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 is supplied by cellular respiration, but we usually just call it respiration for short.

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 Energy is transferred from glucose molecules, which were originally made by plants during photosynthesis.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 while releasing energy in the process. This is why the reaction is exothermic.

  • Remember, energy is being released, not created.

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

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

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 – Does not require oxygen to break down the glucose, but it releases less energy.

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