Why do organisms need energy?

All organisms need energy to live. This energy is used:

to drive the chemical reactions needed to keep organisms alive – the reactions to build complex carbohydrates, proteins and lipids from the products of photosynthesis in plants, and the products of digestion in animals, require energy
movement – in animals, energy is needed to make muscles contract, while in plants, it is needed for transport of substances in the phloem

Respiration is only around 40% efficient. As animals respire, heat is also released. In birds and mammals, this heat is distributed around the body by the blood. It keeps these animals warm and helps to keep a constant internal temperature.

Energy is also used:

for cell division
to maintain constant conditions in cells and the body – homeostasis
to move molecules against concentration gradients in active transport
for the transmission of nerve impulses

	Created by Caitlin Clyne over 4 years ago

Respiration notes from Bitesize