plant tissues, organs and systems

• epidermal tissue


  covers the entire plant

  has a waxy cuticle which helps reduce water loss from the leaf surface
• palisade mesophyll


  contains lots of chloroplasts which allows photosynthesis to progress at a rapid rate
• spongy mesophyll


  lots of air spaces which allow gases - oxygen and carbon dioxide - to diffuse in and out of
• meristem tissue


  made up of stem cells which can differentiate into many cell types, allowing the plant to grow
• what tissues does the leaf organ contain?

  • epidermis
  • palisade mesophyll
  • spongy mesophyll
  • xylem
  • phloem
  • guard cells
• guard cells


  control the opening and closing of the stomata, according to the water content of the plant
• stomata


  -allow the control of gaseous exchange and water loss from the leaf

  • more stomata on the base of the leaf - minimises water loss as this side is cooler and shaded
  • have guard cells which control their opening and closing
• root hair cells


  allow the uptake of water and mineral ions from the soil

  • large surface area - maximises rate of absorption
  • contain lots of mitochondria - release energy for active transport of mineral ions
• translocation


  the movement of dissolved sugars from the leaves to others parts of the plant
• transpiration


  the evaporation of water vapour from the surface of a plant
• how does transpiration work?

  • water molecules from the leaf surface via the stomata
  • water molecules cohere together - more water is pulled up the xylem in an unbroken column
  • more water is take up from the soil - creating a continuous transpiration stream
• how does temperature affect the rate of transpiration?


  -increasing the temperature increases the rate of transpiration

  • higher rate of evaporation and diffusion of water - therefore the rate of diffusion in increased
• humidity -> rate of transpiration


  increasing relative humidity decreases the rate of transpiration

  • high humidity will reduce the water vapour concentration gradient. the rate of evaporation will decrease, and so will the rate of transpiration
• wind -> rate of transpiration 


  increasing wind speed increases the rate of transpiration

  • increased air movement lowers water vapour concentration outside the leaf. this increases the water vapour concentration gradient, thereby increasing rate of evaporation and transpiration
• light intensity -> rate of transpiration 


  -increasing light increases the rate of transpiration

  • the rate of photosynthesis increases, so more stomata open. this allows the rate of evaporation to increase, increasing the rate of transpiration