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.