Why do you think the energy requirements are different in situations?

Well the requirement is dependent on the ways in which the body spends energy. For example in the first case the intensity of work or voluntary activity i.e. intentional activities (such as cycling, swimming) conducted by voluntary muscles affects the amount of energy used, hence the variation in the requirement.

On the other hand, think of all the involuntary activities of our body that are necessary to sustain lire, including circulation, respiration, temperature maintenance, hormone secretion, nerve activity, new tissue synthesis etc. All these involuntary activities of the body, which continue day in and day out without our conscious awareness, require energy. Further, as the food is chewed, digested, absorbed, these metabolic response to food increases total energy expenditure.