L27 Plant Circulation and Gas Exchange

Question 1

what is the most important organ to consider when transporting molecules in plants?

Answer 1

cell wall

Question 2

what is a plant cell wall composed of?

Answer 2

lipid membrane surrounding a number of fixed charges bathed in mobile charges

Question 3

how does a plant cell achieve electron neutrality?

Answer 3

electrons diffuse across the semi-permeable membrane and cause an influx of water

Question 4

what happens when water enters plant cells and they expand?

Answer 4

the pressure of the plasma membrane is equal to the pressure of cell wall against membrane (prevents bursting)

Question 5

what does a cell wall allow plants to achieve?

Answer 5

high pressure systems

Question 6

what is the pressure generated by water influx within a plant cell?

Answer 6

turgor pressure

Question 7

How much pressure does this plant cell wall exert?

Answer 7

1-2megapascals, as much as a nuclear power station

Question 8

what is symplast?

Answer 8

it is interconnecting cytoplasm, shows a high resistance pathway below the cell wall

Question 9

what is apoplast?

Answer 9

a pathway of solutes in interconnecting cell walls showing low resistance pathway

Question 10

how do signals get in and out via cell wall?

Answer 10

they must be small and neutrally charged

Question 11

what is the advantage of xylem cells?

Answer 11

they allow fast transport with low pressure

Question 12

what is the standard veolcity of water/transpiration rate?

Answer 12

4MPa/ second

Question 13

what pressure is required for water movement in a xylem tube with radius 40 microns and length of 100?

Answer 13

0.02MPa

Question 14

does the addition of membranes at the top and bottom of a xylem tube increase or decrease the pressure required for water movement

Answer 14

increase by x10^8

Question 15

when does the flow of water stop?

Answer 15

until the pressure of solution across the wall is matched with atmospheric pressure

Question 16

mew = RTlna + VP

Answer 16

mew = chemical potential
RT = gas temperature constant
ln(a) = log of chemical activity of water
P = pressure in system
V = partial molal volume

Question 17

what is water potential?

Answer 17

difference between turgor pressure and osmotic pressure
/
presure potential + osmotic pressure/ solute potential

Question 18

what is the water potential of pure water?

Answer 18

zero

Question 19

what is water potential reduced by?

Answer 19

solutes, negative pressures and increased by positive pressures

Question 20

can water potential be positive?

Answer 20

no, only 0 or negative

Question 21

how does water move up a tree?

Answer 21

pressure

Question 22

what happens when a plant cell is in a high water environment?

Answer 22

water potential decreases, after awhile pressure potential increases

Question 23

how is pressure potential measured?

Answer 23

zimmerman probe

Question 24

what is the water potential found in environments of atmospheric air?

Answer 24

-30 - drives water transport

Question 25

what controls stomata?

Answer 25

systematic microfibrils

Question 26

what happens stomata under high pressures?

Answer 26

they open/ separate

Question 27

what happens stomata under low pressures?

Answer 27

they close

Question 28

what does the influx of potassium K+ ions cause?

Answer 28

the stomata to open, flow of water in, pressure increases and stomata separate

Question 29

what relationship does decreasing CO2 concentrations have with stomata?

Answer 29

linear

Question 30

what relationship does decreasing CO2 concentrations have with stomata?

Answer 30

linear

Question 31

what is cavitation?

Answer 31

the formation of nitrogen bubbles in plants

Question 32

how do cavitations occur?

Answer 32

by reducing pressures can lead to mortality

Question 33

how is the height of a tree determined?

Answer 33

the pressure of xylem tubes

Question 34

what is interesting about the leaves at the top of trees?

Answer 34

small - closed stomata, higher carbon 13, trees have reached their absolute height