Mass transport in plants

Question 1

Define ‘ Transpiration ‘

Answer 1

Loss of water / Evaporation
From leaves, their stomata on base of leaf

Question 2

How does light intensity affect the rate of transpiration ?

Answer 2

Light intensity - More stomata with higher light intensity therefore higher surface area

Question 3

What affects the rate of transpiration ?

Answer 3

Light intensity
Temperature
Humidity
Wind

Question 4

How does temperature affect the rate of transpiration ?

Answer 4

Faster rate of transpiration
More heat therefore water molecules gain kinetic energy
Faster molecules -> More evaporation

Question 5

How does humidity affect the rate of transpiration ?

Answer 5

Slower rate of transpiration increasing humidity
More water present in the air
Water potential is more positive outside leaf than inside the leaf

Question 6

How does wind affect the rate of transpiration ?

Answer 6

Increase rate of transpiration increasing wind
Wind carries away water vapour surrounding leaf
-> Steepens water potential gradient

Question 7

What goes into the ‘Cohesion - Tension Theory ‘

Answer 7

Cohesion (of water molecules)
Adhesion ( of xylem )
Root pressure

Question 8

How does Cohesion support the cohesion tension theory ?

Answer 8

Water molecules contain positive (H) poles and negative (O) poles
H poles bond to O poles -> binding of molecules
Causes to stick together -> can travel up the xylem as a continuous column of water

Question 9

How does Adhesion support the cohesion tension theory ?

Answer 9

Adhesion - sticking of water molecules to different molecules
Water molecules ‘adhere’ to xylem walls
Narrow xylem -> stronger adhesion

Question 10

How does root pressure support the cohesion tension theory ?

Answer 10

Water inside roots increases pressure in roots
Increase in pressure-> Pushing of water up the xylem

Question 11

Describe the movement of water up the xylem

Answer 11

Water evaporates from stomata in leaves
Lowers pressure
Water pulled up to replace pressure lost
Hydrogen bonds between water allow for continuous column of water up xylem
Water molecules adhere to the xylem walls
Pulling of water creates tension, causing xylem to be narrower.

Question 12

Describe the mass-flow hypothesis for transport of sugars in plant stem

Answer 12

At source, sucrose actively transported into phloem
By companion cells
Lowering WP in phloem
Therefore water enters via osmosis
Producing high hydrostatic pressure
Mass transport toward storage tissue
At roots, sugars unloaded