Topic 4 -19

Question 1

What is the process called through which sucrose moves from source to sink in plants?

Answer 1

Translocation

Translocation involves the movement of solutes in the phloem of plants.

Question 2

What hypothesis explains the movement of dissolved sucrose in the phloem?

Answer 2

The mass-flow hypothesis

The mass-flow hypothesis describes the pressure gradient between sources and sinks.

Question 3

What creates a high hydrostatic pressure (HP) in the phloem during translocation?

Answer 3

Water drawn in due to low water potential

A high concentration of sucrose reduces water potential, causing water to enter and create high HP.

Question 4

What are the sources and sinks in the context of translocation?

Answer 4

Sources: leaf cells (mesophyll cells); Sinks: roots, fruits, seeds, tubers

Sources are where sucrose is produced, and sinks are where it is used or stored.

Question 5

How can sucrose be moved into the phloem?

Answer 5

By the symplast or the apoplast routes

These are two pathways through which sucrose enters the phloem.

Question 6

What evidence supports the mass-flow hypothesis?

Answer 6

Aphid mouthparts exude sap

This observation suggests that the content of the phloem is under pressure.

Question 7

True or False: The mass-flow hypothesis explains why sieve and companion cells need to be alive.

Answer 7

False

The theory does not address the necessity of living sieve and companion cells.

Question 8

What is a weakness of the mass-flow hypothesis regarding movement in the phloem?

Answer 8

Movement can be up and down in the same sieve tube and at different speeds

This inconsistency challenges the simplicity of the mass-flow hypothesis.

Question 9

What role do phloem sieve plates play according to the mass-flow hypothesis?

Answer 9

No obvious role

The function of sieve plates is not clearly explained by the theory.