Mass transport in plants

• Define transpiration.


  Movement of water through a plant (using the xylem) and it's evaporation from leaves
• Describe the process of transpiration

  Water evaporates out the stomata which draws water from the mesophyll cells due to osmosis

  Water is pulled up the xlyem because of cohesion of water molecules this is called transpiration pull

  The xylem is placed under pressure and tension
• What is the cohesion tension theory?

  When the xylem is placed under pressure and tension during transpiration
• What happens to rate of transpiration with increased sunlight and temperature and why?

  Process increases because more stroma open for photosynthesis. This increases evaporation and kinetic energy in the water molecules.

  Eventually the stomata close because the plant has loss too much water, this helps prevent water loss.
• Define translocation

  Movement of organic molecules and some ions throughout a plant
• What is the structure of a phloem

  Sieve tube element - long thin structures

  Plasmodiesmata

  Sieve tube end plate - with perforated walls

  Companion cells - produce ATP
• Explain the process of translocation

  Glucose is made in the source and converted to sucrose

  Sucrose enters companion cell via facilitated diffusion

  Sucrose is co-transported to the sieve tube element / phloem along with H+ ions by the companion cell

  Water potential is lowered

  Water then enters the phloem from xylem due to osmosis

  At the sink end sucrose uses active transport into companion cells and sink

  Water also leaves the phloem into xylem via osmosis

  Hydrostatic pressure is decreased at sink area

  Hydrostatic pressure gradient is made + sucrose moves due to mass flow.