Question

Calculate the unuseful energy (in $\text{cal}$) left after the completion of the following food chain, if $3,600\text{cal}$ is the gross primary production (GPP):

$\text{Algae}\to \text{Fish}\to \text{Hawk}$

• A. $3.6\text{cal}$
• B. $36\text{cal}$
• C. $360\text{cal}$
• D. $0.36\text{cal}$

Answer 1

The correct option is A $3.6\text{cal}$

Given:
Gross primary production, GPP $=3,600\text{cal}$

$60\%$ of this energy is utilised in the metabolism and respiration of the producer (algae)

$⟹3,600(1-\frac{60}{100})=1,440\text{cal}$ is the net primary production (NPP). Now, $75\%$ of NPP is utilised in the death and decay of the producer, i.e. $1440(1-\frac{75}{100})=360\text{cal}$ is available for the primary consumer (fish).

In the similar manner, only $40\%$ of the energy is left after the metabolism and respiration of the primary consumer, i.e. $360(1-\frac{60}{100})=144\text{cal}$ is left. Out of this, $75\%$ is used in the death and decay $⟹144(1-\frac{75}{100})=36\text{cal}$ is passed onto the secondary consumer (hawk).
Finally, after calculating and eliminating the energy utilised in the metabolism and death of the jaguar, only $3.6\text{cal}$ would remain in the end.