7.9 Mass Flow Hypothesis

Question 1

What is translocation?

Answer 1

Mass flow of sucrose and amino acids from source to sink

Question 2

What are features of translocation?

5 features

Answer 2

• It requires energy.
• It transports substances from sources (where they are made, like the leaves) to sinks (where they are used, like the roots).
• The substances are transported through the phloem.
• Water provides the medium in which these substance dissolve for transport in the phloem.
• It maintains a concentration gradient using enzymes.

Question 3

What is the mass flow hypothesis?

Answer 3

Translocation occurs due to pressure gradients

Question 4

How does mass flow hypothesis propose translocation occurs?

Answer 4

Solutes loaded water enters pressure increases solutes removed water leaves pressure decreases pressure gradient

Question 5

What happens at the sink in mass flow hypothesis?

Answer 5

Solutes actively unloaded

Question 6

What evidence supports mass flow hypothesis?

Answer 6

Ringing experiments radioactive tracers aphids metabolic inhibitors

Question 7

What evidence is against mass flow hypothesis?

Answer 7

Sugars don’t only move to highest water potential pressure gradient not high enough