2.2.3: Blood
Not started yet — this one needs some love.
Plasma (liquid component): carries dissolved CO₂, glucose, amino acids, urea, hormones, antibodies.
Red blood cells:
Biconcave disc shape → large surface area for O₂ absorption.
No nucleus → more space for haemoglobin.
Haemoglobin binds to oxygen in the lungs and releases it at the tissues (this is reversible).
White blood cells: part of the immune system.
Phagocytes: engulf and digest pathogens (phagocytosis).
Lymphocytes: produce antibodies and antitoxins.
Platelets: small cell fragments; trigger blood clotting at wound sites (prevents infection and blood loss).
Common exam mistakes
When describing how red blood cells carry oxygen, must mention haemoglobin — just saying they 'carry O₂' without haemoglobin loses marks.
Do NOT say red blood cells produce or create energy — they transport oxygen.
Platelets are cell fragments, not whole cells.
Do not confuse plasma (yellow liquid carrying dissolved substances) with red blood cells (carry oxygen).
Phagocytes engulf pathogens; lymphocytes produce antibodies — do not swap these functions.