Explain how the components of blood are adapted to carry out their functions in the transport of oxygen and defence against pathogens.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Blood is a tissue made up of several components, each with a specific function in the body.
Model answer (5 marks)
Red blood cells contain haemoglobin, which binds oxygen to form oxyhaemoglobin.
Red blood cells lack a nucleus, giving more room for haemoglobin and allowing a greater oxygen load.
Their biconcave shape increases surface area, enhancing diffusion of oxygen and carbon dioxide.
White blood cells defend against pathogens by phagocytosis or by producing antibodies.
Plasma carries dissolved substances such as carbon dioxide, glucose, hormones and urea throughout the body.
Red blood cells lack a nucleus, giving more room for haemoglobin and allowing a greater oxygen load.
Their biconcave shape increases surface area, enhancing diffusion of oxygen and carbon dioxide.
White blood cells defend against pathogens by phagocytosis or by producing antibodies.
Plasma carries dissolved substances such as carbon dioxide, glucose, hormones and urea throughout the body.
Examiner tips
- Use the exact terms: haemoglobin, oxyhaemoglobin, phagocytosis, antibodies, plasma.
- Show the link between structure and function for each component.
- Keep each point brief but complete to hit the 5 marks.
Common mistakes
- Mixing up the functions of plasma and red blood cells.
- Forgetting that red cells have no nucleus.
- Using vague terms like ‘carry’ instead of ‘transport’.
Mark scheme (5 marks)
- Red blood cells contain haemoglobin which combines with oxygen to form oxyhaemoglobin
- Red blood cells have no nucleus, allowing more space for haemoglobin / to carry more oxygen
- Red blood cells have a biconcave shape, which increases surface area for gas exchange / diffusion of oxygen
- White blood cells defend against pathogens by engulfing them (phagocytosis) or by producing antibodies
- Plasma transports dissolved substances including carbon dioxide / glucose / hormones / urea around the body
Related
- All Edexcel A-Level Biology A: Salters-Nuffield (9BN0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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