NCERT Exemplar Solution for CBSE Class 10 Science Chapter: Our Environment
In this article you will get CBSE Class 10 Science chapter 15, Our Environment: NCERT Exemplar Problems and Solutions
Multiple Choice Questions
Question 1. Which one of the following is an artificial ecosystem?
(a) Pond
(b) Crop field
(c) Lake
(d) Forest
Answer. (b)
Explanation: Crop field is an agricultural land created by human.
Question 2. In a food chain, the third trophic level is always occupied by
(a) carnivores
(b) herbivores
(c) decomposers
(d) producers
Answer. (a)
Explanation: Plants occupy the first trophic level, herbivores constitute the second trophic level, carnivores constitute the third trophic level and higher carnivores occupy the fourth trophic level.
NCERT Solutions for CBSE Class 10 Science
Question 3. An ecosystem includes
(a) all living organisms
(b) non-living objects
(c) both living organisms and non-living objects
(d) sometimes living organisms and sometimes non-living objects
Answer. (c)
Explanation: All the interacting organisms in an area together with the non-living constituents of the environment form an ecosystem.
Thus, an ecosystem consists of biotic components comprising living organisms and a biotic components comprising physical factors like temperature, rainfall, wind, soil and minerals.
Question 4. In the given food chain, suppose the amount of energy at fourth trophic level is 5 kJ, what will be the energy available at the producer level?
Grass → Grasshopper → Frog → Snake → Hawk
(a) 5 kJ
(b) 50 kJ
(c) 500 kJ
(d) 5000 kJ
Answer. (d)
Explanation: According to 10 percent law, 90% of the energy captured from the previous trophic level is lost to the environment and only 10 percent is made available to the next trophic level.
In this food chain, at the 4th trophic level, 5 kJ energy is available to the snake
⇒ Energy available to Frog = 10% of 50 kJ
⇒ Energy available to Grasshopper = 10% of 500 kJ
⇒ Energy available to Grass = 10% of 5000 kJ.
Question 5. Accumulation of non-biodegradable pesticides in the food chain in increasing amount at each higher trophic level is known as
(a) eutrophication
(b) pollution
(c) bio-magnification
(d) accumulation
Answer. (c)
Explanation: Accumulation of non-biodegradable pesticides in the food chain in increasing amount at each higher trophic level is known asbio-magnification.
Question 6. Depletion of ozone is mainly due to
(a) chlorofluorocarbon compounds
(b) carbon monoxide
(c) methane
(d) pesticides
Answer. (a)
Explanation: Depletion of ozone is mainly due to chlorofluorocarbons (CFCs).
All other substances except chlorofluorocarbon compounds do not contribute to the depletion of ozone.
Question 7. Organisms which synthesise carbohydrates from inorganic compounds using radiant energy are called
(a) decomposers
(b) producers
(c) herbivores
(d) carnivores
Answer. (b)
Explanation: Organisms which synthesise carbohydrates from inorganic compounds using radiant energy are called producers e.g., all green plants. The producers make the energy from sunlight available to the rest of the ecosystem.
Organisms which consume the food produced, either directly from producers or indirectly by feeding on other consumers are the consumers.
Microorganisms which break-down the complex organic substances into simple inorganic substances used by plants are called decomposers.
Carnivores and herbivores are types of consumers.
Question 8. In an ecosystem, the 10% of energy available for transfer from one trophic level to the next is in the form of
(a) heat energy
(b) light energy
(c) chemical energy
(d) mechanical energy
Answer. (c)
Explanation: The 10% of energy available for transfer from one trophic level to the next in an ecosystem is in the form of chemical energy. The producers capture the energy present in sunlight and convert it into chemical energy which is passed into onto other trophic levels.
Question 9. Organisms of a higher trophic level which feed on several types of organisms belonging to a lower trophic level constitute the
(a) food web
(b) ecological pyramid
(c) ecosystem
(d) food chain
Answer. (a)
Explanation: Organisms of a higher trophic level feeding on several types of organisms belonging to a lower trophic level constitute the food web.
Food chain is a series of organisms through which food energy flows in an ecosystem. Ecosystem constitutes of all the living beings of an area and non-living components of their environment. An ecological pyramid shows the feeding relationship between groups of organisms and also depicts the amount of biomass or energy present at various trophic levels in an ecosystem.
Question 10. Flow of energy in an ecosystem is always
(a) unidirectional
(b) bidirectional
(c) multidirectional
(d) no specific direction
Answer. (a)
Explanation: The flow of energy in the ecosystem is unidirectional. The energy enters the plants (from the sun) through photosynthesis during the making of food. This energy is then passed on from one organism to another in a food chain.
The energy given out by the organisms as heat is lost to the environment, it does not return to be used by the plants again. This makes the flow of energy in ecosystem ‘unidirectional’.
Question 11. Excessive exposure of humans to UV-rays results in
(i) damage to immune system
(ii) damage to lungs
(iii) skin cancer
(iv) peptic ulcers
(a) (i) and (ii)
(b) (ii) and (iv)
(c) (i) and (iii)
(d) (iii) and (iv)
Answer. (c)
Explanation: Excessive exposures of humans to UV-rays results in skin cancer and also damage the immune system of the body.
Question 12. In the following groups of materials, which group(s) contains only non-biodegradable items?
(i) Wood, paper, leather
(ii) Polythene, detergent, PVC
(iii) Plastic, detergent, grass
(iv) Plastic, Bakelite, DDT
(a) (iii)
(b) (iv)
(c) (i) and (iii)
(d) (ii) and (iv)
Answer. (d)
Explanation: The substances which can’t be decayed by the action of microbes are non-biodegradable substances e.g., polythene, Bakelite, PVC, detergent, DDT, plastic etc.
Substances which can be decayed by microbes are called biodegradable substances i.e., Wood, paper, grass etc.
Question 13. Which of the following limits the number of trophic levels in a food chain?
(a) Decrease in energy at higher trophic levels
(b) Deficient food supply
(c) Polluted air
(d) Water
Answer. (a)
Explanation: There is a loss of energy as we go from one trophic level to the next, this limits the number of trophic levels in a food-chain.
Question 14. Which of the statement is incorrect?
(a) All green plants and blue-green algae are producers
(b) Green plants get their food from organic compounds
(c) Producers prepare their own food from inorganic compounds
(d) Plants convert solar energy into chemical energy
Answer. (b)
Explanation: Producers capture the solar energy and convert it into chemical energy. All green plants and certain blue-green algae which can produce food by photosynthesis come under this category and are called the producers.
Question 15. Which group of organisms are not constituents of a food chain?
(i) Grass, lion, rabbit, wolf
(ii) Plankton, man, fish, grasshopper
(iii) Wolf, grass, snake, tiger
(iv) Frog, snake, eagle, grass, grasshopper
(a) (i) and (iii)
(b) (iii) and (iv)
(c) (ii) and (iii)
(d) (i) and (iv)
Answer. (c)
Explanation: The flow of energy from one organism to another taking part at various biotic levels forms a food chain. A food chain describes the feeding relationships between the organisms within that ecosystem.
Food chain (ii) is an aquatic food chain so grasshopper cannot be a part of it.
In food chain (iii), wolf, snake and tiger all are carnivores. There is no herbivore to eat grass or herbivore is missing from the chain.
Question 16. The percentage of solar radiation absorbed by all the green plants for the process of photosynthesis is about
(a) 1%
(b) 5%
(c) 8%
(d) 10%
Answer. (a)
Explanation: The green plants in a terrestrial ecosystem capture about 1% of the energy of sunlight that falls on their leaves and convert it into food energy.
Question 17. In the given figure, the various trophic levels are shown in a pyramid. At which trophic level is maximum energy available?
(a) T4
(b) T2
(c) T1
(d) T3
Answer. (c)
Explanation: The maximum energy is available at first tropic level i.e., T1. After that there is progressive decline in the amount of energy available from producer to higher trophic levels. An average of 10% of the food eaten is turned into its own body and made available for the next level of consumers.
Question 18. What will happen if deer is missing in the food chain given below?
Grass → Deer → Tiger
(a) The population of tiger increases
(b) The population of grass decreases
(c) Tiger will start eating grass
(d) The population of tiger decreases and the population of grass increases
Answer. (d)
Explanation: If deer is missing in the food chain then there will be no herbivore to consume grass, so population of grass will increase.
Tiger will start to die of hunger, so the population of tiger will decrease.
Question 19. The decomposers in an ecosystem
(a) convert inorganic material to simpler forms
(b) convert organic material to inorganic forms
(c) convert inorganic materials into organic compounds
(d) do not breakdown organic compounds
Answer. (b)
Explanation: The microorganisms that break-down the complex organic substances into simple inorganic substances those goes into the soil and are used up once more by the plants.
Question 20. If a grasshopper is eaten by a frog, then the energy transfer will be from
(a) producer to decomposer
(b) producer to primary consumer
(c) primary consumer to secondary consumer
(d) secondary consumer to primary consumer
Answer. (c)
Explanation: Grasshopper feeds on producers (i.e., grass or plants) so, grasshopper is a primary consumer. Frogs are eating grasshopper so they are secondary consumer.
Question 21. Disposable plastic plates should not be used because
(a) they are made of materials with light weight
(b) they are made of toxic materials
(c) they are made of biodegradable materials
(d) they are made of non-biodegradable materials
Answer. (d)
Explanation: Plastics are made up of non-biodegradable material and causes pollution. Hence, use of disposable plastics must be avoided.
Short Answer Type Questions
Question 22. Why is improper disposal of waste a curse to environment?
Answer.
Certain substances when burnt in air releases harmful gases. When these substances dumped in river or sea create water pollution. Some sort of waste materials on dumping inside the ground can make the land infertile.
So, if proper method of waste disposal system is not used then it will contaminate the environment.
Question 23. Write the common food chain of a pond ecosystem.
Answer.
A common food chain of a pond ecosystem is as follows:
Producers (aquatic plants) → Herbivores (Protozoa) → Carnivore (Small fishes) → Large Carnivores (Large Fishes)
Question 24. What are the advantages of cloth bags over plastic bags during shopping?
Answer.
Cloth bags have many advantages over plastic bags, some of them are:
Bags made of clothes can be used again and again by washing or modifying. One can modify these bags in home. Cloth bags are biodegradable and don’t causes pollution.
Question 25. Why are crop fields known as artificial ecosystem?
Answer.
Ecosystems which are made by man are known as artificial ecosystem.
In case of crop fields abiotic and biotic components are selected by humans. The essential process such as sowing seeds, then irrigated and further progress is also kept under observation for getting good yield.
Question 26. Differentiate between biodegradable and non-biodegradable substances. Give examples.
Answer.
Difference between biodegradable and non-biodegradable substances are:
| S. No. | Biodegradable substances | Non-biodegradable substances |
| 1. | Substances that can be broken down into simpler substances by the action of decomposers | Substances that can’t be broken down into simpler substances by the action of decomposers. |
| 2. | These substances do not cause pollution. | These substances cause pollution. |
| 3. | e.g. vegetables, fruits etc. | e.g. polythene, DDT etc. |
Question 27. Suggest one word for each of the following statement/definitions.
(a) The physical and biological world where we live in
(b) Each level of food chain where transfer of energy takes place
(c) The physical factors like temperature, rainfall, wind and soil of an ecosystem
(d) Organisms which depend on the producers either directly or indirectly for food
Answer.
(a) Environment
(b) Trophic level
(c) Abiotic factors
(d) Consumers
Question 28. Explain the role of decomposers in the environment.
Answer.
The 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.
They act as natural cleaning agent by decomposing dead organisms and biodegradable wastes and helps in replenishment of the soil’s nutrients,
Question 29. Select the mis-matched pair in the following and correct it.
| (a) Bio-magnification | Accumulation of chemicals at the successive trophic levels of a food chain |
| (b) Ecosystem | Biotic components of environment |
| (c) Aquarium | A man-made ecosystem |
| (d) Parasites | Organsims which obtain food from other living organisms |
Answer. (b)
An ecosystem consists of biotic components (living organisms) as well as abiotic components (soil, air, water etc.) of environment.
Question 30. We do not clean ponds or lakes, but an aquarium needs to be cleaned. Why?
Answer.
A pond or a lake forms a natural and complete ecosystem. All the food chain presents in these ecosystems are complete. These ecosystems have plenty of producers, consumers and decomposers.
On the other hand an aquarium is an incomplete artificial ecosystem. An aquarium does not have enough population of decomposers to decompose waste material produced by aquatic animals. Due to this reason aquarium needs to be cleaned frequently.
Long Answer Type Questions
Question 31. Indicate the flow of energy in an ecosystem. Why is it unidirectional? Justify.
Answer.
Flow of energy in an ecosystem is as follows:
Sun → Producer → Herbivore → Carnivore
The flow of energy in the ecosystem is unidirectional. The energy enters the plants (from the sun) through photosynthesis during the making of food. This energy is then passed on from one organism to another in a food chain.
The energy given out by the organisms as heat is lost to the environment, it does not return to be used by the plants again. This makes the flow of energy in ecosystem ‘unidirectional’.
Question 32. What are decomposers? What will be the consequence of their absence in an ecosystem?
Answer.
The 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 decomposer acts as cleaning agents of environment by decomposing the dead bodies of plants and animals and help in recycling of materials, replenishment of soil’s nutrients etc.
Following are the consequence of their absence in an ecosystem:
Dead bodies and plants would keep lying and their number will keep on increasing. Their accumulation will cause land and water pollution. Also, substances from which these bodies are made such as soil and water will never be recycled.
Question 33. Suggest any four activities in daily life which are eco-friendly.
Answer.
Four activities in daily life which are eco-friendly:
1. Using bags made of clothes or paper instead of plastic bags.
2. Use public transport, cycling or walking to travel.
3. Switch off fans and lights when not in use.
4. Dump off the biodegradable substances like vegetables and peels of fruits in ground.
Question 34. Give two differences between food chain and food web.
Answer.
| S. No. | Food Chain | Food Web |
| 1. | A food chain shows the feeding relationship between different living things in a particular environment or habitat. | In an ecosystem, several food chains are linked together and intersect each other to form a complex network called food web. |
| 2. | Members of higher trophic level feed upon a single type of organism of the lower trophic level. | Member of higher trophic level can feed upon organisms of the lower trophic levels of other food chains. |
Question 35. Name the wastes which are generated in your house daily. What measures would you take their disposal?
Answer.
Wastes which are generated in our house daily and measures for their disposal are as follows:
Raw vegetable and peels of fruits – can be disposed underground in a nearby garden which on decomposition enriches the soil with nutrients.
Paper wastes like newspaper, books etc – Can be recycled or can also be sold.
Plastic waste like polybags, plastic toys etc – Can be sold in suitable shops where they can be recycled.
Other household waste like pieces of glass, clothes etc – Should be safely dumped in garbage bins placed to collect non-biodegradable waste.
Question 36. Suggest suitable mechanism (s) for waste management in fertiliser industries.
Answer.
Chemicals and harmful gases are the main pollutants which are produced in a fertilizer factory and a suitable waste management is essential for such industries.
These pollutants can be controlled at the point of generation within the factory or nearby treatment plant.
To control air pollution certain adsorption equipments may be fitted in chimneys of fertilizer industries which can absorb harmful pollutants before the smoke is released into atmosphere.
Water mixed with chemicals can be sent to water bodies after treatment in treatment plants within industries. Water can also be sent to any nearby treatment plants with the help of a suitable drainage system.
Question 37. What are the by-products of fertilizer industries? How do they affect the environment?
Answer.
The by-products of the fertiliser industries are oxides of nitrogen and sulphur i.e., SO2, CO, NOX, CO2, H2S, other solid, liquid chemicals and some solid waste material.
These substances usually released in air or dump in river bodies or sea which causes water pollution. These substances when consumed by plants and animals enter the food chain.
By the process of bio magnification these harmful chemicals get concentrated at each trophic level. Human being omnivore eats both plants and animals (or aquatic animals) which is extremely harmful for health. SO2 gas released in atmosphere can cause acid rain which also effect monuments and buildings.
Question 38. Explain some harmful effects of agricultural practices on the environment.
Answer.
Although agriculture is important but there are some harmful effects of agricultural practices on the environment which are as follows:
Excessive cutting down of trees for agricultural purposes causes deforesting and during rain fall it may also result in soil erosion.
Excess drainage of groundwater for irrigation purposes lowers the water table. This results in acute water shortage at many places.
Synthetic fertilizers and pesticides used in the field during rain fall washed away to rivers and other bodies which cause water pollution.
The chemical pesticides, being non-biodegradable accumulates in organisms in increasing amounts at each trophic level commonly known as bio magnification.