Which of the following scenarios a molecule can cross the pl

Which of the following scenarios, a molecule can cross the plasma membrane WITHOUT using a carrier protein?

a. A polar molecule moving against the gradient.

b. A polar molecule moving with the gradient.

c. A non-polar molecule moving against the gradient.

d. A non-polar molecule moving with the gradient.

e. All of these need a carrier protein.

Any kind of short explanation would be appreciated, thanks!

Solution

Plasma membrane is a phospholipid bilayer which is semipermeable membrane allowing only certain kind of molecules to pass through it.

The movement of substances across the plasma membrane can be through diffusion : donot use energy, active transport: uses ATP as energy source.

For a molecule to move across the plasma membrane without using a carrier protein :

A.)the substance must be small and non polar to pass through bilipid layer.

B.) the movement of molecule must be within the concentration gradient.

Polar molecule form aquaporins to pass through the plasma membrane.

Answer: Option D. A non-polar molecule moving with the gradient.