Chapter 3 Degradation of Natural Environment

NIOS Class 12 Environmental Science Chapter 3

INTEXT QUESTIONS 3.1

1. State any two types of environmental degradation caused by humans.

Ans: The consequences of human exploitation are clearly seen in soil erosion, loss of biodiversity and pollution of land, air and water bodies.

2. Give one reason for increase in human population.

Ans: Many factors have contributed to the enormous rise in the human population.

Improved agricultural practices have helped in increasing food production, hence food has become available.
Progress in medicine prevented deaths due to injury and epidemic diseases.
The average longevity of humans has increased since heart, lung and kidney disorders, as well as other diseases, can now be diagnosed and treated through modern medical technology.

3. Why rapid growth of world population a cause for alarm?

Ans: Humans have spoiled the environment by (i) depleting natural resources to a critical level and (ii) causing pollution to natural water bodies and land areas. It has led to the limited availability of natural resources, and the degradation of the environment is a threat to survival.

INTEXT QUESTIONS 3.2

1. What is deforestation?

Ans: Cutting down trees to clear forests is known as deforestation.

2. Give two reasons why trees are cut down by humans.

Ans: Forests have been cleared for various reasons-

1. Developmental activities: As humans began leading a settled life, crop fields, buildings, roads, industries, schools, hospitals, railways and irrigation canals, etc. became necessary developmental activities. Forests were cleared to meet the need for land for the above developmental activities.
2. For timber and wood: Wood is used in building construction, making furniture and other articles for human use. Trees that yield wood grow in forests and are cut down for timber. Use of firewood for cooking and heating, etc., also contributes to deforestation
3. For pastures: Forests are cleared to grow grasses and converted into grassland for grazing by cattle.
4. Shifting cultivation: Shifting cultivation is a system of crop cultivation involving the clearing of the forest and burning the fallen trees to clear the land for raising crops. Crops are grown on the cleared area for a few years and abandoned after a few years as the land loses its fertility. Thereafter, a new forest area is cleared for cultivation, and the same cycle is repeated.

3. State any two consequences of deforestation.

Ans: Consequences of deforestation

Soil erosion: Trees intercept rainfall, and cutting of trees and removal of plants leads to soil erosion. Plants’ roots hold the soil in place. With the loss of protective cover of plants, the topsoil, which is rich in organic matter, is washed away, and the soil loses its fertility.
Landslides: Removal of trees from forests leads to soil erosion. Ultimately causes landslides in hilly areas. This is because the roots of trees hold the soil in position.
Silting: The loss of trees from forests also causes silting of rivers and lakes as loose soil gets washed with rainwater and reaches water bodies.
Loss of wild habitat: Wild animals live in forests. Cutting forests means loss of their habitat, which in turn renders them endangered or even extinct.
Deforestation: Deforestation results in a change in climate since trees make the surroundings humid. Loss of trees leads to loss of humidity. Also, transpiration from plants makes rain clouds, and so rainfall is reduced due to deforestation.
Loss of CO₂ sink: Pollutants released by industries take up CO₂ is taken up by trees. When forests are denuded. This CO₂ sink is lost, and CO₂ collects in the environment.
Pollution: When trees are cut to use for making furniture or paper, the sawmills and paper mills pollute the water in which they dump the waste.
Loss of medicinal and other useful plants: Unique medicinal plants grow in certain forests. They are lost due to deforestation. Aromatic herbs, rubber trees and other useful plants are also lost due to deforestation.

4. Why do wild animals become endangered due to deforestation?

Ans: Wild animals live in forests. Cutting forests means loss of their habitat, which in turn renders them endangered or even extinct.

5. Why does deforestation cause soil erosion?

Ans: Trees intercept rainfall, and cutting down trees and removing plants leads to soil erosion. Plants’ roots hold the soil in place. With the loss of protective cover of plants, topsoil, which is rich in organic matter, is washed away, and the soil loses its fertility.

INTEXT QUESTIONS 3.3

Answer in one sentence:

1. Why are chemical pesticides considered harmful even though they kill insect pests that damage crops?

Ans: Use of pesticides not only kills pests that destroy crops but may also kill many non-pest organisms, which may include even useful species of insects such as pollinators, birds and helpers in dispersal of plant seeds. Pesticides tend to accumulate, and their concentration increases through the food chain and reaches toxic levels in eggs, milk and other food items. (biomagnification)

2. How do chemical fertilizers used in fields reach water bodies?

Ans: Unused fertilizers from agricultural fields are carried away by runoff waters into lakes and rivers, causing pollution. These agrochemicals may even seep through the soil and pollute groundwater.

3. List any three degradational effects of modern agriculture on environment.

Ans:

Forests have been cleared and transformed into farmlands for growing food crops.
Excessive irrigation and poor drainage cause waterlogging and kill plants.
Use of pesticides not only kills pests that destroy crops but may also kill many non-pest organisms, which may include even useful species of insects such as pollinators, birds and helpers in dispersal of plant seeds.

INTEXT QUESTIONS 3.4

Answer in one sentence

1. Why is there water scarcity in cities?

Ans: When water withdrawal exceeds the rate of replenishment of the groundwater table keeps on receding and resulting in drying out of wells. In many areas, excessive withdrawal has depleted groundwater resources, causing acute water scarcity.

2. Where do minerals and metals occur naturally?

Ans: Under the soil and inside the Earth.

3. Give one consequence of mining.

Ans: Mining activities have depleted the stock of mineral resources, particularly fossil fuels.

Depletion of minerals: With the advancement in mining technology and over-exploitation of mining mineral resources, large amounts of lead, aluminum, copper and iron ores have been used up. It is believed that in the next 20 years, silver, tin, zinc and mercury will be depleted to an alarming level if their exploitation continues at the present rate.
Dumping of debris: Extraction of minerals from the earth also produces significant amounts of overburden or debris. Often it is much more as compared to the quantity of mineral obtained. The dug-out loose waste material is dumped on the adjacent land. Dumping of mining waste not only occupies a large land area, but the waste dumps also become a source of soil erosion.
Land subsidence: Excessive mining, especially underground mining, may lead to land subsidence and may also cause landslides. The landscape, too, is spoiled.

4. Name one natural resource that is getting depleted due to industrialization.

Ans: Industrialization that disregards environmental concerns led to environmental degradation, like the following reasons:

Natural resources used as raw materials by industry are depleting rapidly.
Industries generate a lot of toxic gases and liquid effluents, leading to environmental degradation.
Industries generate a large amount of waste, which piles up in the environment. Disposal of waste not only needs land but also pollutes the environment and poses hazards to human health.
Industries use up a lot of fossil fuels as a source of energy. Accelerated consumption of fossil fuels is depleting their stock, as they are limited and non-renewable. But burning of fossil fuels releases CO₂ in the atmosphere, leading to global warming.

INTEXT QUESTIONS 3.5

Answer in one or two words, but not more than one sentence-

1. Name the chemical responsible for Minamata disease.

Ans: Hg/Mercury

2. Why do herbivores increase in number in the forest where lions have been killed by Poachers?

Ans: Without lions to feed on them, the number of herbivores increases in the forest.

3. State one reason for excessive floods due to human activities.

Ans: Sea level rise causes flooding of coastal cities and damage to coastal ecosystems like marshes and swamps.

4. What is the pH of pure rainwater?

Ans: 5-6

5. What combines with seawater to form an oil slick?

Ans: Less volatile components of oil

6. Expand CFC.

Ans: Chlorofluorocarbons

TERMINAL EXERCISE

1. How is the utilization of fossil fuels related to a harmful impact on the environment?

Ans: Industries use up a lot of fossil fuels as a source of energy. Accelerated consumption of fossil fuels is depleting their stock, as they are limited and non-renewable. But burning of fossil fuels releases CO₂ in the atmosphere, leading to global warming.

2. List three reasons for human population explosion.

Ans: Many factors have contributed to the enormous rise in the human population.

Improved agricultural practices have helped in increasing food production, hence food has become available.
Progress in medicine prevented deaths due to injury and epidemic diseases.
The average longevity of humans has increased since heart, lung and kidney disorders, as well as other diseases, can now be diagnosed and treated through modern medical technology.

3. In what way has increase in human population has degraded the environment?

Ans: With a growing population, the requirement for space, shelter, and commodities has exerted enormous pressure on the environment. To provide for these, land use has changed dramatically. It has already been seen that forests have been cleared for the cultivation of grain and fruit crops.

Clearing land for cultivation to grow more food has led to the depletion of natural resources and drastic changes in landscapes.
In many areas, excessive withdrawal has depleted groundwater resources, causing acute water scarcity.
To make houses for so many, stones and other building materials have to be quarried, more rocks have to be blown off, and more water has to be used.
Various modes of transport have been developed which consume growing quantities of fossil fuels such as coal, gas and petroleum, polluting the atmosphere.
The raw materials and fossil fuels, and water needed to run industries for manufacturing these products lead to their depletion.
Overpopulated areas result in congested roads and slum formation, which lack basic amenities like drinking water, drainage, waste disposal, lack of hygienic conditions, and a filthy environment creates potential conditions for public health problems, including the spread of epidemic diseases.
Discharge of untreated effluents and throwing of waste into water bodies have polluted most of the lakes and rivers.
Holy rivers Ganga, Yamuna and others are suffering from pollution due to the discharge of effluents from industries, human settlements, bathing, washing of clothes and throwing of garbage into the river.

4. State three reasons for deforestation.

Ans: Forests have been cleared for various reasons-

Developmental activities: As humans began leading a settled life, crop fields, buildings, roads, industries, schools, hospitals, railways and irrigation canals, etc. became necessary developmental activities. Forests were cleared to meet the need for land for the above developmental activities.
For timber and wood: Wood is used in building construction, making furniture and other articles for human use. Trees that yield wood grow in forests and are cut down for timber. Use of firewood for cooking and heating, etc., also contributes to deforestation.
For pastures: Forests are cleared to grow grasses and converted into grassland for grazing by cattle.
Shifting cultivation: Shifting cultivation is a system of crop cultivation involving the clearing of the forest and burning the fallen trees to clear the land for raising crops. Crops are grown on the cleared area for a few years and abandoned after a few years as the land loses its fertility. Thereafter, a new forest area is cleared for cultivation, and the same cycle is repeated.

5. Write an essay on “impact of deforestation”.

Ans: Cutting of trees in forests is called deforestation. Deforestation has taken place for various purposes at an alarming rate in different parts of the world, resulting in severe loss of wild plants and animals. Forests are cleared for developmental activities, to get timber and wood for building construction, furniture, etc, to grow grasses for grazing cattle, crop cultivation, etc. However, such activities lead to severe consequences that affect every stage of the environment.

Consequences of deforestation.

Soil erosion: With the loss of protective cover of plants, topsoil, which is rich in organic matter, is washed away, and the soil loses its fertility.
Landslides: This soil erosion will ultimately cause landslides in hilly areas because it is the roots of trees that hold the soil in position.
Silting: The loss of trees from forests also causes silting of rivers and lakes as loose soil gets washed with rainwater and reaches water bodies.
Loss of wild habitat: Wild animals will lose their habitat, which in turn renders them endangered or even extinct.
Climate change: Deforestation causes loss of humidity, which in turn will cause a change in the climate. The reduction in transpiration leads to reduced rainfall as well.
Loss of CO₂ sink: Trees collect the CO₂ released from industries and protect the environment. Without these trees, carbon dioxide would accumulate in the environment.
Pollution: Sawmills and paper mills will not only cut down the trees but also pollute the water in which they dump the waste.
Loss of medicinal and other useful plants: Unique medicinal plants such as aromatic herbs, rubber trees and other useful plants are lost due to deforestation.

Thus, deforestation leads to large-scale environmental degradation.

6. Why is modern agriculture held responsible for polluting the air and water?

Ans: Modern agriculture uses synthetic fertilizers that eventually reach the water bodies and pollute them. These fertilizers are either leached through the soil or run off during the monsoon. Excessive nutrients in the water bodies lead to explosive growth of green algae, known as eutrophication, and kill the aquatic life. On the other hand, the industries that manufacture these chemical fertilisers could cause air pollution. Moreover, the excessive use of fertilisers could kill useful non-pest insects that help with pollination, leading to the failure of seed dispersal.

7. Why is the modern influx of humans from villages to cities causing is serious concern to urban planners?

Ans: Industries attracted rural youth to cities, and their migration became easier with the improvement in communication and transport facilities. Growth of cities leads to increasing demand for environmental resources, leading to the following changes –

Cultivated land was lost forever for building houses, industries, roads and other facilities.
A growing urban population created increasing demand for potable water, leading to water scarcity. This compelled urban planners to develop a system that could provide the necessary water.
Black smoke from the industries and vehicles pollutes the environment.
A larger generation of garbage poses another threat that requires proper planning for garbage disposal.
Drainage of domestic and industrial effluents needs to be taken care of.
Measures must be taken to reduce the increasing noise levels that are common in urban environments.
Urban planners must come up with adequate facilities and basic amenities for the people migrating to the cities.

8. Why are greenhouse gases” are considered dangerous?

Ans: Greenhouse gas or CO₂ is considered dangerous as its increase has long-term effects and creates a domino effect. Industrialisation and urbanisation led to the emission of CO₂ in larger amounts into the atmosphere. Excessive concentration of CO₂ in the atmosphere traps heat radiation from the Earth within and does not allow it to escape into outer space. This leads to an increase in the global temperature, called global warming.

Global warming causes a rise in temperature on Earth.
Rise in temperature of the Earth causes polar ice caps to melt, and this water causes a rise in sea level as well.
On the other hand, increased Earth temperature causes water to expand, leading to a rise in water levels.
An increase in sea levels causes flooding in the coastal areas and damages their biodiversity.
Global warming caused a change in rainfall patterns, leading to early maturation of crops, reduced grain size and lower yield.

Thus, greenhouse gas is considered dangerous.

9. Why do environmentalists think that “marine fisheries” may collapse if we are not careful?

Ans: Global warming has driven marine fish towards cooler northern parts of the Earth or to the cool, deeper realms of the ocean. So far, several species of fish and other marine animals have permanently moved to cooler northern regions.

Smaller fish can move faster to cooler areas. This has affected the larger fish, causing them to become extinct. This has led to the collapse of marine fisheries and loss of livelihood for fisherfolk.
Dumping of massive amounts of waste into the sea is also affecting marine life.
Fertilisers and pesticides run off from agriculture cause “eutrophication.”
Oil spills and oil slicks also kill marine life.

All these together cause a collapse in marine fisheries if we are not careful.

10. Write notes on:

i. Mining and environmental degradation

ii. Acid rain

iii. Global warming and greenhouse effect

iv. Biodiversity loss

Ans:

i. Mining and environmental degradation

Mining activities have depleted the stock of mineral resources, particularly fossil fuels.
Removal of vegetation and soil to get access to mineral deposits led to the loss of flora and fauna present in the area.
A large amount of lead, aluminium, copper and iron ores have been used up.
Dumping of mining waste not only occupies a large land area, but the waste dumps also become a source of soil erosion.
Excessive mining, especially underground mining, may lead to land subsidence and may also cause landslides.

ii. Acid rain

Moisture-laden air rises to higher altitudes and condenses to fall as rain or snow. Acid rain is caused by the mixing of oxides of sulphur and nitrogen with rainwater. It causes acidification of water bodies that would kill the fauna and flora. It is toxic to trees and causes corrosion of buildings and marble structures, and archaeological structures.

iii. Global warming and greenhouse effect

Industrialisation and urbanisation led to the emission of CO₂ in larger amounts into the atmosphere. Excessive concentration of CO₂ in the atmosphere traps heat radiation from the Earth within and does not allow it to escape into outer space. This leads to an increase in the global temperature, called global warming.

Global warming causes a rise in temperature on Earth.
Rise in temperature of the Earth causes polar ice caps to melt, and this water causes a rise in sea level as well.
On the other hand, increased Earth temperature causes water to expand, leading to a rise in water levels.
An increase in sea levels causes flooding in the coastal areas and damages their biodiversity.
Global warming caused a change in rainfall patterns, leading to early maturation of crops, reduced grain size and lower yield.

iv. Biodiversity loss

Dwindling forests, the natural habitat of various plants and animals, have vanished, and so have vanished forever many valuable trees and animals. Some are on the verge of extinction, while others are on the borderline.