(a) Fig. 3.1 is a transmission electron micrograph showing two adjacent cells in a leaf. [Figure 3.1]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2018). The mark or mark type is shown in brackets.

1. [3] (a)(i) any three from (polymer/polysaccharide of) ẞ-glucose ;
2. [3] (a)(i) glycosidic, bonds / linkages; A glucosidic
3. [3] (a)(i) (β) 1-4 (glycosidic) bonds ; R if 1-6 also given
4. [3] (a)(i) ref. to (ẞ) glucose units, linked at 180° to each other / alternately orientated / AW ;
5. [3] (a)(i) unbranched (polymer) / straight chain / linear;
6. [3] (a)(i) able to form hydrogen bonds with parallel chains / AW;
7. [1] (a)(ii) chloroplast/granum / thylakoid / middle lamella / large vacuole / nucleus at edge of cell ;
8. [3] (a)(iii) provide energy (for the cell); R produce energy
9. [3] (a)(iii) any two examples ;; e.g. biosynthesis A named example
10. [3] (a)(iii) active transport / proton pumping
11. [3] (a)(iii) movement / described, e.g. movement of, vesicles / chromosomes
12. [3] (a)(iii) endocytosis / exocytosis
13. [2] (b) any two from water molecules are dipoles ; A polar
14. [2] (b) (each water molecule has) σ+ hydrogen (atoms) and a σ– oxygen (atom);
15. [2] (b) the positively charged hydrogen (atom) of one water molecule is attracted to the negatively charged oxygen (atom) of another water molecule ;
16. [2] (b) weak attraction between water molecules ;
17. [2] (c) any two from water molecules are polar;
18. [2] (c) ions are charged ;
19. [2] (c) ref. attraction between water molecules and ions ;
20. [2] (c) AVP; e.g. oxygen σ– faces positive ion