Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): Ecosystems need a constant supply of energy to synthesise the molecules they require.
Reason (R): Ecosystems are not exempt from the Second Law of thermodynamics and must counteract the universal tendency toward increasing disorderliness.
In the light of the above statements, choose the correct 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).
Assertion (A): Ecosystems need a constant supply of energy to synthesise the molecules they require. — True. A is about the need of an ecosystem for energy. Its organisms must keep making complex molecules (proteins, carbohydrates, nucleic acids), and for this a constant supply of energy is needed; it comes from the sun through the producers.
Reason (R): Ecosystems are not exempt from the Second Law of thermodynamics and must counteract the universal tendency toward increasing disorderliness. — True. R is about a law of physics. By the Second Law of thermodynamics, every system tends towards increasing disorderliness, and ecosystems are not exempt from it.
Why R explains A? Complex, ordered molecules tend to break down into simpler, disordered ones. To build them and keep them, an ecosystem must use energy all the time against this tendency. So the Second Law in R is the reason why A says ecosystems need a constant supply of energy. R is the correct explanation of A.
NCERT Extract:
Energy Flow – “… All organisms are dependent for their food on producers, either directly or indirectly. So you find unidirectional flow of energy from the sun to producers and then to consumers. … 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.”