Our Environment (Class 10 Science)

An ecosystem consists of biotic and abiotic factors interacting in complex food chains and food webs. Understanding energy flow and nutrient cycling is ess

Our Environment (Class 10 Science)

An ecosystem consists of biotic and abiotic factors interacting in complex food chains and food webs. Understanding energy flow and nutrient cycling is ess

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TL;DR: An ecosystem consists of biotic and abiotic factors interacting in complex food chains and food webs. Understanding energy flow and nutrient cycling i…

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An ecosystem consists of biotic and abiotic factors interacting in complex food chains and food webs. Understanding energy flow and nutrient cycling is ess

Our Environment MCQs with Answers & Explanations

Q1. An ecosystem includes:

  1. Only plants and animals
  2. Both living organisms and non-living factors ✓ (correct)
  3. Only non-living factors
  4. Only living organisms

Explanation: An ecosystem is a community of living organisms (biotic factors) interacting with physical components (abiotic factors like temperature, soil, water).

Q2. In a food chain, plants are called:

  1. Decomposers
  2. Secondary consumers
  3. Producers ✓ (correct)
  4. Tertiary consumers

Explanation: Plants are producers because they convert solar energy into chemical energy through photosynthesis, forming the base of food chains.

Q3. The percentage of energy transferred from one trophic level to the next is approximately:

  1. 90%
  2. 50%
  3. 25%
  4. 10% ✓ (correct)

Explanation: Only about 10% of energy is transferred to the next trophic level; the rest is lost as heat during respiration and other metabolic processes.

Q4. Decomposers in an ecosystem include:

  1. Bacteria and fungi ✓ (correct)
  2. Carnivores
  3. Herbivores
  4. Plants

Explanation: Decomposers break down dead organic matter and return nutrients to the soil, playing a crucial role in nutrient cycling.

Q5. The ozone layer is important because it:

  1. Traps heat in the atmosphere
  2. Protects from ultraviolet radiation ✓ (correct)
  3. Prevents greenhouse gases
  4. Produces oxygen

Explanation: The ozone layer absorbs harmful ultraviolet (UV) radiation from the sun, protecting living organisms from UV damage.

Q6. Which of the following is a biotic factor in an ecosystem?

  1. Wind
  2. Sunlight
  3. Bacteria ✓ (correct)
  4. Temperature

Explanation: Bacteria are living organisms and thus biotic factors. Temperature, sunlight, and wind are abiotic (non-living) factors.

Q7. The carbon cycle involves all of the following EXCEPT:

  1. Photosynthesis
  2. Combustion
  3. Respiration
  4. Rainfall ✓ (correct)

Explanation: The carbon cycle involves photosynthesis (CO2 uptake), respiration (CO2 release), combustion, and decomposition. Rainfall is part of the water cycle.

Q8. Invasive species in an ecosystem can cause:

  1. Disruption of native species and food webs ✓ (correct)
  2. Improved ecosystem balance
  3. Increased biodiversity
  4. More habitat for organisms

Explanation: Invasive species often outcompete native species, disrupt food webs, and reduce biodiversity.

Q9. The primary source of nitrogen for plants is:

  1. Rainwater
  2. Nitrogen-fixing bacteria in soil ✓ (correct)
  3. Decomposers
  4. The atmosphere

Explanation: Although nitrogen is abundant in the atmosphere, plants cannot use it directly; nitrogen-fixing bacteria convert atmospheric N2 into usable forms.

Q10. Which human activity has the most impact on increasing atmospheric CO2?

  1. Deforestation
  2. Fossil fuel combustion ✓ (correct)
  3. Agricultural practices
  4. All of the above

Explanation: The question asks for the single largest contributor. Burning coal, oil and gas is by far the biggest source of anthropogenic CO₂, which is why "all of the above" cannot be the answer to a "most impact" question.

Q11. What is an ecosystem?

  1. Only animals in an area
  2. Only plants in an area
  3. Living organisms and their physical environment in an area ✓ (correct)
  4. Only soil

Explanation: An ecosystem includes all living organisms (biotic) and non-living things (abiotic) in an area, along with their interactions.

Q12. What are producers in an ecosystem?

  1. Organisms that decompose
  2. Animals that eat plants
  3. Humans
  4. Green plants that make their own food ✓ (correct)

Explanation: Producers are autotrophs, mainly green plants, that produce food through photosynthesis using sunlight.

Q13. What are decomposers in an ecosystem?

  1. Organisms that break down dead organic matter ✓ (correct)
  2. Herbivores
  3. Carnivores
  4. Parasites

Explanation: Decomposers like bacteria and fungi break down dead organic matter and release nutrients back into the soil.

Q14. What is a food chain?

  1. A chain of restaurants
  2. A sequence showing energy transfer from producers to consumers ✓ (correct)
  3. A line of animals
  4. A type of food

Explanation: A food chain is a linear sequence showing the transfer of energy from producers through various levels of consumers.

Q15. What percentage of energy is transferred from one trophic level to the next?

  1. 100%
  2. 25%
  3. 10% ✓ (correct)
  4. 50%

Explanation: Approximately 10% of energy is transferred from one trophic level to the next, with the rest lost as heat and in metabolism.

Q16. What is biomagnification?

  1. Increase in food chain length
  2. Increase in organism size
  3. Growth of biomass
  4. Accumulation of toxic substances in higher trophic levels ✓ (correct)

Explanation: Biomagnification is the accumulation of harmful substances like pesticides in organisms at higher trophic levels in greater concentrations.

Q17. What is the main cause of ozone layer depletion?

  1. Chlorofluorocarbons (CFCs) ✓ (correct)
  2. Methane
  3. Carbon dioxide
  4. Nitrogen oxides

Explanation: CFCs are chlorine-containing compounds that break down ozone molecules in the stratosphere, creating the ozone hole.

Q18. What is the greenhouse effect?

  1. Growing plants in a greenhouse
  2. Trapping of heat in the atmosphere by gases ✓ (correct)
  3. Acid rain
  4. Depletion of ozone

Explanation: The greenhouse effect is the warming of Earth's atmosphere due to infrared radiation being trapped by gases like CO2 and methane.

Q19. Which gas is primarily responsible for global warming?

  1. Argon
  2. Nitrogen
  3. Carbon dioxide ✓ (correct)
  4. Oxygen

Explanation: Carbon dioxide is the major greenhouse gas contributing to global warming, released mainly by burning fossil fuels.

Q20. What is waste management?

  1. Burning waste
  2. Burying waste
  3. Throwing waste away
  4. Minimize waste and dispose responsibly through reduce, reuse, recycle ✓ (correct)

Explanation: Waste management involves reducing waste generation, reusing materials, and recycling to minimize environmental impact.

Frequently Asked Questions

What is biodiversity and why is it important?

Biodiversity refers to the variety of species and genetic variation within an ecosystem. It is important because it maintains ecosystem stability, provides resources for humans, and ensures ecological resilience to environmental changes.

How does pollution affect ecosystems?

Pollution can disrupt food webs by poisoning organisms, reduce biodiversity by making habitats unsuitable, and interfere with nutrient cycles. Bioaccumulation of toxins concentrates pollutants in organisms higher in the food chain.

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