Chapter 7 Human Modified Ecosystems

NIOS Class 12 Environmental Science Chapter 7

INTEXT QUESTIONS 7.1

1. Name two human-modified ecosystems.

Ans: Agro ecosystem, plantation forest, urban ecosystem, rural ecosystem, aquaculture (any two).

2. Give two characteristics of human-modified ecosystems.

Ans: (i) Low species diversity, unsustainable and needs inputs of human beings in the form of energy, fertilizers and irrigation and human care to survive, etc. They are highly susceptible to rapidly spreading diseases. (any two)

INTEXT QUESTIONS 7.2

1. Name any gas that contributes to global warming.

Ans: CO₂ , Methane

2. Write the full form of MIC and AIDS.

Ans: 

• Methyl Isocyanate (MIC),
• Acquired Immune Deficiency Syndrome (AIDS)

3. What causes soil erosion?

Ans: Overgrazing, poor irrigation, over-cultivation, deforestation

INTEXT QUESTIONS 7.3

1. Name five types of plantations.

Ans: Acacia, Lucaenas (Subabus) Prosopis, Sesbannia, Caruarin Jatropa, Monnga and neem (any)

2. Which types of trees are preferred for plantation forests?

Ans: Fast-growing tree species of economic value are preferred.

3. List any two common features of agro ecosystems and plantation forests.

Ans: (Any two)

• (1) Highly simplified.
• (2) Species diversity is very low.
• (3) Food chains are simple and small.
• (4) Depend on human support for survival; need for fossil fuel energy, fertilizers, irrigation, etc.
• (5) Attract a large number of weeds.
• (6) More susceptible to epidemic diseases.
• (7) Suffer from soil erosion.
• (8) Highly unstable.

4. Which plant would you recommend to raise a plantation for obtaining bio-diesel?

Ans: Jatropa curcare

INTEXT QUESTIONS 7.4

1. List any two advantages of rural ecosystems.

Ans: A Clean and natural environment is available, and people have a simple lifestyle.

2. Why do people tend to migrate from villages to cities?

Ans: For better employment, health and education opportunities and for better living amenities.

3. List any two disadvantages of the urban ecosystem.

Ans: Disadvantages of urban ecosystems

• (1) Urban areas consume 75% of the earth’s resources and produce 75% of the waste.
• (2) Urban areas are highly polluted since a growing number of vehicles and industries emit large quantities of pollutants.
• (3) Suffer from the problem of noise pollution caused by industries and transport.
• (4) Urban ecosystems suffer from a serious shortage of water availability.
• (5) High crime rate, unrest and unemployment.
• (6) Increasing population density in cities of the world compels some people to live in slums, e.g. in Mumbai, 3 million people live in slum pavement and squalid settlements which lack basic civic facilities like safe drinking water, waste disposal, health care, etc.

4. Why do you like to go to a hill station during vacations?

Ans: Highly congested and highly polluted (high levels of water, air and noise pollution), shortage of living space leading to slum development. (any two)

INTEXT QUESTIONS 7.5

1. What is the difference between fisheries and aquaculture?

Ans: Aquaculture is the artificial cultivation of aquatic plants and animals, whereas fisheries refers to the capture of fish and other aquatic organisms from seas and other freshwater bodies.

2. Name any two freshwater fishes that are being grown in pond culture.

Ans: Eel, Tilapia, Rohu, Catla, Catfish (any two)

3. Name the fish that is commonly known as aquatic chicken.

Ans: Tilapia

4. In what way do aquacultures affect the mangrove forests?

Ans: Destroys mangrove forests and coastal vegetation.

INTEXT QUESTIONS 7.6

1. List any two advantages of dams.

Ans: Advantages of dams

• (1) Water is released from dams to generate electricity.
• (2) Reduce the use of coal and thereby reduce CO₂ emissions.
• (3) Reduce downstream flooding.
• (4) Reduce river silting below the dam.
• (5) Supply irrigation water for croplands.

2. Name the harmful gas that is released during the burning of plastics.

Ans: Polychlorinated biphenyles (PCB)

3. How does the introduction of an alien species affect the indigenous species?

Ans: Reduced population of natural species.

4. What effect does overgrazing by livestock have on grassland?

Ans: It results in soil erosion and future loss of productivity.

TERMINAL EXERCISE

1. Define human-modified ecosystems.

Ans: Human-modified ecosystems may or may not depend on solar energy, e.g. in an industry, energy is provided in the form of fossil fuel or electricity or both. 

2. Give the differences between natural and human-modified ecosystems.

Ans: 

• The natural ecosystem depends on solar energy for photosynthesis by the green plants. They grow naturally through ecological succession. It has a larger species diversity and is complicated. Prevents soil erosion. Natural ecosystems are stable. 
• Human-modified ecosystems are created by modifying natural ecosystems due to increasing population and human needs. These are simplified and have low species diversity. Suffer from soil erosion. These are highly unstable. 

3. Why do the following conditions lead to stress in a population

a) over-crowding b) over-harvesting c) human intervention

Ans: 

• a) Overcrowding increases the incidence of epidemic diseases such as AIDS, Hepatitis, TB, swine flu, bird flu, etc. 
• b) Over-harvesting: Over-harvesting of edible fish reduces their reproductive rate, and their population starts reducing in number and may become completely extinct after some time. 
• c) Human intervention: Industries which are being made by man to make better use of the primary raw materials produced under natural environmental conditions cause environmental degradation through pollution, land destruction, etc. 

4. Give characteristics of human-modified ecosystems

Ans: Characteristics of human-modified ecosystems

• (1) Highly simplified.
• (2) Species diversity is very low.
• (3) Food chains are simple and small.
• (4) Depend on human (anthropogenic) support for survival; need for fossil fuel energy, fertilizers, irrigation, etc.
• (5) Attract a large number of weeds.
• (6) More susceptible to epidemic diseases.
• (7) Suffer from soil erosion.
• (8) Highly unstable.

5. Write short notes on the following

i) Human population explosion

ii) Industrial pollution

iii) Human health and disease

Ans: 

i) Human population explosion: 

The human population is rapidly increasing in India; consequently, our demand for natural resources is also increasing. The industrialization in India is also increasing at a rapid pace.

The increasing population and growing industrialization are severely affecting the environment in various ways. Some important impacts are briefly described below:

• Pollution caused by industries, 
• Global warming
• An increase in the population is leading to an increase in incidences of epidemic diseases. 
• Over-exploitation of natural resources: 
• Deforestation, over-grazing, intensive cultivation, over-irrigation, etc., result in the loss of topsoil and fertility of the land. Prolonged degradation of the land leads to desertification.
• Water bodies are being increasingly abused with the disposal of all liquid effluents and all other kinds of waste.

ii) Industrial pollution

Pollution refers to the addition of any substance in the environment that has a direct or indirect adverse effect on humans (Lesson 10). The consequences of pollution are many. Industrial accidents that have taken away several lives, e.g. in Bhopal, accidental leakage of MIC (methyl isocyanate) gas from Union Carbide Company killed more than 2000 people within 12 to 72 hours. Many people lost their eyesight and suffered from serious medical complications.

iii) Human health and disease

An increase in the population is leading to increasing incidences of epidemic diseases such as AIDS (Acquired Immuno Deficiency Syndrome), Hepatitis, T.B. (tuberculosis), bird flu, swine flu, Syphilis, Gonorrhoea, cancer and many more diseases. These diseases are caused by environmental pollution or overcrowding.

6. What are the advantages of tree plantation?

Ans: 

• (1) Tree plantations are raised for fruits, oil, rubber, coffee, timber, firewood, pulp wood for making rayon and paper industries.
• (2) Trees are also planted to serve as wind breaks or shelter belts.
• (3) Tree plantations are also raised for controlling soil erosion and for increasing soil fertility.
• (4) Tree plantation provides job opportunities and generates income.

7. List some impacts that are leading to environmental degradation.

Ans: 

• Pollution: All these industries discharge several waste gases and particulate pollutants into the atmosphere. Some of them are as follows:-
  • (i) Gaseous pollutants: Oxides of carbon, nitrogen and sulphur.
  • (ii) Particulate matter: Fine metal dust, fly ash, soot, cotton dust and radioactive substances.
  • (iii) Burning of plastics: Emit poly chlorinated biphenyles (PCBs), which are harmful to lungs and vision.
  • (iv) Accidental release of some poisonous gases 
  • (v) Secondary air pollutants formed from complex reactions between primary pollutants, such as smog and acid rain, which are harmful to all living organisms, buildings and monuments.
• Land use and habitat destruction: Wildlife habitats have been degraded, forests have been cleared, and have also created noise and thermal pollution. 
• Human health: Use of various types of chemicals today has serious health implications.
• Increased sensitivity to diseases: Cultivated species of plants, fish and other domesticated animals have become increasingly sensitive to pests and diseases.
• Genetic resistance: An increased use of insecticides, pesticides and antibiotics has sped up directional natural selection and caused genetic resistance in the pathogens.
• Effect on native populations: The Introduction of new alien species or non-native species reduces the population growth of native species.
• Stress due to over-harvesting: Overgrazing by livestock results in soil erosion and loss of productivity. Effect on nutrient recycling: Use of fertilizers in agricultural fields interferes with the natural biogeochemical cycles.

Additional Study Materials

• Chapter 1 Origin of Earth and Evolution of the Environment
• Chapter 2 Environment and Human Society
• Chapter 3 Degradation of Natural Environment
• Chapter 4 Principles of Ecology
• Chapter 5 Ecosystem
• Chapter 6 Natural Ecosystem