IGCSE Biology glossary
Carbon monoxide
Biology editorial review is supported by the named review panel. Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.
Definition
A toxic gas in tobacco smoke that binds irreversibly to haemoglobin, forming carboxyhaemoglobin. This reduces the oxygen-carrying capacity of the blood because the haemoglobin can no longer bind oxygen, forcing the heart to work harder.
What to include in an exam answer
Carbon monoxide binds to haemoglobin MORE STRONGLY than oxygen (irreversibly). This reduces oxygen carried, which can harm a developing fetus in pregnant smokers and contributes to cardiovascular disease.
Example in context
Explain the effect of carbon monoxide from cigarette smoke on the blood (3 marks): Carbon monoxide binds irreversibly to haemoglobin, forming carboxyhaemoglobin. This reduces the amount of oxygen the blood can carry. The heart has to beat faster to supply enough oxygen to tissues, increasing the risk of cardiovascular disease.
Related syllabus topic
Gas exchange in humans