8.9 - 8.10 - Cellular respiration

8.9 — Energy released in living cells

A germinating seed may look still, but its cells are dividing, building molecules and transporting substances. Those processes need a continuous transfer of energy. The reactions that release this energy happen inside living cells, not only when an organism is moving and not only in animals.

Respiration is exothermic overall. An exothermic reaction transfers energy to its surroundings; during respiration, cells transfer some of the energy released from glucose to metabolic processes, while some is dissipated as heating. Energy is therefore released or transferred, not made, created or produced.

The released energy can be used for:

• active transport across cell membranes
• muscle contraction and movement
• building larger molecules from smaller ones
• cell division, growth and repair

Breathing and respiration are related but different. Breathing ventilates gas-exchange surfaces, helping an animal obtain oxygen and remove carbon dioxide. Cellular respiration is the chemical process in cells. Plants, microorganisms and animals respire, and plant cells continue to respire whether or not photosynthesis is occurring. Oxygen uptake measures aerobic respiration; it cannot measure anaerobic respiration on its own.