Black bears can hibernate for up to 7 months without food or water (lines 1−2).

Suggest and explain how.

During hibernation, the heart rate and the metabolic rate of black bears decrease (lines 3−5).

Use your knowledge of the nervous control of heart rate to describe how these are linked.

In many mammals, 'uncoupling proteins' help to maintain a constant body temperature during hibernation (lines 6−7).

Suggest and explain how.

Climatic change has reduced the survival rate of snowshoe hares in mountain habitats (lines 11−13).

Suggest and explain how.

Snowshoe hares within a population moult at different times (line 15).

Explain how this could ensure the survival of snowshoe hare populations in these mountain habitats.