4.4.4 - Translocation

Question 1

Features of the structure of the phloem.

Answer 1

Made up of sieve tube elements
End walls are perforated to form sieve plates
Companion cells are associated with sieve tube elements

Question 2

What is the place where sucrose is made?

Answer 2

Source

Question 3

What is the place where sucrose is used?

Answer 3

Sink

Question 4

What are 3 things that the phloem transports?

Answer 4

Sucrose
Amino acids
Inorganic ions

Question 5

What is the first stage of the mass flow theory?

Answer 5

Sucrose is actively transported into the phloem, companion cells are involved.

Question 6

What happens after sucrose moves into phloem by active transport?

Answer 6

Water potential is lowered.
Water moves in by osmosis from xylem.

Question 7

What happens after water moves into phloem by osmosis?

Answer 7

Pressure increases
Causes movement towards sink

Question 8

What is sucrose used for in the sink?

Answer 8

Respiration
Stored as starch

Question 9

Why is sucrose stored as starch?

Answer 9

Sucrose is soluble in water so affects water potential.
Starch isn’t.

Question 10

Evidence for mass flow theory.

Answer 10

There is a pressure within sieve tubes, shown by sap being released when cut.
Concentration of sucrose is higher in source than sink.

Question 11

Evidence against mass flow theory.

Answer 11

Function of sieve plates in unclear, they would hinder mass flow.
Not all solutes move at the same speed - they should do if movement is by mass flow.