Read the passage and answer the following questions:
Apart from the deep-sea hydrothermal ecosystem, the primary source of energy for all ecosystems on Earth is the sun. However, only a portion of the incident solar radiation, less than 50 percent, is photosynthetically active radiation (PAR). Autotrophs, such as plants and photosynthetic bacteria, utilise this radiant energy to produce food from simple inorganic substances. Remarkably, plants can capture only 2-10 percent of the PAR, yet this small amount of energy sustains the entire living world. Understanding how solar energy, captured by plants, flows through different organisms within an ecosystem is crucial. In this unidirectional flow of energy, the sun nourishes the producers (often green plants), which serve as the foundation of the ecosystem. In terrestrial ecosystems, herbaceous and woody plants are the major producers, while in aquatic ecosystems, various species like phytoplankton, algae, and higher plants play this vital role. All other organisms, referred to as consumers or heterotrophs, depend on producers for their food requirements. Consumers can be classified based on their feeding habits. Those that directly consume producers, the plants, are called primary consumers. In contrast, if animals eat other animals that, in turn, feed on plants or their products, they are known as secondary consumers. Tertiary consumers, similarly, consume animals from the secondary consumer level. In summary, the entire ecosystem relies on the unidirectional flow of solar energy, starting from the sun to the producers (plants), and then passed on to the various levels of consumers, ensuring the sustenance of life within the ecosystem.
Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): A sparrow can occupy more than one trophic level in the same ecosystem at the same time.
Reason (R): A trophic level represents a functional level, not a species as such, and a sparrow eats seeds and fruits as well as insects and worms.
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Both (A) and (R) are true and (R) is the correct explanation of (A).
A trophic level is the place an organism takes in a food chain on the basis of its food. Some animals eat both plants and animals, so they do not stay at one level.
Assertion (A): A sparrow can occupy more than one trophic level in the same ecosystem at the same time. — True. A is about where a sparrow stands in the food chain. A sparrow is a primary consumer when it eats seeds, fruits and peas, and a secondary consumer when it eats insects and worms.
Reason (R): A trophic level represents a functional level, not a species as such, and a sparrow eats seeds and fruits as well as insects and worms. — True. R is about what a trophic level means. It is fixed by the role an organism plays while feeding, not by its species.
Why R explains A? If trophic levels were fixed for each species, a sparrow could have only one level. Because a level is a function, the same sparrow does the work of a primary consumer when it eats seeds and of a secondary consumer when it eats insects. So R gives the reason for A, and R is the correct explanation of A.
NCERT Extract:
Ecological Pyramids – “… Also a given organism may occupy more than one trophic level simultaneously. One must remember that the trophic level represents a functional level, not a species as such. A given species may occupy more than one trophic level in the same ecosystem at the same time; for example, a sparrow is a primary consumer when it eats seeds, fruits, peas, and a secondary consumer when it eats insects and worms.”