Metabolism (AQA GCSE Biology: Combined Science)

• Metabolism is the sum of all the reactions in a cell or the body – these reactions happen all of the time
• The energy transferred by respiration in cells is used by the organism for the continual enzyme controlled processes of metabolism that synthesise new molecules
• Enzymes control all of the reactions occurring in cells; often the products of one reaction are the reactants for another (and so on)

The products of digestion are used to build substances, and some of these are then broken down – this is metabolism

• Metabolism includes:
  • Conversion of glucose to cellulose in plants to build and strengthen cell walls
  • Conversion of glucose into glycogen in animals and starch in plants for storage
  • The formation of lipid molecules from a molecule of glycerol and three molecules of fatty acids to form triglycerides which are used for energy storage and as insulation in animals
  • In plants: the use of glucose and nitrate ions to form amino acids which in turn are used to synthesise proteins required by cells (such as enzymes)
  • Glucose is broken down in the process of respiration to release energy in all cells
  • In animals, the breakdown of excess proteins to form urea for excretion