The electron micrograph shows part of a cell including a mitochondrion.

X: large/increased SA area for ATP production/electron transport/oxidative phosphorylation/proton pumping 1 mark OR X: small/narrow intermembrane space for generating proton gradient (rapidly/steeply); 1 mark Y: contains enzymes for Krebs cycle/link reaction; 1 mark

a protons pumped across inner membrane of mitochondria/into intermembrane space; 1 mark b using energy released by flow of electrons/by electron transport/by electron carriers; 1 mark c proton gradient established/maintained / proton motive force generated; 1 mark d protons pass/diffuse back through inner membrane/membrane of cristae/to matrix; 1 mark e through ATP synthase; 1 mark f ATP production coupled to flow of protons / ATP from ADP and Pi using energy from protons; 1 mark