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Respiration (Higher)
Aerobic Respiration | Anaerobic Respiration
 

Aerobic Respiration

Aerobic respiration is the release of energy from glucose in the presence of oxygen.  It is a chemical reaction that occurs inside structures called mitochondria in cells.

The reaction is summarised by the equation:

glucose + oxygen → carbon dioxide + water (+ energy)

Energy released is used:

  • To build up larger molecules using smaller ones
  • To enable muscles to contract
  • To produce heat
  • In the active transport of materials across boundaries

The waste products are carbon dioxide and water.

Carbon dioxide is poisonous so is transported from the respiring cells to the lungs where it is breathed out.

Some of the water is used by the body, but some is breathed out.

During vigorous exercise the circulatory system may not be able to supply enough oxygen to the muscle cells for aerobic respiration and they stop contracting efficiently.  The cells may then carry out anaerobic respiration to release more energy.
Anaerobic Respiration

Anaerobic respiration is without oxygen.  It does not break down the glucose completely, so much less energy is released than in aerobic respiration.  Lactic acid is produced, which is poisonous and causes cramp.

The equation for anaerobic respiration is:

glucose → lactic acid (+ a little energy)

After exercise you continue to pant in order to supply more oxygen to oxidise the lactic acid.  The amount of oxygen required is called the oxygen debt.

lactic acid + oxygen → carbon dioxide + water