Edexcel IAL Biology 5.21 Temperature, enzyme activity and Q10

Read both rates at temperatures separated by ten degrees, divide higher by lower and explain trends through kinetic energy, collisions, complexes and denaturation.

[Maximum number: 6]

Quince are fruit that grow on trees.
When a quince falls from the tree, two processes take place: browning and decomposition.

8(a)(i)
- Linear line that increases with temperature and then decreases; accept carefully hand-drawn line sloping up to the optimum. (1)
- Optimum temperature shown at about 40 °C; optimum must be above 30 °C and below 45 °C. (1)

8(a)(ii)
One valid route:
- values at 30 °C and 40 °C chosen, e.g. 50 and 32.5, and 50 and 22.5; (1)
- rates calculated per minute, e.g. (50−32.5)÷5 = 3.5 and (50−22.5)÷5 = 5.5; (1)
- numbers substituted into equation: 5.5 ÷ 3.5 = 1.5714; (1)
- correct answer to 2/3 significant figures with no units: 1.6 / 1.57. (1)
OR using 40 °C and 50 °C: rates 5.5 and 0.5, Q10 = 0.5 ÷ 5.5 = 0.091 / 0.0909. Ecf from reasonable values read from graph.

8(b)(i)
- Mass of monosaccharides calculated to be 1361.3 / correct ratios expressed with more than one decimal place; (1)
- ratios shown correctly as whole numbers or with disaccharide and tetrasaccharide values rounded to one decimal place. Example ratio: monosaccharide 164, disaccharide 7, trisaccharide 1, tetrasaccharide 1; accept disaccharide 6.9 and tetrasaccharide 1.1. (1)

8(b)(ii)
D.
A, B and C are incorrect because inositol and raffinose have the modal concentration. (1)

8(b)(iii)
Indicative content:
General decomposition:
- bacteria and fungi are decomposers;
- decomposers release enzymes for decomposition;
- digested molecules are absorbed into the decomposer;
- carbon dioxide is released.

Carbohydrate decomposition:
- carbohydrases are needed to break down carbohydrates;
- hydrolysis of glycosidic bonds;
- to form monosaccharides;
- monosaccharides taken up by diffusion;
- glucose used in respiration;
- carbon dioxide produced by respiration of glucose.

Specific details relating to carbohydrates in the table:
- one glycosidic bond is broken in disaccharides, two in trisaccharides, three in tetrasaccharides;
- using one/two/three water molecules;
- e.g. sucrose broken down into glucose and fructose;
- monosaccharides do not need breaking down.
Ignore references to starch and amylase.

Levels:
- Level 1: general description of decomposition; 1 mark for one point, 2 marks for three points.
- Level 2: details about decomposition of carbohydrates; 3 marks for two points, 4 marks for three points.
- Level 3: specific details relating to carbohydrates in the table plus mention of respiration releasing carbon dioxide; 5 marks for specific detail for either di-/tri-/tetrasaccharides, 6 marks for specific detail for two of the three types of saccharides.

(a)

Browning takes place when the fruit is cut and exposed to the air. The browning is catalysed by the enzyme polyphenol oxidase (PPO).

The photographs show browning in a quince cut in half.

Freshly-cut quince showing some browning

Cut quince exposed to the air showing extensive browning

Activity of the enzyme PPO at different temperatures was investigated.
The graph shows the results of this investigation.

Figure for Question (a) — Edexcel A-Level Biology A2

[ 6 ]

(i)

Sketch the graph for enzyme activity plotted against temperature for this enzyme.

Use the data from this investigation.

Figure for Question (i) — Edexcel A-Level Biology A2

[ 2 ]

An answer that includes the following points:

- linear line that increases with temperature and then decreases (1)

- optimum temperature shown at (about) $40^{\circ} \mathrm{C}$ (1)

ACCEPT carefully hand-drawn line sloping up to optimum NB line does not have to start at the origin

NB optimum must be above $30^{\circ} \mathrm{C}$ and below $45^{\circ} \mathrm{C}$

(2)

(ii)

Calculate the $\mathrm{Q}_{10}$ for this enzyme, using the data from this investigation, shown in the first graph.

Use the formula

Q_{10}=\frac{R_{t+10}}{R_{t}}

where $R_{t}$ is the initial rate of reaction at $t^{\circ} \mathrm{C}$
and $\mathrm{R}_{\mathrm{t}+10}$ is the initial rate of reaction at $\mathrm{t}+10^{\circ} \mathrm{C}$ .

[ 4 ]

values at $30^{\circ} \mathrm{C}$ and $40^{\circ} \mathrm{C}$ chosen (1)

50 and 32.5 and 50 and 22.5

$(50-32.5) \div 5 / 17.5 \div 5 / 3.5$

and
$(50-22.5) \div 5 / 27.5 \div 5 / 5.5$

CE from reasonable values read from graph

- numbers substituted into equation (1)

$5.5 \div 3.5 / 1.5714$

CE if added 10 to a correct rate from mp 2

OR

- values at $40^{\circ} \mathrm{C}$ and $50^{\circ} \mathrm{C}$ chosen

$0.5 \div 5.5 / 0.090909$

CE if added 10 to a correct rate from mp 2

(4)

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5.21—Temperature, enzyme activity and Q10 question 1

Question (a)

Question (i)

Question (ii)