What is respiration?

The process where stored chemical energy is converted into an energy form that all organisms need to stay alive. It takes place continuously. The equation for respiration is:

Glucose + Oxygen ---> Carbon Dioxide + Water + Energy

C6H12O6 +  6O2    --->         6CO2  +  6H2O  + Energy

1 of 7

Why is respiration important?

·      Muscle Contraction – this takes place even when we don’t realise it e.g. digestion, heart, diaphragm

·      Active Transport – for the movement of ions and molecules

·      Building smaller molecules into larger molecules e.g. amino acids into protein

·      Breaking down larger molecules into smaller molecules e.g. digestion

·      Cell Division

·      Warm Blooded animals use the energy to maintain constant body temperature

2 of 7


The mitochondria are organelles found in cells where respiration takes place. They have a folded inner membrane that provides a large surface area for the enzymes to work in. Found in animal, plant and fungi/algae NOT in viruses or bacteria.

3 of 7

Effects of exercise on the body

Increased heart rate, this increases flow of blood to the muscles. Arteries supplying oxygen dilate to allow more blood through.

The rate and depth of breathing increases. This heavy breathing continues after exercise to pay for oxygen debt.

Glycogen stored in the muscles is converted back to glucose.

Together these factors increase the supply of glucose and oxygen to the muscles, and increase the supply of carbon dioxide removed.

During exercise the muscles contract harder and faster. This means oxygen and glucose must be supplied quicker and carbon dioxide removed faster.

glycogen -------> glucose + oxygen -------> carbon dioxide + water + energy

C24H42O21 ------> C6H12O6 +   6O2     ------->  6CO2 +  6H2O + energy

4 of 7

Anaerobic Respiration

Oxygen Debt– It is caused by lactic acid build up during anaerobic respiration. Oxygen is needed to break the lactic acid down into carbon dioxide and water that can then be excreted. The lactic acid is also taken to the liver to be turned into energy or into glycogen and then stored.

 Anaerobic Respiration – Occurs in the absence of oxygen and produces a smaller amount of energy. It is the incomplete breakdown of glucose and causes a build up of lactic acid.

 Glucose ---> Lactic Acid + Energy

C6H12O6 --->  2C3H6       + Energy

 Drawbacks of Anaerobic Respiration:

o   It only produces 1/20 of the amount of energy produced by aerobic respiration.

o   It produces lactic acid which is poisonous and can lead to muscle fatigue and even death

 Lactic acid is eventually removed from the muscles by blood running through them.

5 of 7

Aerobic respiration

Respiration is a series of reactions in which energy is released from glucoseAerobic respiration is the form of respiration which uses oxygen. It can be summarised by this equation:

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

Energy is shown in brackets because it is not a substance. Notice that:

  • Glucose and oxygen are used up
  • Carbon dioxide and water are produced as waste products

Aerobic respiration happens all the time in the cells of animals and plants. Most of the reactions involved happen inside mitochondria, tiny objects inside the cytoplasm of the cell. The reactions are controlled by enzymes.

6 of 7

Anaerobic Respiration in Plants and Yeast:

Lactic acid is not produced, instead carbon dioxide and ethanol is.

Glucose ---> ethanol + carbon dioxide + energy

C6H12O6 ---> 2C2H5OH +        2CO2            + energy

7 of 7


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Respiration and exercise resources »