Describe the structure and function of the xylem and phloem + adaptations.

xylem: - transports water and mineral ions from the roots to the shoots - made of dead cells - walls strengthened with lignin phloem: - transports organic solutes around the plant - sieve tube elements joined together to form sieve tubes - areas between cells are perforated to form sieve plates which let the phloem contents through - companion cells are connected to the sieve tube elements via plasmodesmata

Describe the movement of water into and across the roots into the xylem.

- water enters root hair cells via osmosis because the soil has a higher water potential than the cell sap - water travels through the route via: - apoplast pathway: through the cell walls - symplast pathway: through cytoplasm via plasmodesmata - casparian strip inside the endodermis is hydrophobic so blocks water and forces it into the symplast pathway so that toxins can be removed - mineral ions are at higher concentration in the xylem than in the root hair cells so move into the xylem via active transport, building up root pressure - this decreases the water potential in the xylem, causing water to move in via osmosis

Describe the process of transpiration.

- water evaporates from surface of mesophyll cells into the air spaces in the spongy mesophyll as water vapour - water vapour exits the leaf via diffusion out of the stomata - water vapour also builds up in the sub-stomatal air spaces, increasing water potential and causing water vapour to move into the surrounding air via diffusion - water lost from the mesophyll cells is replaced by the water pulled from the xylem, maintaining the continuous column of water - this continuous column of water creates tension in the xylem, pulling water up the plant via the cohesion-tension mechanism

Describe the process of translocation.

- at the source, H+ actively transported out of companion cells - this creates a high H+ ion concentration outside of the companion cells and low concentration inside - this causes H+ ions to diffuse back into the companion cells via a co-transport protein, co-transporting sucrose with them - sucrose increases the solute concentration in the companion cells, decreasing the water potential and causing water to move from the xylem into the phloem via osmosis - this increases the hydrostatic pressure - at the sink, sucrose is unloaded from the phloem to the cells that need it - this increases water potential, causing water to move out of the phloem via osmosis into surrounding cells and the xylem - this decreases the hydrostatic pressure, forming a hydrostatic pressure gradient - this hydrostatic pressure gradient causes mass flow of phloem sap down the gradient