The Golgi body, rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER) form part of the internal membrane system of a cell. The membranes have a fluid mosaic structure. Fig. 1.1 is a transmission electron micrograph of one area of a liver cell showing a region with RER and a region with SER. Mitochondria are also visible in the image. [Figure 1.1]

Mark scheme

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

1. [1] structure max 2 marks
2. [1] 1 RER has ribosomes R if context is within lumen or SER does not have ribosomes ;
3. [1] 2 RER, flattened sacs / cisternae, and SER tubular; AW
4. [1] 3 RER continuous with, (external) nuclear membrane; ora I near to nuclear membrane R continuous with internal nuclear membrane
5. [1] 4 ref. to RER, more regular / layered, arrangement or SER more irregular / disorganised, arrangement ;
6. [1] function
7. [1] 5 RER produces / transports, proteins / glycoproteins; A polypeptides A examples of post-translational modification
8. [1] 6 SER produces, lipids / cholesterol / steroids; A stores I produces hormones
9. [1] any two from
10. [1] ref. to phosphate (group) and two fatty acid, chains / tails / residues ; A two hydrocarbon chains
11. [1] correct ref. to attachment, phosphate / fatty acids, to glycerol ;
12. [1] AVP; e.g. ref. to ester bond
13. [1] ref. to additional group e.g. choline-containing
14. [1] ref. to, saturated / unsaturated, (fatty acid tails)
15. [1] award marks from an annotated diagram
16. [1] flattened sacs / cisternae ;
17. [1] stack/layered / described;
18. [1] any one from
19. [1] idea that each cisterna in stack is, separate / not interconnected ;
20. [1] smooth (outer surface) / no ribosomes ;
21. [1] close to, nucleus / RER ;
22. [1] single membrane ;
23. [1] AVP; e.g. two distinct faces
24. [1] ref. to swollen ends to cisternae
25. [1] ignore events occurring before vesicle formation
26. [1] any three from
27. [1] vesicle moves to, cell surface / cell (surface) membrane ; A plasma membrane
28. [1] movement of vesicle via, cytoskeleton / microtubules ;
29. [1] vesicle fuses with (cell surface) membrane (and protein released); AW e.g. vesicle makes contact with membrane and becomes part of it I attaches to / binds to
30. [1] exocytosis; I bulk transport / excreted / secreted allow in context of release only or movement from Golgi and release
31. [1] any one relevant e.g.
32. [1] acts as (self-)antigen / recognition site / cellular recognition / receptor / membrane stability / cell adhesion ; I involved in cell signalling