(a) Describe how the structure of a mitochondrion is related to its function. (b) Explain how rice is adapted to grow with its roots submerged in water.

Mark scheme

Marking points from the official mark scheme (May/June 2021). The mark or mark type is shown in brackets.

1. [9] any nine from: 1 (function is) to make ATP ; 2 ref. to double membrane / outer and inner membrane / envelope ; inner membrane 3 folded / cristae, to increase / for large, surface area ; 4 has, ATP synthase / stalked particles ; 5 has, ETC / carrier (proteins) / cytochromes; 6 (site of) oxidative phosphorylation / chemiosmosis ; 7 impermeable to protons ; intermembrane space 8 has low pH / high concentration of protons ; 9 protons pumped into intermembrane space ; 10 proton gradient between intermembrane space and matrix or protons diffuse from intermembrane space to matrix; matrix 11 contains (co)enzymes for, link reaction / the Krebs cycle ; outer membrane 12 permeable to, pyruvate / reduced NAD / oxygen ; 13 AVP; e.g. ribosomes / DNA, involved in protein synthesis
2. [6] any six from: 1 aerenchyma; 2 in stem and roots ; 3 help oxygen to, move / diffuse, to, roots / submerged parts ; 4 shallow roots; 5 air (film) trapped on underwater leaves / described ; 6 greater internode growth or leaves or flowers grow above water level ; 7 (growth regulated by) gibberellin / ethene ; 8 anaerobic respiration, in roots / underwater / when submerged ; A alcoholic fermentation 9 tolerant to high ethanol (concentration) ; 10 ref. to ethanol / alcohol, dehydrogenase ;