Question

The given figure shows five food chains with humans at the top. Which of these two chains supply the maximum amount of energy to the human?

A) P & Q
B) P & S
C) Q & R
D) Q & S

Answer 1

Hint: Food chain is a network of animals and plants based on eating and being eaten relationships. Each level of the food chain is called trophic level. Energy is passed from one trophic level to another. The amount of energy that is passed depends on the position of the trophic level in the food chain.

Complete step-by-step answer:
A typical food chain starts with the autotrophs or the producers. Plants are designated as producers because they trap the solar energy and convert it into organic matter. Next are the consumers. The animals that eat only plants are the herbivores or the primary consumers. Animals that consume herbivores are called carnivores or the secondary consumers. The apical organisms of the food chain are either tertiary consumers or decomposers.
Energy enters the ecosystem as light energy and is utilized by plants for photosynthesis. The energy is passed on to the next trophic level when living or dead plant matter is consumed by the herbivores. Next, when the herbivores are consumed by carnivores, a part of the energy from herbivores is transferred to them. In this way, energy is transferred from one trophic level to the next until it reaches the decomposer level. The decomposer releases the energy and nutrients back to the atmosphere for further recycling.
According to ecology studies, it has been observed that the amount of energy decreases while transferring from one trophic level to another. This is because a lot of energy is lost in respiration, body movements and heat. The Lindeman’s 10 percent rule states that only 10 percent of the energy received by a trophic level is passed on to the next level. For example, if plants absorb 100 KJ of solar energy, only 10 KJ is transferred to the herbivore level. The carnivore level will receive 0.01 KJ energy.
Therefore, according to the diagram given in the question, in the food chains P & S the human is shown to consume plant matter, rice and maize respectively. The energy is transferred directly from the producer level to the human without any diversification.
However, in the food chains, Q & R, the energy is transferred from the producer level to the herbivore level and then to the human. Thus, as energy is being transferred from the producer level to the human via the herbivore level, the human receives lesser energy than food chains P & S.

Therefore, option B is the correct answer.

Note: Ecosystems are composed of living and nonliving components. These components interact with one another to maintain the stability of the ecosystem in terms of energy flow, nutrient cycling and population. Food chains are a series of organisms that consume one another. This process helps the environment or ecosystem to maintain the energy flow and nutrient cycling in the ecosystem. Each level of a food chain is known as the trophic level. As energy flows from one level to another, it goes on decreasing. Therefore, animals at the apex of the food receive less energy as compared to the animals located at lower trophic levels.