Ecosystem

1. Decomposers like fungi and bacteria are:

i. autotrophs

ii. heterotrophs

iii. saprotrophs

iv. chemo-autotrophs.

Choose the correct answer:

(a) i and iii

(b) i and iv

(c) ii and iii

(d) i and ii

Key Answer: (c) ii and iii

Explanation: Decomposers depend on dead organic matter for nutrition. Hence they are heterotrophs and saprotrophs.

2. The process of mineralisation by micro organisms helps in the release of:

a. inorganic nutrients from humus

b. both organic and inorganic nutrients from detritus

c. organic nutrients from humus

d. inorganic nutrients from detritus and formation of humus.

Key Answer: d. inorganic nutrients from detritus and formation of humus.

Explanation: Mineralisation converts organic matter into inorganic nutrients. Humus is also formed during decomposition.

3. Productivity is the rate of production of biomass expressed in terms of:

i. (kcal m–3) yr–1

ii. g–2 yr–1

iii. g–1 yr–1

iv. (kcal m–2) yr–1

(a) ii

(b) iii

(c) ii and iv

(d) i and iii

Key Answer: (c) ii and iv

Explanation: Productivity is measured as biomass or energy produced per unit area per unit time. Hence units include g m⁻² yr⁻¹ and kcal m⁻² yr⁻¹.

4. An inverted pyramid of biomass can be found in which ecosystem?

a. Forest

b. Marine

c. Grass land

d. Tundra

Key Answer: b. Marine

Explanation: In marine ecosystems, phytoplankton biomass is less than consumer biomass. This creates an inverted biomass pyramid.

5. Which of the following is not a producer?

a. Spirogyra

b. Agaricus

c. Volvox

d. Nostoc

Key Answer: b. Agaricus

Explanation: Agaricus is a fungus and lacks chlorophyll. Therefore it cannot perform photosynthesis.

6. Which of the following ecosystems is most productive in terms of net primary production?

a. Deserts

b. Tropical rain forests

c. Oceans

d. Estuaries

Key Answer: d. Estuaries

Explanation: Estuaries receive nutrients from both rivers and seas. This makes them highly productive ecosystems.

7. Pyramid of numbers is:

a. Always upright

b. Always inverted

c. Ether upright or inverted

d. Neither upright nor inverted.

Key Answer: c. Ether upright or inverted

Explanation: The shape depends on the ecosystem structure. For example, tree ecosystems may show inverted pyramids.

8. Approximately how much of the solar energy that falls on the leaves of a plant is converted to chemical energy by photosynthesis?

a. Less than 1%

b. 2-10%

c. 30%

d. 50%

Key Answer: a. Less than 1%

Explanation: Only a very small fraction of solar energy is fixed by photosynthesis. Most energy is lost as heat or reflected.

9. Among the following, where do you think the process of decomposition would be the fastest?

a. Tropical rain forest

b. Antarctic

c. Dry arid region

d. Alpine region

Key Answer: a. Tropical rain forest

Explanation: Warm and moist conditions favor rapid microbial activity. Hence decomposition is fastest in tropical rain forests.

10. How much of the net primary productivity of a terrestrial ecosystem is eaten and digested by herbivores?

a. 1%

b. 10%

c. 40%

d. 90%

Key Answer: b. 10%

Explanation: Only a small portion of plant biomass is consumed by herbivores. Most enters the detritus food chain.

11. During the process of ecological succession the changes that take place in communities are:

a. Orderly and sequential

b. Random

c. Very quick

d. Not influenced by the physical environment.

Key Answer: a. Orderly and sequential

Explanation: Ecological succession follows predictable stages. Each community modifies the environment for the next stage.

12. Climax community is in a state of:

a. non-equilibrium

b. equilibrium

c. disorder

d. constant change.

Key Answer: b. equilibrium

Explanation: Climax communities are stable and self-sustaining. They remain in balance with the environment.

13. Among the following bio-geo-chemical cycles which one does not have losses due to respiration?

a. Phosphorus

b. Nitrogen

c. Sulphur

d. All of the above

Key Answer: a. Phosphorus

Explanation: Phosphorus cycle lacks a gaseous phase and is not affected by respiration losses. It mainly circulates through rocks and soil.

14. The sequence of communities of primary succession in water is:

a. phytoplankton, sedges, free-floating hydrophytes, rooted hydrophytes, grasses and trees.

b. phytoplankton, free-floating hydrophytes, rooted hydrophytes, sedges, grasses and trees.

c. free-floating hydrophytes, sedges, phytoplankton, rooted hydrophytes, grasses and trees.

d. phytoplankton, rooted submerged hydrophytes, floating hydrophytes, reed swamp, sedges, meadow and trees.

Key Answer: d. phytoplankton, rooted submerged hydrophytes, floating hydrophytes, reed swamp, sedges, meadow and trees.

Explanation: Hydrarch succession progresses from aquatic to terrestrial stages. Gradual sediment accumulation supports advanced plant communities.

15. The reservoir for the gaseous type of bio-geo chemical cycle exists in

a. stratosphere

b. atmosphere

c. ionosphere

d. lithosphere

Key Answer: b. atmosphere

Explanation: Gaseous cycles such as carbon and nitrogen cycles have atmospheric reservoirs. These gases circulate through living and non-living components.

16. If the carbon atoms fixed by producers already have passed through three species, the trophic level of the last species would be.

a. scavenger

b. tertiary producer

c. tertiary consumer

d. secondary consumer

Key Answer: c. tertiary consumer

Explanation: Producers form the first trophic level. After passing through three consumers, the last organism becomes a tertiary consumer.

17. Which of the following type of ecosystem is expected in an area where evaporation exceeds precipitation, and mean annual rainfall is below 100mm

(a) Grassland

(b) Shrubby forest

(c) Desert

(d) Mangrove

Key Answer: (c) Desert

Explanation: Deserts receive very low rainfall and experience high evaporation. Such conditions limit vegetation growth.

18. The zone at the edge of a lake or ocean which is alternatively exposed to air and immersed in water is called:

a. Pelagic zone

b. Benthic zone

c. Lentic one

d. Littoral zone

Key Answer: d. Littoral zone

Explanation: Littoral zones occur near shorelines where water levels fluctuate. They support diverse aquatic life.

19. Edaphic factor refers to:

a. Water

b. Soil

c. Relative humidity

d. Altitude

Key Answer: b. Soil

Explanation: Edaphic factors include soil properties like texture and pH. These factors influence plant distribution.

20. Which of the following is an ecosystem service provided by a natural ecosystem?

a. Cycling of nutrients

b. Prevention of soil erosion

c. Pollutant absorption and reduction of the threat of global warming

d. All of the above

Key Answer: d. All of the above

Explanation: Natural ecosystems provide many services essential for life. These include nutrient cycling, climate regulation and soil conservation.