A-LevelBiologyTransport in plants9700/21 · Oct/Nov 2017 · Q67 Marks

Plants have two transport tissues, xylem and phloem. Fig. 6.1 shows root hair cells.

(a)Describe and explain two ways in which the structure of xylem vessels is adapted to their function. description 1 explanation 1 description 2 explanation 2[2]
(b)Describe two differences between the vessels that transport phloem sap in flowering plants and the vessels that transport blood in mammals.[2]
(c)Explain why the root hair cells in Fig. 6.1 have more mitochondria than the other root cells shown.[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 2017). The mark or mark type is shown in brackets.

[2] (a) mark first two statements given cellulose, cell wall / lining, allows adhesion of water; thick (cellulose) cell wall prevents collapse / idea of providing support (under tension) ; (cell wall impregnated with) lignin, for waterproofing / prevents water loss; lignin, rings / spirals / thickening / AW (of walls), prevents collapse / idea of providing support (under tension); A lignified walls no cytoplasm / lack of contents / hollow / empty (lumen), gives, less resistance to / unimpeded / uninterrupted / unhindered / ease of, flow; A greater volume per unit time / faster rate R continuous, smooth R dead ack of end walls / continuous tube, so, less resistance to / unimpeded / uninterrupted / unhindered / ease of, flow; AW R continuous, smooth pits / pores, for lateral movement / for movement around air bubbles / supplies (water) to (surrounding), cells / tissues ; R holes wide / large diameter / large lumen, so large volume of water can be transported; if max 2 not gained, allow one mark for two correct explanations or descriptions where accompanying descriptions and explanations are in context
[2] (b) two from only sieve tubes / one type, v, arteries, veins and capillaries (any two) A three types; sieve tubes are composed of cells v blood vessels composed of tissues ; A ref. to named tissues sieve tubes, have cytoplasm or blood vessels are, hollow / AW; sieve tubes have sieve plates; ora sieve tubes have companion cells (to fully function); veins have valves; ora ref. to blood vessels and vasoconstriction; ora idea of transport open (phloem) v closed (blood vessels) ; A sieve tubes have plasmodesmata ref. to unidirectional flow in blood vessels ; ora
[3] (c) three from mitochondria, synthesise ATP / carry out aerobic respiration; more ATP needs to be synthesised / increased ATP synthesis ; A need to produce large quantities of ATP to provide more (metabolic) energy; R in context of water uptake for active transport / active uptake ; in context of mineral ions A to move mineral ions against the concentration gradient