Biology- Plants

• Phloem tubes are made of columns of living cells with perforated end-plates to allow stuff to flow through.
• Phloem tubes transport food substances (mainly sugars) both up and down the stem to growing and storage tissues.
• This movement of food substances is known as translocation.

• Xylem vessels are made of dead cells joined end to end with no end walls between them and a lumen (hole) down the middle.
• The thick side walls are made of cellulose: strong and stiff which gives the plant support.
• Xylem vessels carry water and minerals from the roots up the shoot to the leaves in the transpiration stream.

• The cells on plant roots grow into long hairs which stick out into the soil.
• This gives the plant a big surface area for absorbing water from the soil.
• There's usually a higher concentration of water in the soil than there is inside the plant so the water is drawn into the root hair cell by osmosis.

Transpiration:

• The loss of water from the plant.
• Transpiration is caused by evaporation and diffusion of water vapour from inside the leaves.
• This creates a slight shortage of water in the leaf so more water is drawn up from the rest of the plant through the xylem vessels.
• This in turn means more water is drawn up from the roots so there's a constant transpiration stream of water through the plant. The constant stream helps to keep the plant cool and provides the plant with a constant supply of water for photosynthesis. 
• Minerals needed by the plant can be bought in from the soil along with the water.
• The water creates turgor pressure in the plant cells, this helps support the plant and stops it wilting.