(a) Alveoli are the gas exchange surfaces in humans.
(i) State two features of gas exchange surfaces in humans.
(ii) State the name of the organ system alveoli belong to.
(b) State the word equation for aerobic respiration.
(c) Explain why muscle cells have a high rate of respiration.
▶️ Answer/Explanation
(a)(i) Any two from: large surface area; thin surface; good blood supply; good ventilation; moist. These features maximize diffusion rate for efficient gas exchange.
(a)(ii) Respiratory system. Alveoli are the functional units where gas exchange occurs in this system.
(b) The word equation for aerobic respiration is: glucose + oxygen → carbon dioxide + water. This represents the complete oxidation of glucose to release energy.
(c) Muscle cells respire at a high rate because they require constant energy (ATP) for contraction and movement. More respiration provides the necessary energy for muscle function.
Fig. 5.1 shows part of the human gas exchange system.
(a) Identify the structures labelled F and G on Fig. 5.1.
(b) Write the words in the correct order in the boxes to show the structures inspired gases move through to get from outside the body to the blood.
alveoli bronchiole bronchus trachea
(c) The composition of air changes between inspiration and expiration.
(i) Complete the table about how expired air differs from inspired air. Choose the word or phrase from the list.
Each word or phrase may be used once, more than once or not at all.
higher lower the same
(ii) State the name of the substance used to test for the presence of carbon dioxide gas.
(d) The lungs excrete waste gases.
(i) State the name of one other organ that excretes waste substances.
(ii) Circle three other substances that humans excrete.
amino acids mucus glycerol starch haemoglobin urea ions water
▶️ Answer/Explanation
(a)
F: larynx (voice box) ;
G: capillary (tiny blood vessel where gas exchange occurs) ;
(b)
Inspired air travels from the trachea → bronchus → bronchiole → alveoli, where oxygen diffuses into the blood.
(c)(i)
Carbon dioxide: higher (produced as a waste product of respiration) ;
Oxygen: lower (used up in cellular respiration) ;
Water vapour: higher (added during gas exchange in the lungs) ;
(c)(ii)
Limewater turns cloudy in the presence of carbon dioxide.
(d)(i)
Kidney (filters blood to remove urea and excess ions/water).
(d)(ii)
Circled substances: urea (nitrogenous waste), ions (excess salts), water (maintains balance).