OCR F211 - unit 1, Biology thread (Post exam)

Movement of water across root:
1. Minerals pass by active transport across cortex lowering wp, setting up wpg.
2. Water passes by osmosis down wpg across cortex via apolast pathway between cells.
3. Casparian strip blocks apoplast, forcing water into symplast pathway.
4. Water moves through endodermal cells into xylem.

Movement of water up plant:
1. Water is forced into xylem by osmosis creating root pressure that forces water upwards.
2. Water molecules joined together by H-bonds. These forces of cohesion cause water molecules to join into column. When H2O is lost by transpiration, tension in column forces it upwards.
3. Water molecules attached to xylem vessels by adhesion.

Transpiration:
1. Water moves by osmosis from xylem to mesophyll cells.
2. Water is evaporated from mesophyll cells, water vapour collects in air spaces.
3. Water vapour diffuses out of stomata.

Entry of sucrose into sieve tube elements:
1. H+ ions actively transported out of companion cells inceasing conc.
2. H+ ions diffuse back into companion cells via cotransporter proteins bringing in sucrose.
3. Sucrose moves into STEs by diffusion via plasmodesmata.

I'm bored of plants now...........