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Our Environment - Class 10 Science Textbook Solution


Our Environment 
Our Environment Class 10 Extra s with Answers Science Chapter 15
1. Why is it necessary to conserve our environment?
It is necessary to conserve our environment in order to maintain ecological balance.
2. What is a biodegradable substance?
Biodegradable substances are the substances that are broken down by biological processes.
3.Name any two biodegradable and two non-biodegradable pollutants.
Biodegradable: domestic sewage and wood, Non-biodegradable: Plastic and DDT
4. We often use the word environment. What does it mean?
The environment is the physical, chemical and biological conditions of the region.
5. Which two of the following are biodegradable?
Tomato leaves, aluminum wire, synthetic fibre and wool
Tomato leaves and wood.
6. Which of the following are non-biodegradable?
Wool, glass, silver foil and leather
Glass and silver foil.
7. What is the function of ozone in the upper atmosphere?
Ozone shields the surface of the earth from the ultraviolet rays of the Sun.
8.Why should biodegradable and non-biodegradable wastes be discarded in two separate  dustbins?
Biodegradable and non-biodegradable wastes should be discarded in two separate dustbins so that the time and energy required in segregation may be saved and waste may be disposed off quickly.
9. What are the two main components of our environment?
The two components are biotic or living and abiotic or non-living component.
10. List two abiotic components of an biosphere.
Producers, consumers and decomposers are the biotic components of a biosphere. (Any two)
11. Name any two abiotic components of an environment.
Abiotic components of an environment include soil and water.
12. Name two decomposers.
Bacteria and fungi.
13. Write an aquatic food chain.
A food chain that operates in a water body, such as a pond, a lake or an ocean, is known as an aquatic food chain.
14. What will be the amount of energy available to the orrganisms of the 2nd trophic level of a food chain, if the energy available at the first trophic level is 10,000 joules?
On applying the 10% law to the food chain, the organisms of the 2nd trophic level of the
food chain will have 10100 × 10,000 = 1,000 joules of energy.
15. In the following food chain, plants provide 500 J of energy to rats. How much energy will be available to hawks from snakes?
Plants → Rats → Snakes → Hawks
On applying the 10% law to the food chain.
Energy available to snakes from rats = 10% of 500
= 10100 × 500 = 50 J
So, energy available to hawks from snakes = 10% of 50 J
= 10100 × 50 = 5J
16. Draw a food chain with four trophic levels.
Plants → Rats Snakes → Hawks
17. The first trophic level in a food chain is always a green plant. Why?
Why do producers always occupy the first trophic level on every food chain?
The first trophic level is always a green plant because only plants can utilise the radicant energy of the sun and transform it to chemical form during photosynthesis.
18. Which of the following are always at the second trophic level of food chains?
Carnivores, Autotrophs, Herbivores
Herbivores are always at the second trophic level of food chains.
19. The following organisms form a food chain. Which of these will have the highest concentration of non-biodegradable chemicals? Name the phenomenon associated with it.
Insects, Hawk, Grass, Snake, Frog
Hawk will have the highest concentration of non-biodegradable chemicals. The phenomenon associated is biomagnification.
20. State the essential function performed by ozone at the higher levels of the atmosphere.
It shields the surface of the earth from ultraviolet (UV) radiation from the sun.
21. Write the full name of the group of compounds mainly responsible for the depletion of ozone layer.
22. What is an ecosystem?
A unit of biosphere in which biotic and abiotic components interact with each other is an ecosystem.
23. Why is forest considered a natural ecosystem?
A forest is a self-sustaining system, so it is considered as a natural ecosystem.
24. List two examples of natural ecosystem.
Forests, ponds, lakes are examples of natural ecosystem.
25. Name any two man-made ecosystem.
Crop fields, Gardens, Aquarium, Parks.
26. Why are green plants called producers?
Green plants are called producers because they prepare food by photosynthesis using solar energy.
27. List four common waste disposal methods.
Compost, recycling of wastes, landfills and incineration.
28. What is incineration?
Incineration means ‘reducing to ashes’. The burning of substances at high temperature to form ash is called incination.
29. Why is improper disposal of waste a curse to environment?
: Wastes pollute our environment, air, soil and water, and cause harmful effects on all. living organisms.
30. The depletion of ozone layer is a cause of concern. Why?
Ozone layer is very important for the existence of life on earth because it prevents harmful ultraviolet (UV) radiations coming from the Sun to reach the earth.
31. What destructive effect do chlorofluorocarbons bring about in the atmosphere?
CFCs depleter ozone from ozone shield, resulting in increasing the passage of harmful ultraviolet radiation to the earth.
32. Write one negative effect, on the envrionment, of as fluent lifestyle of few persons of a society.
: Affluent lifestyle results in:
•    generation of excessive waste materials.
•    Excessive use of natural resoruces like coal and petroleum which causes pollution.
•    Use of excessive non-biodegradable material in packaging.

Our Environment Extra s Short Answer Type
1 Why are crop fields known as artificial ecosystem?
Crop fields are man-made and some biotic and abiotic components are manipulated by humAnswer: Therefore, they are known as artificial ecosystems.
2. Suggest one word for each of the following statements/definitions:
1.    The physical and biological world where we live in.
2.    Each level of food chain where transfer of energy takes place.
3.    The physical factors like temperature, rainfall, wind and soil of an ecosystem.
4.    Organisms which depend on the producers either directly or indirectly for food.

1.    Envrionment/biosphere
2.    Trophic level
3.    Abiotic factors
4.    Consumers/heterotrophs
3. What are decomposers? What will be the consequence of their absence in an ecosystem?
Decomposers break down the complex organic substances of garbage, dead animals and plants into simpler inorganic substances that go into the soil and are used up again by the plants in the absence of decomposers recycling of material in the biosphere will not take place.
4. Give two examples of decomposers. State their important role in nature.
Bacteria and fungi are decomposers because bacteria and fungi break down the dead and decaying organic matter into simpler substances and provide the nutrients back to the soil.
Importance of decomposers in nature are:
•    They act as natural scavengers.
•    They help in recycling of nutrients.
5. Consider the food chain: Grass + Deer → Lion. What will happen if lions are removed from the above food chain?
Removal of lions from the above food chain will increase the number of deer to such an extent that they will eat up the whole grass. The density of producer like grass will be very much reduced and this will turn the area into a desert.
6. Which of the following belongs to the same trophic level?
Grass, Hawk, Rabbit, Frog, Deer
Grass is producer, hawk and frog are carnivores (top and lower), rabbit and deer are herbivores. Since rabbit and deer are both herbivores, they belong to the same trophic level.
7. Write the common food chain of a pond ecosystem.
Phytoplanktons and aquatic plants small aquatic animal larvae and insects fishes->birds.
8. In a lake contaminated with pesticides, which one of the following organism living in the lake will contain the maximum amount of pesticide?
Small fish, zooplankton, big fish, phytoplankton.
The concentration of pesticide will increase with the rise of trophic level in the food chain.
Phytoplankton Zooplankton → Small fish → Big fish (maximum pesticide)
Therefore, big fishes will have maximum amount of pesticides.
9. What is the percentage of solar energy trapped and utilised?
1% in terrestrial habitats and 0.2% in aquatic ecosystems is the percentage solar energy trapped and utilised.
10. Why does a food chain consist of only three to four steps?
On an average, only 10% of the food available to a trophic level is transferred to the next trophic level. Since, the amount of available energy keeps on becoming less as we move to higher trophic levels, so very little usable energy remains after four trophic levels. That is why a food chain consists of only three to four steps.
11. With the help of an example explain how indiscriminate use of pesticides may result in the degradation of the environment.
Indiscriminate use of pesticides may result in the degradation of the environment. For example, DDT is an organic pesticide which is used to kill pests in crop fields. When it is used in large quantity it can be passed along the food chain from crops to man or other animals and birds and can harm them.
12. State any two practices which can help in the protection of our environment. 
Answer: Two practices which can help in the protection of our environment are:
•    Disposal of the waste after its separation as biodegradable and non-biodegradable material.
•    Judicious use of unleaded petrol and alternate sources of energy.
13. What are the by-products of fertiliser industries? How do they affect the environment?
The harmful by-products are gases such as SO, and NO. They cause extensive air pollution and are responsible for acid rain.
14. The number of malarial patients in a village increased tremendously when large number of frogs were exported from the village. What could be the cause for this?
The food chain in the given situation will be:
Phytoplankton → Zooplankton → Mosquito larva → Frogs In the absence of frogs (as they were exported), more mosquito larvae survived giving rise to large number of mosquitoes. The large number of mosquitoes caused increased incidences of malaria.
15. Mention three harmful effects of using polythene bags on the environment. Suggest an effective alternative to these bags.
Harmful effects of using polythene bags are:
•    Increases soil temperature or adversely effect agricultural products.
•    Land and animals die after consumption of these bags.
•    It causes clossing of drains and may even cause flood like situation. Alternatives are the use of jute bags, paper bags, cloth bags.
16. Why are certain forests considered “biodiversity hot spots”? Suggest any two ways in which an individual can contribute effectively to the management of forests and wildlife.
Certain forest are considered as “biodiversity hot spots” because in a forest, various species are available to contribute to the management of forests and wildlife are:
1.    Avoiding cutting of trees and killing of animals.
2.    Educating people about the importance of forests and wildlife in sustainance of life on the earth.
17. Suggest any two ways by which the balance between the environment and industrial development is maintained so as to help undisturbed survival of the organisms on the Earth.

1.    Judicious use of forest resources for industrial development.
2.    Waste water generated by industries should be recycled.
3.    Alternative resources to conserve natural resources. (Any two)
18. Differentiate between biodegradable and non-biodegradable substances with the help of one example each. List two changes in habit that people must adopt to dispose non-biodegradable waste, for saving the environment.
People should adopt following changes in habit:
1.    Dispose household waste, chemical waste and hospital waste in a landfill.
2.    Broken plastic articles such as buckets, bowls, cups, plates, etc., should be sent to plastic processing factories.
19. Give reason to justify the following:
(i) The existence of decomposers is essential in a biosphere.
(ii) Flow of energy in a food chain is unidirectional.

(i) The existence of decomposers is essential in a biosphere because they breakdown complex organic substances into simple inorganic substances that can be absorbed by the plants. Thus, decomposers:
replenish the soil naturally.
helps in removing the biodegradable waste.
(ii) In a food chain the energy moves progressively through the various trophic levels, it is no longer available to the previous level (i.e., autotrophs) and the energy captured by the autotrophs does not go back to the solar input.
Hence, the flow of energy is unidirectional.
20. What do you mean by biotic and abiotic degradation? Write the effects of it on environment.
Degradation: The process of degeneration of substances into their simpler elemen tary forms is called degradation. It is of two types.
(a) Biotic degradation: The process of degradation of substances by the action of decom posing bacteria fungi etc, is called biotic degradation:
(b) Abiotic degradation: The Process of deterioration of substances by the action of physical, chemical or mechanical process is called abiotic degradation.
Effects of Biotic Degradation:
•    It leads to decomposition of dead organisms.
•    It enables to recycling of nutrients between biotic and abiotic components of ecosystem.
Effects of Abiotic Degradation:
•    It leads to the formation of soil.
•    It leads to formation of fossils, Petroleum etc.
21. What is an ecosystem? List its two main components. We do not clean natural ponds or lakes but an aquarium needs to be cleaned regularly. Why is it so? Explain.
An ecosystem is defined as a dynamic system of biotic and abiotic components and there is a continuous flow of energy between the different components.
Its two main components are:
•    Biotic component/living organisms.
•    Abiotic component/physical factors.
An aquarium needs to be cleaned regularly because it is an artificial and incomplete ecosystem in which natural decomposers are absent and the water is stagnant. Thus, water do not clean itself in an aquarium.
22. “Energy flow in food chains is always unidirectional.” Justify this statement. Explain how the pesticides enter a food chain and subsequently get into our body.
Indicate the flow of energy is an ecosystem. Why is it unidirectional? Justify.
In a food chain the energy moves progressively through the various trophic levels and is no longer available to the organisms of the previous trophic level. The energy captured by the autotrophs does not revert back to the solar input. Thus, energy flow in food chains are said to be unidirectional.
Pesticides used for crop protection when washed away go down into the soil. These pesticides are absorbed by plants which are the producers. On consumption of these plants, the pesticides enter our food chain and being non-biodegrable, these chemicals get accumulated progressively and enter our body.
23. Give two differences between food chain and food web.

24. Why does vegetation habit help us in getting more energy? In terms of energy who is at an advantageous position (vegetarian or a non-vegetarian)? Why?
We know that, vegetarians obtain food directly from plants while non-vegetarians get the food from animals. Animals (herbivores) contain 10% of food energy as compared to plants to a vegetarian will provide only 100 J of food energy to a non-vegetarian. Hence, a vegetarian will be at an advantageous position.
25. Calculate the amount of energy available to tiger in the following food chain if plants have 30,000 J of energy available from the Sun:
Plant → Deer → Tiger
Plants can trap only 1% of the Sun’s energy falling on them. Now, 1% of 30,000 J is 300.
which is the energy available to plants.
The plants are eaten up by deer. According to 10% of 300 J, i.e., 300 J of energy will be available to deer as food.
The deer will transfer 10% of its 30 J energy to the tiger. Thus, the food energy available to the tiger will be 10% J which is 3 J.
26. Give three characteristics of food chain.

1.    A food chain is always straight and proceeds in a progressive straight line.
2.    A food chain helps in understanding the food relationship and interactions among various organisms in an ecosystem.
3.    It also helps to understand the movement of toxic substances in an ecosystem and the problem of their biological magnification.
27. Describe any four modes of disposal of waste.

1.    Disposing of biodegradable wastes in biogas plants so that it can help in the preparation of biogas and manure.
2.    Solid wastes should be buried in urban areas as landfills.
3.    Some solid wastes (plastic, paper and metals) should be recycled.
4.    Large amount of waste must be burnt at high temperature (incineration).
28. What are the advantages of cloth bags over plastic bags during shopping?
Cloth bags:
1.    are capable of carrying more items.
2.    are made of biodegrable materials.
3.    do not pollute our environment.
4.    can be reused.
29. How is ozone formed in the upper atmosphere? What causes its damage?

O + O2 → O3 (ozone)
Certain harmful chemicals such as chlorofluorocarbons (CFCs), are released into the air. These accumulate in the upper atmosphere and react with ozone resulting in reduction of the ozone layer by forming a hole. Thus, ozone layer becomes thinner and gets depleted allowing more ultraviolet rays to pass through the earth’s atmosphere. These radiations are highly damaging to organisms and cause skin cancer, damage to eyes including increased incidence of cataract and damage to immune system of human beings and other animals.

Our Environment Extra s Long Answer Type
1. Suggest any five activities in daily life which are eco-friendly.

1.    Separation of biodegrable and non-biodegradable substances
2.    Gardening
3.    Use of gunny bags/paper bags in place of polythene/plastic bags
4.    Use of compost and vermicompost in place of fertilisers
5.    Harvesting rainwater.
2. Name the wastes which are generated in your house daily. What measures would you take for their disposal?

1.    Kitchen wastes
2.    Paper wastes like newspapers, bags, envelops
3.    Plastic bags
4.    Vegetable/fruit peels/rind
Measures for disposal:
•    Segregation of biodegradable and non-biodegradable wastes.
•    Safe disposal of plastic bags.
•    Vegetable/fruit peels can be placed near trees/plants, which on decomposition will enrich the soil with nutrients.
•    Give paper wastes for recyling.
•    Prepare a compost pit for kitchen wastes.
3. Describe the food web with the example of a land ecosystem.
Food Web: It is the interconnection of different food chains, which correlate at various trophic levels operating in an ecosystem. Each organism is generally eaten by two or more other kinds of organisms. They in turn are eaten by several other organisms. So instead of a straight line the relationship is shown as a series of pranching lens, hence, creating a food web.

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