Lecture 6 - Atmosphere-Plant-Soil Continuum

Question 1

water movement in xylem

Answer 1

moves root to shoot

Question 2

are mature xylem cells alive or dead?

Answer 2

dead

Question 3

are immature xylem cells alive or dead

Answer 3

alive

Question 4

2 cell types that are involved in water flow through the xylem

Answer 4

tracheids and vessels

Question 5

tracheids

Answer 5

primitive water-conducting elements that are present in both gymnosperms and angiosperms

Question 6

what do tracheids look like

Answer 6

long, thin cells with tapered ends and walls reinforced with lignin

Question 7

what allows movement between tracheids

Answer 7

pit-pair

Question 8

pit-pair

Answer 8

2 pits occurring opposite one another in the walls of adjacent tracheid or vessel elements

Question 9

vessels

Answer 9

advanced water-conducting elements that are present only in the angiosperms

Question 10

what are vessel cell sizes dependent on

Answer 10

species and environment dependent

Question 11

what is a special feature of vessels

Answer 11

development of perforation plate

Question 12

are large vessels always better

Answer 12

no

Question 13

wider conduits are ______ (more/less) conductive

Answer 13

more

Question 14

cavitation

Answer 14

a condition wherein an air bubble moves into a vessel

Question 15

embolism

Answer 15

the blocking of a xylem vessel or tracheid by an air bubble or cavity

Question 16

what does disruption to H-bonding lead to

Answer 16

leads to localized break in water column

Question 17

embolized xylem vessel

Answer 17

can no longer hold water and decreases xylem hydraulic conductance

Question 18

what do pit membranes do

Answer 18

they permit water flow and limit embolism spread

Question 19

why does angiosperm have both vessel and tracheid in xylem

Answer 19

as vessels are more vulnerable to embolism, compared to tracheids
they also may evolve their xylem system to maintain water flow under drought conditions

Question 20

cohesion tension theory

Answer 20

water forms a string of water molecules during tis movement through the xylem. the tensile strength of water is high enough to allow water to be pulled through the tracheary elements

Question 21

experimental evidence for tension in xylem sap

Answer 21

high transpiration results in big tension in xylem sap that causes the the xylem walls pulled in towards lumen