The given question is incomplete as there is no figure attached with the question but in general we can answer this question.
Answer: To get energy.
Step-by-step explanation:
The whale eats other organism in order to get energy. The smallest unit of energy is atom. Any of the substance is made of atoms and so is the food that we eat.
The whale will also be dependent for its energy on the food that it eats. It will have smaller fishes and other aquatic animals as a source of energy.
So, to gain energy the living things eat food. Smaller animals are being eaten by the larger fishes as a source of energy.