lecture 5 - plant structure and function - leaves

Question 1

What are stomata?

Answer 1

Each stoma = pair of guard cells and a central pore
Allow balance of water loss and gas exchange
Can be numerous but are small, so only 1-2% of leaf surface

Question 2

What are guard cells?

Answer 2

Are symplastically isolated - no connection to cells around it
Have chloroplasts

Important for the regulation of stomatal aperture- how large the gap is that allows gas exchange

Question 3

What is the process by which stomata open?

Answer 3

Light falls on the guard cell.
H+/ATPase pump activated in plasma membrane causing H+ to move out of the cells and K+ moves in…
…starch is also metabolised to sucrose and malate.
Both result in a fall of the water potential of the cell.
Water moves into the cell by osmosis – causing them to swell.
Unequal thickening of the cell wall of the guard cells causes cells to expand outwards – opening the stomatal pore.

Question 4

What is the importance of ABA?

Answer 4

Control of guard cell turgor by light can be overridden when water is scarce.
Triggered by abscisic acid (ABA).
ABA binds to receptor on the plasma membrane that triggers a number of signalling cascades.
Resulting in the guard cell membrane depolarization, leading to solute loss, followed by water loss hence, drop in guard cell turgor and the stomata close.

Question 5

What things open stomata?

Answer 5

Light

Low CO2

Question 6

What things close stomata?

Answer 6

Water shortage

Question 7

What is stomatal conductance?

Answer 7

rate of CO2 entering OR water vapour exiting through the stomata hence degree of opening

Question 8

light/low CO2 leads to….

Answer 8

K+ influx
Increased turgor
Open stomata

Question 9

ABA synthesis + water stress (detected in the root) leads to

Answer 9

K+ efflux
Decreased turgor
Closed stomata

Question 10

How do plants adapt to survive with less water?

Answer 10

Collect more water eg. deep roots

Store water eg. succulents

Lose less water

Cope without