Movement across the Cell Membrane

Question 1

How do substances move around inside of the cell?

Answer 1

By diffusion.
Doesn’t require any energy - only thermal energy of the surroundings.
Its refereed to as passive process.

Question 2

What happens if there is a concentration difference between 2 places?

Answer 2

The random movement results in the substance diffusing down its concentration gradient from a high to low concentration.

Question 3

What does selectively permeable mean?

Answer 3

Cell membrane can allow some substances through but not others.
Allows materials to be concentrated inside the cells, excluded from cells or simply separated from outside environment.
Called compartmentalisation.

Question 4

Why is compartmentalisation important?

Answer 4

Enables reactions to take place that would otherwise be impossible.
Eukaryotic cells can compartmentalise materials inside organelles.

Question 5

Name the 4 ways that substances can move across the cell membrane?

Answer 5

Lipid diffusion.
Osmosis.
Facilitated diffusion.
Active transport.

Question 6

Describe what lipid diffusion - simple diffusion is?

Answer 6

When a few substances can diffuse directly through lipid bilayer part of the membrane.
Substances that can’t do this are hydrophobic molecules eg steroids, and a few very small hydrophilic molecules, such as H2O, O2, CO2 - membrane is no barrier at all.
Can be switched on and off by the cell.

Question 7

What does it mean that lipid diffusion is a passive process?

Answer 7

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