Paper 2 · November 2019 · Biology
Respiring body cells use up one gas and release another into the blood. Name the gas that is present in a higher proportion in exhaled air than in inhaled air.
Model answer
carbon dioxide
Also accepted: CO2, carbon-dioxide
Explanation
Carbon dioxide is the waste gas made when glucose is broken down in respiration. It passes from the blood into the alveoli, so the air breathed out carries far more of it than the air breathed in.
Derived from ZIMSEC Combined Science 4003/2, November 2019, Q1(a)