Describe the roles of carbohydrates and fats in the human body.

WJEC GCSE Biology (Wales) — 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 and other metabolic processes.
Excess carbohydrates are stored as glycogen in the liver and muscles, or converted into fat for long‑term storage.
Fats act as a concentrated energy store, supplying energy when carbohydrate reserves are low.
Fats also provide insulation to reduce heat loss, form part of cell membranes, and protect organs by cushioning them.

Examiner tips

Use the exact terms ‘glucose’, ‘glycogen’, ‘cellular respiration’ and ‘insulation’ to match the mark scheme.
Show the two storage routes for excess carbohydrates – glycogen and conversion to fat – to earn full marks.

Common mistakes

Confusing carbohydrates with proteins as the main energy source.
Omitting the role of fats in cell membranes or insulation.

Mark scheme (4 marks)

Carbohydrates are used as a source of energy (for respiration / metabolic processes).
Excess carbohydrates can be stored (as glycogen in the liver/muscles OR converted to fat for storage).
Fats are used as an energy store / provide energy (when carbohydrate reserves are low).
Fats are used for insulation (to reduce heat loss) OR to make cell membranes OR to protect organs.

Key terms in this question

carbohydrates · fats