In which case would facilitated diffusion be needed? A. With large polar molecules moving against the concentration gradient.
B. With large non polar molecules moving down the concentration gradient.
C. With very small polar particles moving against the concentration gradient.
D. With very small non polar particles moving down the concentration gradient.

The voltage-gated potassium channels associated with an action potential provide an example of what type of membrane transport?

A. Simple diffusion.

B. Facilitated diffusion.

C. Coupled transport.

D. Active transport.

You are studying the entry of a small molecule into red blood cells. You determine the rate of movement across the membrane under a variety of conditions and make the following observations:

i. The molecules can move across the membrane in either direction.

ii. The molecules always move down their concentration gradient.

iii. No energy source is required for the molecules to move across the membrane.

iv. As the difference in concentration across the membrane increases, the rate of transport reaches a maximum.

The mechanism used to get this molecule across the membrane is most likely:

A. simple diffusion.

B. facilitated diffusion.

C. active transport.

D. There is not enough information to determine a mechanism.

Carrier proteins - exist in two conformations, altered by high affinity binding of the transported molecule. Moves material in either direction, down concentration gradient (facilitated diffusion). EXAMPLE: GluT1 erythrocyte glucose transporter.

Channel proteins - primarily for ion transport. Form an aqueous pore through the lipid bilayer. May be gated. Moves material in either direction, down concentration gradient (facilitated diffusion). EXAMPLES: Voltage-gated sodium channel, erytrhocyte bicarbonate exchange protein.

This might be helpful... because I don't know anything about facilitated diffusion.

for  example, forests have higher evapotranspiration than other ecosystems,  such  as grasslands, because of their deeper roots and greater leaf area. thus forests have a net moistening effect on the atmosphere and become a moisture source for downwind ecosystems.

•there must be variation for the particular trait within a population.

•the variation must be inheritable (that is, it must be capable of being passed on from the parents to their offspring).

•individuals with one version of the trait must produce more offspring than those with a different version of the trait.good

explanation: