataracts, skin
burning, skin cancer etc. It also helps to maintain temperature on the
earth.
Depletion of ozone layer
Decreasing the thickness of ozone layer or formation of hole in it is
called depletion of ozone layer.
A research team led by J.C Farmann, an English scientist has
reported about the depletion of ozone layer for the first time. According
to him, the thickness of ozone was drastically reduced over Antartica
in 1985 AD.
Chlorofluorocarbons (CFCs) are the major chemicals which destroy
the ozone layer. CFCs are of two types, CFC – 11 and CFC – 12. CFCs
were invented by Thomas Mitts in 1930 AD. It is a chemical which
contains the atoms of carbon, hydrogen, chlorine and fluorine. It is
used as a cooling agent or solvent. It is a stable, non-poisonous, non
inflammable and cheap gas. It is cheaper than ammonia and used as
a coolant in the refrigerator. It is also used in aerosol spray can, air
conditioner, plastic production, etc. CFC gas is also released when the
substances made with the use of CFC are burnt. Similarly chemicals
like methyl bromide, methyl chloroform, carbon tetrachloride, etc
also destroy ozone layer.
(i) When the chemicals like CFCs, methyl bromide, methyl chloroform,
carbon tetrachloride, etc are used, elements like chlorine, bromine,
etc are released. The chlorine and bromine molecules react with
ozone molecules and convert them into oxygen. For example,
when CFCs come in contact with u-v raditions, CFCs breaks and
produce nascent chlorine. The nascent chlorine reacts with ozone
to form oxygen (O2) and ClO. The ClO breaks into chlorine (Cl)
and oxygen (O). Nascent chlorine (Cl) and oxygen (O) participate
in a chain reaction and ozone layer gets depleted.
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CFCl3 −→ CFCl2 + Cl (Nascent chlorine)
Cl + O3 −→ ClO + O2
ClO −→ Cl + O
O + O3 −→ 2O2
(ii) Destruction of ozone by oxide of nitrogen
Nitric oxide reacts with ozone to form nitrogen dioxide. It further
reacts with ozone.
NO + O3 −→ NO2 + O2
2NO2 + O3 −→ N2O3 + 2O2
It is estimated that a single chlorofluorocarbon molecule can destroy
1,00,000 molecules of ozone.
Fact &Reason
It is better not to use refrigerators with CFC, why?
Refrigerators with CFC releases chlorofluorocarbons (CFC) which is responsible
for the depletion of the protective layer of the atmosphere ie. ozone. Thus, it is
better not to use refrigerators with CFC.
Effects of ozone layer depletion
When ozone layer of the stratosphere gets depleted, large quantity of
ultra violet radiations can reach the earth's surface. The ultraviolet
radiations have following major effects.
1. Effect on health of human beings
Ultraviolet radiations can cause different diseases such as
cataract, skin cancer, loss of immunity, skin cracks, etc. It may
also affect DNA of human body.
2. Effect on plants and animals
The ultraviolet radiations affect the development of plants. It
reduces the rate of photosynthesis and crop production.
It also hampers the development of aquatic and terrestrial
organisms. Their reproductive ability is also decreased. Larvae
and eggs of aquatic and amphibian animals die due to u-v
radiations. The U-V rays cause cancers to animals too.
3. Global warming
When the ultraviolet (UV) radiations enter the earth's surface
through ozone hole, the heat coming from the sun gets accumulated
and temperature of the earth increases. Thus, global warming
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occurs. Due to global warming, numbers of islands will be covered
by oceans.
Ozone layer protection
The following methods should be used for the conservation of ozone
layer.
a. The use of the appliances that cause the production of CFCs
and oxides of nitrogen should be reduced.
b. The production of green house gases such as carbon dioxide,
carbon monoxide, etc should be reduced.
c. People should be made aware about the adverse consequences
of ozone layer depletion.
Industrial gases
Various types of fuels are used in the industries. At the time of burning
of these fuels, various types of gases are produced. Carbon dioxide
(CO2), sulphur dioxide (SO2), carbon monoxide (CO), nitric oxide (NO),
etc are the gases produced from the industries. These gases are called
industrial gases. In addition to such gases, lead, mercury, cadmium,
arsenic and other toxic chemicals are also produced. The industrial
gases and other toxic chemicals released from the industries reach the
atmosphere and react with the chemicals present in the atmosphere.
These air pollutants remaining in the air is also called industrial
smog. As a result of which, air gets polluted. Polluted air affects the
health of animals and plants.
Effects of industrial gases
1 Sulphur dioxide, nitric oxide, carbon dioxide, etc cause acid rain.
2 Dust, smoke, lead, mercury, etc released from the industries cause
air pollution. They affect the muscular functioning of human
being. They cause blood deficiency and affect mental functioning.
3. Theindustrialgaseshavegreenhouseeffect.So,theycauseglobalwarming.
4. Industrial smog causes eye itching. It reduces transparency of
atmosphere and creates a problem to pilots for flying aeroplanes.
5. It may cause depletion of ozone layer.
Acid rain
Various industrial gases like carbon dioxide, sulphur dioxide, sulphur
trioxide, nitric oxide, nitrogen dioxide, etc react with water and form
acids. When these acids get mixed with rain and fall in the form of
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rain, it is called acid rain.
2SO2 + O2 −→ 2SO3
SO3 + H2O −→ H2SO4 (sulphuric acid)
CO2 + H2O −→ H2CO3 (carbonic acid)
2NO + O2 −→ 2NO2
4NO2 + O2 −→ 2N2O5
N2O5 + H2O −→ 2HNO3 (Nitric acid)
Acid rain corrodes historical monuments like statue, sculptures, etc.
It also increases acidity of soil and affects the production of crops.
Learn and Write
1. Atmosphere is the canopy of the air around the earth. Why?
The atmosphere prevents the entry of the dangerous ultraviolet
radiations to the earth's surface from the sun. It also protects
from meteors and meteorites. It provides suitable temperature
for the survival of life. Therefore, the atmosphere is called the
canopy of the air around the earth.
2. Temperature decreases with increase in altitude in
troposphere. Why?
The solar radiations of short wave easily reach the earth's
surface through atmosphere. The short wave radiations convert
into long waves after striking the earth surface. The long wave
radiations contain heat energy. Thus, the troposphere is heated
from the lower surface to the upper surface.
3. Chlorofluoro carbons (CFCs) cause ozone layer depletion. Why?
When chlorofluoro carbons are used, nascent chlorine atoms
are released into the atmosphere. The nascent chlorine reacts
with ozone molecule to form unstable oxide of chlorine (ClO) and
oxygen molecule (O2). Oxide of chlorine dissociates into nascent
chlorine and oxygen atom again. They react with ozone molecule
and damage them.
CFCl3 U−Vrays→ CFCl2 + Cl (Nascent chlorine)
Cl + O3 U−Vrays→ ClO + O2
ClO U−Vrays→ Cl + O
O + O3 U−Vrays→ 2O2
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Main points to remember
1. The earth is divided into three parts- lithosphere, hydrosphere and
atmosphere.
2. Atmosphere is a layer of air which surrounds the earth. It is divided into
troposphere, stratosphere, thermosphere, mesosphere and exosphere.
3. Troposphere extends to an altitude of 16km above the earth's
surface. Various activities like rainfall, thunderstorm, cloud
formation, frost, etc take place in this sphere.
4. Stratosphere extends from an altitude of 16km to 50km above the
earth's surface. It contains ozone layer which absorbs ultra-violet
radiations.
5. Mesosphere extends from an altitude of 50km to 80km above the
earth's surface. It is the coldest layer.
6. Exosphere is the outermost layer which extends above 720km
from the earth's surface.
7. Ozone is a pale blue gas found in stratosphere.
8. The ozone layer protects the earth from the effect of harmful
radiations coming from the sun.
9. Decreasing the thickness of ozone layer or formation of hole in it
is called depletion of ozone layer.
10. Ozone layer is depleted by the CFCs, methyl chloroform, carbon
tetrachloride, methyl bromide, etc.
11. Ozone layer depletion affects human beings, plants, other animals
and also causes green house effect.
12. The use of the appliances that cause the production of CFCs and oxides
of nitrogen should be reduced to conserve ozone layer.
13. Industrial gases are the gases like carbon dioxide, sulphur
dioxide, carbon monoxide, etc produced from the industries.
14. Falling of acid along with water during rainfall is called acid rain.
Exercise
A. Very short answer questions
1. Define atmosphere.
2. What is ozone hole ?
3. In which layer of the atmosphere is the ozone layer present?
4. Define industrial smog.
5. Define ozone layer depletion.
6. Write any three chemicals that destroy ozone layer.
7. Write down the name of layer of atmosphere which expands in
the region of 80 km to 720 km from the earth's surface.
8. What is troposphere?
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9. What is exosphere?
10. What is stratopause?
11. What is ozone layer?
12. What is acid rain?
13. Define smog.
14. What is full form of CFCs? Write any two sources of CFCs.
15. What is artificial greenhouse?
16. What is greenhouse effect?
B. Short answer questions (2 marks)
1. What would happen if green house gases were not present in
the atmosphere?
2. How does nitrogen oxide destroy ozone layer? Write with
chemical equation.
3. It is better not to use refrigerators with CFC, why?
4. The troposphere is very important for the meteorologists, why?
5. In troposphere, temperature goes on decreasing while going up,
why?
6. The temperature of stratosphere increases with the increase in
height, why?
7. Why is stratosphere called protective sphere?
8. What is thermosphere or ionosphere? Where is it located?
9. How is ozone formed in the stratosphere? Write with chemical
reaction.
10. Which layer of atmosphere is responsible for the change in
weather? Why?
11. "Main cause of depletion of ozone layer is human being.” Clarify
this statement.
12. Write two negative effects due to the ozone layer depletion on
the earth surface.
C. Long answer questions (3 marks)
1. Draw a neat diagram showing the various layers of atmosphere.
2. Mention the adverse effects of industrial gases.
3. Write down the effects of natural greenhouse.
4. Write any three effects of increase of greenhouse gases in the
atmosphere.
D. Very long answer questions (4 marks)
1. Explain the formation and depletion of ozone layer with the
chemical reaction.
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2. Write the name of main chemical which destroys ozone layer.
How is ozone layer depleted by that chemical? Describe with
chemical equation.
3. Following are the findings in a study done on the earth
environment. The temperature of respective environment
is increasing. The number of amphibians are decreasing.
Human beings are suffering from cataracts and skin cancer.
i. What is the cause of above findings?
ii. What is to be done to remain safe from above conditions?
iii. Write one more similar harmful effect to human health.
iv. What happens to the environment temperature at this
condition?
4. "Excessive use of mineral oil and coal help to increase the
greenhouse effect." Justify the statement.
5. Consequences like skin burn and skin cancer were observed
when people take sunbath on the surface of the earth. On the
basis of it answer the given questions.
i) What is the cause of it ?
ii) What is to be done for the control of it?
iii) In such condition, what is the effect of temperature on
environment? Write any two effects.
6. How do industrial gases cause acid rain? Explain with
chemical reaction. Mention the effects of industrial gases.
Project Work
Prepare a chart of the different layers of atmosphere showing their distance from
the earth surface, composition (gases present), average temperature, main activ-
ities that happen and other important features
Glossary
• Retention : keeping or holding something
• Depletion : gradual decrease in quantity, destruction
• Corrode : to destroy something gradually usually due to
chemical action
• Conopy : protective covering
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Chapter
23 The
Universe
Neil Armstrong
He was the first person to step on the
moon.
Estimated Periods: 5 (4T+1P)
Objectives
At the end of the lesson, students will be able to:
• explain the structure of solar system with diagram
• describe comets and meteors found in solar system
• describe galaxies with types
• describe constellation and superstitions about system of zodiac
• explain the importance of sun in the solar system
The universe is a vast space in which all heavenly bodies including
galaxies, stars, constellations, planets, asteroids, comets, etc are
located. The sun is one of the stars of a milkyway galaxy. There are
millions of galaxies in the universe like the milky way galaxy. There
are eight planets including the earth in the solar system. Thus, the
earth is a tiny particle of the universe. Hence, we can say that the
size of the universe is very large. Nobody knows the size and limit of
the universe. Different studies are done about the components of the
universe. The branch of the science which deals with the study of the
universe and its components is called astronomy.
Units used to measure distance in the universe
One body is very far from another body in the universe. Therefore, the
distance between them cannot be measured in kilometer or mile. The
bigger units like light year, astronomical unit, parsec, etc are used.
Light year
It is the distance travelled by the light in one year. Its value is
9.5×1015m.
1 year = 365 days
= 365× 24 hours
= 365×24×60×60 seconds
396Times' Crucial Science Book - 10
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