plant transport

• xylem structure: made of dead cells, has lignin and thick cell wall to withstand pressure,
• xylem is used to transport water and dissolved minerals from roots to the rest of the plant
• transpiration pull= negative pressure at the top of xylem pulls water up, caused by the loss of water through evapouration on the leaf
• adhesion- water forms hydrogen bonds with cellulose in xylem lining
• cohesion- water form hydrogen bonds with each other, helping to hold the water molecules together and pull them up the xylem
• The factors effecting transpiration are: Light intensity, Temperature, Air movement and humidity
• rate of transpiration is measured using a potometer
• translocation= the movement of dissolved substances such as sucrose and amino acids from the leaves to the rest of the plant
• the source- (leaves) the part of the plant that loads assimilates into phloem sieve tubes
• the sink-(roots) the part of the plant that removes assimilates from phloem sieve tubes
• structure of phloem cells= living cells, sieve plate at ends of cells, have companion cells
• process of translocation- water potential is effected by concentration of sugars, osmosis creates changes in w.p and create a pressure gradient, active transport is then involved with movement of sucrose
• Cohesion tension theory- transpiration of water through stomata occurs when the water potential of the leaf is lower than the water potential of the air so water is pulled up from xylem creating negative pressure, a water column is formed by hydrogen bonds between water molecules
• the mass flow hypothesis is : Sucrose moves from companion cells into sieve tube elements by active transport. This reduces the water potential of the sieve tube element.
• how is the sieve tube element adapted for mass transport?

  • it has few organelles and very little cytoplasm so there is an easier flow of substances
• How is companion cell adapted for transport of sugars between cells? - mitochondria release energy from ATP for active transport to take place
• how is pressure generated in the phloem?

  • sucrose is actively transported out of phloem
  • causing a lower water potential
  • so water moves into phloem by osmosis
• how can tracers be used to show transport in plats?

  radioactive substances are supplies to the leaf got the plant, we can then detect the movement of the substances throughout the plant
• a limitation of the mass flow hypothesis is the fact that not all solutes move at the same speed, like mass flow hypothesis believes
• describe the process of translocation/transport of sugars in plants:

  • sucrose is actively transported into the phloem/sieve element
  • By companion cell
  • This Lowers water potential in phloem/sieve element
  • water enters by osmosis
  • This Produces high pressure
  • Mass transport towards sink/roots
  • At sink/roots sugars are unloaded