Which must a animal do for cellular respiration to begin?

I’m doing some practice exam questions for biology, and i’m not sure how to do these 3 parts to the question.

What function does the limb sever in each animal? how are the limb bones of the four animals similar? based on these similarities what can be inferred about the evolution of the four animals.

The distant ancestors of tigers may have had bodies without stripes. use the theory of natural selection to explain how tigers may have evolved to have stripes.