Aerobic and anaerobic respiration

Cellular respiration is a continuous process that occurs in all living cells to release the energy needed for life. It is an exothermic reaction, meaning it transfers energy to the environment. This energy is used by organisms for:

• Chemical reactions to build larger molecules (like proteins and fats),

• Movement,

• Keeping warm.

Respiration can occur in two ways:

1. Aerobically (with oxygen), which releases a lot of energy.

2. Anaerobically (without oxygen), which releases much less energy.

Aerobic respiration

Most organisms, including humans, rely on aerobic respiration for their energy needs. This process uses oxygen to fully break down glucose into carbon dioxide and water, transferring a large amount of energy in the process.

The word equation for aerobic respiration is: 

glucose + oxygen → carbon dioxide + water

The symbol equation for photosynthesis is:

C6H12O6 + O2 → CO2 + H2O

You should notice that the chemicals for this reaction are the same as for photosynthesis but the reactants and products have been switched around. 

Anaerobic respiration

Anaerobic respiration occurs when there is not enough oxygen available for aerobic respiration. This happens, for example, during vigorous exercise in muscles when the oxygen supply can’t keep up with demand. In anaerobic respiration, glucose is only partially broken down, producing lactic acid in animals, which can lead to muscle pain and fatigue. This process transfers much less energy than aerobic respiration.

The word equation for anaerobic respiration in animals is: 

glucose → lactic acid

The word equation for anaerobic respiration in plant and yeast cells is:

glucose → ethanol + carbon dioxide

In yeast, this process is called fermentation and is important in industries that produce bread and alcoholic drinks. However, both lactic acid in animals and ethanol in plants and yeast are toxic, and over time, they can cause damage to cells.

Comparing aerobic and anaerobic respiration