Transport in the Xylem (Needs root transport added)

Question 1

What is Transpiration

Answer 1

Evaporation of water from a plant leaf

Question 2

What evidence is there for the cohesion-tension theory?

Answer 2

If air enters a xylem, tree can no longer draw up water as continuous column broken
Water doesn’t leak out broken vessel due to negative pressure

Question 3

How does Water move in the xylem and up the stem (big question)

Answer 3

Water evaporates from mesophyll cells via transpiration
Water molecules from H bonds and stick via cohesion
Continuous unbroken column formed across mesophyll cells and down the xylem
As water evaporates from mesophyll into air spaces beneath stoma, water is drawn up behind it due to cohesion
Column of water pulled up xylem as a result- transpiration pull

Question 4

How does water move across cells of leaf

Answer 4

Mesophyll cells lose water via transpiration
Cell now have low water potential, draws in water from surrounding cells
Surrounding cells water potential decreases
Water taken in by other cells via osmosis

Question 5

Drawbacks of potometer

Answer 5

Some of water could be used in photosynthesis or metabolism

Question 6

Use of potometer

Answer 6

Measure rate of volume of water taken up by plant
Measures rate of transpiration

Question 7

Control Measures of Potometer

Answer 7

Temperature
Light intensity
Humidity
Wind

Question 8

Why is the diameter of a tree smaller in daytime than night?

Answer 8

During the day when transpiration is at its highest, there is more negative pressure in the xylem that pulls the xylem walls inwards.
At night, less negative pressure means the xylem walls are not pulled inwards, increasing tree diameter.