ROUTERA

Chapter 14 Ecosystem

Class 12th Biology Chapter MCQs

1. Which of the following is an abiotic component of the ecosystem?

  • A) Plants
  • B) Animals
  • C) Water
  • D) Fungi

Answer: C
Explanation: Water is an abiotic component, meaning it is a non-living factor that influences the ecosystem. Plants, animals, and fungi are biotic components.

2. The term "biome" refers to:

  • A) A group of ecosystems
  • B) A community of organisms
  • C) A group of populations
  • D) A physical environment

Answer: A
Explanation: A biome is a large geographical biotic unit characterized by a particular climate and associated vegetation, encompassing multiple ecosystems.

3. The major source of energy for the ecosystem is:

  • A) Sunlight
  • B) Wind
  • C) Water
  • D) Soil

Answer: A
Explanation: Sunlight is the primary source of energy in an ecosystem, which is captured by plants during photosynthesis and passed through the food chain.

4. Which of the following is true about primary producers in an ecosystem?

  • A) They are herbivores
  • B) They convert solar energy into chemical energy
  • C) They are decomposers
  • D) They consume organic material

Answer: B
Explanation: Primary producers (such as plants and algae) convert solar energy into chemical energy through the process of photosynthesis.

5. In a food chain, the organisms that directly consume producers are known as:

  • A) Secondary consumers
  • B) Tertiary consumers
  • C) Primary consumers
  • D) Decomposers

Answer: C
Explanation: Primary consumers are herbivores that directly consume producers (plants).

6. Which of the following represents a food chain?

  • A) Grass → Grasshopper → Frog → Snake
  • B) Grass → Deer → Tiger
  • C) Grass → Cow → Human
  • D) All of the above

Answer: D
Explanation: All options represent different food chains, where energy flows from producers to primary consumers, and then to higher trophic levels.

7. The process by which the energy from food is used by organisms for growth, reproduction, and other activities is known as:

  • A) Respiration
  • B) Photosynthesis
  • C) Excretion
  • D) Transpiration

Answer: A
Explanation: Respiration is the process through which organisms release energy from food to fuel their metabolic activities.

8. The total dry weight of living organisms in an ecosystem is called:

  • A) Biomass
  • B) Productivity
  • C) Primary productivity
  • D) Net primary productivity

Answer: A
Explanation: Biomass refers to the total dry weight of all living organisms in a given area or ecosystem.

9. In an energy pyramid, the energy decreases at each trophic level. The reason for this is:

  • A) Only 10% of the energy is transferred from one trophic level to the next
  • B) Energy is used by organisms for growth and reproduction
  • C) Energy is lost as heat
  • D) All of the above

Answer: D
Explanation: At each trophic level, energy is lost due to metabolism, growth, reproduction, and as heat, and only about 10% of the energy is passed on to the next level.

10. Which of the following is the correct sequence of trophic levels in a terrestrial ecosystem?

  • A) Producer → Primary consumer → Secondary consumer → Tertiary consumer
  • B) Primary consumer → Producer → Secondary consumer → Tertiary consumer
  • C) Secondary consumer → Producer → Primary consumer → Tertiary consumer
  • D) Tertiary consumer → Primary consumer → Producer → Secondary consumer

Answer: A
Explanation: The correct sequence in a terrestrial ecosystem starts with producers, followed by primary consumers (herbivores), secondary consumers (carnivores), and tertiary consumers.

11. Which of the following biogeochemical cycles involves the atmosphere as its main reservoir?

  • A) Water cycle
  • B) Carbon cycle
  • C) Nitrogen cycle
  • D) Phosphorus cycle

Answer: B
Explanation: The carbon cycle involves the atmosphere as the main reservoir, where carbon is stored in the form of carbon dioxide (CO₂).

12. In the nitrogen cycle, nitrogen fixation is carried out by:

  • A) Plants
  • B) Nitrogen-fixing bacteria
  • C) Decomposers
  • D) Animals

Answer: B
Explanation: Nitrogen-fixing bacteria convert atmospheric nitrogen (N₂) into forms like ammonia (NH₃) that plants can use.

13. The energy flow in an ecosystem is:

  • A) Cyclic
  • B) Unidirectional
  • C) Bidirectional
  • D) Multidirectional

Answer: B
Explanation: Energy flow in an ecosystem is unidirectional, starting from producers and flowing through various trophic levels to decomposers.

14. Which of the following organisms is most likely to occupy the top of a food chain?

  • A) Grass
  • B) Grasshopper
  • C) Snake
  • D) Lion

Answer: D
Explanation: Lions are apex predators and occupy the top of the food chain, consuming other animals.

15. Which of the following ecosystems has the highest biodiversity?

  • A) Desert
  • B) Forest
  • C) Grassland
  • D) Ocean

Answer: B
Explanation: Forests, especially tropical rainforests, are known for their high biodiversity, supporting a wide variety of species.

16. Which of the following is an example of an autotroph?

  • A) Cow
  • B) Lion
  • C) Plant
  • D) Fungus

Answer: C
Explanation: Plants are autotrophs, meaning they can produce their own food through photosynthesis.

17. Which of the following is the main role of decomposers in an ecosystem?

  • A) Convert solar energy into chemical energy
  • B) Break down dead organisms and recycle nutrients
  • C) Consume producers
  • D) Prey on herbivores

Answer: B
Explanation: Decomposers break down dead organic matter and recycle nutrients back into the ecosystem.

18. The pyramid of energy is always:

  • A) Inverted
  • B) Broad at the top and narrow at the bottom
  • C) Broad at the bottom and narrow at the top
  • D) Irregular in shape

Answer: C
Explanation: The pyramid of energy is always broad at the bottom and narrow at the top, showing that energy decreases at each trophic level.

19. Which of the following is a primary factor in the rate of decomposition in an ecosystem?

  • A) Temperature
  • B) Soil pH
  • C) Water availability
  • D) All of the above

Answer: D
Explanation: The rate of decomposition is influenced by temperature, soil pH, and water availability, all of which affect microbial activity.

20. What is the main function of the nitrogen cycle in an ecosystem?

  • A) To return oxygen to the atmosphere
  • B) To convert nitrogen into a usable form for plants
  • C) To release carbon dioxide into the atmosphere
  • D) To recycle water through evaporation

Answer: B
Explanation: The nitrogen cycle ensures that nitrogen is converted into forms that plants can use, such as ammonia or nitrate.

21. In the energy pyramid, the trophic level that has the greatest amount of energy is the:

  • A) Producer level
  • B) Primary consumer level
  • C) Secondary consumer level
  • D) Tertiary consumer level

Answer: A
Explanation: Producers (such as plants) capture solar energy and have the greatest amount of energy in the pyramid.

22. Which of the following is the primary source of energy for producers in an ecosystem?

  • A) Chemical energy
  • B) Heat energy
  • C) Solar energy
  • D) Mechanical energy

Answer: C
Explanation: Solar energy is the primary energy source for producers, which convert it into chemical energy through photosynthesis.

23. Which of the following biomes has the least amount of precipitation?

  • A) Desert
  • B) Rainforest
  • C) Tundra
  • D) Grassland

Answer: A
Explanation: Deserts receive very little precipitation, usually less than 25 cm per year.

24. Which of the following ecosystems has the highest net primary productivity?

  • A) Ocean
  • B) Forest
  • C) Desert
  • D) Grassland

Answer: B
Explanation: Forests, particularly tropical rainforests, have the highest net primary productivity due to high photosynthesis rates.

25. The process of photosynthesis in plants is responsible for the:

  • A) Breakdown of glucose
  • B) Conversion of solar energy into chemical energy
  • C) Release of carbon dioxide into the atmosphere
  • D) Formation of oxygen from carbon dioxide

Answer: B
Explanation: Photosynthesis in plants converts solar energy into chemical energy, stored in the form of glucose.

26. In a food chain, which of the following would be classified as a tertiary consumer?

  • A) Grasshopper
  • B) Frog
  • C) Hawk
  • D) Snake

Answer: C
Explanation: A hawk is a tertiary consumer, as it preys on other carnivores (secondary consumers), occupying the highest trophic level.

27. Which of the following is a characteristic of an autotrophic organism?

  • A) It can feed on other organisms for nutrition
  • B) It produces its own food through photosynthesis or chemosynthesis
  • C) It decomposes dead organisms
  • D) It obtains energy from organic matter

Answer: B
Explanation: Autotrophic organisms (e.g., plants, algae) produce their own food through processes like photosynthesis or chemosynthesis.

28. Which of the following is the most significant factor that influences the rate of primary productivity in an ecosystem?

  • A) Temperature
  • B) Availability of nutrients
  • C) Solar radiation
  • D) Precipitation

Answer: C
Explanation: Solar radiation is the most significant factor influencing the rate of primary productivity as plants depend on sunlight for photosynthesis.

29. Which of the following types of organisms are responsible for nitrogen fixation?

  • A) Bacteria
  • B) Fungi
  • C) Green plants
  • D) Decomposers

Answer: A
Explanation: Nitrogen-fixing bacteria, such as Rhizobium, convert atmospheric nitrogen (N₂) into ammonia (NH₃), making nitrogen available to plants.

30. In an ecosystem, energy is transferred from one trophic level to another. The efficiency of energy transfer is usually about:

  • A) 100%
  • B) 50%
  • C) 10%
  • D) 1%

Answer: C
Explanation: The energy transfer efficiency between trophic levels is about 10%, meaning only 10% of the energy is passed on, and the rest is lost as heat.

31. Which of the following is an example of a detritivore?

  • A) Earthworm
  • B) Grasshopper
  • C) Lion
  • D) Deer

Answer: A
Explanation: An earthworm is a detritivore that feeds on dead organic matter and helps in the decomposition process.

32. The process through which carbon dioxide is removed from the atmosphere is called:

  • A) Respiration
  • B) Photosynthesis
  • C) Transpiration
  • D) Combustion

Answer: B
Explanation: Photosynthesis by plants removes carbon dioxide (CO₂) from the atmosphere and converts it into organic compounds.

33. Which of the following best describes the relationship between plants and herbivores in an ecosystem?

  • A) Predation
  • B) Symbiosis
  • C) Competition
  • D) Herbivory

Answer: D
Explanation: Herbivory is the relationship where herbivores feed on plants, with plants being consumed but generally not killed.

34. Which of the following is a component of the biotic part of an ecosystem?

  • A) Air
  • B) Temperature
  • C) Water
  • D) Fungi

Answer: D
Explanation: Fungi are living organisms and part of the biotic components of an ecosystem, as opposed to abiotic factors like air, temperature, and water.

35. Which of the following is a characteristic of a climax community?

  • A) It is constantly changing
  • B) It has a high rate of primary productivity
  • C) It is in a state of equilibrium and does not undergo further change
  • D) It is dominated by pioneer species

Answer: C
Explanation: A climax community is stable and in equilibrium, where species composition remains relatively unchanged unless there is a major disturbance.

36. Which of the following is an example of a primary consumer?

  • A) Lion
  • B) Grasshopper
  • C) Frog
  • D) Vulture

Answer: B
Explanation: A grasshopper is a primary consumer because it feeds on plants (producers).

37. Which of the following cycles does not have a gaseous phase?

  • A) Water cycle
  • B) Carbon cycle
  • C) Nitrogen cycle
  • D) Phosphorus cycle

Answer: D
Explanation: The phosphorus cycle does not have a gaseous phase, as phosphorus is primarily found in solid form in rocks and soil.

38. Which of the following is an example of a secondary consumer?

  • A) Deer
  • B) Snake
  • C) Cow
  • D) Grass

Answer: B
Explanation: A snake is a secondary consumer because it feeds on primary consumers (such as rodents).

39. What is the primary role of producers in an ecosystem?

  • A) Convert inorganic substances into organic substances
  • B) Decompose dead organic matter
  • C) Feed on other organisms
  • D) Release carbon dioxide into the atmosphere

Answer: A
Explanation: Producers (like plants) convert inorganic substances (like CO₂ and water) into organic substances (glucose) through photosynthesis.

40. The primary source of energy for all ecosystems is:

  • A) Water
  • B) Soil
  • C) Sunlight
  • D) Wind

Answer: C
Explanation: Sunlight is the ultimate source of energy for most ecosystems, as it is converted into chemical energy by producers through photosynthesis.

41. In a tropical rainforest, the highest biodiversity is found in the:

  • A) Soil
  • B) Canopy
  • C) Forest floor
  • D) Understory

Answer: B
Explanation: The canopy of a tropical rainforest is home to the highest biodiversity, with various species of plants, animals, and microorganisms.

42. Which of the following best describes the role of decomposers in the ecosystem?

  • A) Produce energy through photosynthesis
  • B) Recycle nutrients by breaking down dead organisms
  • C) Consume producers and primary consumers
  • D) Convert solar energy into chemical energy

Answer: B
Explanation: Decomposers break down dead organisms and organic matter, recycling essential nutrients back into the ecosystem.

43. Which of the following ecosystems has the lowest net primary productivity?

  • A) Coral reefs
  • B) Desert
  • C) Tropical rainforest
  • D) Grassland

Answer: B
Explanation: Deserts have the lowest net primary productivity due to limited water availability and low vegetation growth.

44. The productivity of an ecosystem is primarily dependent on:

  • A) Temperature
  • B) Solar energy
  • C) Water availability
  • D) Soil composition

Answer: B
Explanation: Solar energy is the primary factor influencing primary productivity in an ecosystem, as it drives photosynthesis in producers.

45. Which of the following biomes has the lowest average annual temperature?

  • A) Tropical rainforest
  • B) Tundra
  • C) Desert
  • D) Grassland

Answer: B
Explanation: Tundra is the coldest biome, with an extremely low average annual temperature.

46. Which of the following is the characteristic of a pioneer species?

  • A) It is the last species to colonize an area
  • B) It thrives in stable, mature ecosystems
  • C) It is the first species to colonize a new or disturbed area
  • D) It is a large, long-lived species

Answer: C
Explanation: Pioneer species are the first to colonize an area after a disturbance, often being hardy species like lichens or mosses.

47. Which of the following best describes the shape of a typical ecological pyramid?

  • A) Narrow at the bottom, broad at the top
  • B) Broad at the bottom, narrow at the top
  • C) Equal at all levels
  • D) Inverted

Answer: B
Explanation: A typical ecological pyramid is broad at the bottom (producers) and narrow at the top (top consumers), indicating the loss of energy at higher trophic levels.

48. Which of the following factors does not influence the rate of decomposition?

  • A) Temperature
  • B) Moisture
  • C) Size of decomposing material
  • D) Wind speed

Answer: D
Explanation: Wind speed does not have a significant effect on the rate of decomposition, unlike temperature, moisture, and material size.

49. Which of the following is the main characteristic of a food web?

  • A) It consists of only primary producers and primary consumers
  • B) It shows the energy flow in a single linear chain
  • C) It consists of multiple interconnected food chains
  • D) It only includes carnivores and herbivores

Answer: C
Explanation: A food web is a network of multiple interconnected food chains, showing the complex feeding relationships in an ecosystem.

50. Which of the following is not part of the carbon cycle?

  • A) Photosynthesis
  • B) Respiration
  • C) Nitrogen fixation
  • D) Combustion

Answer: C
Explanation: Nitrogen fixation is part of the nitrogen cycle, not the carbon cycle, which involves processes like photosynthesis, respiration, and combustion.