Q.17 Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R.
Assertion A: Food chains are short.
Reason R: There is a loss of 10% of energy at each trophic level
In the light of the above statements, choose the most appropriate answer from the options given below:
1. Both A and R are correct and R is the correct explanation of A
2. Both A and R are correct but R is NOT the correct explanation of A
3. A is correct but R is not correct
4. A is not correct but R is correct
Food Chains Short Due to 10% Energy Rule
Food chains remain limited in length primarily because energy diminishes rapidly across trophic levels. The correct answer is 1. Both A and R are correct and R is the correct explanation of A.
Correct Answer
Food chains typically span 3-5 trophic levels because only ~10% of energy transfers to the next level, with 90% lost as heat, metabolism, and waste per Lindeman’s 10% rule. After 4-5 levels, insufficient energy sustains higher predators, directly explaining their shortness.
Option Explanations
1. Both Correct, R Explains A (Correct)
The 10% energy transfer efficiency limits viable trophic levels to 4-6 maximum, as energy drops exponentially (e.g., 1000 → 100 → 10 → 1 units).
2. Both Correct, R Not Explanation (Incorrect)
R precisely causes A’s shortness; without rapid energy loss, chains could extend indefinitely, but 10% rule enforces ecological limits.
3. A Correct, R Incorrect (Incorrect)
Both hold true: chains average 3-4 links in nature, and ~10% (often cited as 10-20%) transfer is standard from field studies.
4. A Incorrect, R Correct (Incorrect)
Chains are empirically short (rarely >5 levels), validated across ecosystems, while R’s energy loss principle underpins food web dynamics.
