Question

In an experiment freshly hatched larvae of an insect (Khapra beetle) were reared on a basal diet (complete diet without cholesterol) with increasing amounts of cholesterol. Results obtained are shown in the given graph.
The graph indicates
1)Cholesterol is an essential dietary requirement for Khapra beetles.
2)Growth of Khapra beetle is directly proportional to cholesterol concentration.
3)Cholesterol concentration of 2µg/g diet is the optimum level.
4)Growth of Khapra beetle is inhibited when cholesterol concentration exceeds 5 µg/g diet.

Answer 1

Hint: Growth curve is the curve which shows the increase in the size and mass during the development of an organism. The growth curve is sigmoidal in nature showing gradual increase at the beginning, rapid increase in the middle and further slow increase till it attains a constant level.

Complete answer:
According to the question, the hatched larvae of Khapra beetles were reared on the complete diet without cholesterol with increasing amounts of cholesterol.
The graph obtained weight of the larvae versus the amount of cholesterol is a sigmoid curve. This means that the growth curve is in a normal pattern.

It consists of three phases-
Lag phase- Which shows that the larvae were adjustable with the cholesterol.
Log phase- The larvae grew significantly.
Stationary phase- At a certain cholesterol level the insects do not require further cholesterol.
This shows that the growth of the Khapra beetle depends on a certain amount of cholesterol.

If the growth of the Khapra beetle would have been directly proportional to the cholesterol, then the graph would have been a straight-line showing increase in the concentration will result in an increase of weight.

According to the graph, the weight of larvae at 2µg/g of diet is 1mg. It increases as the cholesterol level increases. So, it is not the optimum value.

After 5µg/g of cholesterol, the growth remains constant. It means that after this quantity the growth is unaffected and not inhibited.

Hence, the correct answer is option (A)

Note: The Exponential growth occurs in the system where the resources are in plenty but the number of individuals is less. But when the individuals become more, the resources start depleting. This results in levelling off of the growth rate.