8.1.7—Blood cells

The formed components of blood have different roles: red blood cells transport respiratory gases, white blood cells contribute to defence, and platelets help blood clot. Identify each group from several structural clues, then connect the clues to its role.

• Red blood cells: no nucleus, biconcave disc shape and haemoglobin → more room for haemoglobin and a large exchange surface → reversible oxygen transport in the blood.
• White blood cells: cells with nuclei and varied specialised forms → they can carry out defence roles rather than acting as uniform gas carriers. In images, use nuclear evidence: monocytes have a kidney/bean-shaped nucleus, neutrophils have a multi-lobed nucleus and lymphocytes have a large, dark-staining nucleus.
• Platelets: small cell fragments rather than complete nucleated cells → they can gather at a damaged vessel and contribute to the clotting response, helping reduce blood loss.

Recognition boundary: colour or size alone is not enough. Combine nucleus/shape evidence with the expected blood role, and do not treat platelets as white blood cells or red blood cells as defence cells.

White blood cells are a varied group, so “white cell” is not one single shape. Staff-only visual brief: three aligned blood-component profiles with red-cell biconcavity/haemoglobin, white-cell nuclear diversity and platelet fragments; do not generate or bind an image.