The Cell Membrane

Question 1

State the organelles that contain membranes

Answer 1

• Endoplasmic reticulum
• Chloroplast
• Mitochondria

Question 2

What is the purpose of the membrane in the endoplasmic reticulum

Answer 2

Forms a transport system

Question 3

What is the function of membranes in mitochondria and chloroplast

Answer 3

Controls entry and exit of materials

Question 4

What is the cell membrane made up of

Answer 4

Phospholipids

Question 5

What does the phospholipid head contain, and describe its significance

Answer 5

The head contains phosphate and glycerol, making it polar/hydrophillic

Question 6

What does the phospholipid tail contain, and describe its significance

Answer 6

The tail contains 2 fatty acids, which makes it non-polar/hydrophillic

Question 7

Describe how bilayers form

Answer 7

• The cell membrane forms a barrier between the outside of the cell and the inside
• Both the outside of the cell (tissue fluid) and inside of the cell (cytoplasm) are mainly water, therefore the hydrophillic heads orient themselves outwards
• The hydrophobic tails orient themselves away from water, and therefore point inwards

Question 8

Explain how the phospholipid bilayer interacts with water

Answer 8

• The hydrophobic polar fatty acid tails orient themselves away from water
• The hydrophilic, non-polar glycerol and phosphate heads orient themselves towards water

Question 9

Why must the cell membrane be able to move

Answer 9

To enable transport of substances in or out the membrane

Question 10

Describe the process of exocytosis

Answer 10

Vesicles produced within the cell can transport molecules such as proteins to the cell surface, and secrete these proteins through

Question 11

Describe the process of endocytosis

Answer 11

Molecules enter the cell and are transported by a vesicle via endocytosis

Question 12

Why are phospholipids fluid

Answer 12

Cells need to change shape

Question 13

Describe the role of cholesterol in the cell membrane

Answer 13

• Cholesterol increases the rigidity and stiffness of the membrane.
• This limits the lateral (side to side) movement of the phospholipids, allowing the cell membrane to retain its shape

Question 14

Why is the phospholipid bilayer selectively permeable

Answer 14

Due to the properties of the phospholipids

Question 15

What must a molecule be in order to pass through the phospholipid bilayer

Answer 15

Lipid soluble

Question 16

To be lipid soluble, a molecule must be…

Answer 16

• Non-polar
• Uncharged

Question 17

State the 2 types of transport protein

Answer 17

• Channel protein
• Carrier proteins

Question 18

Describe the properties of the 2 transport proteins, and why this makes the cell membrane selectively permeable

Answer 18

They’re specific, due to their specific 3D tertiary structures, so they can only transport certain molecules

Question 19

What other proteins are found in the cell membrane

Answer 19

• Receptors
• Membrane bound enzymes
• Transport proteins

Question 20

Describe the structure of receptors

Answer 20

Often glycoproteins, which are proteins with a carbohydrate attached.

Question 21

Describe what happens when a specific molecule binds to the receptor

Answer 21

A response is triggered within the cell

Question 22

Describe the function of membrane bound enzymes

Answer 22

They catalyse reactions on the cell surface

Question 23

Describe the function of call identify markers

Answer 23

• Commonly known as antigens
• Each cell has a distinctive antigen with a different structure, allowing for identification
• These can be proteins or glycolipids (carbohydrates with a lipid attached)

Question 24

Why is the phospholipid bilayer described as a fluid mosaic

Answer 24

The cell membrane is made up of many smaller components, with varying size and shape

Question 25

What do we call proteins that span the whole phospholipid

Answer 25

Intrinsic proteins
- They have non polar regions to make them lipid soluble

Question 26

What do we call proteins that are embedded in the membrane

Answer 26

Extrinsic proteins (pointing outwards)
- They are polar, so they aren’t found with the fatty acid tails

Question 27

Explain how the structure of the cell membrane enables it to act as a selectively permeable barrier

Answer 27

• Selectively permeable means that only specific substances can pass through the membrane
• As the bilayer is made from phospholipids, only lipid soluble molecules (which are non-polar and charged) can pass directly through it
• As these proteins have a highly specific 3D tertiary structure, only particular molecules with the correct shape can be transported through them