Respiration is a chemical reaction that releases energy from glucose molecules. Enzymes use the energy released from the glucose molecules to synthesise new molecules.

Glucose can also be useful as a starting point for many chemicals. For example, in plant cells, glucose is converted into cellulose to build and strengthen cell walls. For storage, glucose is converted to starch in plants and glycogen in animals.

Metabolism is the sum of all of the chemical reactions in the body. The energy for these reactions is provided by cellular respiration

We can divide metabolic reactions into two categories:

  • The Breakdown of molecules
  • The Synthesis of molecules

Breakdown of Molecules

Complex molecules are broken down into simpler molecules. For example the reactions in digestion:

  • Complex carbohydrates → Simple sugars
  • Proteins → Amino acids
  • Lipids 3 fatty acids + glycerol

These complex molecules are broken down so that they are small enough to be absorbed in the small intestine.

Synthesis of Molecules

Simpler molecules form more complex molecules. For example:

  • Simple sugars Complex carbohydrates
  • Amino acids Proteins
  • 3 fatty acids + glycerol Lipids

Reactions such as these aid in growth and repair.