evidence for translocation

what are 2 pieces of evidence that translocation occurs in the phloem?

• Plant supplied with radioactively labelled CO2, then radioactively labelled carbon appears in the phloem (as sucrose)

• Ringing a tree (removing phloem) results in sugars collecting above the ring (as there is nothing for it to be transported in)

what is evidence that translocation requires energy? (3)

• Companian cells have many mitochondria

• No translocation when metabolic poison used

• Sugars move up to 10,000 times more quickly by mass flow than by diffusion

what is evidence of translocation? (2)

• pH of companion cells is higher (more alkali) than surrounding cells

• Sucrose concentration higher in source than sink

how do studies with aphids provide evidence for translocation?

• There is pressure in the phloem

• The pressure in the phloem is lower closer to the sink than the source

• The sucrose concentration in the phloem sap is higher near to the source than near the sink
   

what is evidence against translocation? (3)

• Not all solutes in phloem move at the same rate

• Sucrose moves to all parts of the plant at same rate (not more quickly to areas of low concentration of sucrose)

• Role of sieve plates?