Transport in plants

Xylem and phloem
1. Xylem transports water and mineral ions, the phloem transports dissolved substances such as sugars.
2. Xylem
  1. Very long, tube like structures formed from cells joined end to end
  2. No end walls, the cells are dead
  3. Walls thickened with lignin helps supports the xylem from collapsing and waterproofs it.
  4. The pits allow water to move in and out
3. Phloem
  1. Purely a transport tissue and not used for support
  2. Sieve tube elements are living. Contain little cytoplasm and have no nucleus. The sieve parts are at the end walls which allow solutes to pass through
  3. Companion cells, for every sieve tube element there is a companion cell. Has many mitochondria to make ATP.
Water transport
1. Water enter a plant through root hair cells
  1. Water from the soil diffuses into the root cells down the water potential gradient
2. Water moves through the root into the Xylem
  1. Water travel into the xylem via the root cortex
  2. Apoplast, symplast and vacuolar pathways
    1. Water reaches the Casparian Strips (waxy) and forces the water into the symplast pathway. Easy for water to diffuse through membrane in the xylem)
3. Up the Xylem and out at the leaves
  1. Water leaves the xylem and moves into the cells in the leaves. It evaporates from the cells walls into the spaces. When the stomata open the vapor moves out
4. Against gravity
  1. From root to leaves is called transpiration stream
    1. Water molecules are cohesive and form a column, the whole column moves up when vapor escapes
    2. Adhesion: water is also attracted to the wall of the xylem vessel
Transpiration
1. Evaporation of water from a plants surface
2. The lighter, hotter, lower humidity and winder it is, increases the transpiration rate
3. Potometers measure the water uptake
  1. Cut the shoot at a slant. No air bubbles. Insert shoot underwater. Make sure it's airtight. Dry the leaves. Keep conditions constant. Record the movement of bubble.
4. Xerophytic Plants
  1. Less stomata and they are sunk in pits
  2. Spines instead of leaves
  3. Thick, waxy layer
  4. Curled leaves inside and a layer of hair
Translocation
1. Movement of dissolved substances
2. The source is where a substance is made. The sink is the area where it is used up
3. Sucrose is loaded into the phloem by an active process. ATP by the companion cells, to actively load H+ out of their cytoplasm. Set up a diffusion gradient and the H+ diffuse back in.
  1. As the concentration of sucrose builds up they diffuse into the sieve tube elements.
    1. At the source, sucrose enters, reducing water potential, so water also enters.
      1. At the sink they sucrose is removed and increases water potential so water also leaves the phloem. The pressure gradient pushes solutes along the sieve tubes
4. Ring of bark (+)
  1. Different sinks (-)
5. Aphids (+)
  1. Sieve plates (-)
6. Metabolic inhibitor (+)

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Transport in plants

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