transport in plants - phloem

Question 1

explain how how translocation occurs

Answer 1

H+ ions are actively transported out of companion cell

glucose from photosynthesis cells is converted to sucrose

H+ return to companion cell through co transport protein with sucrose (facilitated diffusion)

sucrose diffuses from companion cell to sieve tube element through the plasmodesma

this lowers the water potential ion the sieve tube element

there is a higher water potential is the xylem

water moves into the sieve tube element by osmosis which creates a high hydrostatic pressure

sucrose at the sink is actively transported into the sink cells where it is converted into starch or used in respiration

sieve tube at the sink end has a higher water potential than the xylem sio water moves by osmosis back into the xylem

this creates a low hydrostatic pressure at the sink end of the sieve tube element

sucrose moves by mass flow down the hydrostatic pressure gradient from source to sink