Explain how the components of blood enable it to carry out its transport functions in the body.

Edexcel A-Level Biology A: Salters-Nuffield (9BN0) — 8 Grey Matter · Explain · 5 marks · View as Markdown

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

Blood is a tissue that transports many different substances around the body. It contains red blood cells, white blood cells, platelets and plasma.

Model answer (5 marks)

1. Erythrocytes contain haemoglobin, which binds oxygen.
2. Haemoglobin carries oxygen to tissues.
3. Erythrocytes are biconcave and anucleate, giving a large surface area for oxygen uptake and more space for haemoglobin.
4. Plasma transports dissolved substances such as nutrients, hormones, urea and carbon dioxide.
5. Platelets are involved in clotting, preventing blood loss and entry of pathogens.

Examiner tips

  • Use the exact terms (haemoglobin, biconcave, anucleate).
  • Show the link between structure and function for each component.
  • Keep each point concise and separate.
  • Mention the main transport role of plasma for dissolved substances.

Common mistakes

  • Confusing platelets with white blood cells.
  • Omitting the anucleate feature of erythrocytes.

Mark scheme (5 marks)

  1. Erythrocytes (red blood cells) contain haemoglobin
  2. Haemoglobin binds to / carries oxygen, allowing transport of oxygen to tissues
  3. Erythrocytes are biconcave / anucleate, giving a large surface area for oxygen uptake / more space for haemoglobin
  4. Plasma transports dissolved substances such as nutrients, hormones, urea or carbon dioxide / dissolved gases around the body
  5. Platelets are involved in blood clotting, preventing blood loss / entry of pathogens

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