Get summaries, questions, answers, solutions, notes, extras, PDF and guides for Chapter 13 Our Environment: Class 10 Science textbook, which is part of the syllabus for students studying under SEBA (Assam Board), NBSE (Nagaland Board), TBSE (Tripura Board), CBSE (Central Board), MBOSE (Meghalaya Board), BSEM (Manipur Board), WBBSE (West Bengal Board), and all other boards following the NCERT books. These solutions, however, should only be treated as references and can be modified/changed.
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Summary
Our environment is everything that surrounds us. It includes living things like plants, animals, and tiny microorganisms. It also includes non-living things such as air, water, soil, and sunlight. All these parts interact in an area, forming an ecosystem. A forest is a natural ecosystem, while a garden is human-made. In any ecosystem, all parts are connected and depend on each other.
Living things in an ecosystem get energy in different ways. Plants are producers because they make their own food using sunlight. Animals are consumers because they eat other organisms. Herbivores eat plants. Carnivores eat other animals. Omnivores eat both. When plants and animals die, decomposers like bacteria and fungi break them down. This returns nutrients to the soil, which plants use to grow. This cycle is vital for a healthy ecosystem.
Energy moves through an ecosystem in a food chain, showing who eats whom. For example, grass is a producer. A grasshopper eats the grass, a frog eats the grasshopper, and a snake might eat the frog. Each step is a trophic level. When energy moves from one level to the next, only about 10% is passed on. The rest is used or lost as heat. This energy loss means food chains are usually short, with few levels. Many interconnected food chains form a food web.
Human activities can introduce harmful chemicals, like pesticides, into the environment. These chemicals can enter food chains. They are not easily broken down and build up in organisms at each higher trophic level. This is called biological magnification. Animals at the top of the food chain, including humans, can end up with the highest amount of these harmful substances.
Our actions also affect the Earth’s atmosphere. The ozone layer, high in the atmosphere, shields us from the sun’s harmful ultraviolet (UV) radiation. Certain man-made chemicals, like CFCs once used in refrigerators, have damaged this protective layer. Global efforts are reducing these chemicals to help the ozone layer heal.
We generate a lot of waste. Some waste, like fruit peels, is biodegradable. Decomposers can break it down naturally. Other materials, like plastics, are non-biodegradable. They do not break down easily and can pollute the environment for a long time, harming wildlife. It is important to manage waste by reducing, reusing, and recycling to protect our environment.
Textbook solutions
Intext Questions and Answers I
1. What are trophic levels? Give an example of a food chain and state the different trophic levels in it.
Answer: Each step or level of the food chain forms a trophic level. An example of a food chain, stating the different trophic levels, is as follows:
- The autotrophs or the producers are at the first trophic level.
- The herbivores or the primary consumers come at the second trophic level.
- Small carnivores or the secondary consumers are at the third trophic level.
- Larger carnivores or the tertiary consumers form the fourth trophic level.
2. What is the role of decomposers in the ecosystem?
Answer: The role of decomposers in the ecosystem is that microorganisms, comprising bacteria and fungi, break down the dead remains and waste products of organisms. These microorganisms are the decomposers as they break down the complex organic substances into simple inorganic substances that go into the soil and are used up once more by the plants. This action ensures the natural replenishment of the soil.
Intext Questions and Answers II
1. Why are some substances biodegradable and some non-biodegradable?
Answer: Some substances are biodegradable because they are broken down by biological processes. Enzymes are specific in their action, and specific enzymes are needed for the break-down of a particular substance. Substances that are not broken down in this manner are said to be non-biodegradable. Because of this specificity of enzymes, many human-made materials like plastics will not be broken down by the action of bacteria or other saprophytes; these materials will be acted upon by physical processes like heat and pressure, but under the ambient conditions found in our environment, these persist for a long time.
2. Give any two ways in which biodegradable substances would affect the environment.
Answer: Two ways in which biodegradable substances would affect the environment are:
(i) When acted upon by microorganisms like bacteria and fungi, biodegradable substances such as dead remains and waste products of organisms are broken down into simple inorganic substances that go into the soil and are used up once more by the plants, contributing to the natural replenishment of the soil.
(ii) The breakdown of biodegradable substances by decomposers helps in clearing dead remains and waste products of organisms, preventing their accumulation in the environment.
3. Give any two ways in which non-biodegradable substances would affect the environment.
Answer: Two ways in which non-biodegradable substances would affect the environment are:
(i) These substances may be inert and simply persist in the environment for a long time.
(ii) These substances may harm the various members of the eco-system.
Intext Questions and Answers III
1. What is ozone and how does it affect any ecosystem?
Answer: Ozone (O3) is a molecule formed by three atoms of oxygen. While ozone is a deadly poison, at the higher levels of the atmosphere, it performs an essential function. It shields the surface of the earth from ultraviolet (UV) radiation from the Sun. This radiation is highly damaging to organisms, for example, it is known to cause skin cancer in human beings. Since the ozone layer protects against the ultraviolet radiation from the Sun, its presence is crucial for ecosystems, and damage to this layer could damage the environment.
2. How can you help in reducing the problem of waste disposal? Give any two methods.
Answer: You can help in reducing the problem of waste disposal through methods such as:
(i) Carrying cloth-bags to put purchases in while shopping. This is an environment-friendly practice that helps reduce waste, particularly plastic waste.
(ii) Reducing the generation of waste material by changing attitudes towards the use of disposable items. Improvements in life-style have resulted in greater amounts of waste material generation, and changes in attitude have a role to play, as more and more things we use are becoming disposable, contributing to the problem.
Exercise Questions and Answers
1. Which of the following groups contain only biodegradable items?
(a) Grass, flowers and leather
(b) Grass, wood and plastic
(c) Fruit-peels, cake and lime-juice
(d) Cake, wood and grass
Answer: Substances that are broken down by biological processes are said to be biodegradable. Many human-made materials like plastics will not be broken down by the action of bacteria or other saprophytes. Therefore, the groups from the options provided that contain only biodegradable items are:
(a) Grass, flowers and leather
(c) Fruit-peels, cake and lime-juice
(d) Cake, wood and grass
Group (b) is not included because plastic is a non-biodegradable material.
2. Which of the following constitute a food-chain?
(a) Grass, wheat and mango
(b) Grass, goat and human
Answer: A food chain is a series of organisms in which each organism is eaten by the next, showing the flow of energy from producers to consumers.
Option (a) lists grass, wheat, and mango, which are all producers and do not show a sequence of one organism eating another.
Option (b) Grass, goat and human, constitutes a food-chain because grass (a producer) is eaten by a goat (a primary consumer), which in turn is eaten by a human (a secondary consumer). This represents a sequence of organisms feeding on one another. Thus, the group that constitutes a food-chain is (b) Grass, goat and human.
3. Which of the following are environment-friendly practices?
(a) Carrying cloth-bags to put purchases in while shopping
(b) Switching off unnecessary lights and fans
(c) Walking to school instead of getting your mother to drop you on her scooter
(d) All of the above
Answer: (d) All of the above
4. What will happen if we kill all the organisms in one trophic level?
Answer: If all the organisms in one trophic level are killed, it will disrupt the entire food chain. The organisms in the next higher level will lose their food source and may die, while those in the level below may increase in number due to the absence of predators or consumers. This imbalance can lead to the collapse of the ecosystem, affecting energy flow and nutrient cycling.
5. Will the impact of removing all the organisms in a trophic level be different for different trophic levels? Can the organisms of any trophic level be removed without causing any damage to the ecosystem?
Answer: Yes, the impact of removing a trophic level differs depending on which level is removed, but no level can be eliminated without harming the ecosystem. If producers are removed, energy flow stops and all other organisms eventually die. Removing herbivores leads to overgrowth of plants and starvation of carnivores. If carnivores are removed, herbivore populations may grow unchecked and damage vegetation. Without decomposers, waste accumulates and nutrients are not recycled. Every trophic level is essential for maintaining balance in the ecosystem.
6. What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?
Answer: Biological magnification is the phenomenon where harmful chemicals that are not degradable get accumulated progressively at each trophic level in a food chain. As human beings occupy the top level in any food chain, the maximum concentration of these chemicals gets accumulated in their bodies.
Yes, the levels of this magnification will be different at different levels of the ecosystem because these chemicals get accumulated progressively at each trophic level, with the maximum concentration of these chemicals accumulating in organisms at the top level.
7. What are the problems caused by the non-biodegradable wastes that we generate?
Answer: The problems caused by the non-biodegradable wastes that we generate are that these substances may be inert and simply persist in the environment for a long time or may harm the various members of the eco-system. The disposal of the waste we generate is causing serious environmental problems.
8. If all the waste we generate is biodegradable, will this have no impact on the environment?
Answer: Even biodegradable waste can affect the environment if not properly managed. Biodegradable substances are broken down by biological processes, but large quantities can overwhelm natural systems. For example, excessive biodegradable waste can lead to the depletion of oxygen in water bodies during decomposition, harming aquatic life. It can also cause bad odours and attract pests. So, even though biodegradable waste eventually breaks down, improper disposal can still damage the environment.
9. Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?
Answer: Damage to the ozone layer is a cause for concern because ozone at the higher levels of the atmosphere performs an essential function: it shields the surface of the earth from ultraviolet (UV) radiation from the Sun. This radiation is highly damaging to organisms; for example, it is known to cause skin cancer in human beings. Since the ozone layer protects against ultraviolet radiation from the Sun, damage to it could damage the environment.
The steps being taken to limit this damage include an agreement forged by the United Nations Environment Programme (UNEP) in 1987 to freeze CFC production at 1986 levels. It is now mandatory for all manufacturing companies to make CFC-free refrigerators throughout the world.
Extras
Additional MCQs (Knowledge Based)
1. What are the non-living constituents, such as temperature, rainfall, and soil, in an environment called?
A. Biotic components
B. Abiotic components
C. Ecological components
D. Physical components
Answer: B. Abiotic components
35. The process by which UV radiation splits molecular oxygen (O₂) into free oxygen atoms (O), which then combine with other O₂ molecules to form ozone (O₃), occurs in the:
A. Lower atmosphere
B. Higher levels of the atmosphere
C. Earth’s core
D. Hydrosphere
Answer: B. Higher levels of the atmosphere
Additional MCQs (Competency Based)
1. Assertion (A): The ozone layer in the upper atmosphere is crucial for life on Earth.
Reason (R): Ozone (O₃) is formed from oxygen (O₂) by the action of UV radiation and it absorbs harmful UV rays from the sun.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (a) Both A and R are true and R is the correct explanation of A.
25. Assertion (A): All human-made materials, like plastics, eventually biodegrade naturally in the environment.
Reason (R): Physical processes like heat and pressure can act upon these materials, but under ambient environmental conditions, many persist for a long time.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (d) A is false but R is true.
Additional Questions and Answers
1. What is an ecosystem?
Answer: All the interacting organisms in an area together with the non-living constituents of the environment form an ecosystem.
36. Why are some substances biodegradable and others non-biodegradable?
Answer: Substances that are broken down by biological processes are said to be biodegradable. This breakdown is facilitated by enzymes, which are specific in their action; specific enzymes are needed for the break-down of a particular substance. Substances that are not broken down in this manner are said to be non-biodegradable. Many human-made materials like plastics will not be broken down by the action of bacteria or other saprophytes because the necessary enzymes to break them down are not present or effective.
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