A-LevelBiologyTransport in mammals9700/22 · Feb/Mar 2019 · Q48 Marks

In a double circulatory system, blood passes through the heart twice in one complete circuit of the body. The complete circuit consists of the pulmonary circulation and the systemic circulation.

(a)Fig. 4.1 is a diagram of a vertical section through the mammalian heart. The differences in the thickness of cardiac muscle in the walls of the four chambers of the heart are shown. [Figure 4.1] Explain, with reference to their functions, the difference in the thickness of the walls of the left ventricle and right ventricle of the heart.[3]
(b)The alveolus is the gas exchange surface in mammals. For efficient oxygen uptake, a steep diffusion gradient is maintained between the alveolar air and the blood. Suggest how the steep diffusion gradient for oxygen is maintained at the gas exchange surface.[2]
(c)Compared to when they were non-smokers, the ability of people who smoke tobacco to deliver oxygen to their body tissues is reduced. Two causes of this reduction include: • a decrease in the volume of air per breath moving towards the alveoli • a decrease in the ability of red blood cells to carry oxygen.
(c)(i)Suggest one reason why smoking tobacco, even after only a short time, may cause a decrease in the volume of air per breath moving towards the alveoli.[1]
(c)(ii)Explain why smoking tobacco causes a decrease in the ability of red blood cells to carry oxygen.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Feb/Mar 2019). The mark or mark type is shown in brackets.

[max 3] any three from:
right ventricle pumps blood to lungs (and back to heart) and left ventricle pumps blood to (rest of) body (and back to heart) / AW;
(so) short(er) / less, distance (for blood to travel) / ora ;
less resistance (to, flow / overcome) / ora ;
less force / lower pressure, required / ora;
[max 2] any two from:
ventilation / breathing (movments) / inspiration / inhalation, brings in oxygen ;
blood flow (in pulmonary capillaries) removes oxygen ;
oxygen binding to haemoglobin / oxyhaemoglobin formation, (removes oxygen) ;
deoxygenated blood arriving / blood arriving low in oxygen ;
[max 1] any one from:
in context of, airways / trachea / bronchi:
less air because:
diameter of lumen decreases / ref. to smooth muscle contraction;
inflammation;
thicker layer of mucus ;
smoke present in inhaled air (so lower proportion of air) ;
AVP;
[max 2] any two from:
carbon monoxide (present in smoke) binds to haemoglobin ;
ref. to competitive / permanent / irreversible, binding;
presence of carbon monoxide (from smoke) lowers affinity of haemoglobin for oxygen ;
ref. to carboxyhaemoglobin formed ;
comparatively less haemoglobin per red blood cell to bind oxygen ;

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