| Define translocation | The movement of dissolved substances (assimilates) to where they are needed in the plant and is an active process. |
| What is the source | They provide the assimilates to the plant from the reactions or storage for transport. Where substances are loaded |
| Give examples of sources | Leaves, roots and stems |
| What is a sink | They use the assimilates |
| Give examples of sinks | Growing roots and meristems |
| What is the mass flow hypothesis - Source | - solutes are loaded into the sieve tubes of phloems at the source
- this lowers the water potential inside the sieve tubes, so water enters the tubes by osmosis from the xylem and companion cells
- this creates a high pressure inside the sieve tubes at source end of the phloem |
| What is the mass flow hypothesis - Sinks | - at the sink end, solutes are unloaded from the phloem
- usually happens by diffusion
- the removal of solutes increases water potential inside the sieve tubes, so water also leaves the tubes by osmosis
- this lowers the pressure inside the sieve tubes |
| What is the mass flow hypothesis - Flow | - the result is a pressure gradient from the source ed to the sink end
- this gradient pushes solutes along the sieve tubes towards the sink
- when they reach the rink, the solutes will be used or stoewd |
