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.

………………………………………………………………………………………………………… [1] (ii) State the metabolic pathway that has pyruvate as an end product.

………………………………………………………………………………………………………… [1] (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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……………………………………………………………………………………………………….. [3] [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 between

6C 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) mammals

pyruvate is, reduced / converted, to lactate; NAD red is oxidised; one step reaction / catalysed by lactate dehydrogenase; yeast pyruvate 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.

7

8

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 mark

OR

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