Metabolism
Build confidence in Metabolism for GCSE Biology with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. Metabolism is the sum of all the reactions in a cell or the body, both building larger molecules and breaking others down.
Free downloads
These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
Metabolism is the sum of all the reactions in a cell or in the body. These reactions are controlled by enzymes and are driven by the energy released from respiration.
Some reactions build larger molecules from smaller ones. Glucose molecules are joined to form starch, glycogen and cellulose. Glycerol and three fatty acids combine to make a lipid molecule. Glucose and nitrate ions form amino acids, which are joined to make proteins.
Other reactions break molecules down. Lipids are broken into glycerol and fatty acids, and excess protein is broken down to produce urea, which is excreted by the kidneys.
Revision notes
What metabolism means
Metabolism is the sum of all the reactions happening in a cell or in the body.
These reactions are catalysed by enzymes, and the energy transferred by respiration is used to drive them.
Building up molecules
Glucose is converted to starch, glycogen and cellulose. Glycerol plus three fatty acids forms a lipid molecule.
Glucose combined with nitrate ions forms amino acids, which are then joined to make proteins.
Breaking down molecules
Lipids are broken down into glycerol and fatty acids.
Excess protein is broken down to produce urea, which is transported to the kidneys and excreted in urine. This is called deamination.
Key points
- Metabolism is the sum of all reactions in the body.
- Reactions are controlled by enzymes.
- Energy from respiration drives metabolic reactions.
- Glucose forms starch, glycogen and cellulose.
- Glycerol and three fatty acids make a lipid.
- Excess protein is broken down to urea.
Worked examples
Example 1
Define metabolism. [1 mark]
Model answer
Metabolism is the sum of all the reactions taking place in a cell or in the body (1 mark).
Example 2
Name the molecules that combine to form a lipid. [2 marks]
Model answer
One molecule of glycerol (1 mark) and three fatty acid molecules (1 mark).
Example 3
Explain what happens to excess protein in the body. [2 marks]
Model answer
Excess protein is broken down to produce urea (1 mark), which is transported in the blood to the kidneys and excreted in the urine (1 mark).
Common mistakes
Saying metabolism is just respiration.
Respiration is one metabolic reaction; metabolism is the sum of all of them.
Giving two fatty acids for a lipid.
A lipid is one glycerol and three fatty acids.
Saying excess protein is stored.
It cannot be stored — it is broken down to urea and excreted.
Forgetting enzymes control the reactions.
Metabolic reactions are enzyme-catalysed, which is usually worth a mark.
Exam tips
- Use the phrase sum of all reactions in your definition.
- Remember the ratio: one glycerol to three fatty acids.
- Name urea and the kidneys when discussing excess protein.
- Mention that enzymes catalyse metabolic reactions.
Key terms
- Metabolism
- The sum of all reactions in a cell or the body.
- Urea
- The waste product formed from excess protein.
- Glycerol
- A molecule that combines with fatty acids to form a lipid.
- Deamination
- The breakdown of excess amino acids to form urea.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.