3.3.7: Transplocation

Question 1

What is translocation?

Answer 1

Transport of assimilates through a plant.

Question 2

Where does translocation occur?

Answer 2

-Phloem

Question 3

Describe active loading.

Answer 3

-Sucrose loaded into sieve tube by active process.
-involves the use of energy from ATP in companion cells.
-Energy from ATP used to actively transport H+ out of companion cells.
-Increases their conc. outside the cells (conc. gradient created.
-H+ diffuse back into companion cells through cotransporter proteins accompanied by sucrose molecules.
(sucrose mol. moving against conc. gradient.
-As conc. sucrose is high in companion cells, it diffuses through plasmodesmata into the sieve tube element.

Question 4

How does sap move up and down the phloem?

Answer 4

• Mass flow.
• Soln. sucrose amino acids, other assimilates.
• Flows up or down plant as requires.
• Flow caused by difference in hydrostatic pressure at the two ends of the tube, pressure gradient.
• Water enters tube at source, increasing pressure
• Water leaves tube at sink, reducing pressure

Question 5

Describe movement of sap in phloem

Answer 5

• Sucrose actively loaded into sieve tube element and reduces WP.
• Water flows by osmosis and ↑ HSP in sieve tube element. (at source)
• Sap moves down ST from high to low HSP.
• Sucrose moved out of ST by surrounding cells. WP in ST ↑
• Water moves out od ST and reduces HSP (at sink)

Question 6

What is a source, give examples.

Answer 6

• Part of plant loading assimilates into ST.
• Roots in early spring, energy stored as starch is converted to sucrose and moved to other parts enabling growth.
• Leaf, photosynthesises, produces sugars, converted to sucrose and loaded into phloem ST. Transported to meristems or roots for storage.

Question 7

What is a sink, give examples.

Answer 7

• Anywhere that removes assimilates from ST.
• Sucrose used for respiration and growth (meristems)
• OR. converted to starch for storage in a root.