TRANSPIRATION

Question 1

transpiration stream

Answer 1

• continual flow of water in roots, up stem and out via stomata

Question 2

factors affecting transpiration (3)

Answer 2

• genetic factors, i.e number/size/distribution of stomata
• environmental i.e temp, humidity, air movement
• light intensity

Question 3

how does temp affect transpiration? (4)

Answer 3

• temp increase lowers water pot. of atmosphere,
• increases KE of water moecules increasing rate of evaporation from mesophyll cells
• if stomata are open speeds up rate of diffusion
• high to temp causes water to diffuse more quickly decreasing water pot. around leaf

Question 4

Humidity (4)

Answer 4

• air inside leaf is saturated with water so relative humidity is 100% and humidity around leaf is never >100
• water gradient between leaf and atmosphere, when open causes water vapour to diffuse out down gradient
• transpiration in still air causes layer of saturated air at the surface of leaves causing rings of decreasing humidity
• water vapour diffuses down this gradient away from the leaf

Question 5

Air movement (3)

Answer 5

• wind blows away humid air at the leaf’s surface
• increases water gradient between inside and outside, therefore water diffuses out of stomata
• faster air = faster transpiration

Question 6

Light intensity

Answer 6

• controls degree of stomatal opening
• most plants stomata open more as LI increases therefore increasing transpiration
• so stomata widest at mid day, closed at night

Question 7

do transpiration factors act independently?

Answer 7

no

Question 8

what does a potometer measure and what is it used for? (2)

Answer 8

• measures water uptake (but transpiration is basically the same)
• used to measure transpiration

Question 9

how to set up a potometer (8)

Answer 9

• cut leafy shoot underwater (to prevent air entering xylem)
• under water, fill potometer (prevent air bubbles)
• fit shoot into potometer with rubber tubing (prevent air bubbles in xylem or apparatus
• remove potometer and shoot, seal joints w/ vasaline and dry carefully
• introduce air bubble into capillary tube
• measure distance bubble moves in given time
• repeat and calculate mean distance
• use to compare different transpiration factors