Why does an endotherm's metabolic rate increase above the upper lethal temperature? And why does ...

The Q10 effect (see Chapter 4) has taken over in the region above the upper lethal temperature, and the animal can no longer control its own metabolism. As the body temperature rises, biochemical processes speed up and the heat that they release warms the body still more and increases the rate of metabolism even further. This cycle causes an explosive increase in body temperature that leads to death. The Q10 effect is also responsible for the decrease in metabolic rate below the lower lethal temperature: as the body temperature begins to fall, biochemical processes slow down and produce less heat, accelerating the drop in body temperature and further slowing metabolism until the animal dies of hypothermia.

You are always so helpful