A-LevelBiologyCell membranes and transport9700/41 · May/June 2019 · Q19 Marks

Fig. 1.1 shows part of a cell in a growing region of a plant. [Figure 1.1]

(a)(i)State the type of protein represented by A.[1]
(a)(ii)Proteins B, C and D are transport proteins. Identify proteins B, C and D. B C D[3]
(b)Describe the effects on the cell wall of many hydrogen ions moving into the cell wall.[3]
(c)Explain the consequences of an influx of potassium ions into the cell.[2]

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Mark scheme

Marking points from the official mark scheme (May/June 2019). The mark or mark type is shown in brackets.

[1] (auxin) receptor (protein) / auxin binding protein ;
[3] B - proton / H+ / hydrogen ion, pump ; C - potassium / K+ / ion, channel / pore ; D - aquaporin ;
[3] any three from: 1 (cell wall) pH decreases / becomes more acidic; 2 expansins; 3 break/loosen, non-covalent, bonds / cross-links ; between cellulose and, hemicellulose / matrix / calcium pectate or between cellulose microfibrils ; 5 cell wall, expands / stretches OR microfibrils move past each other; 6 due to turgor pressure (on wall);
[2] any two from: 1 water potential, decreases / becomes more negative; 2 water moves into cell, by osmosis / down water potential gradient ; 3 cell, expands / increases in volume / elongates ;

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