Phosphoinositide 3-kinase (PI3K) and protein kinase B (PKB) are enzymes involved in the regulation of blood glucose concentration. Fig. 6.1 shows a cell-signalling pathway involving insulin, PI3K and PKB in a muscle cell.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2025). The mark or mark type is shown in brackets.

1. [4] (a) any four from : 1 less / no, PKB, activated / stimulated; 2 fewer / no, vesicles, move to / fuse with, cell surface membrane ; 3 fewer/no, GLUT4 (transport proteins) added to (cell surface) membrane or (cell surface) membrane, less / not, permeable to glucose ; 4 less/no, glucose taken up by facilitated diffusion (into muscle cells) ; 5 blood glucose concentration, (remains) high(er) / does not decrease ;
2. [7] (b) any seven from : 1 (biosensor has) glucose oxidase (immobilised on recognition layer) ; 2 blood sample added ; 3 glucose (in blood) passes through, partially / selectively, permeable membrane ; 4 glucose oxidase, oxidises glucose / converts glucose / catalyses glucose reaction ; 5 gluconic acid and hydrogen peroxide formed; 6 reaction converted to a current (by transducer); 7 current is amplified ; 8 digital / numerical / quantitative, reading ; 9 size of current is proportional to glucose concentration ; 10 instant result / accurate ;