BIOPHYSICS N°8 (T/F)

Nonpolar molecules such as steroids and O2 cannot diffuse through biological

membranes by non-mediated transport.

False

In active transport a specific molecule is transported from low concentration to

high concentration, that is, along its concentration gradient.

False (against concentration gradient)

Facilitated diffusion occurs when the transported molecule needs a carrier across

the membrane.

True

Ions may pass through the hole or orifice by passive diffusion, in which case the

protein that allows this transport to occur is called a pump.

False

The transmembrane protein may use external energy to actively force ions from one

side of the plasma membrane to the other, in which case it will be an ion channel.

False

The driving force of the non-mediated flow of substance through a medium is its chemical potential gradient.

True

Electric potential is a scalar quantity associated with an electric field and is

measured in Coulombs per Joule, or Volts.

True

A substance diffuses in the direction that eliminates its concentration gradient at a rate proportional to the magnitude of this gradient.

True

The rate of diffusion of a substance through a membrane does not depend on its solubility in the membrane's non-polar core.

False

Cotransport is the simultaneous transport of two or more substances by two

transport systems in the same direction.

False

Uniport of charged substrates could be electrophoretically driven by the membrane potential of the cell.

True

Electrogenic transport changes the electrical potential difference across the

membrane.

True

If charged particles of the same magnitude and sign of the charge are transported in one direction or charged particles of the different magnitude and same sign of the charge are transported in opposite directions, then the transport is electrogenic.

True

Hydrophobicity of molecules is an important requirement for simple diffusion

across the membrane, as the interior of the phospholipid bilayer is hydrophilic.

False (interior is hydrophobic)

The voltage between any two points in an electric field is equal to the difference

in potential energy per unit charge between the two points.

True

Simple diffusion means that molecules can pass directly through the membrane.

True

Diffusion always occurs against a concentration gradient.

False (down concentration gradient)

Einstein showed that diffusion coefficient and mobility can be related by the

equation: u=DRT, where T is absolute temperature and u is particle's mobility.

False (D=uRT)

Mobility of uncharged particles can be defined as the velocity of a molecule per unit driving force.

True (u = v/F)

Free diffusion of charged particles is also called electrophoresis.

True

Faraday's constant is dimensionless.

False (C x mol^-1)

The work done by the electrostatic force is path-independent.

True

Diffusion is a spontaneous process and its ΔG is negative.

True

Drift is the movement of uncharged particles in electric fields.

False (Movement of charged particles in electric field)

Flux can be expressed as the ratio between the concentration of the transported substance and velocity.

False

Ions in solution in the context of biological cells experience the effect of both concentration and electrical gradients.

True

For the one-dimensional diffusion in a uniform medium, the concentration gradient is constant and the concentration of diffusing molecules is a linear function of time.

False

Ion channels allow the passage of simple ions like hydrogen, potassium or sodium through the plasma membrane by passive diffusion.

True

Phospholipids bilayer membranes are impermeable to charged molecules.

True

When talking about diffusion, the term net flux of matter is used, because diffusion is a random (stochastic) process, with molecules moving in both directions.

True