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NCERT Class 10 Science Our Environment: Exercise Solutions

Step-by-step working for every question of End-of-chapter exercises in NCERT's Class 10 Science book, chapter “Our Environment”, written by Shishya. Each question is in our own short words; open the NCERT chapter for the exact wording and figures.

1. Exercises Q1

   Which 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?

   1. Biodegradable items are those that can be broken down by microorganisms into simpler substances.
   2. Grass, flowers, fruit peels, cake, lime juice, wood, and grass are all natural organic materials that decompose easily.
   3. Leather comes from animal skin; microorganisms break it down (slowly), so all three items in (a) are biodegradable.
   4. Plastic is a synthetic material that does not decompose naturally, so option (b) is incorrect.
   5. Option (c) contains fruit peels, cake, and lime juice, all of which are biodegradable.
   6. Option (d) contains cake, wood, and grass, all of which are biodegradable.

   Answer: (a), (c) and (d): grass, flowers and leather; fruit peels, cake and lime juice; cake, wood and grass

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2. Exercises Q2

   Which is a food chain: (a) grass, wheat, mango (b) grass, goat, human (c) goat, cow, elephant (d) grass, fish, goat?

   1. A food chain shows the transfer of energy from one organism to another through feeding relationships.
   2. Option (a) lists three producers (plants) that do not eat each other, so it is not a food chain.
   3. Option (c) lists three herbivores that do not eat each other, so it is not a food chain.
   4. Option (d) has grass eaten by fish, but fish are not typically eaten by goats, breaking the logical flow.
   5. Option (b) shows grass being eaten by a goat, and the goat being eaten by a human, forming a valid trophic sequence.

   Answer: (b) grass, goat, human

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3. Exercises Q3

   Which are environment-friendly: (a) carrying cloth bags when shopping (b) switching off unneeded lights and fans (c) walking to school instead of being dropped on a scooter (d) all of these?

   1. Carrying cloth bags reduces the use of single-use plastic, which helps prevent pollution.
   2. Switching off unneeded lights and fans saves electrical energy and reduces the load on power plants.
   3. Walking to school instead of using a scooter cuts down on fuel consumption and air pollution.
   4. Since all three actions help protect the environment, the correct choice is all of these.

   Answer: (d) all of these

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4. Exercises Q4

   What happens if all organisms in one trophic level are killed?

   1. If all organisms in a specific trophic level are killed, the energy flow in the ecosystem is disrupted.
   2. The trophic level immediately above it will face a severe shortage of food and may start dying due to starvation.
   3. The trophic level immediately below it will have no predators to control their population, leading to a rapid increase in their numbers.
   4. This imbalance causes a chain reaction that affects the stability and health of the entire ecosystem.

   Answer: The ecosystem becomes unstable as the food chain is broken, leading to starvation in higher levels and overpopulation in lower levels.

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5. Exercises Q5

   Does removing a whole trophic level have different effects at different levels? Can any level be removed without harming the ecosystem?

   1. Removing the producer level (plants) is impossible because all other organisms depend on them for energy.
   2. Removing the primary consumer level (herbivores) causes a massive increase in plant biomass and a collapse of the carnivore population.
   3. Removing the secondary consumer level (carnivores) leads to an overpopulation of herbivores, which then overgraze and destroy the vegetation.
   4. Removing the top predator level (tertiary consumers) causes the prey population to explode, leading to severe damage to lower trophic levels.
   5. Each level plays a specific role in the flow of energy and the balance of populations within the ecosystem.
   6. Therefore, removing any single trophic level disrupts the food chain and harms the ecosystem's stability.

   Answer: Yes, removing a whole trophic level has different effects at different levels, and no level can be removed without harming the ecosystem.

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6. Exercises Q6

   What is biological magnification? Is it different at different levels of an ecosystem?

   1. Biological magnification is the process where the concentration of harmful chemicals increases as they move up the food chain.
      why?

      Magnification m = height of image ÷ height of object (= −v/u for a mirror, v/u for a lens). A negative m means a real, inverted image; a positive m a virtual, erect one.

   2. These chemicals, such as pesticides, are not easily broken down by the body and accumulate in the tissues of organisms.
   3. At the producer level, the concentration of these chemicals is the lowest because plants absorb small amounts from the soil or water.
   4. As herbivores eat the producers, they consume all the accumulated chemicals from the plants, leading to a higher concentration in their bodies.
   5. Carnivores that eat herbivores accumulate even more chemicals because they consume many prey items, each containing the stored toxins.
   6. Therefore, the concentration of these non-biodegradable substances is different at each trophic level, increasing progressively towards the top.
   7. Top carnivores, which are at the highest trophic level, have the maximum concentration of these harmful chemicals in their bodies.

   Answer: Biological magnification is the increase in concentration of harmful chemicals at successive trophic levels; yes, it is different at different levels, with the highest concentration found in top carnivores.

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7. Exercises Q7

   What problems do the non-biodegradable wastes we produce cause?

   1. Non-biodegradable wastes like plastics and metals cannot be broken down by microorganisms.
   2. These wastes accumulate in the soil and block the pore spaces.
   3. This accumulation prevents water and air from reaching the roots of plants.
   4. As a result, the soil becomes infertile and unable to support plant growth.
   5. Such wastes also clog drainage systems, leading to waterlogging and the spread of diseases.
   6. Animals often mistake these wastes for food, which can cause injury or death.
   7. Therefore, non-biodegradable wastes cause long-term environmental pollution and harm to ecosystems.

   Answer: Non-biodegradable wastes cause soil infertility, block drainage systems, spread diseases, and harm animals by being mistaken for food.

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8. Exercises Q8

   If all our waste were biodegradable, would it have no impact on the environment?

   1. Biodegradable waste is broken down by microorganisms into simpler substances like water, carbon dioxide, and humus.
   2. The process of decomposition releases gases such as methane and carbon dioxide, which are greenhouse gases.
   3. These gases contribute to the greenhouse effect, leading to global warming and climate change.
   4. Decomposition also produces foul smells and can attract pests like flies and rats, affecting local hygiene.
   5. If large amounts of biodegradable waste are dumped in water bodies, it reduces oxygen levels, harming aquatic life.
      why?

      Oxidation is gain of oxygen (or loss of hydrogen); reduction is loss of oxygen (or gain of hydrogen). In a redox reaction one substance is oxidised while another is reduced.

   6. Therefore, even biodegradable waste has negative impacts on the environment if not managed properly.

   Answer: No, it would still have an impact on the environment due to greenhouse gas emissions, foul smells, pest attraction, and water pollution.

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9. Exercises Q9

   Why is damage to the ozone layer a concern, and what is being done to limit it?

   1. The ozone layer in the stratosphere absorbs most of the harmful ultraviolet (UV) radiation from the sun.
   2. Damage to this layer allows more UV rays to reach the Earth's surface.
   3. Excess UV radiation causes skin cancer, cataracts, and weakens the immune system in humans.
   4. It also harms crops, marine life, and reduces agricultural productivity.
   5. The main cause of ozone depletion is the release of chlorofluorocarbons (CFCs) from refrigerants and aerosols.
   6. To limit this damage, the Montreal Protocol was signed in 1987 to phase out the production of ozone-depleting substances.
   7. Countries have replaced CFCs with safer alternatives like hydrofluorocarbons (HFCs) and are monitoring atmospheric levels.

   Answer: Damage to the ozone layer is a concern because it increases harmful UV radiation, leading to health issues like skin cancer and harming ecosystems; the Montreal Protocol and the phase-out of CFCs are being done to limit it.

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