Solute transport Flashcards
ion diffusion is driven b y
chemical potential difference x membrane permeability
chemical potential difference is driven by differences in –
concentration, pressure, and electric potential (voltage)
– are large driving forces
concentration and voltage differences
at equilibrium, there may remain a – as well as a small concentration gradient across the membrane
membrane potential (voltage difference)
a substantial voltage difference may be generated even though the number of unbalanced ions is –
negligible
a membrane potential of – may be generated by a concentration difference across the membrane of 0.001%
-100 mV
all living cells exhibit a membrane potential due to the – between the inside and outside of the cell
asymmetric ion distribution
membrane potential can be determined by – the cell and external solution with microelectrodes
probing
Nerst equation gives the – expected across a membrane at equilibrium if the voltage across the membrane is known
concentration gradient
Goldman equation predicts the diffusion potential from Na+, K+, Cl_ the ions with the – cellular concentrations
highest
for most ions, experimentally determined ion concentrations differ from Goldman equation prediction indicating –
active transport
cytosol and – differ strongly in ion uptake
vacuole
– is taken up passively by both cytosol and vacuole unless concentration is very low, then it is taken up actively
K+
Na+ and Ca2+ and excess protons are – out of the cytosol into the vacuole and extracellular spaces
actively pumped out
anions are – into the cytosol
actively taken up
effects of ATP can be provided by using – to poison mitochondria, which depletes ATP
CN-
when CN- is added to cell, the membrane potential falls to that – by the Goldman equation (also cytosol becomes acidic because H+ remains in cell)
predicted
facilitate the passage of selected ions and other polar molecules
transport proteins (transporters)
in arabidopsis, about – of all genes code for transporters
5%
can be specialized to only allow one direction ion movement
channels
carrier mediated transport is –
passive or active
secondary active transport can be –
symport or antiport
vacuole has a low pH relative to the cytoplasm
hyperacidic
rate of ion uptake =
rate of protein activity
Michaelis-Menten kinetics: rate of ion uptake plotted against –
ion concentratio
A saturation (Michaelis-Menten) curve appears
rate increase and then stabilizes
max rate of uptake
Vmax
ion concentration to drive 50% to Vmax
Km
low Km
high affinity
ions are mostly absorbed through –
root hairs
at endodermis, the ions but enter the – because of the suberized Casparian strip
symplast
casparian strip control ion entering xylem and prevents – out of xylem to the soil via apoplast
diffusion of ions
