Transpiration and cohesion tension theory

Question 1

HowWhat is transpiration?

Answer 1

= loss of water vapour from the stomata by evaporation

Question 2

What 4 factors affect transpiation?

Answer 2

= light intensity
= temperature
= humidity
= wind

Question 3

How does light intensity affect transpiration?

Answer 3

= positive correlation
= more light causes more stomata to open= larger surface area for evaporation

Question 4

How does temperature affect transpiration?

Answer 4

= posiitve correlation
= water molecyles have more kinetic energy, moving faster, increases rate of evaporation and transpiration

Question 5

How does humidity affect transpiration?

Answer 5

= negative correlation
= more water vapour in the air will make the water potential more positive outside the leaf reduces water potential gradient
=

Question 6

How does wind affect transpiration?

Answer 6

= positive correlation
= more wind will blow away humid air containing water vapour, maintaining concentration gradient

Question 7

how does water evaporate out of the leaf but a whole collum of water moves up to replace it agaisnt gravity?

Answer 7

= cohestion tension theory, cohesion, adhesion and root pressure

Question 8

What is cohesion?

Answer 8

= water are di-polar, enables hydrogen bonding between water molecules, creates cohesion between the molecules0 water molecules tend to stick together
= water travels up the xylem as a continious water column

Question 9

What is adhesion?

Answer 9

= adhesion is water molecules stick to other molecules the walls of the xylem, narrower the xylem the bigger impact

Question 10

What is root pressure?

Answer 10

= as water moves into the roots by osmosis
= increases volume of liquid inside so pressure increases, inside roots,
- this incfrease in pressure in the roots forces water above it upwards (positive)

Question 11

How does water move up the xylem?

Answer 11

= water evaporates out the stomata on leaves, loss of water volume so lower pressure where water evaporated
= when water is lost from transpiration, more water is pulled up the xylem to replace it, moves due to negative pressure, as water voluem decreaes,pulls water below it
= due to hydrogen bonding between wate rmolcues, cohesive, this creates a collum of water within the xylem
= water molecules stick to the side of the xylem, helps pull the collum upwards
= as the collum water is pulled up the xylem it creates tension, pulls xylem, becomes narrower, increases adhesion

Question 12

Use your knowledge of leaf structure to explain why less water is lost through the upper surface of leaves than is lost through the lower surface.

Answer 12

= waxy cuitle is thicker at the top layer
= more stomata at the bottom