Lecture 5 - Atmosphere-Plant-Continuum

Question 1

how is transpirational pull generated in leaves

Answer 1

water diffuses from the air space of the leaf to air outside through the stomata. water vapor lost is replaced by evaporation from the water film that coats the mesophyll cells

Question 2

how does water move through the leaf

Answer 2

1) stomata open
2) water vapor diffuses from internal air space, down its concentration gradient, into the air
3) net loss of water vapor causes air-water-interface to recede towards outer microfibrils and establish a water potential gradient
4) H-bonding/cohesion transmits tension at surface to bulk water
5) time-dependent buildup of surface tension
6) water is pulled towards air-water-interface

Question 3

how does cohesion play a part in the air-water-interface

Answer 3

strong forces of cohesion between water molecules allows transmission of tensional component into the bulk phase of water within cell wall

Question 4

rate of water loss from air-water-interface =

Answer 4

rate of water delivery (pulled from interior sources)

Question 5

cells that make up the xylem

Answer 5

tracheid and xylem parenchyma cells

Question 6

cells that make up the phloem

Answer 6

companion cell, sieve element, phloem parenchyma

Question 7

apoplasmic (apoplastic) pathway

Answer 7

water moves through the intercellular spaces with no entry into cells

Question 8

symplasmic (symplastic) pathway

Answer 8

water moves through the cells via plasmodesmata

Question 9

transcellular pathway

Answer 9

water moves across the plasma membrane

Question 10

flow within each pathway determined by:

Answer 10

-magnitude of water potential gradient
-tissue capacitance
-resistance to water flow

Question 11

plasmodesmata

Answer 11

microchannel connecting between plant cells through the cell wall