Transport in the Xylem Part II

Potometer

an instrument that measures the rate of transpiration

What does the photometer specifically measure?

Measures the amount of water is taken up by a stem

What does the use of potometer assume?

It assumes all water taken in is lost by transpiration

Where can the data from using a potometer be used for?

can be used to calculate the rate of water uptake (volume/time)

What are five factors that affect transpiration rate?

Temperature, wind speed, humidity, light intensity, and water shortage

As temperature increases, transpiration…

increases

As wind speed increases, transpiration…

increases

As humidity increases, transpiration…

decreases

As light intensity increases, transpiration…

increases (stomata open for gas exchange)

As water shortage increases, transpiration…

decreases (stomata close)

What three things control/have influence in the movement of water through the xylem?

Root pressure, transpirational pull, and cohesion/adhesion (capillary effect)

How does root pressure affect the movement of water in the xylem?

water entering the roots pushes the water already in the plant; further up the xylem

How does transpirational pull affect the movement of water in the xylem?

as water evaporates out through the stomata, water column is pulled upwards

How does cohesion/adhesion affect the movement of water in the xylem?

water molecules stick to each other and to the walls of the xylem

Applications of cohesion to the xylem

-allows water in the root cortex cells to be pulled into the xylem

-as water evaporates out the stomata, the water column is pulled upwards

Applications of adhesion to the xylem

-maintains the water column within the xylem

-prevents it from falling to the roots by sticking to the sides of the xylem

Why does adhesion occur?

Because water is polar and forms H bonds