Science — AI-generated practice question

Carbon dioxide is a highly soluble gas — it dissolves readily in plasma and is transported mainly in dissolved form (as bicarbonate ions) in the blood. Its relatively high solubility means no carrier molecule is needed.

Oxygen, however, is poorly soluble in water/plasma. If it had to rely on simple dissolution, the amount transported would be far too little to meet the body's needs. Therefore, oxygen binds with the special pigment haemoglobin (present in red blood corpuscles), which has a high affinity for oxygen, enabling the blood to carry sufficient quantities of oxygen to all body cells.

Source: Chapter 5, Section 5.4.1 – Transportation in Human Beings

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• Examiners expect two contrasting reasons — one for CO₂ (high solubility → dissolves in plasma) and one for O₂ (low solubility → needs haemoglobin).
• Mention that O₂ is carried by red blood corpuscles containing haemoglobin, not just floating free.
• Avoid writing vague answers like "CO₂ is a waste gas" — the key scientific reason is solubility difference.
• 3 marks = ~2-3 sentences per gas, totalling ~70-80 words. Keep it focused.