Transport across cell membranes

Question 1

What does a plasma membrane allow?

Answer 1

Different conditions to be established inside and outside the cell.

Question 2

Describe a phospholipid.

Answer 2

Phosphate molecule - hydrophilic head

2 fatty acid chains - hydrophobic tail.

Question 3

What are the 3 functions of phospholipids in cell membranes?

Answer 3

• Make the membrane flexible and self-sealing,
• Prevent water soluble substances entering and leaving the cell,
• Allowing lipid soluble substances to enter and leave the cell.

Question 4

What are three functions of cholesterol in the cell membrane?

Answer 4

• Reduce lateral molecules,
• Makes membranes less fluid at high temperatures,
• prevents leakage of water and dissolved ions from the cell.

Question 5

What are glycolipids?

Answer 5

Carbohydrate covalently bonded with a lipid.

Question 6

Why can’t molecules diffuse across the cell-surface membrane?

Answer 6

• Not lipid soluble,
• Too large,
• Of the same charge,
• Electrically charged (polar).

Question 7

Define diffusion.

Answer 7

The net movement of particles from a region of high concentration to a region of low concentration until evenly distributed.

Question 8

Define Osmosis.

Answer 8

The passage of water from a region of a higher water potential to a region of a lower water potential through a selectively permeable membrane.

Question 9

Define active transport.

Answer 9

The movement of molecules or ions into or out of a cell from a region of low concentration to a region of high concentration using energy released from ATP.

Question 10

Why is co-transport in the small intestine necessary?

Answer 10

Diffusion can only achieve equal concentrations on either side of the cell membrane so not all of the glucose can be absorbed. So co-transport absorbs glucose against the concentration gradient.