Cellular Respiration

cellular respiration

Cellular Respiration is the process that takes place in cells to convert food into energy. Here we explain the key terms ATP, ADP, and the formula for cellular respiration.


Stored in muscles as ATP (adenosine triphosphate), the body converts molecules of Carbon, Hydrogen, Oxygen, and Nitrogen into energy.

Formula for cellular respiration

When your body needs energy, it breaks down ATP into ADP (Adenosine Diphosphate) using the enzyme ATPase. The process breaks the high-energy Phosphate (P) bond and so provides energy for use by the body.

This is the formula for cellular respiration:

ATP = ADP + P +Energy

The process of cellular respiration means we won’t run out of energy. This is because the human body is also capable of resynthesising ATP. As a result, this allows the body to continue producing energy.

To do this it must use energy to reverse the equation shown above. This is an endothermic reaction because it requires energy. The breakdown of ATP is exothermic because it produces energy. However, resynthesising ATP needs less energy than breaking it down produces.

This is the formula for resynthesis:

Energy + ADP +P = ATP

Cellular respiration and energy systems

Cellular respiration uses two basic energy systems. These are aerobic respiration and anaerobic respiration.

Aerobic respiration

Aerobic Respiration, meaning ‘with oxygen’. Long-term activities such as steady-paced exercise, and day-to-day activities predominantly use aerobic respiration. For example, long-distance runners can keep going as long as they breathe in and convert enough oxygen from the air. If they run too fast then they start to tap into the anaerobic system.

Anaerobic respiration

Anaerobic Respiration or ‘without oxygen’ produces fast bursts of energy for short, powerful bursts. For example, if the long-distance runner begins to sprint as fast as they can, they are unable to breathe enough oxygen in to keep going. They become ‘out of breath’ and begin to rely more on the anaerobic energy system (without oxygen).

The Anaerobic system divides into two further systems:

  • ATP-PC
  • Lactic acid

All energy systems work together, but the intensity and type of activity will determine which system is predominant.

cellular respiration Adenosine phosphates
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