Transport in Plants

Question 1

What is transpiration?

Answer 1

The loss of water vapour from the stomata by evaporation.

Question 2

How can transpiration rate be measured?

Answer 2

Using a potometer.
Plus a capillary tube, cut plant, air bubble from reservoir of potometer. You let one out and measure the radius of the capillary tube and the position of the bubble. Set timer, after measure the distance travelled. Calculate volume of water uptake and divide by time taken.

Question 3

Why are potometers not totally accurate?

Answer 3

Some water is used during hptosynthesis and metabolism so not all water is lost via transpiration.

Question 4

What is the formula for rate of transpiration?

Answer 4

Rate = pi x r2 x l/t
r=radius of capillary tube
t=time taken

Question 5

List the factors that affect the rate of transpiration

Answer 5

1. Light intensity
   2.Temperature
   3.Humidity
   4.Wind

Question 6

How does light intensity affect trabspiration rate

Answer 6

Positive correlation.
More light=more open stomata=larger surface area for evaporation.
This is because stomata close in the dark and even low light intensity causes them to open.

Question 7

How does temperature affect rate of transpiration?

Answer 7

Positive correlation.
More heat=more KE=faster moving molecules so more evaporation.
Too high and stomata close, dramatically reducing rate.

Question 8

How does humidity affect rate of transpiration?

Answer 8

Negative Correlation.
More water vapour in air increases water potential outside the leaf, reducing water potential gradient.

Question 9

How does win/air movement affect rate of transpiration?

Answer 9

Positive correlation.
More wind will blow away humid air containing water vapour = maintenance of water potential gradient.
Still air = negative correlation. Humidity increases lowering concentration gradient.