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Plant Phys > Solute Transport - 9 > Flashcards

Solute Transport - 9 Flashcards

1
Q

Define solute transport

A

the exchange of solutes in plants within their cells, local environment and among tissues and organs

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2
Q

Define transport

A

molecular and ionic movement from one location to another

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3
Q

Define translocation

A

The movement of photosynthate (specifically photosynthetic components) from sources to sinks in the phloem

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4
Q

Define passive transport

A

spontaneous movement down a gradient of free energy or chemical potential from concentrations of high to low (does not require energy)

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5
Q

Define active transport

A

the movement against a gradient of chemical potential. It requires energy and is not spontaneous

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6
Q

What are the 4 major forces that drive transport

A
  1. concentration
  2. hydrostatic pressure (pressure exerted from the fluid)
  3. gravity
  4. electric fields
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7
Q

Chemical potential is defined by…

A

defined as the sum of the concentration, electrical and hydrostatic potentials

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8
Q

the two main forces that drive transport (____ and ____) are integrated by a term called _____

A

concentration gradients and electrical-potential gradients
electrochemical potential

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9
Q

Define membrane permeability

A

The extent to which a membrane permits the movement of a substance

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10
Q

What 3 factors does membrane permeability depend on

A
  1. lipid composition
  2. chemical properties of the solutes
  3. the membrane proteins that facilitate the transport of specific substances
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11
Q

Define diffusion potential

A

the potential (voltage) difference that develops across a semipermeable membrane as a results of the differential permeability of solutes with opposite charges
(ex. lots of K+ on one side and little Cl- making it positive and vise versa for other side and therefore making a diffusion potential/voltage difference)

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12
Q

Define Nerst potential

A

the electrical-potential difference for an ion

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13
Q

What does the relationship known as the Nerst equation state

A

that at equilibrium, the difference in concentration of an ion between two compartments is balanced by the voltage difference between compartments

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14
Q

What can be implied if the predicted internal concentration is higher than the observed? What if the observed is higher than predicted? The same?

A

if predicted>observed, then active transport to inhibit
if observed>predicted, then active transport to facilitate
if =, then passive transport

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15
Q

Plant cells have several internal compartments, what two compartments are most important in determining the ionic relations of plant cells

A

cytosol and vacuole

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16
Q

Explain type of transport for potassium ions

A

accumulated passively by both the cytosol and vacuole

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17
Q

Explain type of transport for sodium ions

A

pumped actively out of the cytosol into the extracellular space and vacuole

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18
Q

Explain type of transport for excess protons

A

actively removed from cytosol (where the cytosol is near neutral and the vacuole is more acidic meaning more H+)

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19
Q

Explain type of transport for anions

A

actively taken up by the cytosol

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20
Q

Explain type of transport for calcium

A

actively transported out of the cytosol and vacuole

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21
Q

Explain Goldman equation vs. Nerst equation

A

Goldman is a modified version of Nerst, and includes all permeant (all substances that can pass) and therefore gives a more accurate value for diffusion potential

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22
Q

What causes plants and fungi to often show more negative membrane potentials than those calculated from the Goldman equation

A

the excess voltage comes from the electrogenic plasma membrane H+-ATPase

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23
Q

What two components make up the membrane potentials of plant cells

A
  1. diffusion potential
  2. component resulting from electrogenic ion transport (translocation of net charge)
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24
Q

Explain permeability of both biological and artificial membranes in terms of small and large molecules
and why

A

both have similar permeabilities for small/nonpolar molecules
but biological membranes are more permeable to large ions (sugars and water) compared to artificial bilayers.
because biological membranes contain transport proteins that facilitate passage of selected ions and molecules

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25
Q

What are the 3 main categories of transport proteins

A
  1. channels
  2. carriers
  3. pumps
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26
Q

Define channels

A

are transmembrane proteins that function as a selective pore which ions can diffuse across the membrane. transport through channels are always passive and depends on pore size and electric charge

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27
Q

Explain gates on channel transmembrane proteins

A

gates open and close the pore in response to signals. most gates are usually closed.

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28
Q

What 5 signals regulate the channel/gate activity

A
  1. membrane potential changes
  2. ligands
  3. light
  4. hormones
  5. post-translational modifications (ex. phosphorylation)
29
Q

Define carrier transmembrane proteins

A

specialize in transport of specific inorganic and organic ions as well as metabolites. substances are transported by binding to a specific site. passive transport or secondary active transport

30
Q

What causes carrier proteins to transport molecules slower

A

because it requires a conformational change in the protein when binding before being able to transport

31
Q

Explain secondary active transport of carrier proteins

A

a carrier must couple the energy uptake transport of a solute with another that releases energy so that the overall free energy change is negative. Uphill paired with downhill transport

32
Q

Define primary active transport

A

involves coupling directly to a source of energy such as ATP hydrolysis or absorption of light

33
Q

Define pumps

A

membrane proteins that carry out primary active transport. They mostly transport inorganic ions

34
Q

What are the 2 types of ion pumps and explain each

A
  1. electrogenic transport = ion transport that involves net movement of charge across the membrane
  2. electroneutral transport = involves no net movement of charge
35
Q

What is the principal ion that is electrogenically pumped across the membrane of most plants, fungi and bacteria

A

H+

36
Q

Explain plasma membrane H+ATPase potentials

A

it generates electrochemical potential of H+ across plasma membrane while vacuolar H+ATPase and the H+ pyrophosphatase electrogenically pump proteins into the lumen of the vacuole and golgi cisternae

37
Q

What are the two types of secondary active transport and explain each

A
  1. symport = both transported solutes are moved in same direction
  2. antiport = two solutes move in opposite directions
38
Q

What does secondary active transport use to drive the transport of substances against their electrochemical potential

A

proton motive force generated by electrogenic H+ transport

39
Q

Many transport proteins have been identified at the ____ level and characterized using ____ and ____ technique

A

molecular level
electrophysiological and biochemical techniques

40
Q

Transport across a biological membrane is typically energized by one _____ system coupled to ____

A

one primary active transport system
ATP hydrolysis

41
Q

Secondary active transport proteins are carried out by carrying _____ down the energy gradient

A

one or two H+

42
Q

Genome sequence comparison has shown us what about what in plant genomes for most transport functions

A

that gene families rather than individual genes exist in plant genomes

43
Q

_____ has revolutionized the study of transporter proteins

A

transporter gene identification

44
Q

What allows for the remarkable plasticity for genes to thrive under broad conditions (3)

A
  1. variation in transport kinetics
  2. modes of regulation
  3. differential tissue expression within a gene family
45
Q

Plant NH4+ transporters are ____ that…

A

facilitators
promote NH4+ uptake down its free energy gradient

46
Q

Because No3- is negatively charged, it imposes…

A

an electric charge imposes an energy requirement for uptake of NO3- (provided by a symport with H+)

47
Q

Once nitrogen is incorporated into organic molecules, what are the 2 main mechanisms that distribute it throughout the plant

A
  1. peptide transporters = important for mobilizing nitrogen reserves during seed germination and senescence
  2. amino acids = constitute an important form which nitrogen is distributed long distances in plants
48
Q

How have plant cations evolved mechanisms to avoid accumulation of toxic levels of Na in the cytosol

A

mechanisms extrude Na across plasma membrane, sequester salt in vacuole and redistribute Na within the plant body to avoid accumulation

49
Q

Plant cation channels are classified according to ______ and ______

A

ionic selectivity and regulatory mechanisms

50
Q

Explain Ca2+ cations transporters

A

it is an important second messenger in signal transduction, is tightly regulated, and Ca2+ enters cytosol passively via channels and is actively removed from cytosol by pumps and antiporters

51
Q

What is the importance of malate

A

contributes to the increase in cellular solute concentration that drives water uptake into the guard cells leading to stomatal opening

52
Q

metal ions are usually present at ______ concentrations in soil solution, so they are typically transported by ______ transporters

A

low
high-affinity

53
Q

Why may it be useful to uptake undesirable metals

A

they may be useful in the detoxification of soils by uptake of contaminants into plants (phytoremediation - cleaning of soils with live plants).
metal ions usually chelated with other molecules then must be transported for distribution throughout the plant via the transpiration stream to be properly discarded

54
Q

Define metalloids and examples

A

elements that have properties of both metals and nonmetals
Boron and Silicon

55
Q

How do Silicon and Boron enter cells and are exported

A

enter via aquaporin-type channels and exported via efflux transporters
(arsenite can also enter roots via silicon channel because of similar chemical structure)

56
Q

Function of aquaporins

A

protein channels that facilitate water movement, they facilitate flux of water and other specific molecules (boric acid and silicic acid) across membranes and its regulation allows for rapid changes in water permeability in response to environmental stimuli

57
Q

Why is H+-ATPase activity important

A

regulates cytosolic pH and controls cell turgor which drives leaf and flower movement (organ movement), stomatal openings, and cell growth

58
Q

Plasma membrane H+-ATPase activity is reversibly controlled by what

A

autoinhibitory domain

59
Q

What does the tonoplast regulate

A

since plants increase size by taking up water into the central vacuole, tonoplast regulates traffic of ions and metabolites between the cytosol and vacuole

60
Q

What are the 2 types of proton pumps found in the vacuolar membrane and what are their functions

A
  1. V-ATPase and H+-pyrophosphatases
    both function = regulate proton motive force across the tonoplast which drives the movement of solutes across the membrane via antiport mechanisms
61
Q

Explain light-stimulated plasma membrane ATPase activity as the driving force for guard cells swelling and stomatal opening

A
  1. blue light activates H+-ATPase by signal transduction
  2. activation of H+-ATPase hyperpolarizes plasma membrane
  3. K+ moves into guard cell
  4. malate accumulates in cytosol bc of chloroplast starch degradation
  5. K+ then enters vacuole (which is inside the guard cell) along with Cl_ and malate2-
  6. these ions entering causes a lower water potential inside the vacuole which causes water to also enter
  7. vacuoles expand and increased turgor pressure causes stomatal opening
62
Q

Why are mineral nutrients readily diffused through the cell wall

A

because its a fluid filled lattice of polysaccharides so they can diffuse easily

63
Q

What is it called when ions can diffuse across a tissue or carried through water flow through the cell wall without ever entering a living cell

A

apoplast transport

64
Q

plant cells are interconnected by _____ in the ____ transport system

A

plasmodesmata (cytoplasmic bridges, that are small cylindrical pores) in the symplast system.

65
Q

When a solute enters the roots, what two wats can it be taken up

A
  1. into the cytosol of an epidermal cell
    or
  2. diffuse through apoplast into the root cortex and enter the symplast through a cortical or epidermal cell
66
Q

casparian strip

A

prevents apoplastic diffusion of solutes into the stele (central part of root or stem) - instead solutes enter the stele by diffusion from endodermal cells to pericycle and xylem parenchyma cells

67
Q

What does the casparian strip allow for

A

allows nutrient uptake to be selective, and prevents ions from diffusing back out of the roots through the apoplast

68
Q

Define xylem loading

A

process where ions exit the symplast of a xylem parenchyma cell and enter the conducting cells of the xylem for translocation to the shoot

69
Q

What does the plasma membranes of xyelm parenchyma cells contain

A

proton pumps, aquaporins, and variety of ion channels and carriers specialized for influx or efflux

Plant Phys (15 decks)

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