Transport in Plants

• Functions of xylem and phloem:

  • To transport substances from source, where they are taken in or made, to the sinks, where they are used
  • To support the stem
• Phloem and xylem in the leaf

  
• Phloem and xylem in the stem

  
• Phloem and xylem in the root

  
• Root hair cell:

  • Function: to absorb water and minerals from the soil
  • They have an elongated shape for more surface area which increases the rate of absorption of water by osmosis and ions by active transport

  
• Pathway taken by water:

  1. Water enters root hair cell from moist soil via osmosis because water potential is higher in soil than in cytoplasm.
  2. Water passes through the cortex cells by osmosis but mostly by “suction”.
  3. Water and minerals are forced to cross the endodermis.
  4. Water enters xylem then leaves when it gets to mesophyll cells

  
• Transpiration: evaporation of water at surfaces of the mesophyll cells followed by loss of water vapour from plant leaves, through stomata.
• Water leaves mesophyll cells, into air spaces created by irregular shape of spongy mesophyll cells, then diffuses out of the stomata.
• Wilting: occurs if water loss is greater than water uptake – cells become flaccid, tissues become limp and plant no longer supported