A-LevelBiologyEnergy and respiration9700/41 · Oct/Nov 2017 · Q610 Marks

Chemiosmosis is the term used to describe the synthesis of ATP using a proton gradient across a membrane in a mitochondrion or chloroplast. It was first demonstrated by Peter Mitchell in 1961. (a) • In some of his experiments, Peter Mitchell used mitochondria that had been isolated from cells. • The mitochondria were kept in liquid, in glass dishes, to which ADP, Pi and other substances were added. • The temperature, pH and water potential were kept constant. • After a period of time he checked for the presence of ATP. The contents of some of the dishes are shown in the table below. Complete the table using a tick (✓) if ATP was produced and a cross (✗) if no ATP was produced. dish contents mitochondria + ADP + Pi + acetyl CoA + oxygen mitochondria + ADP + Pi + acetyl CoA mitochondria + ADP + Pi + low concentration of protons (H+) mitochondria + ADP + Pi + high concentration of protons (H+) (b) Explain the consequences to a mitochondrion if the water potential of the liquid in the dishes is higher than the water potential of the mitochondrial matrix. (c) State the specific role of oxygen in the mitochondrion. (d) Name the enzyme used to produce ATP in chemiosmosis. (e) Describe the role of the inner mitochondrial membrane (crista) in chemiosmosis.

(a)Complete the table using a tick (✓) if ATP was produced and a cross (✗) if no ATP was produced. dish contents mitochondria + ADP + Pi + acetyl CoA + oxygen mitochondria + ADP + Pi + acetyl CoA mitochondria + ADP + Pi + low concentration of protons (H+) mitochondria + ADP + Pi + high concentration of protons (H+) [2]
(b)Explain the consequences to a mitochondrion if the water potential of the liquid in the dishes is higher than the water potential of the mitochondrial matrix.[2]
(c)State the specific role of oxygen in the mitochondrion.[1]
(d)Name the enzyme used to produce ATP in chemiosmosis.[1]
(e)Describe the role of the inner mitochondrial membrane (crista) in chemiosmosis.[4]

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Mark scheme

Marking points from the official mark scheme (Oct/Nov 2017). The mark or mark type is shown in brackets.

[2] 6(a) (table with marks 2 or 3 correct = 1 mark, 4 correct = 2 marks) mitochondria + ADP + Pi + acetyl CoA + oxygen (✓) ; mitochondria + ADP + Pi + acetyl CoA (✗) ; mitochondria + ADP + Pi + low concentration of protons (H+) (✗) ; mitochondria + ADP + Pi + high concentration of protons (H+) (✓) ;
[2] 6(b) two from: water enters (mitochondrion / matrix); by osmosis / down the water potential gradient ; membranes ruptured / mitochondrion bursts ;
[1] 6(c) final electron (and proton) acceptor (in ETC);
[1] 6(d) ATP synth(et)ase;
[4] 6(e) four from: 1 (site of) electron transport chain ; 2 moves / pumps, protons / H+, to inter-membrane space ; 3 electrochemical / proton / H+, gradient ; 4 protons / H+, diffuse to matrix ; 5 through, stalked particles / ATP synth(et)ase ; 6 ADP + Pi → ATP ; 7 oxidative phosphorylation ;

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