Circulation in Plants

What is chemical potential?

The sum of the concentration, electrical, and hydrostatic potentials

What is fick’s first law?

The movement of molecules by diffusion always proceeds spontaneously down a gradient of free energy or chemical potential until equilibrium is reached

The spontaneous “down hill” movement is called ____

passive transport

Passive transport occurs spontaneously down a chemical potential gradient if the _____

chemical potential is higher outside the cell than inside the cells

What is simple diffusion?

diffusion of a substance through the lipid portion of the plasma membrane without going through a protein channel

What do ion channels open in response to?

Voltage, stretching of the membrane, and chemical factors

calcium is almost always ______ out the cell

actively transported

What is one of the most important signaling ions in eukaryotes?

calcium

What is facilitated diffusion?

Ion channels that only allow certain ions to pass. These can open and close in response to voltage changes, stretching of the membrane or chemical changes

What is the predominant ion in plant cells?

Potassium

What are the two channel classes potassium channels in plants can be subdivided into?

Non-voltage gated and voltage gated

In organisms other than bacteria, potassium voltage-gated channels are repeated ___ times.

four

Voltage gated potassium channels in higher plants and animals contain _______

six transmembrane domains

s4 is the voltage-sensor characterized by _____

the array of positively charged amino acids

P loop is the selectively loop that only allows ______ to pass through the channel

K+

Non voltage gated channels are found in the cells of _____, within the cell in the tonoplast

phloem, shoots, and roots

The transport of two ions or sugars at one time occurs in _____

plants and animals

Plant cells can also accumulate a neutral solute, such as sucrose, by ______

cotransporting h+ down the steep proton gradient

What is osmosis?

it determines the net uptake or water loss by a cell and is affected by solute concentration and pressure

What is water potential?

it is a measurement that combines the effects of solute concentration and pressure

Water potential determines the _____

direction of movement of water

Water flows from regions of _____

higher water potential to regions of lower water potential

The movement of substances against a chemical potential is ______

active transport

Active transport occurs when?

the chemical potential outside the cell is less than inside the cell against the concentration gradient

In higher plants, membrane potential is established through

active transport - use energy in the form of ATP and a H+ by proton pumps

Na+ is compartmentalized into vacuoles and in to the root by ____

Na+/H+ exchangers = antiporters

In animals, Na+, K+ ATPase _____

mediates sodium efflux

Plant cells use the electrochemical energy of H+ gradients to cotransport other solutes by ______

indirect active transport (pumps do no use energy themselves)

Sugars

Transport in phloem, bulk flow

H2O and minerals

transport in xylem, transpiration

Efficient long distance transport of fluid requires bulk flow, the movement of a fluid driven by _____

pressure

Water moves through water by ___

Bulk flow

Water uptake is mostly confined to the _____

Root hairs near the root tips

What are the 2 major compartments in a plant?

apoplast and symplast

What is the apoplast?

Everything external to the plasma membrane including cell walls, extracellular spaces, and the interior of vessel elements and tracheids

What is the symplast?

Consists of the cytosol of the living cells in a plant, as well as the plasmodesmata

What is the transmembrane route?

across cell walls and through the cells

Water moves in the root via ____

apoplast, symplast, and transmembrane pathways

Water movement in the apoplast is obstructed by the _______ in the endodermis that forces water to move symplastically through aquaporins in the endodermal cells and pericytes and then into the xylem

Casparian strip

Xylem transports water and minerals from _____

roots to shoots

Phloem translocates photosynthetic products from _____

sources (leaves) to sinks (other tissues)

When transpiration is low or absent the continued transport of solutes into xylem fluid leads to a decrease in ______

solute potential and an overall decrease in water potential

Water is absorbed creating a positive hydrostatic pressure in the ____

Xylem

The conducting cells of xylem are _____ providing a low resistance pathway for the transport of water

dead at maturity

What are the two types of xylem conducting cells?

Single celled tracheid and multicellular vessel elements

_____ drives the transport of water and minerals from roots to shoots via the xylem

transpiration

Most water and mineral absorption occurs near _____. where root hairs are located and the epidermis is permeable to water

root tips

Root hairs account for much of the surface area of _____

roots

Active transport of essential minerals from the soil into the root hairs causes the concentration of essential minerals to be _____

greater in the roots than the soil

The ____ is the innermost layer of the cells in the root cortex

endodermis

The endodermis surrounds the _____

vascular cylinder (steele)

After soil solution enters the roots, the extensive surface area of cortical cell membranes enhances uptake of water and _____

selected minerals

Transfer to the stele must be _____

symplastic

Water and minerals in the apoplast must cross the plasma membrane of an endodermal cell to enter the _____

vascular cylinder

The endodermis regulates and transports needed minerals from the ______

Soil into the xylem

Apoplastic transfer occurs between the _______

pericycle and tracheids and vessel elements (is both active and passive transport)

What is xylem sap?

Water and dissolved minerals and is transported from roots to leaves by bulk flow

The transport of xylem sap involves _____, the evaporation of water from a plant’s surface

transpiration

Water flows into the roots due to the active transport of dissolved nutrients pulling water with it, this is called _____

Root pressure

Positive root pressure (push force) is relatively ____ and is a minor mechanism of xylem bulk flow

weak

Root pressure sometimes results in _____, the exudation of water droplets on tips or edges of leaves

guttation

What are the 4 forces that contribute to transport water from the root hairs to the xylem, up the xylem and to the leaves?

Transpiration, adhesion, cohesion, and tension

Bulk flow differs from diffusion in what ways?

It is driven by differences in pressure potential not solute, occurs in hollow dead cells not living, moves the entire solution not just water or solutes, and is faster

What is transpiration?

The pulling of water up the xylem using the energy of evaporation and the tensile strength of water

Water vapor in the airspaces of a leaf diffuses down and exits the leaf via ______

stomata to the drier outside air

The rate of transpiration is regulated by ______

stomata

_____ help balance water conservation with gas exchange for photosynthesis

guard cells

Transpiration also results in ______, which can lower the temperature of a leaf and prevent denaturation of various enzymes involved in photosynthesis and other metabolic processes

evaporative cooling

What is adhesion?

The attractive force between water molecules and other substances

Adhesion helps to offset the effects of _____

gravity

What is cohesion?

The attractive force between molecules of the same substance

Water’s cohesive force within the xylem gives it a _____

tensile strength

Drought, stress, or freezing can cause _____, the formation of a water vapor pocket by a break in the chain of water molecules

cavitation

The cohesion of the water molecules caused by hydrogen bonding allows unbroken columns of water to be pulled up the tracheids and vessels of the _____

Stem xylem

Thick secondary walls prevent vessel elements and tracheids from ______

collapsing under negative pressure

What is tension?

A stress placed on an object by a pulling force

Phloem translocation moves the products of photosynthesis from the mature leaves to areas of ______

growth and storage

Phloem translocation also transmits ___________ and other substances throughout the body

chemical signals and redistributes ions

Unlike in xylem, phloem translocation is not defined by _____

gravity

In angiosperms, _____ are the conduits for translocation

sieve-tube elements

_____ is an aqueous solution that is high in sucrose and it travels from a sugar source to a sugar sink

Phloem sap

A _____ is a organ that is a net producer of sugar, such as mature leaves

Sugar source

A ____ is an organ that is a net consumer or storer of sugar, such as a tuber or bulb

sugar sink

A storage organ can be both a sugar sink in ____ and a sugar source in _____

summer; winter

_______ enhance solute movement between the apoplast and symplast

companion cells

What is loading?

loading of the companion cell and sieve tube elements may be by apoplast or symplast pathways

What is uptake of water?

water diffuses from the xylem as a result of decreased water potential in the sieve tube

Phloem sap moves through a sieve tube by ______

bulk flow driven by positive pressure called pressure flow

The _______ explains why phloem sap always flows from source to sink

pressure flow hypothesis

What is unloading?

Sucrose can be actively unloaded or move by diffusion into the sink cell, from the sieve tube elements via companion cells

What is water recycled?

Water diffuses from the phloem to the xylem as a result of increased water potential in the sieve tube