Chapter 36: Resource Acquisition in Vascular Plants

Question 1

Phyllotaxy

Answer 1

arrangement of leaves on a stem; most angiosperms have alternate phyllotaxy with 137.5 degrees between leaves

Question 2

Self-pruning

Answer 2

programmed cell death; occurs when leaves respire more than they photosynthesize

Question 3

Leaf area index

Answer 3

ratio of upper total leaf surface divided by surface area of land where plant grows

Question 4

Apoplast and symplast

Answer 4

Apoplast: consists of everything external to the plasma membrane of living cells; includes cell walls, dead cells, extracellular spaces
Symplast: consists of the entire mass of cytosol of all living cells of plants, including plasmodesmata

Question 5

What is used instead of sodium ions in plant cells?

Answer 5

Hydrogen ions help establish the membrane potential and are used in cotransporters

Question 6

Water potential

Answer 6

Water potential is a physical property that predicts the direction water flows; water moves from higher water potential to lower water potential
Water potential = solute potential + pressure potential

Question 7

Solute potential

Answer 7

Also known as osmotic potential; directly proportional to molarity; in pure water, it is 0; when solutes are added, it becomes more negative

Question 8

Pressure potential

Answer 8

Pressure potential refers to the physical pressure on a solution; negative or positive.

Question 9

Plasmolysis

Answer 9

Plasmolysis refers to when the protoplast shrinks away and pulls away from the cell wall; occurs when a cell is put into a solution with lower water potential

Question 10

Permeability of aquaporins

Answer 10

Permeability decreases due to increases in cytosolic Ca2+ concentration or decrease in cytosolic pH

Question 11

Casparian strip

Answer 11

Minerals in the apoplast encounter the Casparian strip, a selective permeable membrane, a belt made of suberin, impeding movement.

Question 12

How is xylem sap pushed?

Answer 12

At night, when minerals and ions accumulate at the Casparian strip, they lower the water potential, causing water to flow in

Question 13

Guttation

Answer 13

Occurs when more water enters the leaves than is transpired

Question 14

Cohesion-tension hypothesis

Answer 14

Proposed by John Joy and Henry Dixon; proposes that transpiration provides the pull for xylem sap; cohesion pulls it the entire length

Question 15

How is negative pressure generated according to the cohesion-tension hypothesis?

Answer 15

A negative pressure potential develops at the surface of the leaf cell walls; water vapor lost by transpiration is initially replaced by evaporation from the water film coating mesophyll cells.
The evaporation of the water film results in the air-water interface to become more curved, increasing surface tension and rate of transpiration.

Question 16

How does surface tension contribute to the cohesion-tension hypothesis?

Answer 16

Increased surface tension pulls water from surrounding cells and air spaces. An increase in negative pressure potential lowers water potential.

Question 17

Cavitation

Answer 17

Cavitation, the formation of a water vapor pocket, in xylem (usually more often in vessel elements than tracheids), block water channels of the xylem

Question 18

How does bulk flow differ from osmosis?

Answer 18

Bulk flow occurs from the different in pressure potential, and occurs in hollow, dead cells

Question 19

Stomata opening and uptake of ions?

Answer 19

Stomata opens when K+ (along with malate and Cl-) ions accumulate from neighboring cells coupled with H+, lowering water potential causing water to enter, making the guard cells turgid.

Question 20

How does light stimulate stomata opening?

Answer 20

Light stimulates blue-light receptors, which activate proton pumps in guard cells.

Question 21

Abscisic acid and function?

Answer 21

Abscisic acid is produced in roots and leaves; it responds to water deficiency, causing stomata to close, reducing wilting, but also photosynthesis.

Question 22

Xerophytes

Answer 22

Plants adapted to arid environments

Question 23

Pressure-flow Hypothesis

Answer 23

Loading of sugar into sieve tube elements results in lower water potential; water enters, forcing sugar transport

Question 24

Self-thinning

Answer 24

Occurs when there is more sugar sinks than sources

Question 25

Viral movement proteins

Answer 25

Produced by plant viruses; cause plasmodesmata to dilate enabling viral RNA to pass through