Translocation

Question 1

What is translocation?

Answer 1

• Its and energy requiring process that happens in the phloem
• translocation moves substances from sources to sinks

Question 2

What is a sink?

Answer 2

-the area where the sugars are used

Question 3

What is a source?

Answer 3

• Substance where sugars are made

Question 4

How do enzymes maintain a conc gradient?

Answer 4

• by changing the dissolved substances at the sink. This makes sure there’s always a lower conc at the sink than at the source

Question 5

Explain phloem transport

Answer 5

• Active transport is used to actively load the solutes into the sieve tubes of the phloem at the source.
  This lowers the water potential inside the ST, so water enters the tubes by osmosis from the xylem and companion cells
  This creates a high pressure inside the ST at the source end of the phloem,
• At the sink end, solutes are removed from the phloem to be used
  The increases the water potential inside the ST, so water also leaves the tubes by osmosis
  This lowers the pressure inside the ST
• The result is a pressure gradient from the source end to the sink end.
  This gradient pushes solutes along the ST to where they’re needed

Question 6

What is active loading and how does it work?

Answer 6

• used to move substances into the companion cells from surrounding tissues, and from the companion cells into the sieve tubes, against a conc grad.
• The conc of sucrose is usually higher in the companion cells than the surrounding tissue cells, and higher in the sieve tube cells than the companion cells
• So sucrose is moved to where it needs to go using active transport and co-transporter proteins:
• In the companion cell, ATP is used to actively transport H+ ions out of the cell and into the surrounding tissue cells
• This sets up a conc gradient - there are move H+ ions in the surrounding tissue than in the companion cell
• An H+ ion binds to a co-transport protein in the companion cell membrane and re-enters the cell (down the conc)
• Sucrose mole are then transported out of the companion cells and into the ST by the same process

Question 7

What is ATP?

Answer 7

One of the products of respiration. the breakdown of ATP supplies the initial energy needed for the active transport of the H+ ions