1. Crossword!

2. Translocation: The movement of assimilates up and down the phloem
Source:
Where sucrose is released into the phloem
Sink:
Where sucrose is removed from the phloem

3. On WB: Identify Source and Sink
Plant adds water at the root, sucrose is loaded into the phloem at the second layer of leaves, and is transported to the flower via the phloem
Water moves up the xylem, the leaves of the new bud add the sucrose and it us taken up by the roots

4. Translocation Phloem Companion cell nucleus Sieve tube elements
Mitochondria
Sieve plates
cytoplasm

5. Hydrogen ions out of the cell
ATP
Active Transport
Hydrogen ions out of the cell

6. Creates Diffusion Gradient
More hydrogen
Less hydrogen

7. Sucrose co-transporter

10. Hydrogen and Sucrose diffuse into the companion cell

11. Sucrose builds up in companion cell: Diffusion gradient
More Sucrose
Less
Sucrose

12. Sucrose diffuses into sieve tube elements via the plasmodesmata

13. Hydrogen Ions pumped out – active transport Creates Diffusion Gradient
Sucrose and hydrogen diffuse in – co-transporter
Sucrose diffuses into sieve tube via plasmodesmata
Phloem
Companion cell
Co-transporter
Active transport
ATP
mitochondria
Plasmodesmata
Diffusion Gradient
Cytoplasm
Sieve tube
Hydrogen
Diffusion

14. Water moves out of sieve tube element and reduces hydrostatic pressure
Source
Sucrose is actively loaded into sieve tube element and this reduces water potential
Low Ψ
Water follows by osmosis and increases the hydrostatic pressure in the sieve tube element
Higher Pressure!
Water moves down sieve tube from high hydrostatic pressure at source to low hydrostatic pressure at sink
Sucrose removed from sieve tube and increases water potential in the sieve tube
High Ψ
Lower Pressure!
Water moves out of sieve tube element and reduces hydrostatic pressure
Sink

15. Evidence: How we know the phloem is used
Radioactive carbon dioxide used in photosynthesis shows in the phloem
Aphid feeding on plant – mouthparts take food from phloem

16. Evidence: How we know energy is needed
Companion cells have mitochondria
Translocation can be stopped with a poison that inhibits ATP
Rate of sugars is so high energy must be needed

17. Evidence: How we know this mechanism is used
pH of companion cell is higher than other cells
Concentration of sucrose is higher in source than sink

18. Evidence: Evidence against Not all solutes move at same rate
Sucrose is moved at same rate
Why sieve plates?