Chapter 36: Resource Acquisition in Vascular Plants Flashcards
(25 cards)
Phyllotaxy
arrangement of leaves on a stem; most angiosperms have alternate phyllotaxy with 137.5 degrees between leaves
Self-pruning
programmed cell death; occurs when leaves respire more than they photosynthesize
Leaf area index
ratio of upper total leaf surface divided by surface area of land where plant grows
Apoplast and symplast
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
What is used instead of sodium ions in plant cells?
Hydrogen ions help establish the membrane potential and are used in cotransporters
Water potential
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
Solute potential
Also known as osmotic potential; directly proportional to molarity; in pure water, it is 0; when solutes are added, it becomes more negative
Pressure potential
Pressure potential refers to the physical pressure on a solution; negative or positive.
Plasmolysis
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
Permeability of aquaporins
Permeability decreases due to increases in cytosolic Ca2+ concentration or decrease in cytosolic pH
Casparian strip
Minerals in the apoplast encounter the Casparian strip, a selective permeable membrane, a belt made of suberin, impeding movement.
How is xylem sap pushed?
At night, when minerals and ions accumulate at the Casparian strip, they lower the water potential, causing water to flow in
Guttation
Occurs when more water enters the leaves than is transpired
Cohesion-tension hypothesis
Proposed by John Joy and Henry Dixon; proposes that transpiration provides the pull for xylem sap; cohesion pulls it the entire length
How is negative pressure generated according to the cohesion-tension hypothesis?
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.
How does surface tension contribute to the cohesion-tension hypothesis?
Increased surface tension pulls water from surrounding cells and air spaces. An increase in negative pressure potential lowers water potential.
Cavitation
Cavitation, the formation of a water vapor pocket, in xylem (usually more often in vessel elements than tracheids), block water channels of the xylem
How does bulk flow differ from osmosis?
Bulk flow occurs from the different in pressure potential, and occurs in hollow, dead cells
Stomata opening and uptake of ions?
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.
How does light stimulate stomata opening?
Light stimulates blue-light receptors, which activate proton pumps in guard cells.
Abscisic acid and function?
Abscisic acid is produced in roots and leaves; it responds to water deficiency, causing stomata to close, reducing wilting, but also photosynthesis.
Xerophytes
Plants adapted to arid environments
Pressure-flow Hypothesis
Loading of sugar into sieve tube elements results in lower water potential; water enters, forcing sugar transport
Self-thinning
Occurs when there is more sugar sinks than sources
