Net primary productivity of an ecosystem is equal to
- A.gross primary productivity plus respiration
- B.gross primary productivity minus the energy used by plants in respiration
- C.the total sunlight falling on the ecosystem
- D.the biomass of all the consumers
Correct answer
Explanation
The correct answer is B. Gross primary productivity is the total amount of energy that producers fix by photosynthesis. Plants use a part of it for their own respiration, and what remains stored in plant bodies is the net primary productivity. That remainder is the food actually available to herbivores, so it decides how much life the ecosystem can support.
Option A adds respiration instead of subtracting it and would give a figure larger than the energy actually captured. Option C is wrong because green plants capture only a small fraction of the sunlight that reaches them, the rest being reflected or passing through. Option D describes the standing biomass of consumers, which is a stock at a moment in time, not a rate of production. Productivity is always expressed per unit area per unit time.
Read the full article: Ecosystem and Food Chains: Components, Levels and Pyramids
Practice Questions
View allThe term ecosystem was coined by which scientist?
- A.A. G. Tansley
- B.Charles Darwin
- C.Raymond Lindeman
- D.Charles Elton
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The British botanist Arthur George Tansley used the word ecosystem in 1935 for a unit in which living organisms and their non-living surroundings are treated together as one system exchanging energy and matter.
Read the full explanation →In a food chain, green plants are called
- A.Producers
- B.Primary consumers
- C.Decomposers
- D.Secondary consumers
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Green plants make their own food from carbon dioxide and water by photosynthesis, using the energy of sunlight, so they are also called autotrophs.
Read the full explanation →The ten per cent law of energy transfer in a food chain was given by
- A.A. G. Tansley
- B.Raymond Lindeman
- C.Odum
- D.Ernst Haeckel
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It says that only about ten per cent of the energy present at one trophic level is passed on to the next, since the rest is used in respiration and other life processes and is lost to the surroundings as heat.
Read the full explanation →Which of the following ecological pyramids is always upright?
- A.Pyramid of numbers
- B.Pyramid of biomass
- C.Pyramid of energy
- D.All three are always upright
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Energy is lost as heat at every transfer from one trophic level to the next, so a higher level can never hold more energy than the level below it.
Read the full explanation →Bacteria and fungi that break down dead plants and animals are known as
- A.Producers
- B.Decomposers
- C.Herbivores
- D.Omnivores
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They feed on dead bodies, fallen leaves and waste matter, break the complex organic substances into simple ones and release nutrients back into the soil, water and air, where plants can take them up again.
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