Topic 3 - Potometer [15]

Question 1

Billy wants to do the same experiment but with a different species of plant, what must be controlled?

Answer 1

Same number and size of leaves

so there is same opportunity for transpiration as surface area same

Question 2

If the air bubble moved 15.28mm in 1 minute through the tube, which is 0.5mm in radius. what would the rate of transpiration be?
(hint - volume of cylinder is πr2)

Answer 2

πr2L divided by time taken

π x 0.5^2 x 15.28 = 12mm min^-1

Question 3

Why must all joints of the equipment be covered in petroleum jelly

Answer 3

Petroleum jelly will prevent water leaking out in other ways than evaporation out the plant.
Petroleum jelly is waterproof.

Question 4

Why must the plant shoot be cut underwater

Answer 4

Because of Cohesion-Tension, the Xylem is in negative pressure, constantly pulling water upwards. if it was to be cut in the air then it would begin to pull air up and destroy the constant column of water, preventing transpiration. Cut underwater.