Diffusion Across Membranes

Question 1

Describe simple diffusion.

Answer 1

Molecules in a concentrated area bump into each other and as they do this the distance between them becomes greater until they eventually become evenly dispersed.

Question 2

What does the phrase “moving down the concentration gradient” mean?

Answer 2

It means that molecules are going from an area of high concentration to an area of low concentration.

Question 3

Why can water molecules not pass through the membranes?

Answer 3

They are polar and insoluble in lipid.

Question 4

What five things affect the rate of diffusion?

Answer 4

Temperature
Diffusion distance
Surface area
Size of diffusing molecule
Concentration gradient

Question 5

What are the channel proteins called which allow water into the cell?

Answer 5

Aquaporins

Question 6

Describe facilitated diffusion.

Answer 6

This is where a molecule is unable to simply diffuse into the cell as it is usually too large. In this case carrier proteins are used. The molecule which wishes to diffuse into the cell binds to the carrier protein and this causes the CP to open which then allows the molecule to pass out into the cell cytoplasm or into the extracellular fluid.