Nerves and Hormones

Learning objectives:

 To learn about aerobic and anaerobic respiration plants.


All living cells need energy to stay alive. Respiration is a chemical reaction that occurs in all living cells to produce energy.

There are two types of respiration:

Aerobic respiration

Aerobic respiration can only occur in the presence of oxygen.
Oxygen taken in from the air combines with the glucose take from food. The two combined produce carbon dioxide, water and energy is released as well.
Respiration occurs in a part of the cell called the mitochondria


There are many uses for the energy released from respiration.

  • It is used to build larger molecules from smaller molecules. An example of this is making protein from amino acids
  • In animals the energy used from respiration can be used for movement. For the muscles to contract energy is required
  • In mammals and birds, those animals who are considered to be warm blooded, require the energy produced from respiration to maintain a constant body temperature
  • In plants, the energy is required to build larger molecules such as starch, proteins and nitrates

Anaerobic respiration

Anaerobic respiration occurs when there is not enough oxygen. In humans a common situation is during exercise when the oxygen supply is less than the demand from the cells. Therefore the cells have to use anaerobic respiration to get the energy. However you do not get the same products. Anaerobic respiration produces a substance called lactic acid.


Anaerobic respiration can also be used to make alcohol. This reaction occurs in microorganisms such as bacteria and yeast, which use glucose to form carbon dioxide and ethanol. This process is known as fermentation


Oxygen debt

The process of anaerobic respiration can lead to oxygen debt. Oxygen debt is when the amount of oxygen entering the body is less than required by the muscles. Therefore your heart, lungs, and blood cannot keep up with the demand.
Therefore after you stop doing the exercise you will keep breathing heavily to ensure that enough oxygen enters the system to enter the muscles and to ensure all the harmful lactate and carbon dioxide.