Section B Answer one question. (a) Describe how adrenaline can stimulate liver cells to convert glycogen to glucose. [7] (b) Describe the role of abscisic acid (ABA) in the closure of stomata during times of drought. [8]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2020). The mark or mark type is shown in brackets.

1. [7] (a) any seven from: 1 adrenaline, binds / joins, to receptor; 2 on (cell surface) membrane of liver cells ; 3 activates / stimulates, G protein ; 4 activates/ stimulates, adenyl(yl) cyclase ; 5 cyclic AMP made from ATP ; 6 (cAMP is) second(ary) messenger ; 7 (cAMP) activates / stimulates / binds to, kinase ; 8 enzyme cascade ; 9 amplifies signal ; 10 (activates) glycogen phosphorylase ;
2. [8] (b) any eight from: 1 ABA is a stress hormone; 2 ABA, released / produced / increases, during drought ; in context of guard cell 3 ABA binds to its receptor on (cell surface) membrane ; 4 stops, H+ / H ions / protons, leaving (guard cell cytoplasm) ; 5 Ca2+ enters; 6 Ca2+ is a second(ary) messenger ; 7 (Ca2+/C/K+) channel (proteins) open ; 8 Cl⁻ / anions, leave; 9 K+ leave; 10 water potential (in cell) increases ; 11 water leaves by osmosis ; 12 volume of, cell / vacuole, decreases ; 13 cell becomes flaccid closing, stoma / pore ;