CBSE Class 10 Science Chapter-15 Our Environment – Free PDF Download
Free PDF download of Important Questions with Answers for CBSE Class 10 Science Chapter 15 – Our Environment prepared by expert Science teachers from latest edition of CBSE(NCERT) books only by CoolGyan to score more marks in CBSE board examination.
CBSE Class 10 Science Chapter-15 Our Environment Important Questions
CBSE Class 10 science Important Questions Chapter 15 – Our Environment
3 Mark Questions
1. DDT that was sprayed in minute amount on food plants was detected in high concentration in man? How did it happen? Explain.
Ans. This occurs due to biological magnification. When pesticides like DDT are used to protect crops from diseases and pests. These non-biodegradable substances enter the soil. From soil these substances are absorbed by plants along with water and minerals. The food plants when consumed by organisms, they get accumulated at different trophic levels. As the human beings occupy the top position in any food chain, maximum concentration of such harmful chemicals get accumulated in the bodies of man.
2. Describe how ozone layer is formed?
Ans. Formation of the ozone layer-
(a) During the origin of life Earth, some of underwater micro-organisms were to photosynthesize due to molecular oxygen 
was released in atmosphere.
(b) This oxygen is released to stratosphere where it began to react with ultraviolet radiations from sun to form free oxygen (O).
(c) Free oxygen combines with molecular oxygen to form 
Formation of ozone
3. What are the major components of environment?
Ans.
4. Why are the same substances biodegradable and some non-biodegradable?
Ans. The micro-organisms like bacteria and other decomposers organisms (called saprophytes) present in our environment specific in their action. They break down the materials or products made from natural materials (paper) as they have some peculiar enzymes for this process. But as enzymes are specific in their action, these cannot break down many man-made materials likes plastic. These can be acted upon by physical processes but not by biological processes. Therefore, these types of substances persist for long time and cannot be decomposed into simpler substances.
5. Explain why a food chain consists of few steps only? Write a food chain having five steps.
Ans. Food chains consist of few steps only because in food chain energy decreases at each successive trophic level, due to this energy available at higher trophic level reduce step by step. If a food chain has six or more than six steps, energy is not sufficient for the survival of organism at that trophic level.
Plants
Grasshopper Insect Frog Snake
6. What is the difference between food chain and food web?
Ans.
7. What is biological magnification? Illustrate with the help of example.
Ans. It is a process of increase in concentration of persistent pollutant per unit weight of the organisms with the rise in trophic level.
8. What are the ill effects of ozone layer depletion?
Ans. Ill effect of ozone depletion.
(1) Human health: –
(a) It cause skin cancer.
(b) Eye diseases like cataracts.
(c) Supresion of the immune system.
(2) Agriculture and plant life: – Growth leaf development of most plant species decrease abundantly on exposure to high concentration of UV radiation which are filtered by ozone layer.
(3) Marine environment: – UV radiation filtered through the depleted ozone layer directly damage.
(a) Photosynthesizing phytoplankton presents in the sea which also help in reducing the global warming.
(b) Young fishes.
(c) Shrimp, crabs larvae and other small animals.
(d) Material degradation: – The lives of many plastics have been found to be shortened due to exposure to UV radiations.
9. What is the significance of food chains?
Ans. Significance of food chain
(a) It is a means of transfer of food from one trophic level to another.
(b) It provides information about the living component of an ecosystem.
(c) It helps us in understanding the interactions and interdependence amongst different organism in an ecosystem.
(d) It is a pathway for the flow of energy in any ecosystem.
10. How Garbage pollution can be controlled?
Ans. Pollution of garbage can be controlled by-
(a) Recycling of certain wastes products like plastic and paper.
(b) Making use of biodegradable products as much as we can.
(c) Producing biogas from the organic wastes.
(d) Separation of biodegradable and non-bio-degradable waste during disposal.
(e) Making the compost of biodegradable wastes by burying them under soil.
11. What are the components of an ecosystem? Explain with examples
Ans. An ecosystem has two major components-
(1) Biotic components- It includes producers (plants), consumers (animals) and decomposers (bacteria and fungi).
(a) Producers- Organisms which are able to photosynthesis are called producers. It includes all green plants.
(b) Consumers- Organisms which depends upon other are called consumers. It is of few types-
(i) Herbivores- Animals which directly depends upon plants.
(ii) Carnivores- These animals eat herbivores.
(iii) Secondary carnivores- Animals which depends upon carnivores.
(iv) Tertiary carnivores- Largest animals which depends upon secondary carnivores.
(a) Decomposers- These organisms depend upon dead plants and animals. They change complex organic substances into simple inorganic substances.
(1) Abiotic components- Non-living components. It include physical and chemical factors such as light, water, soil, air temperature, oxygen, carbon, nitrogen and other nutrients.
12. Write any three activities which are eco-friendly.
Ans. (a) Making the compost of biodegradable wastes by burying them under soil.
(b) Use of cloth bags instead of polythene bags.
(c) Using CNG in vehicles instead of petrol or diesel.
13. Energy transfer is said to be unidirectional whereas biochemical transfer is said be cyclic. Why?
Ans. Energy flow is unidirectional because as it transfers from one trophic level to next trophic level, it reduces only 10% is available at Successive level from previous level. Nutrient flow is cyclic because nutrients returned back into nutrient pool from the dead bodies of plants and animals by the decomposition of micro- organisms from nutrient pool. They are utilized again by plants.
14. Give difference between produces and consumers. Mention one example of each.
Ans.
15. There are no predators for tiger or lion. Why?
Ans. Lions and tigers are at the highest trophic level. They are largest animals which feed upon the secondary carnivores like wolves etc. they are not killed and eaten by other animals.
16. What are the measures to protect ozone depletion?
Ans. Measure to protect ozone layer-
(a)Concern over increasing global ozone depletion led to international restrictions in the use and manufacture of CFCS and halons.
(b) International concern over the seriousness of the problems associated with ozone layer depletion led to the adoption of Vienna convention for the protection of the ozone layers in 1985.
(C) Promotion of an international treaty known as Montreal protocol (1987), to which over 140 countries agreed to the reduction and eventual phasing out of the manufacture and use of most ozone depleting substances.
17. Describe three biotic component of ecosystem. Also give examples.
Ans. Biotic components of ecosystem are-
(a) Producers- All the green plants have a unique capability to synthesis organic substance such as sugar and starch by the process of photosynthesis. Therefore, they are called producers.
(b) Consumers- These are the living organisms which depend directly or indirectly on plants for their food. Consumers may be herbivore, carnivores, and omnivores.
(c) Decomposers- Decomposers are the organisms which depend upon the dead and decaying organisms their waste material. They form important link between living and non-living components.
18. What is the role of decomposers in an ecosystem?
Ans. Decomposers decompose all the organic matter trapped in body, body parts and waste of organisms and returned back to environment. Hence, they are the important link between living and non-living components of environments. They play a vital role in biochemical or nutrient cycle and removing the organic garbage from our surroundings. They play an important role in changing our surrounding.
19. What will happen if we kill all the organisms in one trophic level?
Ans. The food chain would end and ecological balance would be affected-
(a) If the herbivores are killed, then the carnivores would not able be to get food and would die.
(b) If carnivores are killed, then the population of herbivores would increase to unsustainable level.
(c) If producers are killed, then the nutrient cycle in the area would not be completed.
19. What is Ozone? How does it affect any ecosystem?
Ans. Ozone is an isotope of oxygen i.e. it is a molecule formed by three atoms of oxygen. At the higher levels of the atmosphere, ozone performs an essential function. It shields the surface of the earth from ultraviolet (UV) radiations from the sun. These radiations are highly damaging to organisms. Ultraviolet rays can cause skin cancer.
20. Why are some substances biodegradable and some non-biodegradable?
Ans. Substances which can be acted upon by microorganism (decomposer) are called biodegradable. For example- vegetable wastes, paper, cotton etc. On the other hand, materials which are not acted upon by decomposers are called non-biodegradable. For example- plastic, glass, polyethene etc.
21. Give any two ways in which biodegradable substances would affect the environment.
(a) They will serve as breeding ground for flies and mosquitoes which are carriers of 3 disease like cholera, malaria etc. Give any two ways in which non-biodegradable substances would affect the environment.
(b) They produce foul smell, thus causing air pollution.
Ans. (a) Excess use of non-biodegradable pesticide and fertilizers run off with rain water to water
bodies cause water pollution.
(b) They may choke the sever system of city or town that may overflow over roads.
22. What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?
Ans. The phenomenon of progressive increase in concentration of certain harmful non-biodegradable chemicals such as DDT at different levels of food chain is called biological magnifications.
The concentration of harmful chemicals will be different at different trophic levels. It will be lowest in the first trophic level and highest in the last trophic level of the food chain.
23. Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?
Ans. Ozone layer stops ultraviolet radiations from the Sun from reaching the earth. Ultraviolet rays cause cancer, cataract and damage to the immune system of human beings.
In 1987, United Nations Environment Programme (UNEP) succeeded I forging an agreement between nations to freeze chlorofluorocarbons (CFCs) production to 1986 levels. CFCs are the main cause of ozone layer depletion.
24. Why some substances are degraded and others not?
Ans. Different components of food are changed to simpler substances by digestive enzymes and these enzymes are very much specific in nature and action. Similarly, substances are broken down by bacteria and saprophytes. They are also very specific in action and break down of the particular substance. Therefore, some substances are biodegradable and other are non-biodegradable.
25. What will happen if all the carnivores are removed from the earth?
Ans. If all the carnivores are removed from the earth, the population of herbivores will increase. Large population of herbivores will overgraze. As a result, all plants will disappear from the earth surface and ultimately the earth may become a desert. The biosphere will get disturbed which will lead to end of life on earth.
27. What will happen to grasslands if all the grazers are removed from there?
Ans. If all the grazers are removed from grassland, grass will grow unchecked. It may help the growth of some organisms harmful to the animals and the animals which feed on the grazers will die of starvation. The biogeochemical cycle will stop and the whole biosphere will get disturbed.
28. The number of malarial patients in a village increase tremendously, when a large number of frogs were exported from the village. What could be the cause for it? Explain the help of food chain?
Ans. Phytoplankton —*Zooplankton * Mosquito larva—* Frog
In the absence of frog, more mosquito larva survive, giving rise to large number of mosquitoes which cause increase incidence of malaria.
29. What are decomposers and what is the importance of them in the ecosystem?
Ans. The micro-organisms which break down the complex organic substances into simple inorganic substances e.g. bacteria, fungi. Decomposers decompose the complex substances into simple ones so that plants can use it again.
30. Why food chains consist of three or four steps only?
Ans. Since so little energy is available for the next level of consumers and for this reason food generally consists of three or four steps. The loss of energy at the each step is so great that very little usable energy remains after four tropic levels.
31. What will happen if decomposers are not there in the environment?
Ans. If decomposers are not there in the environment, the breakdown of the complex organic substances into simple substances will not take place and natural replenishment of the soil will not take place. So, presence of decomposers is essential for the replenishment of soil and biogeochemical cycle of elements or substances.
32. Are plants actually producers of energy?
Ans. No, plants are not actually producers of energy, they can trap the energy of sun and can convert solar energy into chemical energy in the form of carbohydrates and other food materials so they are called transducers.
33. Look at the following figures. Choose the correct one and give reason for your Choice.
Ans.
Fig. “A” is correct.
• In an ecosystem, the number of individuals at producer level is maximum. This number reduces at each successive level. Therefore, the shape is a pyramid with broader base and tapering apex.
• On an average 10% of the food changes into body mass and is available for the next level of consumers.
34. It is the responsibility of the government to arrange for the management and disposal of waste. As an individual you have no role to play. Do you agree? Support your answers with two reasons.
Ans. I do not agree. As an individual, I also have the responsibility and can contribute in the following ways:
(i) Cut down waste generation.
(ii) Make compost pit for bio degradable waste.
(iii) Recycle non biodegradable waste.