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All living organisms such as human beings, plants, animals, microorganisms, and other matter in the surrounding, coordinate together to form an environment. Every environment consists of an ecosystem that functions individually. An ecosystem comprises both biotic (living matter) and abiotic (non-living matter) components. We know that food is the basic source of energy for all living organisms and different organisms adapt different methods of consumption.
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Also Read: Eco-System - What are its components?
In an ecosystem, some biotic components act as a producer, some as consumers and some as decomposers. All of these are necessary for the environment to sustain itself healthily. The consumers and the decomposers feed themselves through the food prepared by the producers. This cyclic method of consumption is described as the food chain and the interdependence of all the organisms in an ecosystem is represented as a food web.
What are Food Chains and Food Webs?
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A food chain is divided into several trophic levels. The producers (plants) or autotrophs are on the first level of the food chain. They use sunlight and water to prepare food for the consumers or the heterotrophs. The second level of the food chain comprises the herbivores or the primary consumers that depend entirely on the autotrophs for their food. The third level of the food chain comprises the secondary consumers or small carnivores that depend on the herbivores for their food. The fourth and the last level of the food chain comprises Carnivores or tertiary consumers that depend on the herbivores or small carnivores for their food.
Flow of energy from one organism to another is represented by a food chain. The autotrophs that function as the first level of a food chain acquire solar energy and prepare their food through photosynthesis. This food is consumed by the herbivores that stand at the second level of the food chain and therefore the energy obtained by plants is transferred to the next level. The process continues until the energy reaches the last level of the food chain. The proportion of energy transferred decreases with the shift in level in the food chain, therefore, the first level in the food chain receives the maximum energy while the last level receives the lowest amount of energy transferred.
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Why do food chains consist of three or four steps only?
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The first level of the food chain receives the maximum amount of energy. The plants capture the maximum amount of solar energy. Around 1% of the solar energy falls on the leaves to carry out the process of photosynthesis. When the food produced by plants is eaten by herbivores, the energy is transferred to them and some part is lost in the process of digestion. An average of 10% of the remaining is transferred to the next level. Until the transfer is continued up to the last level, very little or no energy is transferred. Therefore, the depletion of energy while its transfer from one level to another, makes conditions for the food chain to last to a maximum of three or four steps only. The above explanation of the transfer of energy can be understood by a simple flow chart.
Sunlight > Producers > Herbivores > Carnivores > Top Carnivores
The Impact of Human Activities on the Ecosystem
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We have learnt about the transfer of energy from one trophic level to another but with the consumption of the food prepared by the producers, harmful chemicals are also transferred to the next trophic levels. For example,
- Chemicals like pesticides and weedicides are used to keep the plants healthy, these plants are consumed by herbivores on the second trophic level, the same is eaten by small carnivores and large carnivores. Therefore, a small portion of these chemicals is transferred to each trophic level.
- Human activities like waste disposal, usage of CFCs in vehicles and discharge of harmful industrial waste in rivers also lead to huge environmental degradation. The chemicals that are released in water bodies can be consumed by the fishes present there. The fishes are then consumed by small or large carnivores. Therefore, the pollutants can also be consumed by organisms at different trophic levels.
Also Read: Ozone Layer and How it is getting depleted
Sample Questions
Question: Explain an example of a Food Chain. (1 mark)
Solution: A food chain is a sequential flow of energy from one trophic level to another. An example of a Food Chain is Grass>Grasshopper>Frog>Snake>Hawk
This means that the first trophic level i.e., Grass is consumed by the Grasshopper that lies on the second trophic level followed by a frog, a snake and a hawk at further trophic levels.
Question: Distinguish between a food chain and a food web. (1 mark)
Solution: A food chain directs a monotonous flow of energy to different trophic levels. The energy transfer is generally at a hierarchical level. Whereas, a food web is a complex structure of food chains that directs the energy flow into multiple directions. It shows the interdependence of different organisms in an ecosystem.
Question: Describe the effects of changes in a food web. (1 mark)
Solution: Any change in the food web may drastically affect the ecosystem in the long run. It may affect the survival of the decomposers and the producers that act as a functional group. This may happen if the link between any food chain breaks. It may create an imbalance in the ecosystem and may affect the survival of several other species.
Question: What happens when predators, such as wolves are removed from the food web? (1 mark)
Solution: Wolves are the top predators or the top carnivores that survive on small carnivores. The major difference that will occur when predators such as wolves are removed from the web is an overpopulation of their prey species. Both predators and the prey balance each other. If the preys are removed the predators will starve and automatically die. Therefore, if the top predators are removed from a food chain, it will cause a rise in the prey species and will cause an imbalance in the ecosystem.
Question: What role do humans play in the food web? (1 mark)
Solution: The human species is considered an omnivore, which means it feeds on both plants and animals. Humans can directly consume plants and their products and act on the second trophic level or consume animals like fish, hen or goat and act on the third trophic level. Therefore, humans play both direct and indirect roles in the food web.
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