Metabolism — AQA GCSE Biology
Test yourself on Metabolism with AQA GCSE practice questions.
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Metabolism explained
Metabolism includes both building up and breaking down substances.
Read the full explanation
Sugars, amino acids, fatty acids and glycerol are the small molecules used to synthesise larger storage and structural molecules, and they are also released when those larger molecules are broken down. Glucose molecules join by condensation reactions to form starch, glycogen or cellulose. Amino acids join in a specific sequence to form proteins. Fatty acids and glycerol combine to form lipids such as fats and oils. In breakdown, carbohydrates are hydrolysed to sugars, proteins to amino acids, and lipids to fatty acids and glycerol. These reactions are controlled by enzymes. Understanding this helps explain digestion, growth, repair, energy storage and the movement of substances in living organisms.
Your focus
- Identify the small molecules used to synthesise carbohydrates, proteins and lipids.
- Describe the breakdown products of carbohydrates, proteins and lipids.
- Explain why these synthesis and breakdown reactions are important in living organisms.
Metabolism exam tips
Marking Points
- Sugars such as glucose are the building blocks for carbohydrates, including starch, glycogen and cellulose.
- Amino acids are the building blocks of proteins, joined in a sequence determined by genes.
- Fatty acids and glycerol combine to form lipids such as fats and oils.
- Breakdown reactions release these small molecules: carbohydrates to sugars, proteins to amino acids, and lipids to fatty acids and glycerol.
- Both synthesis and breakdown are enzyme-controlled metabolic reactions.
- The importance lies in growth, repair, energy storage and the release of usable molecules for respiration and other processes.
Examiner Tips
- 💡Use a two-column table for synthesis and breakdown, listing the small molecules and the large molecules for each row.
- 💡When explaining importance, link each molecule to a named process such as growth, repair, storage or respiration.
- 💡Use the terms monomer and polymer only if you can also name the specific examples, such as glucose and starch.
Common Mistakes
- Saying proteins are made from sugars: correct this by stating that proteins are synthesised from amino acids.
- Confusing the breakdown products of lipids with those of carbohydrates: correct this by stating that lipids break down to fatty acids and glycerol, while carbohydrates break down to sugars.
- Describing synthesis as digestion: correct this by explaining that synthesis builds larger molecules from smaller ones, whereas digestion is a breakdown process that releases smaller molecules.