Adipocytes are cells found in adipose tissue in mammals. These cells absorb glycerol and fatty acids to make triglycerides for long-term storage. Fig. 4.1a shows a glycerol molecule and three fatty acids. Fig. 4.1b shows the triglyceride molecule formed from these components.

Mark scheme

Marking points from the official mark scheme (May/June 2022). The mark or mark type is shown in brackets.

1. [1] ester ;
2. [1] condensation ;
3. [3] 1 (hydrocarbon chains of) different lengths / Y is longest / Z is shortest ; A correct numbers of carbon atoms in each fatty acid (X 18, Y 20 and Z 16) if no ref. to different lengths
4. [3] 2 Z saturated, X and Y unsaturated; A only Z is saturated
5. [3] 3 X polyunsaturated, Y monounsaturated;
6. [3] 4 X 3, Y 1, Z 0 double (C=C) bonds; only Z only has single / C-C) bonds
7. [3] or
8. [3] (for whole molecule) X 4 double bonds, Y 2 double bonds, Z 1 double bond;
9. [2] any two from:
10. [2] 1 (hydrocarbon / fatty acid tails, are) non-polar / have no polar groups / not charged ; A equal sharing of electrons in molecule
11. [2] 2 not soluble / insoluble, (in water) ;
12. [2] 3 cannot form hydrogen bonds with water ; I repel water
13. [2] any two from:
14. [2] 1 no, hydrophilic / polar / phosphate, head / part, to, interact with / AW, water ; I triglycerides are hydrophobic
15. [2] 2 cannot form hydrogen bonds with water ; I repel water
16. [2] 3 cannot form a bilayer ; in water triglycerides, form micelles / form spheres / ball shaped / form globules / do not form thin films / AW ;