Cellular respiration and why it's important

All organisms respire in order to release energy to fuel their living processes. The respiration can be aerobic, which uses glucose and oxygen, or anaerobic which uses only glucose.

Releasing energy

Respiration releases energy from food in the form of ATP and heat - it is an exothermic process.

Don't confuse respiration with breathing, which is ventilation. Respiration happens in cells.

Why organisms need energy

Respiration is a series of enzyme-controlled reactions that are needed to convert the stored chemical energy in food into a useable form and in manageable amounts.

Respiration is only around 40 per cent 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 used:

  • for cell division.
  • for synthesis of complex organic molecules.
  • for the contractions of muscles needed for movement.
  • 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.

Investigating aerobic respiration in germinating peas

Germinating peas grow rapidly. This growth process requires a lot of energy for cell division, so the rate of respiration in germinating peas is high.

One way to measure the rate of respiration is to measure the heat produced in the process.

Experiment on aerobic respiration using germinating peas


  • Vacuum flask - to prevent heat loss from the container.
  • Thermometer - to measure increases in temperature.
  • Cotton wool - as a bung in the top of the flask.
  • Germinating peas.

In Flask A - germinating peas

In Flask B - germinating peas which have been disinfected

In Flask C - boiled, disinfected peas


Flask A

The germinating peas will produce the most heat. Peas will carry out respiration to release the energy needed for growth and heat energy is produced as it is an exothermic reaction. The peas are also covered in microbes which also respire producing heat.

Flask B

The germinating peas which have been disinfected will produce less heat than Flask A. The peas will respire to grow but the microbes will have been killed by the disinfectant. This means there are fewer organisms respiring and so less heat produced.

Flask C

This is the control experiment. In this experiment heat was not produced because the peas have been boiled to denature the enzymes which catalyse respiration. They were then disinfected to remove any microbes that might decompose the dead peas.