plant organisation

• Epidermal tissue - covers the whole plant
• Palisade Mesophyll Tissue - part of the leaf where most photosynthesis happens
• Spongy Mesophyll tissue - contains big air spaces to allow gases to diffuse in and out of cells
• Xylem and Phloem - transport things like water, mineral ions and food around the plant
• Meristem tissue - found in the tips of shoots and roots, and can differentiate which allows the plant to grow
• Phloem -

  • made of columns of elongated living cells with small pores that allow sap to flow through
  • transport food substances
  • transport goes in both directions
  • this process is called translocation
• Xylem -

  • made of dead cells with a hole down the middle, they're strengthened by material called Lignin
  • they carry water and mineral ions from the roots, stem and leaves
  • the movement of water from roots, through Xylem and out the leaves is called the transpiration stream
• transpiration is the loss of water from the plant
• transpiration rate is affected by four main things

  • light intensity
  • temperature
  • air flow
  • humidity
• when the plant has lots of water, the guard cells fill with it and become turgid - this makes the stomata open so gases can be exchanged for photosynthesis
• when the plant is low on water, the guard cells become flaccid, making the stomata close - this helps stop too much water vapour from escaping