Translocation Flashcards
What is translocation?
The movement of solutes to where they are needed in the plant.
Where does translocation occur?
In the phloem.
Translocation moves solutes from where to where?
Sources to sinks. The source of a solute is where its made (high concentration) and the sink is where its used up (lower concentration).
What do enzymes help to maintain?
The concentration gradient from the source to the sink by changing the solutes at the sink. This ensures that there is always a lower concentration at the sink than the source.
What is the mass flow hypothesis?
1) sucrose moves the companion cells into sieve tube elements by active transport.
2) Lowers water potential inside sieve tubes.
3) Water enters phloem by osmosis - increases hydrostatic pressure at the source end.
4) Solutes move down the pressure gradient towards the sink end of the phloem and are used up.
5) Increased water potential inside sieve tubes - water leaves tubes by osmosis.
6) Hydrostatic pressure is maintained between source and sink - solutes are pushed along the sieve tubes towards the sink.
7) Solutes are then used and stored.
What is the supporting evidence for the mass flow hypothesis?
- if a ring of bark is removed from a woody stem, a bulge forms above the ring. The fluid from the bulge has a higher concentration of sugars that the fluid from below the ring. This suggests that there is a downward flow of sugars.
What objections are there for the mass flow hypothesis?
Sugar travels too many different sinks, not just to the one with the highest water potential, as the model would suggest.
