When a section of lung tissue is viewed using a light microscope, it is possible to identify the trachea, the bronchus, the bronchioles and the alveoli.

Mark scheme

Marking points from the official mark scheme (Feb/Mar 2020). The mark or mark type is shown in brackets.

1. [3] 4(a) trachea and bronchus (max 1):
2. C-shaped cartilage rings in trachea vs, irregular / plates of, cartilage in bronchus ;
3. more mucous glands in trachea / fewer mucous glands in bronchus ;
4. pseudostratified / description, epithelium in trachea vs columnar epithelium in bronchus ;
5. bronchus and bronchiole (max 1):
6. cartilage in bronchus or no cartilage in bronchiole ;
7. many goblet cells in bronchus vs few or no goblet cells in bronchiole / more goblet cells in bronchus / fewer goblet cells in bronchiole;
8. mucous glands in bronchus or no mucous glands in bronchiole ;
9. more smooth muscle in bronchus / less smooth muscle in bronchiole ;
10. bronchiole and alveolus (max 1):
11. ciliated epithelium / ciliated cells / cilia / columnar epithelium / cuboidal epithelium, in bronchiole
12. or
13. squamous / pavement, epithelial cells in alveolus ;
14. thick wall / wall of several layers, in bronchiole, vs, thin / single layered, wall in alveolus ;
15. smooth muscle in bronchiole or no smooth muscle in alveolus ;
16. [4] 4(b) one mark for correct order:
17. G1, S, G2;
18. G1 phase:
19. transcription or translation or polypeptide / protein / enzyme, synthesis or (named) organelle synthesis ;
20. S phase:
21. DNA replication / formation of 2 (sister) chromatids ;
22. G2 phase:
23. as G₁ or microtubule synthesis or centriole replication or mitochondria division or check for / correct, errors in replication of DNA;