Transpiration

Question 1

How does water enter the leaf?

Answer 1

via the xylem instem

Question 2

What is transpiration?

Answer 2

evaporation of water and diffusion of water vapour

Question 3

What is the surface of cells in a leaf covered with?

Answer 3

water, which evaporates from the surface of the cells

Question 4

1st stage of transpiration

Answer 4

internal leaf spaces contain a high concentration of water vapour so it diffuses out, down a concentration gradient

Question 5

2nd stage of transpiration

Answer 5

continuous evaporation means water potential of cell in leaf decreases so water moves via osmosis from adjacent cells

Question 6

3rd stage of transpiration

Answer 6

water potential of these cells decrease so water passes into them too

Question 7

4th stage of transpiration

Answer 7

this continues all the way back to the xylem, so water continuously moves out of xylem to adjacent cells

Question 8

What is tension?

Answer 8

the term for water continuously being pulled out of the xylem

Question 9

Transpiration stream meaning

Answer 9

movement of water into the root, up the xylem and out of the leaf

Question 10

How does water travel against gravity?

Answer 10

-cohesion between water molecules
-adhesion between water and molecules in xylem walls

Question 11

Name of process that means water can move upwards?

Answer 11

capillary action

Question 12

What is the transpiration pull?

Answer 12

when water is removed from the top of the xylem vessels due to transpiration so more water moves up via capillary action

Question 13

What is cohesion tension theory?

Answer 13

transpiration pull, cohesion and adhesion combined to pull water into roots, up the stem and out of the leaves

Question 14

What is each stoma surrounded by?

Answer 14

2 guard cells

Question 15

Function of guard cells

Answer 15

determine whether stoma is open or closed

Question 15

When are the stomata open and why?

Answer 15

-under light conditions as photosynthesis is possible, so CO2 can diffuse in

Question 16

When are the stomata closed and why?

Answer 16

-close at night to reduce water loss as there’s no light for photosynthesis
-close when the water level in soil is low (hormones sent from root), to reduce water loss

Question 17

Stage 1 of how stomata open

Answer 17

-light conditions trigger solutes (K+) to be transferred into the guard cells, which lowers their water potential

Question 18

Stage 2 of how stomata open

Answer 18

water moves into the guard cells by osmosis, so they become turgid

Question 19

Stage 3 of how stomata open

Answer 19

-as water enters, the guard cells’ rings of cellulose force them to expand lengthwise
-thickened cell walls mean they expand unevenly

Question 20

End result of stomata opening

Answer 20

guard cells develop curved shape which allows stoma to open so water vapour can diffuse out

Question 21

What are the 5 factors affecting transpiration?

Answer 21

-light intensity
-relative humidity
-temperature
-air movement
-water in soil

Question 22

How does light intensity affect transpiration?

Answer 22

-light causes stomata to open to allow CO2 in and water vapour out for photosynthesis
-increase light intensity, increase rate of transpiration
-rate of transpiration stops increasing when all stomata are open

Question 23

How does humidity affect transpiration?

Answer 23

-humidity tells us concentration of water vapour as a percentage of the maximum
-large concentration gradient between inside and outside of leaf means water vapour will diffuse out faster

Question 24

How does temperature affect transpiration? (2)

Answer 24

-high temps mean water molecules have more kinetic energy so the rate of evaporation from internal surfaces of the leaf is greater -high temps also mean humidity decreases so the concentration gradient is larger and transpiration is faster

Question 25

How does air movement affect transpiration?

Answer 25

-removes water vapour that has built up around external surfaces of leaf, increasing the concentration gradient and the rate of transpiration

Question 26

How does water in soil affect transpiration?

Answer 26

-less water in soil releases hormone which triggers stomata to close and reduces rate of transpiration