O-LevelBiologyTransport in Plants5090/21 · Oct/Nov 2022 · Q610 Marks

The diagram shows some cells from the lower part of a transpiring leaf. [Figure: leaf cells with lower epidermis, A, B, C, D and arrows 1, 2, 3]

(a)(i)Identify cell type B. B .................................................................................................................[1]
(a)(ii)Water travels from A to D. The arrows on the diagram represent the movement of water molecules during transpiration. With reference to these arrows, name and define each process taking place. arrow 1 .................................................................................................................................................................................... .................................................................................................................................................................................... arrow 2 .................................................................................................................................................................................... .................................................................................................................................................................................... arrow 3 .................................................................................................................................................................................... ....................................................................................................................................................................................[6]
(b)Leaves from different plant species transpire at different rates in the same environmental conditions. Suggest and explain structural differences in the lower surface of these leaves which might produce differences in the transpiration rate.[3]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2022). The mark or mark type is shown in brackets.

[1] spongy mesophyll ;
[1] osmosis ;
[1] is the movement (of water molecules) from an area of higher water potential to lower water potential across a partially permeable membrane AW;
[1] evaporation ;
[1] is the change from liquid (water) to (water) vapour / gas ;
[1] diffusion;
[1] is the (net random) movement (of molecules) from a high to lower concentration / down a concentration gradient ;
[1] the surface area of the leaf ;
[1] the greater the surface area of the leaf, the greater the surface for evaporation;
[1] the thickness of the cuticle ;
[1] the thicker the cuticle, the greater the barrier for water molecules ;
[1] the number / density of stomata ;
[1] as density of stomata increase, more places for water to escape from ;
[1] size of stomata ;
[1] as size of stomata increases, so does area from which water can be lost;
[1] sunken stomata / ridged epidermis / curled up leaves ;
[1] sunken stomata / ridged epidermis / curled up leaves increase humidity ;
[1] hairs / projections ;
[1] hairs / projections increase humidity ;