The answer is cell division
A) weapons for an evolutionary arms race w/ disease causing organisms
The ultimate source of energy (for most ecosystems) is the sun<span>. The ultimate fate of energy in ecosystems is for it to be lost as heat. Energy and nutrients are passed from organism to organism through the food chain as one organism eats another.</span>
When you shiver, that's actually how you help yourself stay warm! It's your immediate instinct reaction to do so when you're cold, so there will be more heat produced, and they occur by your muscles moving. =)