Translocation

Question 1

What is translocation?

Answer 1

> Movement of assimilates through the phloem

Question 2

Active loading

Answer 2

> sucrose is loaded into the sieve tube using ATP in the companion cells
Hydrogen ions are transported out of the companion cell creating a conc gradient
proteins only allow H+ ions in if they’re accompanied by sucrose
Sucrose diffuses into the sieve tubes

Question 3

Movement of sucrose

Answer 3

> moves by mass flow in sap
mass flow is called by difference in hydro-static pressures at the ends of the tubes
water enters at the source, increasing the pressure and leaves through the sink reducing the pressure
Sap moves from source to sink

Question 4

Source

Answer 4

> sucrose entering the sieve tube element makes the water potential inside the sieve tube negative
water moves into the sieve tube by osmosis, increasing hydrostatic pressure at the source

Question 5

Sink

Answer 5

> sucrose leaves through the plasmodesmata at the sink
this courses WP to increase so water leaves the sieve tube
reduces hydrostatic pressure in the sink

Question 6

Movement of sucrose along phloem

Answer 6

> sucrose is actively loaded into the source of the sieve tube and reduced WP
water follows by osmosis and increases the hydrostatic pressure in the sieve tube element
sap moves down the sieve tube from high HSP to low HSP in the sink
sucrose is removed from the sieve tube by surrounding cells and increases the WP in sieve tube
water moves out of the sieve tube and reduces the HSP