AQA GCSE Biology

Revision Notes

4.2.3 Metabolism

Metabolism: Basics

  • 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)

Metabolic Substrates

Metabolism, downloadable IGCSE & GCSE Biology revision notes

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

Exam Tip

You should be able to explain the importance of sugars, amino acids, fatty acids and glycerol in the synthesis and breakdown of carbohydrates, proteins and lipids.

Use of Metabolites

  • 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

Exam Tip

All of the features of metabolism listed are covered in more detail in the relevant topics but you should be aware of how they all link together here.

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Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.

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