3.b. Permeability of the membrane

Question 1

What types of substances can and can’t pass through a phospholipid membrane?

Answer 1

• Lipid-soluble molecules CAN

- Water-soluble molecules CANNOT

Question 2

Give three examples of lipid soluble molecules

Answer 2

CO2, O2, Vitamin A

Question 3

Give three examples of water-soluble molecules

Answer 3

Glucose, Ions, Polar molecules

Question 4

How do lipid-soluble molecules pass through the membrane?

Answer 4

They dissolve in the phospholipid and diffuse across the membrane

Question 5

Is the phospholipid layer hydrophilic or hydrophobic? How does this affect the permeability of the membrane?

Answer 5

Hydrophobic, so lipid-soluble substances pass more easily than water-soluble substances

Question 6

How do water-soluble molecules pass through the membrane?

Answer 6

They pass through intrinsic proteins which form water-filled channels

Question 7

Membranes are ‘selectively permeable’. What does this mean?

Answer 7

Permeable to water molecules and some other small molecules but not to larger molecules