Cell Surface Membrane

Question 1

What is the cell surface membrane?

Answer 1

• Membrane that surrounds cells and forms the boundary between the cell cytoplasm and the environments ( like a barrier ).

Question 2

What are some purposes of plasma membranes?

Answer 2

• Allows for different conditions to be established inside and outside a cell.
• Controls which substances enter and leave the cell ( It is partially permeable, so they let some

Question 3

What does it mean for the cell surface to be partially permeable?

Answer 3

Only some molecules are able to pass through the membrane, but not others.

Question 4

What are the different methods that substances can move across the cell surface membrane?

Answer 4

• Diffusion
• Osmosis
• Active Transport

Question 5

What part of the cell surface membrane are phospholipids present?

Answer 5

The phospholipids are present as a bi-layer ( they form the bi-layer ).

Question 6

Why are phospholipids able to form a bi-layer in the cell membrane?

Answer 6

• Hydrophobic tails of both phospholipid layers point into the centre of the cell membrane, as they are repelled by water on both sides.
• Hydrophillic heads of both phospholipid layers point to the outside of the cell surface membrane, attracted by water on both sides.

Question 7

How is lipid soluble material able to enter the cell?

Answer 7

Through the phospholipid bi-layer.

Question 8

What are the functions of the phospholipid bilayer?

Answer 8

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

Question 9

What is the fluid mosaic model’s purpose?

Answer 9

Describing the arrangement of molecules in the membrane.

Question 10

What is the fluid part of the cell surface membrane?

Answer 10

• Individual phospholipid molecules can move relative to one another.
• This provides the membrane a flexible structure that is constantly moving and changing shape.

Question 11

What is the mosaic part of the cell surface membrane?

Answer 11

• Proteins are embedded in the phospholipid bi layer vary in shape, size and pattern akin to a mosaic tile.

Question 12

Why can most molecules not move across the membrane freely?

Answer 12

• They are not soluble in lipids, and thus cannot move through the phospholipid bi-layer
• Have the same charge as the protein channels, resulting in them repelling each other.
• Electrically charged, and there are not able to pass through the non polar hydrophobic tails in the phospholipid bi-layer.
• Too big to pass through the channels in the membrane.

Question 13

How do proteins allow large molecules and ions to pass through the membrane?

Answer 13

• Proteins are scattered through the bi-layer.

* Some are channel proteins and carrier proteins, which can allow large molecules to pass through the membrane.

Question 14

What is the purpose of receptor proteins?

Answer 14

Present on the cell surface membrane, they allow the cell to detect chemicals released from other cells, chemicals signal to the cell to respond in a certain way.

Question 15

What are glycoproteins?

Answer 15

Proteins with an attached polysaccharide chain.

Question 16

What are protein channels?

Answer 16

Proteins which form water filled tubes to allow water soluble ions to diffuse across the membrane into the cell.

Question 17

How do carrier proteins work?

Answer 17

They bind to the ions, then change shape in order to move these molecules across the membrane.

Question 18

What are the functions of proteins in the membrane?

Answer 18

• Provide structural support.
• Act as channels transporting water-soluble substances across the membrane.
• Allow active transport across the membrane through carrier proteins.
• Form cell surface receptors for identifying cells.
• Help cells adhere together.
• Act as receptors.

Question 19

Where are cholesterol molecules present?

Answer 19

Bi-layer

Question 20

What are the functions of cholesterol in the cell surface membrane?

Answer 20

• Make the membrane less fluid at high temperatures.
• Prevent leakage of water and dissolved ions from the cell.
• Causes phospholipids to be packed together, restricting the movement of phospholipids, making the cell more rigid, without making the whole cell too rigid.

Question 21

How do cell surface membranes support the cell structure?

Answer 21

• Cholesterol molecules fit between phospholipids, they are able to bind to the hydrophobic tails of the phospholipids, causing them to pack more closely together.
• This results in the phospholipid movement being restricted, and makes the membrane less fluid and more rigid.

Question 22

How does cholesterol help prevent leakage of water and dissolved ions?

Answer 22

They are hydrophobic, and present in the cell surface membrane.

Question 23

What are glycolipids?

Answer 23

Carbohydrate covalently bonded with lipids.

Question 24

What are the functions of glycolipids in the membrane?

Answer 24

• Act as recognition sites
• Help maintain stability of the membrane
• Help cells attach to one another to form tissues.

Question 25

Where are glycolipids present?

Answer 25

• Carbohydrate section is present from phospholipid bi-layer to the outside of the cell.

Question 26

What are the functions of glycoproteins?

Answer 26

* Act as recognition sites * Help cells join together to form tissues * Allow cells to recognise each other.

Question 27

Where are glycoproteins present?

Answer 27

Glycoprotein's carbohydrate chains are attached to many extrinsic proteins on the outer surface of the cell membrane.