Translocation Flashcards
What is translocation?
The movement of dissolved substances from source to sink
What is ‘source to sink’?
from where it’s made to where it’s used up.
How does phloem loading occur?
Hydrogen ions are actively pumped from companion cell into surrounding tissues
H ions bind to co transport protein and re enter companion cell down diffusion gradient
Sucrose molecules are co transported with the H ions against its conc gradient
Sucrose then moves into the sieve tubes via diffsion
How are companion cells adapted for their function?
Lots of mitochondria for energy for active transport.
Describe how the assimilates move down the phloem?
Due to assimilates in the sieve tubes, there is a low water potential.
Water moves from xylem into phloem down gradient
This creates turgor pressure at one end of the phloem
The solution moves down the pressure gradient to the rest of the plant
How does sucrose get from source to the companion cells?
apoplast route - through the cell walls
How does phloem unloading occur?
sucrose is unloaded at any point to the cells that need it. This is done via diffusion. Sucrose then rapidly moves away or is converted into glucose to maintain the concentration gradient out of the phloem.
Why does the pressure at the bottom of the phloem decrease?
due to assimilates leaving the phloem, the water potential increases causing the water to leave via osmosis back into the xylem
