Translocation

Question 1

What is translocation?

Answer 1

Movement of solutes from place to place
Sugars are transported from sources to sinks

Question 2

What are sources?

Answer 2

Sites of sugar production e.g. leaves

Question 3

What are sinks?

Answer 3

Where the sugars will be used or stored e.g. roots and buds

Question 4

What are plasmodesmata?

Answer 4

Small channels that connect the cytoplasm of plant cells to each other, forming a living bridge between cells
Each cell is not completely isolated by the cell wall

Question 5

What are companion cells?

Answer 5

Companion cells provide metabolic support to the sieve elements

Which is important as they lose many of their organelles as they become specialised

They rely on companion cells for repair and maintenance

Question 6

What does the mass flow hypothesis suggest?

Answer 6

The mass flow hypothesis suggests that the phloem sap is pushed from source to sink
by a hydrostatic pressure gradient
caused by osmosis

Question 7

Describe the process of translocation in plants

Answer 7

1) H+ ion actively transported out of the companion cells

2) the sucrose is then co-transported into the companion cells and actively transported into the phloem

3) there is a low water potential at the top of the phloem
- water diffuses from the xylem into the phloem via osmosis
- high hydrostatic pressure

4) the water and sucrose then travel down the phloem
- water diffuses out of the phloem into the xylem as there’s a high water potential in the phloem
- low hydrostatic pressure (hydrostatic pressure gradient established)

5) the sucrose is then actively transported into the companion cell

6) sucrose diffuses into the sink via facillitated diffusion