Describe the role of each of the following nutrients in the human body: carbohydrates, proteins, and lipids.

Eduqas GCSE Biology — 1.3.1 Diet and nutrition · Describe · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Carbohydrates are the main source of energy for the body, providing glucose for cellular respiration.
Proteins are required for growth and repair of cells and tissues.
Lipids act as a long‑term energy store and provide insulation.
Lipids also form cell membranes and can be used to produce hormones and protect organs.

Examiner tips

Use the exact terms: energy, growth and repair, insulation, cell membranes, hormones, protection.
Keep each point brief – one sentence per nutrient – to fit the 4‑mark structure.
Mention the main function first, then a secondary role where appropriate.

Common mistakes

Writing ‘lipids are used for digestion’ – not a key role in the scheme.
Using plural ‘carbohydrates’ as a noun phrase instead of ‘carbohydrate’ – examiners expect the singular form.
Including extra details such as ‘proteins are made of amino acids’ – not needed for 4 marks.

Mark scheme (4 marks)

Carbohydrates are used as a source of energy (for respiration)
Proteins are used for growth and repair (of cells/tissues)
Lipids (fats/oils) are used as an energy store / provide insulation
Lipids are also used to make cell membranes (accept: used to make hormones / used to protect organs)

Key terms in this question

carbohydrates · proteins · lipids