Question

Study the food chain given below:

A. In the given food chain, the amount of energy available at the fourth trophic level is 10 kJ, what will be the energy available at the producer level?
B. Is it possible to have three more trophic levels in the above food chain? Justify.
C. Which of these trophic levels will have the maximum amount of pesticide, if it had washed down in the water body from agricultural fields. Why?

Hint:

Use the 10 percent law: multiply by 10 to go down a level. Pesticides are not broken down, so they build up along the chain.

Answer 1

Step 1: Read the food chain:
Phytoplankton is the producer (first trophic level). Zooplankton is the second level, small fishes the third level and large fish the fourth level.
We use the 10 percent law: only 10% of the energy of a level passes to the next level.

Step 2: Part A: Energy at the producer level:
The fourth level has 10 kJ. This is 10% of the third level, so the third level has \( 10 \times 10 = 100 \) kJ.
The third level is 10% of the second level, so the second level has \( 100 \times 10 = 1000 \) kJ.
The second level is 10% of the producers, so the producers have \( 1000 \times 10 = 10000 \) kJ.
\[ \text{Energy at producer level} = 10 \times 10 \times 10 \times 10 = 10^{4} \text{ kJ} \]

Step 3: Part B: Three more trophic levels:
The chain already has four levels. Three more would make seven levels.
Starting from 10000 kJ at the producers, the energy at levels 4, 5, 6 and 7 would be 10 kJ, 1 kJ, 0.1 kJ and 0.01 kJ. The seventh level gets only 0.01 kJ, which is far too little to support any organism.
So it is not possible. The loss of energy at each step is so large that very little usable energy is left for the higher levels. This is why food chains have only three to five trophic levels.

Step 4: Part C: Level with the most pesticide:
Pesticides washed into the water are absorbed by the phytoplankton. They are not broken down by the body and are not removed easily, so they stay in the body.
Each consumer eats many organisms of the lower level, so the pesticide gets collected and becomes more concentrated at every step. This is called biological magnification.
The large fish is at the top of the chain, so it has the maximum amount of pesticide.

Final Answer:
A. 10000 kJ. B. No, because too much energy is lost at every level. C. Large fish, because of biological magnification. \[ \boxed{\text{A. 10000 kJ; B. Not possible; C. Large fish}} \]