Cell Membranes - The Basics

Question 1

What are cell membranes made from?

Answer 1

Lipids

Proteins

Carbohydrates

Question 2

What model was suggested to describe the arrangement of molecules in the membrane?

Answer 2

The fluid mosaic model

Question 3

Why is the bilayer fluid?

Answer 3

Because the phospholipids are constantly moving

Question 4

What do channel and carrier proteins allow?

Answer 4

Large molecules and ions to pass through membrane

Question 5

What do receptor proteins on the cell-surface membrane allow the cell to do?

Answer 5

Detect chemicals released from other cells

Question 6

What are proteins called that have a carbohydrate attached to them?

Answer 6

Glycoproteins

Question 7

What are lipids called that have a carbohydrate attached to them?

Answer 7

Glycolipids

Question 8

If the centre of the bilayer is hydrophobic, what doesn’t it allow through it?

Answer 8

Water soluble substances

Question 9

What does cholesterol do to the membrane?

Answer 9

It gives it stability.

Question 10

What does cholesterol bind to?

Answer 10

Hydrophobic tails of the phospholipids, causing them to pack together more closely. This restricts the movement of the phospholipid making the membrane more rigid.

Question 11

How are membranes affected by temperatures below 0 °C?

Answer 11

• phospholipids have a lack of energy and therefore movement
• packed close together and the membrane is rigid
• channel and carrier proteins denature which increases the permeability
• Ice crystals may pierce membrane which makes it highly permeable when it thaws

Question 12

How are membranes affected between 0°C and 45°C?

Answer 12

• phospholipids can move
• membrane partially permeable
• as temp increases, movement increases
• increases permeability

Question 13

What happens to membranes at temperatures above 45°C?

Answer 13

• phospholipids bilayer breaks down
• membrane more permeable
• water in cell expands, puts pressure on membrane
• channel and carrier proteins denature
• increases permeability

Question 14

How do you investigate cell membrane permeability?

Answer 14

1. Cut 5 equal pieces of beetroot and rinse.
2. Place in 5 different test tubes containing 5cm3 of water.
3. Put each test tube into a water bath at a different temp for the same length of time.
4. Remove pieces of beetroot leaving just the coloured water.
5. Switch colorimeter on and stabilise for 5 mins. Use a blue filter.
6. Add distilled water to a cuvette and put in machine. Calibrate to 0.
7. Transfer coloured liquid to new cuvette.
8. Put in colorimeter and record absorbency.
9. Repeat for each test tube.
10. Higher absorbance, higher permeability