The diagram shows the main parts of the human breathing system, including the trachea, the two bronchi and the lungs. During exercise, oxygen must be delive...
Question 1 Report
The diagram shows the main parts of the human breathing system, including the trachea, the two bronchi and the lungs. During exercise, oxygen must be delivered rapidly from the lungs to the muscles so that they can respire aerobically and release the energy needed for movement. Air is drawn in through the trachea, passes along each bronchus and reaches the tiny air sacs, where gases are exchanged with the blood flowing past them.
(a) Name the tiny air sacs in the lungs where gas exchange takes place. [1]
(b) State which gas passes from the air in the lungs into the blood. [1]
(c) Explain how the oxygen taken into the blood is used during aerobic respiration in a muscle cell. [3]
(d) During exercise the breathing rate increases. Explain the advantage of this increase to the athlete. [3]
(e) At rest a person breathes in 500 cm3 of air per breath and takes 15 breaths per minute. Calculate the total volume of air breathed in during one minute. Show your working. [2]
Answer Details
This question links the breathing system to aerobic respiration in muscle and includes a ventilation-rate calculation.
(a) Name the air sacs [1] Alveoli. These are the tiny sacs at the ends of the airways where gas exchange with the blood happens.
(b) Gas passing into the blood [1] Oxygen. It diffuses from the air in the alveoli, where its concentration is high, into the blood, where it is lower.
(c) How the oxygen is used in aerobic respiration [3] The oxygen diffuses into (is carried to) the muscle cell; there it reacts with glucose in aerobic respiration; releasing energy for muscle contraction and producing carbon dioxide and water. In words: glucose + oxygen gives carbon dioxide + water (+ energy).
(d) Advantage of faster breathing during exercise [3] Faster breathing means more oxygen is taken into the blood per minute; and more carbon dioxide is removed; so the muscles can respire aerobically faster and release more energy for exercise. This also helps limit the build-up of lactic acid from anaerobic respiration.
(e) Minute volume [2] Total air per minute = tidal volume multiplied by breaths per minute: \( 500 \times 15 = 7500\ \text{cm}^3 \) per minute (1 mark working, 1 mark answer with unit).
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