Respiration

Respiration is the body’s way of releasing energy from food. When oxygen is involved, loads of energy can be generated. Without oxygen, respiration produces far less energy.

Aerobic and anaerobic respiration

Respiration is the process by which organisms break down glucose to release energy. We need energy to carry out important biological processes, including:

• Building large molecules, such as proteins and carbohydrates

• Movement (muscle contraction)

• Maintaining body temperature

Respiration is an exothermic process because it releases energy. It can be either aerobic (involves oxygen) or anaerobic (does not involve oxygen).

Aerobic respiration uses oxygen to convert glucose into carbon dioxide and water. It releases much more energy that anaerobic respiration so it is more efficient. The equation for aerobic respiration is given below:

Anaerobic respiration occurs when there is no oxygen available to our cells, e.g. if we are exercising vigorously and our heart can’t pump blood fast enough.

In animals, glucose is broken down into lactic acid. This process produces much less energy compared to aerobic respiration. The equation for anaerobic respiration in animals is given below:

A slightly different form of anaerobic respiration happens in plants and yeast, where glucose is broken down into ethanol and carbon dioxide. This reaction is used in industrial processes, such as brewing beer and wine. It is also used in baking bread, since the carbon dioxide causes bread to rise.

Response to exercise

During exercise, muscles contract more often and need more energy. Cells need to respire more to provide the extra energy needed for muscle contraction.

To ensure that cells have enough glucose and oxygen for respiration, the heart needs to pump blood around the body faster so our heart rate increases. We also breathe much quicker and more deeply (breathing rate and breathing volume increases) to get more oxygen into our body and to supply the muscles with more oxygenated blood.

If we cannot get enough oxygen to our cells, aerobic respiration will stop and be replaced by anaerobic respiration. Anaerobic respiration causes the build-up of lactic acid which can result in cramps and muscle fatigue. In the liver, lactic acid can be converted into glucose by combining it with oxygen — we continue breathing deeply after exercise to obtain enough oxygen. The oxygen needed for lactic acid breakdown is referred to as an oxygen debt.

Metabolism

Metabolism refers to all of the chemical reactions that take place inside the body. The energy that is produced in respiration is used in metabolic reactions, including:

• The conversion of glucose into carbohydrates (starch, glycogen and cellulose)

• The conversion of glycerol and fatty acids into lipids (triglycerides)

• The synthesis of amino acids from glucose and nitrates

• To conversion of amino acids into proteins

• Respiration (because we need some energy to get the process going).

• The breakdown of excess proteins to form urea for excretion

If respiration did not take place then we wouldn’t have the energy needed to build molecules such as carbohydrates, lipids and proteins - these biological molecules are important components of our cells.