phloem and xylem

to transport water to the leaves

they are composed of long, skinny tubes that run from the roots to the leaves. the xylem is made up of hollow cells, lignin and pits

vessel elements and tracheids

long, hollow cells that conduct water and that water passes through. they have pits to allow the transfer of water as they have no end walls

much larger and connect end to end with end walls to allow rapid water transport

when water moves from the roots to the leaves via the xylem, water then evaporates at the stomata of the leaf during gas exchange, this process is passive.

at water evaporates from the stomata, the air pressure in the leaf becomes lower than in the roots. as water molecules stick together (cohesion) and adhere to the xylem (adhesion) which allows water to be drawn up.

regulate the opening and closing of the stoma , two on either side of each stoma

potassium ions are pumped into guard cells and water will diffuse via osmosis making the guard cells turgid, opening the stoma. when potassium ions are pumped out of the cell, osmosis will occur making the cells flaccid and stoma closed

temperature, light, humidity, wind and water avliabilty

is the movement of sucrose around the plant from the source to the sink (tissue of a plant where substances are stored), its an active process

sieve element cells and companion cells

they are long and narrow and connected to each other, they have sieve tube elements, and sieve tube plates and lateral sieve areas to transport things between cells

glucose is produced in the leaf cells, this is the source, glucose is then pumped into campanion cells where they diffuse across the phloem and are transported as sucrose

due to an increased concentration of sugar molecules, water will diffuse into the sieve cells from the xylem, making the sieve cells turgid

the increase in the turgor pressure forces the contents of the phloem into the required cells, fruit cells and or root cells where it is then actively transported

once the sugar molecules are unloaded into the sink cells, the turgor pressure will return to normal and the water will diffuse back into the xylem