Question

Which two of the following statements about food chains are correct?
(a) Removal of 80% tigers resulted in increased growth of
vegetation.
(b) Removal of most carnivores resulted in increased population
of deer.
(c) Length of food chain is limited to 3–4 trophic levels due to
energy loss.
(d) Length of the food chain may vary from 2–3 trophic levels.

• A. a, b
  
• B. a, d
  
• C. c, d
  
• D. b, c

Answer 1

The correct option is D b, c

Characteristics of the food chain
The food chain is the linear sequence where nutrients and energy get transferred when one organism eats another. A sequence of eating and being eaten in an ecosystem is represented by the food chain. The following are the characteristics of a food chain:-

• A food chain starts with the plants or producers and usually ends with a tertiary consumer.
• Producers (plant) → Primary consumers → Secondary consumers→ Tertiary consumers.
• The decrease in the population of any organism of a trophic level will have an impact on other trophic levels.
• The energy flow is unidirectional.
• The energy flow decreases as we go up the trophic levels due to the $10\%$ law. The law states that only \10% of the energy is transferred to each trophic level as we go up the trophic levels. Hence, the number of trophic levels is limited.

Effect of removal of tigers
The removal of tigers will cause an increase in the herbivores which in turn will cause a decrease in vegetation as the herbivores depend upon plants for food. Therefore, the removal of tigers cannot cause an increase in vegetation.
Thus the statement “Removal of 80% tigers resulted in increased growth of vegetation” is incorrect

Effect of removal of most carnivores
The removal of most carnivores will result in an increased population of deer because carnivores are dependent on other animals like deer for their food.
Therefore the statement “Removal of most carnivores resulted in an increased population of deer” is correct.

Length of a food chain
Length of the food chain is limited to $3–4$ trophic levels due to energy loss because according to the $10\%$ law, only $10$ percent of the energy is transferred from one trophic level to another trophic level.
Therefore, the statement “Length of the food chain is limited to 3–4 trophic levels due to energy loss” is correct.

Number of trophic levels in a food chain
A food chain is generally $3-4$ trophic levels long as it contains a producer, primary consumer, and secondary consumer. It cannot contain only two trophic levels.
Therefore the statement “Length of the food chain may vary from $2–3$ trophic levels” is incorrect

Final answer
c. b,c