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:
Statement I: Ecosystems are not exempt from the Second Law of thermodynamics.
Statement II: Ecosystems need a constant supply of energy to break down the molecules they require, to counteract the universal tendency toward increasing disorderliness.
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Statement I is true but Statement II is false
Energy flows through an ecosystem in one direction, from the sun to producers and then to consumers. Ecosystems also follow the Second Law of thermodynamics: there is a universal tendency toward increasing disorderliness, so the ordered molecules of living things must be built and kept up with a steady input of energy.
Statement I: Ecosystems are not exempt from the Second Law of thermodynamics. — True. NCERT says that ecosystems are not exempt from this law. Like any other system, they tend toward disorder unless energy keeps coming in.
Statement II: Ecosystems need a constant supply of energy to break down the molecules they require, to counteract the universal tendency toward increasing disorderliness. — False. The energy is needed to synthesise (build) the molecules they require, not to break them down. Breaking molecules down goes along with disorder; building them works against it.
NCERT Extract:
Energy Flow – “… So you find unidirectional flow of energy from the sun to producers and then to consumers. Is this in keeping with the first law of thermodynamics? Further, ecosystems are not exempt from the Second Law of thermodynamics. They need a constant supply of energy to synthesise the molecules they require, to counteract the universal tendency toward increasing disorderliness.”