Triglycerides and phospholipids are types of lipid. Fig. 2.1 shows the structure of one type of phospholipid known as phosphatidylcholine. F1 and F2 are fatty acid residues. [Figure 2.1]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2017). The mark or mark type is shown in brackets.

1. [2] two from
2. cell (surface) membrane / plasma membrane / phospholipid bilayer, damaged / AW ; A phospholipids are in cell surface membrane (and will be broken down by phospholipase)
3. cell, bursts / lyses / lysis / ruptures ; haemolysis is neutral
4. cell contents / AW / haemoglobin, leaks out / AW ; I water
5. [4] allow, fatty acids / fatty acid tails / hydrocarbon chains, for fatty acid residues
6. both have / similarities (max 3)
7. glycerol (residue) ;
8. fatty acids ; I ref. to saturation, R both have, two / three, fatty acids
9. ester, bonds / linkages ;
10. C and H and O ;
11. double bonds ; A both have C=O
12. differences (max 3)
13. triglyceride / fat / oil / lipid
14. no, choline / nitrogen
15. A no / small / delta, charges
16. or
17. phosphatidylcholine / phospholipid
18. has, choline / nitrogen ;
19. A choline / nitrogen, ion
20. A charged / ionic
21. three fatty acid residues
22. or one extra fatty acid residue ;
23. A triglyceride has three ester bonds
24. or
25. R if comparison includes phosphatidylcholine and the number of fatty acid residues is incorrect
26. no, phosphate (group) / phosphorus
27. A no, phosphoester / phosphodiester bond
28. or
29. has phosphate ;
30. A has phosphoester / phosphodiester bond
31. [3] smooth endoplasmic reticulum ; A smooth ER RSER R if more than one organelle given R endoplastic
32. two from
33. membranous / membranes ; A ref. to vesicles, formed / bud off R envelope / double membrane
34. tubular; A cisternae but R if described as flattened
35. fluid filled, channels / sacs ;
36. not associated with ribosomes ;