A-LevelBiologyTransport in plants9700/22 · Feb/Mar 2018 · Q45 Marks

Fig. 4.1 is a diagram of a section through part of a young root. [Figure 4.1]

(a)Describe the pathways by which water passes from the soil to the cells of the cortex shown in Fig. 4.1.[4]
(b)There is a greater density of mitochondria in the cytoplasm of cell X than in the cytoplasm of a cell of the cortex. Suggest why this is so.[1]

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Mark scheme

Marking points from the official mark scheme (Feb/Mar 2018). The mark or mark type is shown in brackets.

[4] I any part of the pathway beyond cortical cells I incorrect mechanisms any four from: correct ref. to, apoplastic pathway and symplastic pathway / apoplast and symplast ; 1 2 cell wall route ; 3 further detail; e.g. between, cellulose fibres / spaces between cells does not cross (cell) membranes 4 entry into, root hair cell by, crossing (partially permeable) cell surface membrane / osmosis ; 5 (then) cytoplasmic route / within cytoplasm ; 6 from cell to cell via plasmodesmata ; 7 vacuolar route ; A crosses, tonoplast/ vacuolar membrane
[1] any one from: for active transport of mineral ions; A for mineral ion uptake against a concentration gradient for, ATP / energy, for active transport;

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