Respiration

This lesson covers: 

  1. What respiration is and why it is important
  2. Aerobic respiration
  3. Anaerobic respiration in humans and microorganisms

What is respiration and why is it important?

Respiration is a chemical reaction that releases energy from the breakdown of glucose in cells.

It occurs in all living cells and is essential for providing energy for life processes like protein synthesis, muscle contraction and maintaining body temperature.


There are two main types of cellular respiration:

  1. Aerobic - This requires oxygen.
  2. Anaerobic - This does not require oxygen.

Aerobic respiration

Diagram showing the process of aerobic respiration in a mitochondrion, including glucose, oxygen, carbon dioxide, and water.

Aerobic respiration:

  • Occurs in mitochondria and uses oxygen.
  • Releases a large amount of energy.
  • Produces the waste products are carbon dioxide and water.


Overall word equation:

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

Anaerobic respiration

Anaerobic respiration:

  • Occurs in the cytoplasm.
  • Releases less energy than aerobic respiration.
  • Is used when oxygen levels are low.
  • Has different waste products in different organisms.

Anaerobic respiration in humans

Illustration of a person cycling with a zoomed-in view of a muscle producing lactic acid during anaerobic respiration.

In humans, anaerobic respiration produces lactic acid.


This can build up in muscles during intense exercise leading to cramp and pain.


Overall word equation:

glucose → lactic acid (+ energy)

Anaerobic respiration in yeast

Diagram showing anaerobic respiration in yeast producing carbon dioxide for bread and alcohol for alcoholic drinks.

In yeast, anaerobic respiration produces carbon dioxide and ethanol (alcohol).


This process is called fermentation and is used to produce beers, wines, and bread.


Overall word equation:

glucose → carbon dioxide + ethanol (+ energy)