Describe how red blood cells and plasma each contribute to the transport of substances in the blood.

Cambridge International IGCSE Biology (0610) — 9.4 Blood · Describe · 4 marks · View as Markdown

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

Model answer (4 marks)

Red blood cells contain haemoglobin, which binds to and carries oxygen.
Red blood cells transport oxygen from the lungs to the tissues.
Plasma is a liquid that carries soluble nutrients such as glucose, amino acids and ions.
Plasma also transports hormones, carbon dioxide and urea.

Examiner tips

Use the exact terminology: haemoglobin, oxygen, plasma, nutrients, hormones, CO₂, urea.
Show the two distinct roles – cellular (RBC) and fluid (plasma).
Mention at least one nutrient and one non‑nutrient substance in plasma.

Common mistakes

Confusing plasma with whole blood or omitting the word haemoglobin.
Failing to name a non‑nutrient substance carried by plasma.
Using vague terms like "blood" instead of specifying red blood cells or plasma.

Mark scheme (4 marks)

Red blood cells contain haemoglobin which binds to / carries oxygen
Red blood cells transport oxygen from the lungs to the tissues / cells (of the body)
Plasma is a liquid that carries / transports soluble nutrients (e.g. glucose / amino acids / ions)
Plasma also transports hormones / carbon dioxide / urea (accept any one named substance other than nutrients already credited)

Key terms in this question

red blood cell · plasma