Cellular Respiration

Organisms need energy for many processes. For example:

  • Cell division
  • Growth and repair
  • Building larger molecules from smaller ones (e.g., joining amino acids to form proteins)
  • Active transport
  • Muscular contraction – So that we can move
  • Maintaining our body temperature – So that chemical reactions in our body can take place and so that we can stay warm

The energy required for these processes comes from cellular respiration, often simply referred to as respiration.

Cellular respiration is an exothermic reaction which occurs continuously in living cells. Energy is transferred from glucose molecules, which were originally made by plants during photosynthesis. The energy released from breaking down glucose fuels a majority of our living processes.

Cellular respiration involves breaking down glucose molecules, releasing energy in the process. Therefore, the reaction is exothermic.

  • Remember, energy is being released during cellular respiration, not created.

The diagram below illustrates the relationship between photosynthesis and cellular respiration:

Diagram illustrating the cyclical relationship between photosynthesis and cellular respiration, showcasing the transfer of energy and matter.

Respiration produces carbon dioxide, which is used in photosynthesis, completing the cycle.

Types of Respiration

There are two different types of respiration:

  • Aerobic respiration – Oxygen is required to break down glucose, which produces carbon dioxide and water while releasing energy in the process.
  • Anaerobic respiration – This process does not require oxygen to break down glucose and releases less energy compared to aerobic respiration.

OxygenRequiredNot required
Glucose breakdownCompleteIncomplete
Product(s)Carbon dioxide and waterAnimal cells: lactic acid

Plant cells and yeast: carbon dioxide and ethanol
Energy releasedRelatively large amountRelatively small amount

You’ve used 10 of your 10 free revision notes for the month

Sign up to get unlimited access to revision notes, quizzes, audio lessons and more

Sign up