Unit 4

Populations & Environment

ATP & Respiration

Practice Exam Questions

1. Fig. 1 shows the link reaction and the Krebs cycle.

Fig. 1

(a) (i) State the precise location of the reactions shown in Fig. 1.

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(ii) State the metabolic pathway that has pyruvate as an end product.

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(b) Label on Fig. 1, the stages where,(i) decarboxylation reactions occur; label these with the letter C. [2]

(ii) dehydrogenation reactions occur; label these with the letter H. [3]

(c) Describe the role of NAD in respiration.

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(d) Compare the fate of pyruvate in anaerobic respiration in yeast and mammalian cells.

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(e) Explain why, in the absence of oxygen, the electron transfer chain in the mitochondria does not operate.

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[Total: 17]

2

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13.

14.

15.

16.

17.

18.

Answers and markscheme

1 (a) (i) matrix of the mitochondrion; 1

(ii) glycolysis; 1

(b) (i) C between6C and 5C;5C and 4C;between pyruvate and acetyl CoA; 2 max

(ii) H at:NAD NADH in link reaction;3 places where NAD NADH in Krebs cycle;FAD FADH in Krebs cycle; 3

(c) reduced in, glycolysis / link reaction / Krebs;transports electrons / hydrogen ions;to inner membrane of mitochondrion;oxidised;releases electrons and hydrogen ions;used in ETC to form gradient of hydrogen ions;used to drive synthesis of ATP; 3

(d) mammalspyruvate is, reduced / converted, to lactate;NAD red is oxidised;one step reaction / catalysed by lactate dehydrogenase;

yeastpyruvate is decarboxylated;CO2 is produced;ethanal;reduced / converted, to ethanol; 4 max

(e) oxygen is needed for the final step;final, hydrogen / electron, acceptor;without it NAD red is not oxidised; 3

[Total: 17]

2

3

4

5

6.

8

7

9

10

11

12.

13.

14

15

16

17

18

(ii) 30 [however derived] = 2 marks [Note; question concerns ATP made in mitochondria only]

If incorrect figure given then only 1 max possible – check working for any two correct intermediate figures in correct context, e.g.:

2.5 x 10 [from NADH] AND 1.5 x 2 [from FADH] = 1 markOR

2 x 2.5 (from glycolysis NADH) AND 2ATP (from Krebs cycle) = 1 mark 2