Phloem, xylem and Transpiration

• Phloem are made of columns of elongated living cells with small pores to allow cell sap to flow through
• Phloem transport food substances (mainly dissolved sugars)made in the leaves to the rest of the plant for immediate use e.g. in growing regions or for storage
• phloem transport goes both ways which is called translocation
• Xylem tubes take water up
• xylem are made of dead cells joined end to end with no end walls between them and a hole down the middle. strengthened with a material called lignin
• xylem carry water and mineral ions from the roots to the stem and leaves
• the movement of water from the roots through the xylem and out of the leaves is called the transpiration stream
• Transpiration is the loss of water from the plant
• Transpiration is caused by the evaporation and diffusion of water from a plants surface. most transpiration happens at the leaves
• evaporation causes a shortage of water in the leaf and so more water is drawn up through xylem vessels to replace it
• constant Transpiration stream throught the plant
• Transpiration rate is affected by the light intensity:

  brighter,higher rate

  temperature:

  warmer,faster rate

  air flow:

  stronger wind,higher rate

  humidity:

  drier the leaf,better rate
• guard cells are adapted to open and close stomata to control the amount of water loss.

  sensitive to light so dont lose water when missing out on photosynthesis

  stomata on underisde of a leaf