plant organ system

• what is translocation?

  movement of dissolved sugars from the leaves to other parts of the plant through the phloem
• what is transpiration?

  evaporation of water vapour from the surface of a plant
• role of guard cells & stomata

  control gas exchange & water loss
• what is the transpiration stream?

  movement of water in the xylem from the roots to the leaves
• what is the function of the xylem?

  carry water & mineral ions from the roots to the stem & leaves
• how is the xylem adapted for its function?

  • made of dead cells joined end to end w no end walls between them which forms a continuous hollow tube - allows the movement of water & mineral ions from the roots to the leaves
  • strengthened by lignin - makes it strong & waterproof
• how is the phloem adapted for its function?

  • made of elongated living cells
  • end walls have small pores in them - allow cell sap to flow through
  • contains cytoplasm
• how does temperature affect the rate of transpiration?

  • increase in temp increases the rate of transpiration
  • because there's a higher rate of evaporation & diffusion of water
• how does humidity affect the rate of transpiration?

  • increase in humidity decreases the rate of transpiration
  • high humidity will reduce the water vapour concentration gradient
• how does air flow affect the rate of transpiration?

  • increase in air flow increases the rate of transpiration
  • because it lowers the water vapour concentration outside the leaf, this increases the concentration gradient
• how does light intensity affect the rate of transpiration?

  • increase in light intensity increases the rate of transpiration
  • because the rate of photosynthesis increases so more stomata are open, so the rate of evaporation increases