Plant organ system- transport inplants

• PHLOEM

  • transports sugars made from photosynthesis from leaves to plant, called TRANSLOCATION
  • includes transport to growing areas of stems and roots, dissolved sugars needed to make new cells
  • also transports sugars to storage organs, food storage for winter
• TREES

  • phloem is located in a ring under the bark, makes young trees vulnerable to damage by animals
  • if a complete ring of bark is eaten, phloem can stop working, tree will die
• XYLEM

  • transports water and mineral ions from roots to stem and leaves
  • mature xylem cells are dead
  • xylem makes up bulk of wood in trees (phloem is under)
• Sugars:

  • used for respiration, make new cells, growth
• Mineral ions:

  • needed for production of proteins (nitrate ions > amino acids)
  • making chlorophyll (magnesium)
  • phosphorus for cell membrane
• Water:

  • needed for photosynthesis, needed for turgidity
  • cytoplasm presses against cell wall to give support to young plants
• Transpiration

  • loss of water from leaf by evaporation via stomata
  • as water evaporates from leaf, more water is pulled up from xylem to take its place - transpiration stream
• TRANSPIRATION STREAM

  1. water is lost from leaves by transpiration
  2. water moves out xylem into cells in the leaves by osmosis
  3. this pulls columns of water up the xylem vessels
  4. water enters xylem vessels from roots by osmosis
• FACTORS ON TRANSPIRATION

  • windy - increase transpiration, wind moves water in air away to maintain a low concentration in air for osmosis (moves high concentration of water to low)
  • increase temperature > increase evaporation > increase transpiration
  • high humidity - decrease transpiration, wrong gradient for osmosis
  • any factor that increases photosynthesis increases transpiration, as more stomata open to let CO2 in leaf and let water out, like light intensity
• Controlling water loss

  • waxy cuticle - thick waxy layer to prevent water loss
  • stomata found on leaves underside to protect from direct sunlight, reduce evaporation of water
  • WILTING:
  • leaves collapse and hang down - reduce SA available for water loss by evaporation
  • STOMATA CLOSE:
  • stop photosynthesis, risk overheating but prevent water loss
  • plant remains wilted until temperature drops, it rains or the sun goes away