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Summary of the Chapter-13/15-Our Environment:
- The different elements of an ecosystem rely on each other.
- Producers convert sunlight into energy, which is then used by other parts of the ecosystem.
- Energy decreases as it moves through successive trophic levels, which limits the number of levels in a food chain.
- Human activities affect the environment.
- The use of chemicals such as CFCs has put the ozone layer at risk. Since the ozone layer shields us from harmful ultraviolet radiation from the Sun, its depletion can harm the environment.
- Waste produced can be either biodegradable or non-biodegradable.
- The management and disposal of waste are causing significant environmental issues.
NCERT Based MCQ with Explanation:
1. Which of the following is considered a biotic component of an ecosystem?
(a) Soil
(b) Water
(c) Plants
(d) Sunlight
Explanation: Biotic components include all living organisms in an ecosystem, such as plants, animals, and microorganisms. Abiotic components, like soil, water, and sunlight, are non-living parts of the ecosystem.
2. In a food chain, which organisms are known as producers?
(a) Herbivores
(b) Carnivores
(c) Decomposers
(d) Green plants
Explanation: Producers, like green plants, create their own food through photosynthesis, forming the base of a food chain.
3. Which trophic level contains the least amount of energy in a food chain?
(a) Producers
(b) Primary consumers
(c) Secondary consumers
(d) Tertiary consumers
Explanation: Due to energy loss at each trophic level, tertiary consumers (e.g., large carnivores) receive the least energy compared to other levels.
4. What is the primary cause of ozone layer depletion?
(a) Carbon dioxide
(b) Methane
(c) Chlorofluorocarbons (CFCs)
(d) Sulfur dioxide
Explanation: CFCs, used in refrigerants and aerosols, release chlorine atoms when they break down in the stratosphere, which leads to the destruction of ozone molecules.
5. Which of the following is a non-biodegradable substance?
(a) Fruit peels
(b) Paper
(c) Plastic
(d) Vegetable waste
Explanation: Plastic is non-biodegradable, meaning it cannot be broken down naturally by microorganisms, unlike biodegradable items like fruit peels and paper.
6. Which of the following is an example of a natural ecosystem?
(a) Aquarium
(b) Garden
(c) Pond
(d) Crop field
Explanation: Natural ecosystems exist without significant human intervention. A pond is a natural ecosystem, while an aquarium, garden, and crop field are artificial ecosystems created by humans.
7. What is the primary function of decomposers in an ecosystem?
(a) Consuming producers
(b) Recycling nutrients
(c) Competing with consumers
(d) Capturing sunlight
Explanation: Decomposers, like bacteria and fungi, break down dead organisms and waste products, returning essential nutrients to the environment.
8. The energy available at each trophic level in a food chain decreases by approximately:
(a) 90%
(b) 50%
(c) 25%
(d) 10%
Explanation: According to the 10% law, only about 10% of the energy is transferred to the next trophic level, while 90% is lost as heat or used in life processes.
9. Which of the following organisms would be at the second trophic level in a food chain?
(a) Plants
(b) Herbivores
(c) Carnivores
(d) Decomposers
Explanation: Herbivores, which consume plants (producers), occupy the second trophic level in a food chain.
10. What is biological magnification?
(a) An increase in population at higher trophic levels
(b) Accumulation of harmful chemicals at each trophic level
(c) Decrease in energy levels at each trophic level
(d) Increased oxygen production by producers
Explanation: Biological magnification refers to the progressive concentration of harmful substances, such as pesticides, in the bodies of organisms at higher trophic levels.
11. Which of the following is an abiotic component of an ecosystem?
(a) Bacteria
(b) Fish
(c) Temperature
(d) Plants
Explanation: Abiotic components are non-living factors in an ecosystem, such as temperature, water, and soil. Living organisms like bacteria, fish, and plants are biotic components.
12. What type of consumers are directly dependent on producers for food?
(a) Herbivores
(b) Carnivores
(c) Omnivores
(d) Parasites
Explanation: Herbivores feed directly on producers, such as plants, and occupy the second trophic level in a food chain.
13. Which of the following is an example of a decomposer?
(a) Rabbit
(b) Fungi
(c) Cow
(d) Eagle
Explanation: Fungi break down dead organic matter into simpler substances and are classified as decomposers.
14. In an ecosystem, energy flow is:
(a) Bidirectional
(b) Unidirectional
(c) Cyclic
(d) Random
Explanation: Energy flows in one direction in an ecosystem, from producers to consumers, and is eventually lost as heat, rather than being recycled.
15. The ozone layer primarily protects living organisms from:
(a) Infrared radiation
(b) Ultraviolet radiation
(c) Visible light
(d) X-rays
Explanation: The ozone layer absorbs harmful ultraviolet (UV) radiation from the Sun, protecting living organisms from its damaging effects, such as skin cancer.
16. What percentage of solar energy do green plants capture in a terrestrial ecosystem?
(a) 10%
(b) 50%
(c) 1%
(d) 5%
Explanation: Green plants in a terrestrial ecosystem capture about 1% of the solar energy that falls on their leaves, which they use for photosynthesis.
17. Which of the following forms the first trophic level in a food chain?
(a) Carnivores
(b) Herbivores
(c) Decomposers
(d) Producers
Explanation: Producers, like green plants, form the first trophic level as they capture solar energy and convert it into chemical energy through photosynthesis.
18. Which of the following is a human-made ecosystem?
(a) Ocean
(b) Forest
(c) Desert
(d) Aquarium
Explanation: An aquarium is a human-made ecosystem where aquatic plants and animals are kept in an artificial environment.
19. The progressive buildup of harmful chemicals in organisms at higher trophic levels is known as:
(a) Eutrophication
(b) Biomagnification
(c) Deforestation
(d) Recycling
Explanation: Biomagnification is the process in which harmful chemicals, like pesticides, accumulate in higher concentrations in organisms at the top of the food chain.
20. What happens to the energy lost at each trophic level?
(a) It is recycled back to producers
(b) It is lost as heat
(c) It is stored in the ecosystem
(d) It increases with each trophic level
Explanation: As energy is transferred from one trophic level to the next, most of it is lost as heat during metabolic processes.
21. What would happen if all the decomposers in an ecosystem disappeared?
(a) There would be more plants
(b) Nutrient cycling would stop
(c) Energy transfer would increase
(d) The ecosystem would remain unchanged
Download Full PDF (100+ MCQ) with Explanation !22. Which of the following substances contributes to the depletion of the ozone layer?
(a) Nitrogen
(b) Carbon dioxide
(c) Chlorofluorocarbons (CFCs)
(d) Methane
23. The gradual accumulation of pesticides like DDT in the food chain is an example of:
(a) Biological magnification
(b) Decomposition
(c) Respiration
(d) Photosynthesis
24. Which of the following is NOT a biodegradable substance?
(a) Vegetable peels
(b) Paper
(c) Plastic bags
(d) Leaves
25. What is the term used to describe the complex network of interconnected food chains in an ecosystem?
(a) Food chain
(b) Food web
(c) Trophic level
(d) Energy pyramid
26. Which of the following pollutants is responsible for acid rain?
(a) Carbon monoxide
(b) Sulfur dioxide
(c) Chlorine
(d) Ozone
27. How much energy is typically transferred from one trophic level to the next in a food chain?
(a) 1%
(b) 10%
(c) 25%
(d) 50%
28. What is the primary cause of global warming?
(a) Carbon dioxide emissions
(b) Ozone depletion
(c) Sulfur dioxide emissions
(d) Deforestation
29. Which type of waste is most likely to accumulate in the environment if not properly disposed of?
(a) Biodegradable
(b) Non-biodegradable
(c) Organic
(d) Food waste
30. What role do herbivores play in the food chain?
(a) They produce energy
(b) They consume producers
(c) They decompose dead organisms
(d) They consume carnivores
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