Ecosystem Class 12 NEET MCQ

1. Which process returns carbon from the atmosphere to the producers?

a) Respiration
b) Decomposition
c) Photosynthesis
d) Fermentation

Answer:

c) Photosynthesis

Explanation:

During photosynthesis, plants absorb carbon dioxide from the atmosphere and convert it into glucose.

2. What is the primary role of decomposers in an ecosystem?

a) Photosynthesis
b) Predation
c) Decomposition of organic matter
d) Nitrogen fixation

Answer:

c) Decomposition of organic matter

Explanation:

Decomposers break down dead organic material and waste, recycling nutrients back into the ecosystem.

3. Which ecosystem has the highest productivity?

a) Desert
b) Ocean
c) Tropical rainforest
d) Tundra

Answer:

c) Tropical rainforest

Explanation:

Tropical rainforests, with their diverse flora and high rainfall, have the highest primary productivity among the given options.

4. In a food chain, energy is transferred from:

a) Carnivore to herbivore
b) Decomposer to producer
c) Producer to herbivore
d) Herbivore to decomposer

Answer:

c) Producer to herbivore

Explanation:

The basic flow of energy in a food chain is from producers (like plants) to consumers (like herbivores).

5. Which component of the ecosystem is considered biotic?

a) Soil
b) Water
c) Plants
d) Air

Answer:

c) Plants

Explanation:

Plants are living entities and are therefore considered a biotic component of the ecosystem.

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

a) Carbon cycle
b) Nitrogen cycle
c) Phosphorus cycle
d) Oxygen cycle

Answer:

c) Phosphorus cycle

Explanation:

The phosphorus cycle primarily involves the soil and rocks, lacking a gaseous phase.

7. Orchid living on the tree is an example of …………..?

a) Parasitism
b) Predation
c) Commensalism
d) Mutualism

Answer:

c) Commensalism

Explanation:

Orchids living on trees are examples of commensalism. The orchid derives a benefit (a place to live), while the tree neither benefits nor is harmed.

8. Population of which of the following will be highest in the food chain?

a) Decomposer
b) Primary Producer
c) Photosynthetic organism
d) Secondary consumers

Answer:

b) Primary Producer

Explanation:

In a food chain, primary producers form the base and their population is typically the highest because they support all other trophic levels.

9. Who is the food component of the grazing food chain?

a) Consumer
b) Decomposer
c) Photosynthetic living organism
d) Photosynthetic consumers

Answer:

c) Photosynthetic living organism

Explanation:

In a grazing food chain, the food component is primarily composed of photosynthetic organisms (like plants) that produce their own food.

10. System resulting from the interaction of all known living factors and the population of all species of a unit area is…

a) Ecology
b) Genetics
c) Science of plants and animals
d) Ecosystem

Answer:

d) Ecosystem

Explanation:

An ecosystem encompasses all living (biotic) and non-living (abiotic) factors in a specific area and their interactions.

11. In which of the following are plants included in any food chain?

a) Primary Producer
b) Primary consumer
c) Primary predator & producer
d) Primary decomposer

Answer:

a) Primary Producer

Explanation:

Plants serve as the primary producers in a food chain as they produce their own food through photosynthesis and form the base for the food chain.

12. Which of the following is the correct statement for the food chain?

a) Every chain formed by nutritional relations, is used to understand energy flow.
b) Energy component of the food chain forms the trophic level.
c) Inter-relation amongst different food chains forms the food web.
d) All of the given

Answer:

d) All of the given

Explanation:

All the provided statements correctly describe aspects of the food chain and its dynamics in ecology.

13. Which of the following uses maximum energy?

a) Primary consumer
b) Secondary consumer
c) Decomposer
d) Primary Producers

Answer:

d) Primary Producers

Explanation:

Primary producers, like plants, utilize sunlight to produce energy through photosynthesis, thus using the most energy.

14. Through which of the following does energy enter an ecosystem?

a) Herbivores
b) Producer
c) Decomposer
d) Primary producers

Answer:

d) Primary producers

Explanation:

Primary producers, like plants, capture sunlight and convert it into usable energy for the ecosystem.

15. Why is algae placed in the first place of the food chain?

a) Algae is first to synthesize food.
b) Algae is first to consume food.
c) Every living organism can utilize food.
d) None of the given.

Answer:

a) Algae is first to synthesize food.

Explanation:

Algae, as primary producers, synthesize food through photosynthesis, placing them at the beginning of the food chain.

16. In which of the following are wheat-eating pigeons included?

a) Decomposer
b) Primary consumer
c) Primary producers
d) Secondary consumer

Answer:

b) Primary consumer

Explanation:

Pigeons that eat wheat are herbivores, making them primary consumers in the food chain.

17. Which of the following is placed at the uppermost (highest) level of ecological pyramids?

a) Herbivores
b) Carnivores
c) Primary and Secondary Producers
d) Primary and Secondary consumers

Answer:

b) Carnivores

Explanation:

In ecological pyramids, carnivores typically occupy the highest trophic levels as they feed on other consumers.

18. As we proceed in the food chain, biomass…

a) Remains the same
b) Decreases
c) Increases
d) Initially the same and later keeps decreasing.

Answer:

b) Decreases

Explanation:

As we move up the food chain, biomass generally decreases due to energy loss at each trophic level.

19. In an ecosystem, the source of energy is…

a) ATP
b) Sun
c) The Green plant
d) Sugar

Answer:

b) Sun

Explanation:

The primary source of energy for an ecosystem is the Sun, which provides light energy that primary producers convert to chemical energy.

20. Who is the primary consumer of a biotic community?

a) Herbivores/ Grazing animals
b) Omnivores
c) Scavengers
d) Carnivores

Answer:

a) Herbivores/ Grazing animals

Explanation:

Primary consumers are herbivores that directly consume primary producers or plants.

21. In which of the following are weeds placed?

a) Primary producers
b) Secondary consumer
c) Primary consumer
d) Decomposer

Answer:

a) Primary producers

Explanation:

Weeds are plants and thus are categorized as primary producers since they perform photosynthesis.

22. When does the energy flow start in an ecosystem?

a) When the material cycle starts
b) When the sun rises
c) When any living organism gains food
d) When light energy is converted to chemical energy

Answer:

d) When light energy is converted to chemical energy

Explanation:

Energy flow in an ecosystem begins when primary producers convert sunlight (light energy) into chemical energy through photosynthesis.

23. Which of the following options is correct for the storage place of phosphorus and nitrogen respectively?

a) Consumer
b) Parental rock and environment
c) Environment and producers
d) Environment and parental rock

Answer:

b) Parental rock and environment

Explanation:

Phosphorus is mainly stored in parental rocks and is released upon weathering, while nitrogen is primarily found in the environment, particularly the atmosphere.

24. Which of the following is the trophic level of the orchid staying on a mango tree?

a) First
b) Tertiary/Third
c) Second
d) Fourth

Answer:

c) Second

Explanation:

The orchid on a mango tree is an example of commensalism. The orchid is an epiphyte and directly uses sunlight for photosynthesis, placing it at the second trophic level.

25. Which age group in the pyramid indicates less reproductive potential?

a) Bell shaped
b) Inverted Bell shaped
c) Triangular
d) All of them have equal (same) potential

Answer:

a) Bell shaped

Explanation:

A bell-shaped age pyramid indicates a stable population with fewer young individuals, suggesting a reduced reproductive potential.

26. It is correct for the ecosystem…….

a) (Plants, Animals, Microorganisms) + Abiotic environment
b) Community formed by various species present in a particular region.
c) Animal, plants, and micro-organisms.
d) Abiotic factors

Answer:

a) (Plants, Animals, Microorganisms) + Abiotic environment

Explanation:

An ecosystem consists of all living organisms (biotic) and their physical environment (abiotic) interacting within a particular area.

27. What is the original source of energy for living organisms?

a) Carbohydrate
b) Sunlight
c) ATP
d) Lipid

Answer:

b) Sunlight

Explanation:

The sun is the primary source of energy, driving photosynthesis in primary producers which forms the basis for energy in all trophic levels.

28. Which of the following is a gaseous cycle?

a) Sulphur cycle
b) Carbon cycle
c) Phosphorous cycle
d) Nitrogen cycle

Answer:

b) Carbon cycle

Explanation:

The carbon cycle is a gaseous cycle as it involves the exchange of carbon between the atmosphere and living organisms.

29. At Each trophic level, in which form is energy lost?

a) Heat
b) Chemical
c) Light
d) None

Answer:

a) Heat

Explanation:

Energy is primarily lost as heat at each trophic level due to the inefficiencies in energy transfers.

30. Which source of eutrophication is the modern source of phosphorus?

a) Detergent
b) Fertilizer
c) Fecal of animals
d) Rivers

Answer:

a) Detergent

Explanation:

Modern detergents often contain phosphates, which when released into water bodies can lead to eutrophication.

31. It helps in the absorption of phosphorous?

a) Leaves
b) Mycorrhiza
c) Root
d) Stem

Answer:

b) Mycorrhiza

Explanation:

Mycorrhizal fungi form symbiotic relationships with plant roots, aiding in the absorption of phosphorus from the soil.

32. In a day, how many times does an individual inspire and expire (breathe)?

a) 10,000
b) 20,000
c) 40,000
d) 50,000

Answer:

b) 20,000

Explanation:

On average, an individual breathes about 12-20 times per minute, which amounts to around 17,000-28,000 breaths per day, approximating to 20,000 for this question.

33. What percentage of total metabolic energy is produced through the fermentation of lactic acid?

a) 80%
b) 70%
c) 100%
d) 40%

Answer:

d) 40%

Explanation:

Fermentation of lactic acid is a less efficient process compared to aerobic respiration, producing only a fraction of the total possible energy.

34. Which adaptation is observed only in xerophytes?

a) CAM
b) Hatch-Slack
c) TCA
d) C3 cycle

Answer:

a) CAM

Explanation:

CAM (Crassulacean Acid Metabolism) is an adaptation seen in many xerophytic plants allowing them to fix CO2 at night, minimizing water loss during hot days.

35. What type of pyramid can be inverted in aquatic ecosystems?

a) Pyramid of numbers
b) Pyramid of biomass
c) Pyramid of energy
d) All of the above

Answer:

b) Pyramid of biomass

Explanation:

In some aquatic ecosystems, producers (like phytoplankton) have less biomass than consumers (like zooplankton), leading to an inverted pyramid of biomass.

36. Which of the following ecosystems covers the smallest part of the Earth’s surface?

a) Marine
b) Freshwater
c) Desert
d) Grassland

Answer:

b) Freshwater

Explanation:

Freshwater ecosystems, including lakes, rivers, and ponds, cover a smaller portion of Earth’s surface compared to marine and terrestrial ecosystems.

37. Which zone in a pond or lake is the open water area where sunlight does not penetrate all the way to the bottom?

a) Littoral zone
b) Limnetic zone
c) Profundal zone
d) Benthic zone

Answer:

b) Limnetic zone

Explanation:

The limnetic zone is the open water area where light does penetrate but not to the bottom. It’s where most of the photosynthesis occurs.

38. Which biome is characterized by a vast expanse of grass with few trees?

a) Tundra
b) Savanna
c) Boreal forest
d) Rainforest

Answer:

b) Savanna

Explanation:

Savannas are grasslands interspersed with occasional trees, mainly found in parts of Africa, South America, and India.

39. What is the process by which atmospheric nitrogen is converted into a usable form for plants?

a) Nitrogen fixation
b) Nitrification
c) Denitrification
d) Ammonification

Answer:

a) Nitrogen fixation

Explanation:

Nitrogen fixation involves the conversion of atmospheric nitrogen into a form (like ammonia) that plants can use.

40. Which of the following is a tertiary consumer?

a) Grass
b) Grasshopper
c) Frog
d) Snake

Answer:

d) Snake

Explanation:

In a typical food chain, a snake would eat a frog (secondary consumer), which ate a grasshopper (primary consumer), which ate grass (producer).

41. Which ecosystem has the least variation in annual temperature?

a) Desert
b) Tropical rainforest
c) Grassland
d) Boreal forest

Answer:

b) Tropical rainforest

Explanation:

Tropical rainforests, located near the equator, have a consistent temperature throughout the year.

42. In an ecosystem, which component is responsible for the recycling of nutrients?

a) Producers
b) Primary consumers
c) Secondary consumers
d) Decomposers

Answer:

d) Decomposers

Explanation:

Decomposers break down dead organic material, thus ensuring nutrients are returned to the soil to be used again by producers.

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