The concentration of pesticides such as DDT increases at each higher trophic level of a food chain. This phenomenon is called
- A.Eutrophication
- B.Biomagnification
- C.Ecological succession
- D.Biodegradation
Correct answer
Explanation
The correct answer is B, biomagnification. DDT and mercury compounds are not broken down in the body and are not excreted, so they build up in the tissues of every organism that takes them in and are passed on to whatever eats it. The concentration therefore rises at each step, and top carnivores such as fish-eating birds and human beings receive the largest dose; in birds it caused eggshells to become thin and break.
Option A, eutrophication, is the excessive growth of algae in a water body enriched by fertilisers and sewage, which strips the water of oxygen. Option C, ecological succession, is the gradual change of a community over time until it reaches a stable climax stage. Option D, biodegradation, is the breaking down of substances by microorganisms, which is exactly what DDT resists.
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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