36 Chapter Flashcards
Phyllotaxy
The arrangement of leaves on a stem.
-Determined by the shoot apical meristem
Alternate phyllotaxy/ spiral phyllotaxy
One leaf per node
Opposite phyllotaxy
Two leaves per node
Whorled phyllotaxy
More than two leaves per node
Self-pruning
Programmed cell death and eventual shedding
In low light conditions, horizontal leaves capture sunlight much more effectively than vertical leaves. In sunny regions, horizontal leaves may be damaged from overly intense light, while vertical leaves are not and light penetrates more deeply to lower leaves.
True
Leaf area index
The ratio of the total area of the tip surfaces of the leaves to the area of ground covered by the plant.
Mycorrhizae
Mutualistic associations between roots and fungi.
Two major pathways of transport:
Apoplast
Symplast
Apoplast
Consists of everything external to the plasma membrane of living cells and includes cell walls, extracellular spaces, and the interior of dead cells such as vessel elements and tracheids.
Symplast
Consists of the entire mass of cytosol of all the living cells in a plant, as well as the plasmodesmata, the cytoplasmic channels that interconnect them.
Three routes for transport within a plant tissue or organ:
The apoplastic route
Symplastic route
Transmembrane routes
Apoplastic route
Water and solutes move along the continuum of cell walls and extracellular spaces.
Symplastic route
Water and solutes move along the continuum of cytosol.
Transmembrane route
Water and solutes move out of one cell, across the cell wall, and into the neighboring cell, which may pass them to the next cell in the same way.
Water potential
The physical property that predicts the direction in which water will flow.
-A quantity that includes the effects of solute concentration and physical pressure.
If a plant or seed is immersed in a solution that has a higher water potential, water will…
Move into the cell or seed
ψ
Water potential.
Greek letter pronounced “sigh” (psi)
Plant biologists measure water potential in a unit of pressure called a __________
Megapascal
The ψ of pure water in a container open to the atmosphere under standard conditions is 0 MPa.
True
One MPa is equal to about 10 times atmospheric pressure at sea level.
True
Water potential equation
ψ = ψsubS + ψsubP
Solute potential (osmotic potential)
ψsubS
Pressure potential
ψsubP
The solute potential of a solution is directly proportional to its molarity.
True
The solute concentration of a solution is always expressed as a negative number.
True
Pressure potential is the _____
Physical pressure on a solution
Turgor pressure
When the protoplast presses against the cell wall.
Water moves from regions of higher water potential to regions of lower water potential.
True
Flaccid
Limp
Plasmolysis
When the protoplast shrinks and pulls away from the cell wall.
Turgid
Very firm
Wilting
When leaves or stems droop as a result of cells loosing water.
Aquaporin channels affect the rate at which water moves osmotically across the membrane.
True
Bulk flow
The movement of liquid in response to a pressure gradient.
The bulk flow of material always occurs from higher to lower pressure.
True
Unlike osmosis, Bulk flow is independent of solute concentration.
True
The endodermis functions as…
A last checkpoint for the selective passage of minerals from the cortex into the vascular cylinder.
Casparian strip
A water impermeable ring of suberin in the endodermis cells of plants that blocks the passive flow of water and solutes into the stele by way of cell walls.
-Present in the apoplastic route
Transpiration
The loss of water vapor from leaves and other aerial parts of the plant.
Root pressure
A push of xylem sap generated by water flowing in from the root cortex
Guttation
The exudation of water droplets that can be seen in the morning on the tips or edges of some plant leaves.
Dew
Condensed atmospheric moisture
Cohesion-tension hypothesis
Proposes that transpiration provides the pull for the ascent of xylem sap, and the cohesion of water molecules transmits this pull along the entire length of the xylem from shoots to roots.
Negative pressure potential (tension) lowers water potential.
True
The tension produced by transpirational pull lowers water potential in the root xylem to such an extent that water flows passively from the soil, across the root cortex, and into the vascular cylinder.
True
Cavitation
The formation of a water vapor pocket
Evaporation lowers the water potential at the air-water interface, thereby generating the negative pressure (tension) that pulls water through the xylem.
True
When guard cells lose water and become flaccid, the pore closes.
True
The changes in turgor pressure in guard cells result primarily from the reversible absorption and loss of K+.
True
Stomata open when guard cells actively accumulate K+ from neighboring epidermal cells.
True
Three cues that contribute to stomatal opening at dawn:
Light
CO2 depletion
Internal “clock” in guard cells
Circadian rhythms
Cycles with intervals of approximately 24 hours
Abscisic acid
A hormone that signals guard cells to close stomata.
Freely available water allow plants to keep stomata open and take up more CO2.
True
Xerophytes
Plants adapted to arid environments.
Translocation
The transport of the products of photosynthesis.
Phloem sap
The aqueous solution that flows through sieve tubes
Sugar source
A plant organ that is a net producer of sugar, by photosynthesis or by breakdown of starch.
Sugar sink
An organ that is a net consumer or depository of sugar.
Pressure flow
Positive pressure used in bulk flow
Self-thinning
Process where plant aborts some flowers, seeds, or fruits
Symplastic domains
Interconnected regions within a plant where cytoplasm can freely flow.
