NCERT Exemplar Class 10 Science Solutions

Chapter 15-Our Environment-MCQs

Multiple Choice Questions
Q.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.
Q.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.
Q.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.
Q.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.
Q.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 as bio-magnification.
Q.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.
Q.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.
Q.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.
Q.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.
Q.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’.
Q.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.
Q.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.
Q.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.
Q.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.
Q.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.
Q.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.
Q.17. In the given figure, the various trophic levels are shown in a pyramid. At which trophic level is maximum energy available?


a) $T_{4}$
b) $T_{2}$
c) $T_{1}$
d) $T_{3}$
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.
Q.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.
Q.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.
Q.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.
Q.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.