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48 Cards in this Set

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___ is the most plentiful positively charged ion (cation) outside of the cell, while ___ is the most plentiful inside.
sodium Na+

potassium K+
the high concentration of sodium outside the cell is balanced chiefly by extracellular ___, the high concentration of potassium inside is balanced by ____.
Cl- chlorine

a variety of negatively charged intracellular ion (anions)
the differential distribution of ions inside and outside the cell is controlled in part by ___&____.
by the activity of membrane transport proteins and in part by the permeability characteristics of the lipid bi layer it self
the hydrophobic interior of the lipid bi layer creates a barrier to the passage of _____ including ___
most hydrophilic molecules including ions
given enough time, virtually any molecule will diffuse across a lipid bi layer. the rate at which it diffuses, however, varies enormously depending on __&___
on the size of the molecule and its solubility properties
small nonpolar molecules such as O2 and CO2 readily dissolve in lipid bi layers and therefore rapidly diffuse across them, why
cells require this permeability to gases for the cell respiration processes
what two kinds of molecule diffuse across the plasma membrane?
small nonpolar molecules and uncharged polar molecules (if they are small enough)
uncharged polar molecule diffuse rapidly across a bi layer, if they are small enough. ___&____for example cross fairly rapidly, ___crosses less rapidly and ____crosses hardly at all.
water and ethanol
lipid bilayers are highly impermeable to all ___&___no matter how small.
ions and charged molecules
they molecules charge and their strong electrical attraction to water molecules inhibit them from entering they hydrocarbon phase of the bi layer
membrane transport proteins fall into two classes: what are they ?
transporters and channels
what does the set of membrane transport proteins present in the plasma membrane or in the membrane of an intra-cellular organelle determine?
exactly which solutes can pass into and out of that cell or organelle
each type of membrane has its own characteristic set of ____
transport proteins
what is the basic difference between transporters and channels?
the way they discriminate between solutes
channels discriminate mainly on the basis of __and __
size and electric charge: if a channel is open an ion or a molecule that is small enough and carries the appropriate charge can slip through, as through a narrow trapdoor
a transporter allows passage only to those molecules or ions that __
fit into a binding site on the protein,it then transfers these molecules one at a time by changing its own conformation, acting more like a turnstile than an open door
molecules will spontaneously flow down hill from a region of ___ concentration to a region of ___concentration provided a pathway exists. such movements are called passive because they need no other driving force
high to low
a solute can move spontaneously across the membrane down its concentration gradient into the cell by passive transport sometimes called __
facilitated diffusion
only _____can carry out active transport, but both ___and ___can carry out passive transport

transporters and channels
transport against a concentration gradient ______requires an input of energy
active transport

many of these transporters are called PUMPS
the plasma membrane contains transporters that import nutrients such as ___, ___, and ____

the lysosome membrane contains ___ transporter that acidifies they lysosome interior

and the inner membrane of mitochondria contains transporters for important the ___that mitochondria use as fuel for generating ATP and for exporting ATP once it is synthesized
sugars amino acids nucleotides


the hormone ___stimulates the liver cell to produce large amounts of glucose by the breakdown of ___

for glucose, which is an uncharged molecule, the direction of passive transport is determined solely by ___
its conc gradient
most cell membranes have a voltage across them, a difference in electrical potential on each side of the membrane, which is referred to as the __
membrane potential
this difference in potential exerts a force on any molecule that carries an electric charge.
the cytoplasmic side of the plasma membrane is usually at a ____potential relative to the outside, and this tends to pull ____charged solutes into the cell and drive ____charged ones out.
the net force driving a charged solute across the membrane is a composite of two forces. what are they ?
one due to the conc gradient and the other due to the voltage across the membrane
the net force driving a charged solute across the membrane is a composite of two forces one due to the conc gradient and the other due to the voltage across the membrane

this net driving force is called the ____of the given solute
electrochemical gradient

this gradient determines the direction of passive transport across the membrane
for some ions, the voltage and concentration gradient work in the same direction, creating a a relatively steep electrochemical gradient. this is the case for __
because of opposing effects ___has a small electrochemical gradient across the membrane despite its large concentration gradient and therefore there is little net movement of __across the membrane
cells carry out active transport in three main ways. name them
1. coupled transporters
2. ATP driven pumps
3. light driven pumps
describe couple transporters
couple the uphill transport of one solute across the membrane to the downhill transport of another
describe ATP driven pumps
couple uphill transport to the hydrolysis of ATP
describe light driven pumps
couple uphill transport to an imput of energy from light,
mainly found in bacterial cells
the ATP driven sodium pump in animal cell hydrolyzes ATP to ADP to transport sodium out of the cell; this pump is therefore not only a transporter, but also an ____ called ___
enzyme called ATPase

at the same time, the protein couple and outward transport of ___ to an inward transport of ____. the pump is therefore commonly know as the ____


sodium potassium pump
the sodium potassium pump account for ___ or more of their the total ATP consumption
the inward electrochemical driving force for ___ is large, as it includes the driving force due to the concentration gradient and the driving force in the same direction due to the voltage gradient
the net driving force for movement of __across the membrane is close to zero. the electric force pulling __into the cell is almost exactly balanced by the concentration gradient tending to drive it out.
the diffusion of water is known as ___.
if the concentration of solutes inside the cell is higher than that outside, water will move ___ by osmosis, causing the cell to ____

if a cell is placed in a high salt solution, however, water will

water will move in by osmosis

causing the cell to swell

water will rush out
cells contain specialized water channels called
the driving force for the water movement is equivalent to a difference in water pressure and is called
osmotic pressure
plant cells are prevented from swelling by their _____and so can tolerate a large osmotic difference across their plasma membrane
tough cell walls
cells use different tactics to avoid osmotic swelling.
describe these methods for
an animal cell
a plant cell
and a protozoan
the animal cell keeps the intracellular solute concentration low by pumping out ions

the plant cells tough cell wall prevents sweeling

the protozoan avoids swelling by periodically ejecting the water that moves into the cell
the plasma membrane is permeable to water, and if the total conc of solutes is low on one side of the membrane and high on the other, water will tend to move across it untill ___
the solute concentrations are equal
osmosis together with the active transport of ions into the cell, result in a ____that keeps plant cells distended with water, with the cell wall tense
turgor pressure
what are some of the functions of turgor pressure ?
holds plant stems rigid and leaves extended

plays a part in regulating gas exchange through the stomata
stomata open on the underside of a leaf.
the opening and closing of these pores is controlled by the sausage shaped ____cells that surround them
guard cells
an influx of ___into the cytosol through ___channels is often used as a signal to trigger other intracellular events, such as the secretion of signal molecules and the contraction of muscle cells
___like sodium, is also kept at a low conc in the cytosol compared with its conc in the extracellular fluid, but it is much less plentiful than sodium, both inside and outside cells
eucaryotic cells in general maintain very low conc of free ca two plus in their cytosol and face of very much higher extracellular ca two plus conc.

this huge conc difference is achieved mainly by means of ____and ____
by means of ATP driven Ca two plus pumps in both the plasma membrane and the endoplasmic reticulum membrane, which actively pump ca two plus out of the cytosol