Chapter 35 Biol 2130
root pressure
pressure potential that develops in roots to drive water against gravity
events at source tissues and sink tissues create a pressure potential gradient in phloem, which moves the water in phloem sap down the gradient, carried by bulk flow
pressure-flow hypothesis
cohesion-tension
pulls water up from roots by transpiration
cytosol and plasmodesmata
symplastic
casparian strip
wax impregnating endodermis cells, waterproof an forces apoplast to leave the walls with a barrier doesnt affect water and ions from the symplastic route
Low turgor pressure (So/si)
Sink
High turgor pressure (So/si)
Source
doesnt affect transpirational pool
larger air space in leaf interior
increases transpirational pull
larger diameter of stomatal pores
pericycle
layer of cells between endodemis and vascular tissye
how can vessel elements withstand such strong mPA and not collapse?
lignin (like cartilage) secondary cell wall reinforcement
trichomes
little hairs to shield deep pits of hidden stomata from the atmosphere/ slow loss of water vapor by creating a layer of still air surrounding the stomata
a very thick cuticle and wax on a plant means they
live in a dry soil
Growing season source
mature leaves and stems that produce sugar in excess of their needs
Surface tension occurs at _ that form as water evaporates from the walls of leaf cells, and it it transmitted downward via _ bonding between water molecules
menisci
capillary action
movement of water up a narrow tube/ pulls water up to minimize air-water interface
does transpiration power the pressure-flow hypothesis? how?
no, turgor pressure in phloem near source tissues and turgor pressure in the phloem near sink tissues generate the necessary force
Surface tension in stems
not present
surface tension in roots
not present
How do sources supply sinks, location-wise?
on the same side of the plant(left/right) , and same end (root/ apical meristems)
CAM
open stomata at night and store CO2 that diffuses by adding it to organic compoinds, which are released during the day when sunlight is available.
Adhesion in leaves
opposes gravity
adhesion in stems
opposes gravity
sieve-tube elements
phloem
dry soil
water doesn't flow freely inbetween the particles, so the tension lowers the water potential of the soil water.
warm air
water molecules move farther apart, exert lower pressure
_ measure of the tendency of water to move down its potential energy gradient and is expressed as megapascals (MPa)
water potential
cohesion
water sticks strongly to eachother and pulled easily by adhesion
Steps of cohesion-tension
water vapor diffuses out of the leaf, and water evaporates inside the leaf too. water is pulled out of the xylem from that, and pulled up the water which is all connected to each other in the xylem Water is pulled out of the root cortex from that, which pulls water from the soil to the root.
trachieds and vessel elements
xylem
guttation
xylem sap that collects because the stomata were closed and didnt evaporate so it kept leakin overnight
adhesion
water attached to glass pulled against gravity
Which of the following plant organs may act as a source for translocation of sugars inside a plant? See Section 35.4 ( page 739) .
Mature leaves photosynthesize, manufacturing sugars.
Which of these are symbiotic associations (w root hairs)
Mycorrhizae are mutualistic associations of roots and fungi.
_____ provide(s) the major force for the movement of water and solutes from roots to leaves.
Transpiration, the evaporation of water from leaves, exerts a pull that bears the primary responsibility for the movement of water and solutes from roots to leaves.
High light intensity _ xylem pressure
Decreases
Where do the sieve tube elements communicate with companions?
Plasmodesmata
transpiration rate when the stomata close
decrease when stomata close
sieve tube elements and their companions are _ (Dead or Alive) at maturity, and _ secondary cell walls.
Alive; lack
In roots the _____ forces water and solutes to pass through the plasma membranes of _____ cells before entering the _____.
Casparian strip ... endodermis ... xylem. The Casparian strip is a waterproof barrier that forces water and solutes to pass through the plasma membranes of endodermis cells.
Surface tension in leaves
Generates pull
_____ cells are the cells that regulate the opening and closing of stomata, thus playing a role in regulating transpiration.
Guard
_____ bonds are responsible for the cohesion of water molecules.
Hydrogen bonds among water molecules are responsible for the tendency of those molecules to stick together.
Solute potential of irrigated water before and after a long hot day of evaporation
Irrigation water contains low concentrations of salts, so the solute potential will be near zero. As water evaporates, salts remain in the soil, lowering the solute potential.
According to the pressure-flow hypothesis, what mechanism causes the movement of phloem sap from sources to sink tissues? See Section 35.4 ( page 739) .
Pressure potential differences between source and sink. These differences cause a flow of sugars in the phloem.
Label each target to indicate if the interaction between the molecules inside the rectangle contributes to surface tension (T), adhesion (A), or cohesion (C). Note that one target should be left blank because the molecules inside that rectangle are not involved in any of these interactions.
Surface tension most commonly occurs at air-water interfaces, where it resists breakage of the surface. Hydrogen bonds tend to pull water molecules at the surface together, reducing the curvature of the surface. Cohesion tends to keep water molecules that are away from surfaces from separating. Adhesion makes water stick to hydrophilic surfaces, such as cell walls. a. T, b. T, c. C d. N/A e. C f. A g. A
what if a plant couldn't develop the casparian strip?
The plant would not be able to exclude toxic solutes from the xylem, since water would not be forced through living cytoplasm of endodermal cells on its way to the xylem.
Imagine a plant without phloem. For sugars to move from one region of the plant to another, what must happen? See Section 35.4 ( page 739) .
The sugars would be actively transported from cell to cell. ATP-mediated protein transport is still possible.
Tension
When pressure is negative. Draws liquid up through straw.
salt adapted species
accumulate solutes in their root cells, to lower their solute potential. have enzymes to increase the concentration of organic molecules in the cytoplasm, to keep the water potential of their tissues lower than the salty soils in order to absorb whatever water is available.
A pressure gradient is generated by the _ transport of sugars into _ in source tissues, coupled with the transport of sucrose out of _ elements at sink tissues.
active;seive-tube;seive-tube
meniscus
air-water interface where water is being pulled against gravity and gravity pushes towards the middle surface
During the growing season, what are the sinks?
apical meristems, lateral meristems, developing flowers, seeds and fruits, and storage cells .
porous cell wall movement but needs to go through the cytoplasm of the endodermal cell to move to the xylem
apoplastic
Water's properties of surface tension, cohesion, and adhesion are central to the ability of transpiration to pull water up from the roots to the leaves through the xylem. Sort each statement into the appropriate bin to indicate if the change described in the statement would increase, decrease, or not affect the pull that transpiration generates in the xylem of a tree.
below
how does xylem stay in one long column?
bulk flow
capillary action
can draw water up the cell of the xylem
trachieds and vessel elements are (d or A) _ at maturity, and _ secondary cell walls
dead; have
transpiration rate when a rain shower starts
decrease when it rains (since very little evaporation would occur)
Some plants growing in arid climates have small leaves and thick waxy cuticles on the upper epidermis. This is an adaptation for _____. See Section 35.3 ( page 738) .
decreasing water loss from leaves. Plants in arid climates may also have stomata only on their lower leaf epidermis. The stomata may be in pits, protected from water loss by hairlike epidermal extensions called trichomes.
early growing season sink
developing leaves
transpiration rate when dry air blows in
increase as dry air blows in.
inside skin/ between cortex and vascular tissue
endodermis
wilt
entire tissue looses turgor pressure
dry air
few water molecules present, pressure low, more evaporation
surface-tension
force among air-water interface. water on top can only bond with below or beside waters, and strong attractive forces that bind them tightly to minimize surface area
unloading phloem
gives sucrose to sink; higher water potential than xylem; turgor pressure drops;
cortex
ground tissue that stores carbohydrates
example of root pressure
guttation
loading phloum
high sucrose concentration; receives from source; lower water potential than xylem; high turgor pressure
Water moves from areas of _ solute potential to _ solute potential.
high; low
solution with _ concentrations of solutes have _ solute potentials
high; low
hypotonic solution
hypertonic cell, so the NET movement would be into the cell to reduce the concentration
The channels indicated by the pointer, are _____. The figure shows a structure of the root. The arrow indicates the channel between the cell from the outer layer of the root and the inner one.
plasmodesmata. Water and ions can pass from cell to cell via these channels. Also, recall that plasmodesmata are a type of cell junction.
turgor pressure in living cells is always
positive
pushing/high turgor pressure
positive (unfavorable) water pressure
rainy or foggy air
potential may be equal to the water potential of leaves
adhesion in roots
present but no contribution
Cell wall and other factors determine the
pressure potential
where does phylum sap move between?
sieve plate
_ concentration of solutes in a cell or tissue
solute potential
Water moves by osmosis from xylem into sieve-tube elements near _ and cycles back to xylem near _.
sources; sinks
tranpiration
stomata are open and the air outside the leaves are drier than the air inside the leaves
early growing season source
storage cells in roots and stems
C4
take CO2 and fix it, store it in bundle-sheath cells, when the calvin cycle operates. so it never really fully opens its stomata
why does water flow from the xylem to the phloem at high sucrose concentrations?
the phloem has a low solute potential, much higher than just water alone, so it moves over across the selectively permeable membrane to sieve tubes, which makes turgor pressure build.
transpiration creates tension (straw sucks) from roots to leaves, what "charges" this?
the sun/ solar powered
dry species coping
the water potential drops because of solute potential dropping below the soil's water potential
how is the small tension at the meniscus enough to pull so much water, steep enough to overcome gravity?
there are many leaves pulling and many menisci
decreases transpirational pull
thicker film or water on surface of mesophyll cells, higher relative humidity in air around leaf, lower rate of water evaporation from surface of mesophyll cells, less curvature of water surface on mesophyll cell walls
movement of sugars by bulk flow in multiple directions throughout a plant- from sources to sinks specifically
translocation
aquaporin and water channels
transmembrane
Cohesion in leaves
transmits pull
cohesion in roots
transmits pull
cohesion in stems
transmits pull
to move _ the plant; water moves _ the water-potential gradient.
up;down
salty soil
very low solute potential, much lower than water potential in the plant roots
To view the animation, click here. Then click on the image to start the animation. This is an animation of the movement of water and ions through the root
via the apoplastic route. The animation illustrates water and ions moving along a cell wall continuum.