Respiration is the opposite to photosynthesis. The cells oxidise(burn) sugar to release the chemical potential energy uinto useable forms of energy to support life sustaining processes.


The equation above represents the process of respiration.

To burn sugar we need to supply a flame. This provides the activation energy to start the reaction. As the reaction proceeds a great deal of energy is given out with little control of its production. Click to see a 1Mb video of the energy given off as sugar burns. If animals and plants were to burn their sugar in such a way they would soon perish in a ball of flame.

On the other hand, the burning of sugar in a cell has many small steps. Each step is controlled by a special protein called an enzyme. The large activation energy seen when sugar is burnt externally is broken down into smaller activation energies overcome by body temperature. At each step the small amount of energy released can be stored as chemical potential energy.

Research the following words by simply clicking on each one.



What is a catalyst?
Why is an enzyme?
Why is an enzyme considered a catalyst?

How does an enzyme and catalyst work?