Paper 2 · Specimen 2020 · Biology
A student breathes out through a delivery tube into limewater and compares that air with the air in the room. Compared with inhaled air, exhaled air contains
Aless oxygen and more carbon dioxide, because oxygen is used in respiration and carbon dioxide is produced.
Bmore oxygen and more carbon dioxide, because both gases are produced by respiration in the tissues.
Cmore oxygen and less carbon dioxide, because oxygen is released when glucose is broken down.
Dless oxygen and less carbon dioxide, because both gases are absorbed by the moist lining of the lungs.
Explanation
Respiration in the body cells uses oxygen and produces carbon dioxide as a waste gas. Air leaving the lungs has therefore given up some of its oxygen and picked up carbon dioxide, which is why exhaled air turns limewater milky much faster than room air does.
Derived from ZIMSEC Combined Science 4003/2, Specimen Paper N2020, Q1(a)