Plant cell organisation

• Six plant tissues :

  1. Epidermal tissue - covered with a waxy cuticle in the leaf to reduce water loss . Cells in the upper layer are transparent to let light through
  2. Palisade mesophyll tissue - where most photosynthesis happens ( so there are lots of chloroplasts )
  3. Spongy mesophyll tissue - has air spaces to allow the diffusion of gases
  4. Xylem
  5. Phloem
  6. Meristem tissue - found at the growing tips of shoots and roots . The cells can differentiate into many types of cell so the plant can grow

  
• Xylem :

  • no ends - hollow tubes that are made of dead cells

  • lignin for strength

  • transports water and mineral ions from roots ( bottom ) to stem and leaves ( top ) where it can be used for photosynthesis

  • Xylem tissue carries water in the transpiration stream

  
• Phloem :

  • elongated living cells

  • small pores in end walls let cell sap through

  • good substances ( mainly dissolved sugars ) are moved from leaves to the rest of the plant

  • food molecules can either be used immediately or stored

  • translocation - the process in which food is is moved through phloem tubes. • phloem cells are arranged to form long columns called phloem tubes .

  
• Leaves are organs . Together with the roots and stem they form an organ system that transports substances around the plant
• • Carbon dioxide diffuses directly into the leaf from outside air through lots of little holes called stomata which are scattered through the lower epidermis 
  • It moves up the leaf and enters spongy mesophyll tissue 
  • Moves up to palisade mesophyll tissue 
  • Above this is upper epidermis which is another layer of epidermal tissue 
  • Once photosynthesis has produced sugar molecules , they're carried to the rest of the plant by the phloem .
• Main problem leaves face - water loss : Xylem continually brings water up from roots for palisade cells to use in photosynthesis but this water can be loss through top and bottom of leaf 
• • Stomata keeps open for as short time as possible to maximise carbon dioxide absorption but minimise water loss 
  • Stomata are at the bottom of the leaf because it's more shaded and cooler so less water will evaporate .