translocation

features of phloem tissue?

sieve tube elements
companion

structure of sieve tube elements?

holes for continuous flow of sugar
no nucleus + few organelles for max. space
living

role of companion cells?

provide ATP for active transport

first part of translocation?

• at source, H+ ions actively transported out of companion cells using ATP

• H+ ions diffuse back in via co-transporter protein bringing sucrose with it

• sucrose moves into sieve tube elements

second part of translocation?

• sucrose movement into sieve tube elements decreases WP

• water enters by osmosis from xylem vessels, creating high hydrostatic pressure

third part of translocation?

• at sink, sucrose is actively transported out/used in respiration, increasing WP

• water moves out by osmosis, reducing pressure

• sap moves from source to sink down the pressure gradient by mass flow

how do tracers prove sugars are transported by the phloem?

• provide plants w/ radioactively labelled CO2

• sugar made in PS will contain this CO2

• thin stem slices cut + placed on an x-ray film that turns black when exposed to RA material

• sections with sugar on stem will go black, highlighting the phloem

how does the ringing experiment prove sugars are transported by the phloem?

• ring of back containing the phloem peeled off tree trunk

• causes trunk to swell above the removed area

• swelling is filled with sugar

• showing on removal of the phloem, sugar can no longer be transported