Section B Answer both questions in this section. Write your answers in the spaces provided. (a) Explain the 'lock and key' hypothesis of enzyme action using a named example. (b) Explain, using examples, why proteins are essential for all living organisms.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2021). The mark or mark type is shown in brackets.

1. [1] any five from: enzyme + name, e.g. amylase ;
2. [1] substrate + name, e.g. amylose/starch ;
3. [1] enzyme + has an active site ;
4. [1] specificity of enzyme AW ;
5. [1] substrate fits into active site / enzyme-substrate complex formed ;
6. [1] named product formed ;
7. [1] enzyme unchanged at end of reaction ;
8. [1] any five from: growth / new cells ;
9. [1] repair ;
10. [1] energy in absence of carbohydrates/fats ;
11. [1] muscle ;
12. [1] hair / nails / skin ;
13. [1] hormones ;
14. [1] enzymes ;
15. [1] antibodies ;
16. [1] named protein, e.g. haemoglobin, fibrinogen ;
17. [1] cell membrane / carrier protein ;
18. [1] blood clotting ;