AIIMS 2003 Botany Metabolism Assertion Reason Question

To analyze the given question, let’s break down the assertion and reason and then evaluate their truthfulness.

Assertion: "Smaller the organism, higher is the rate of metabolism per gram weight."
Reason: "The surface area is large as compared to the volume."

Explanation of the Assertion

The assertion states that smaller organisms tend to have a higher metabolic rate per gram of body weight. This phenomenon is well observed in biology. For instance, small mammals like mice have a higher metabolic rate than larger animals like elephants. The basal metabolic rate (BMR) is often measured in terms of energy expenditure per unit mass (e.g., mg of ATP produced per gram of body weight), and smaller organisms typically show a higher metabolic rate.

Explanation of the Reason

The reason provided states that "the surface area is large as compared to the volume." This statement is somewhat misleading. In fact, as organisms get smaller, the surface area-to-volume ratio increases. This means that a smaller organism has more surface area relative to its volume when compared to a larger organism. This higher ratio allows for more efficient exchange of gases and nutrients, which can support a higher metabolic rate.

Evaluating the Truthfulness of the Statements

1. Is the assertion true? Yes, the assertion is true. Smaller organisms do have a higher rate of metabolism per gram weight.
2. Is the reason true? The reason is also true but its implications are misrepresented. While it is true that smaller organisms have a larger surface area-to-volume ratio, this does not directly explain why smaller organisms have a higher metabolic rate per gram weight. The reason implies a relationship that is not correctly established in the context of the assertion.

Conclusion

• The correct answer is (C): "If Assertion is true statement but Reason is false." The assertion is true, but the reason does not adequately explain the assertion.

Why Other Options are Incorrect

• Option (A): This option suggests that both the assertion and reason are true and that the reason correctly explains the assertion. This is incorrect because the reason, while true in its own right, does not correctly elucidate the assertion.

• Option (B): This option states that both the assertion and reason are true, but the reason is not the correct explanation. This is incorrect because the reason is true but does not support the assertion in a direct explanatory manner.

• Option (D): This option claims that both the assertion and reason are false, which is incorrect since the assertion is true.

Key Concept

The relationship between an organism's size and its metabolic rate can be explained by the principles of allometry, which studies the relationship of body size to shape, anatomy, physiology, and behavior. The metabolic rate can be modeled with the formula:

$$B = k \cdot M^{3/4}$$

where $B$ is the metabolic rate, $M$ is the mass of the organism, and $k$ is a constant. This relationship supports the assertion that smaller organisms exhibit higher metabolic rates per gram due to their higher surface area-to-volume ratios, which facilitate more efficient metabolic processes.

In summary, while both the assertion and reason contain elements of truth, the reason does not serve as a proper explanation of the assertion, leading us to conclude that the correct choice is (C).