transpiration

transpiration

plants absorb water through the roots which then moves up the plant and released into the atmosphere as water vapour through pores in the leaves.

transpiration stream

the movement of water up the stem via the roots and xylem.

cohesion tension theory

• Adhesion: water forms H bonds to molecules on xylem walls.

• Cohesion: water forms H bonds to eachother allowed water to move against gravity.

1) water transport in roots

Root hair cells: hairs to increase surface area, thin cell walls for quick diffusion.

symplastic/apoplastic routes

• Apoplastic: water travels via cell walls and intercellular spaces. Cohesive water molecules creates continuous flow.

• Symplastic: water travels via cytoplasm(plasmodesmata). Next cell will be hypertonic so moves via osmosis.

casparian strip

forces apoplast pathway to turn into a symplastic pathways so toxic substances can be filtered and stopped from entering xylem. (moves through selective membranes)

2) water transport in xylem(stem)

cohesion allows water to move up the xylem and against gravity. Pulled by tension from above.

3) water in leaves

• thin layer of water on cells evaporates.

• high conc of water vapour in space.

• causes water potential to decrease and water pulled from xylem.

• diffuses out of cell via stomata.