Chapter 36 Flashcards
phloem transports photosynthetic products from _____ to ______
sources to sinks
xylem transports water and minerals from ____ to _____
roots to shoots
stem has what two purposes?
- as conduits for water and nutrients
2. supporting structures for leaves
true or false:
Roots are less competitive with other roots from the same plant than with roots from different plants
true
mycorrhizae
is a symbiotic association composed of a fungus and roots of a vascular plant.
- this helps plants colonize land
- increase the surface area for absorbing water and minerals
what are the two major pathways through plnats
- apoplast
2. symplast
apoplast
consists of everything external to the plasma membrane
-includes cell walls, extracellular spaces, and the interior of vessel elements and tracheids
symplast
consists of the cytosol of the living cells in a plant as well as the plasmodesmata
what are the tree transport routes for water and solutes ?
- the apoplastic route- through cell walls and extracellular spaces
- the symplastic route- through the cytosol and plasmadesmata
- the transmembrane route- across cell walls
what controls short distance movement of substances?
plasma membrane permeability
what type of transport occur in plants?
both active and passive
membrane potential in plants is established through what?
pumping H+ by proton pumps
- *proton pump hydrolyzes ATP and uses the energy to pump hydrogen ions out of the cell
- produces membrane potenetial and proton gradient used to transport different molecules
what is in plant cell membranes that allow only cetains ions to pass
ion channels
stomata opens in what three cues
- light induces guard cells to take up K+
- decrease of CO2 in leaf air space
- internal clock
guard cells may close stomata during the day if what three things happen?
- deficiency in water
- production of abscisic acid
- high temperatures increases CO2 in air space
water potential
a measurement that combines the effects of solute concentration and pressure
- determines direction of movement of water
- water flows from regions of high water potential to low
- potential refers to water’s capacity to perform work
what is the water potential equation?
Ψ =ΨS +ΨP
(ΨS = solute potential)
(ΨP = physical pressure on solution)
turgor pressure
the pressure exerted by the plasma membrane against the cell wall, and the cell wall against the protoplast
protoplast
the living part of the cell, which also includes the plasma membrane
aquaporins
transport proteins in the cell membrane that allow the passage of water
-affect the rate of water movement across the membrane
where does the most water and mineral absorption occur?
near root tips, where root hairs are located and the epidermis is permeable to water
what accounts for much of the surface area of roots?
root hairs
endodermis
the intermost layer of cells in the root cortex
-surrounds vascular cylinder and is the last checkpoint for selective passage of minerals from the cortex into the vascular tissue
what ways can water cross the cortex?
either via symplast or apoplast
waxy casparian strip
of the endodermal wall and blocks apoplastic transfer of minerals from the cortex to the vascular cylinder
-water and minerals in the apoplast must cross the plasma membrane of the endodermal cell (cell in casparian strip) to enter the vascular cylinder
what are the steps for water and minerals to go into the tracheids and vessel elements
The endodermis regulates and transports needed minerals from the soil into the xylem
• Water and minerals move from the protoplasts of endodermal cells into their cell walls
• Diffusion and active transport are involved in this movement from symplast to apoplast
• Water and minerals now enter the tracheids and vessel elements
xylem sap
the water and dissolved minerals that are transported from roots to leaves by bulk flow
- involves transpiration (the evaporation of water from the plants surface)
- transpired water is replaced as water travels up from the roots
root pressure
the pressure given by roots since water flows in from the root cortex
-sometimes results in guttation which is the exudation of water droplets on tips or edges of leaves
what helps water and minerals go up the xylem?
- root pressure (relatively weak and is a minor mechansim of moving water upwards)
- cohesion and adhesion (allows for water to stay connected and not go down on behalf of gravity)
- negative pressure
- transpiration pull (which causes negative pressure)
is the xylem made of dead or alive cells?
dead hollow cells
when the guard cells are turgid what happens?
when the guard cells are flaccid what happens?
- guard cells bow outward and the pore between them opens
2. guard cells become less bowed and pore closes
When guard cells are hypertonic with potassium ions what happens?
water enters and makes the guard cells turgid
when guard cells are hypotonic with potassium ions what happens?
water leaves the guard cell and makes them flaccid
what can cause stomata to close during the daytime?
drought, high temp, and wind
what does abscisic acid do?
it is produced in response to water deficiency and causes the closure of stomata
xerophytes
plants adapted to arid climates
what are some adaptations to reduce transpiration?
- xerophytes
- thick cuticle
- stomata mostly on underside of leaves
- shed leaves
- cacti store water
- CAM plants (only open stomata at night)
translocation
the products of photosynthesis are transported through phloem
in angiosperms what are the conduits for translocation
sieve tube elements
phloem sap
aqueous solution that is high in sucrose
sugar travels from source to sink or sink to source
source to sink
sugar source
an organ that is a net produced of sugar such as mature leaves
sugar sink
an organ that is net consumer or storer of sugar, such as tuber or bulb
what is unique about some storage organs?
they can be a sugar sink in summer and sugar source in winter
does sugar move by symplastic or apoplastic pathways?
it can move by symplastic or both symplastic and apoplastic
what do companion cells do?
enhance solute movement between the apoplast and symplast
phloem loading requires what?
active transport
- proton pumping and cotransport of sucrose and H+ enable the cells to accumulate sucrose
- at sink the sugar molecules diffuse from the phloem to sink tissues are followed by water
pressure flow
phloem sap moving through a sieve tube by bulk flow driven by positive pressure
self thinning
the dropping of sugar sinks such as flowers, seeds, or fruits
