Water absorbed by plant roots travels by different pathways from root hairs to the xylem. Fig. 6.1 shows these pathways in the root of Ranunculus acris. [Figure 6.1]

Mark scheme

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

1. [2] A - endodermal (cell); A endodermis / passage cell B - apoplast(ic);
2. [5] five from: 1 water potential gradient, between leaves and roots ; A water potential gradient across the root (root hair to xylem / across cortex) 2 diffusion out (via stomata) of water vapour ; evaporation of water from mesophyll cell, surfaces / walls / membranes ; (transpiration from leaves) creates transpiration pull; tension is, set up / present, in xylem vessels ; cohesion between water molecules (in xylem or in roots) ; 3 4 5 6 hydrogen bonding between water molecules ; 7 8 adhesion of water molecules to cellulose (in wall of xylem vessels) ; A to hydrophilic parts of lignin 9 movement of water from apoplast through endodermis by osmosis; 10 AVP; e.g. idea that water columns extend from centre of root to root hairs (and to soil water)
3. [2] two from: pathway C is slower accept ora for pathway B is faster greater resistance ; water passes across membranes ; water flows through, cytoplasm / plasmodesmata ; A ora ref. to intercellular spaces A protoplast osmosis occurs ; R through plasmodesmata ref. to water passes through vacuoles ;
4. [2] assume answer is about facilitated diffusion unless told otherwise – accept ora for active transport two from: movement is, down a concentration gradient ; passive / ATP not required / (metabolic) energy not required ; carrier and channel proteins are involved ;