Some activities that cell requires energy may include cell division, active transport, protein synthesis etc.
In human, Cells get their energy by the food we eat. The nutrients in the food breaks down into soluble and simple molecules in stomach and small intestine and it is absorbed through the small intestine and assimilated into the cells, becoming part of it, providing the uses for each type of nutrient. And of course, many of them is the energy source.
Definitely i would expect them to concern themselves with your problems when they are so beset with their own. Beset means having a lot of trouble with something, or having to deal with a lot of something causes problems. For example in a sentence; With the amount of traffic nowadays, even a trip across town is beset with dangers.
A host cell is the answer.
