mass transport in plants exam qs

Question 1

The mass flow hypothesis is used to explain the movement of substances
through phloem.
Use your understanding of the mass flow hypothesis to explain how
pressure is generated inside this phloem tub

Answer 1

• sucrose actively transported into phloem
• lowers water potential
• low water potential causes water to move into phloem from xylem by osmosis

Question 2

A different student used coloured water to investigate the movement of water in leaf stalks of celery
Explain why the coloured water moves up the stalks

Answer 2

• water is lost by transpiration
• this lowers water potential and creates negative pressure
• this pulls water up the xyxlem
• cohesion and adhesion of molecules maintains a continuous column

Question 3

The student used a sharp scalpel to cut the celery. Describe how she
should ensure she handled the scalpel safely during this procedure.

Answer 3

• cut away from the body
• cut on a hard non slip surface ie a board or tile

Question 4

Unlike plants, Ulva lactuca does not have xylem tissue.
Suggest how Ulva lactuca is able to survive without xylem tissue.

Answer 4

Short diffusion pathway (to cells)

Question 5

.
(a) Describe the cohesion-tension theory of water transport in the xylem.

Answer 5

• water evaporates from plant
• low water potential creates negative pressure which pulls water up the xylem
• hydrogen bonding between water molecules creates a continuous column
• adhesion of water molecules to xylem walls, pulls water up faster