(a) Glycolysis is a biochemical pathway that occurs in the cytoplasm of cells. In glycolysis, a molecule of glucose is metabolised to two molecules of pyruvate. The process is outlined in Fig. 1.1. [Figure 1.1]

Mark scheme

Marking points from the official mark scheme (May/June 2023). The mark or mark type is shown in brackets.

1. [1] any one from: glucose is activated/made reactive ; becomes unstable ; cannot leave cell; energy level increased ; concentration gradient maintained;
2. [1] any one from: carrier / acceptor / provider, of, hydrogen (atoms) / electrons or provider of H ions and electrons ; R H ions alone used for redox reactions ; used to reduce, ethanal / pyruvate ;
3. [1] substrate-linked / substrate level;
4. [3] any three from: 1 (inner) mitochondrial membrane impermeable (to pyruvate); 2 carrier (protein); A symport / MPC (mitochondrial pyruvate carrier) 3 lower concentration of pyruvate outside mitochondrion ora or against concentration gradient; 4 oxygen available ; 5 ATP/energy ;
5. [3] any three from: 1 decarboxylation; A description 2 dehydrogenation / oxidation, (of pyruvate) ; A description 3 reduced NAD produced ; 4 formation of, acetyl coenzyme A / acetyl CoA ;