Fig. 1.1A is a photomicrograph of healthy lung tissue. Fig. 1.1B is a photomicrograph of lung tissue from a person with emphysema, a chronic obstructive pulmonary disease (COPD). The images are both at magnification × 40. [Figure 1.1]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2018). The mark or mark type is shown in brackets.

1. [1] bronchiole; I respiratory / terminal, before bronchiole
2. [1] (actual diameter) = image / observed, length, ÷ magnification; A (A =) I ÷ M or magnification triangle
3. [1] 300 μm ; (12000/40) A 275 μm (11000/40) A 288 μm (11500/40) A 313 μm (12500/40) A 325 μm (13000/40)
4. [1] correct direction of movement of both respiratory gases ; e.g. oxygen from alveolus towards blood and carbon dioxide from blood to alveolus ; oxygen enters the blood system and carbon dioxide leaves A red blood cell / haemoglobin, as ref. to blood
5. [1] diffusion (of, oxygen / carbon dioxide) or movement, down a concentration gradient / from high(er) to low(er) concentration ; A implied e.g. oxygen enters blood from a higher concentration I diffusion of gases
6. [1] detail of pathway ; R ref. to cell walls e.g. across, alveolar wall / squamous (epithelial) cells across endothelium / capillary wall; A squamous cells in context of capillary crosses two layers of cells (alveolar wall and capillary wall)
7. [1] higher rate of exchange / increased rate of diffusion / steeper concentration gradient ; A more oxygen to blood per unit time / more carbon dioxide to alveolus per unit time I more efficient gas exchange I better gas exchange / faster diffusion
8. [1] AVP;; e.g. larger surface area (for, gas exchange / diffusion)
9. [1] AVP;; e.g. shorter diffusion distance ref. to (greater) ability to, stretch / recoil (for ventilation to maintain gradient) or ref. to elasticity (more v fewer elastic fibres is not sufficient)