More on Movement Across the Cell Membrane

Question 1

What is facilitated diffusion?

Answer 1

Its the diffusion of a substance across a membrane through a trans-membrane protein molecule.
Transport proteins tend to be specific for one molecule, so substances can only cross a membrane that contains appropriate protein.
Passive diffusion.

Question 2

Why is facilitated diffusion passive?

Answer 2

No energy is involved and substances can only move down their concentration gradient.

Question 3

What are the 2 kinds of transport proteins in facilitated diffusion?

Answer 3

Channel proteins.

Carrier proteins.

Question 4

What are channel proteins?

Answer 4

They form a water-filled channel in the membrane.
This allows charged substances to diffuse across the membrane.
Most channels are gated allowing the cell to control entry and exit of ions.
Cells can change permeability to certain ions.

Question 5

In channel proteins, what ions can diffuse across the membrane through specific ion channels?

Answer 5

Na+.
Ca2+.
K+.
Cl-.

Question 6

What are carrier proteins?

Answer 6

They have a binding site for specific solute and constantly flip between 2 states so that the site is alternating open to opposite sides of the membrane.