Diffusion

Question 1

What is facilitated diffusion?

Answer 1

Facilitated diffusion describes the net movement of particles down a concentration gradient (i.e. from a region of high concentration to a region of lower concentration).
Facilitated diffusion is a passive process so it does NOT use energy.

Question 2

Why is facilitated diffusion used?

Answer 2

Some materials are too large to move through the membrane.
Other materials are polar molecules that are repelled by the hydrophobic part of the membrane.
These materials move across the membrane by facilitated diffusion.

Question 3

Channel proteins

Answer 3

Facilitated diffusion takes place through channel proteins.
Channel proteins allow polar compounds to avoid the non-polar central layer of the plasma membrane.
The non-polar layer would slow or prevent entry into the cell.
Aquaporins are channel proteins that allow water to pass through the membrane.

Question 4

Carrier proteins

Answer 4

Facilitated diffusion takes place through carrier proteins.
When a substance binds to carrier proteins, there is a change in the shape of the carrier protein.
This change in shape moves the substance from the outside of the cell to the inside

Question 5

What are the factors that affect diffusion?

Answer 5

The bigger the difference in concentration between two areas.
The greater the concentration gradient and the faster the rate of diffusion.

Question 6

Membrane surface area

Answer 6

The larger the surface area of the membrane that a substance is diffusing through, the faster the rate of diffusion.

Question 7

Thickness of membrane

Answer 7

The thicker the exchange surface, the slower the rate of diffusion.

Question 8

Channel proteins or carrier proteins

Answer 8

The higher the concentration gradient, the faster the rate of facilitated diffusion until an equilibrium is reached and the rate will level off.
The number of channel or carrier proteins affects the rate of facilitated diffusion. The more proteins, the faster the rate