Membranes

Question 1

State 5 roles of membranes within cells and at the surface of cells. (F)

Answer 1

• compartmentalisation
• controls movement of molecules into or out of a cell
• controls movement of molecules into or out of organelles
• cell signalling
• site of chemical reactions

Question 2

Define the term “compartmentalisation”.

Answer 2

The formation of separate membrane-bound areas in a cell.

Question 3

Explain why compartmentalisation is useful to cells.

Answer 3

• metabolism has many different reactions
• compartmentalisation allows specific conditions required e.g. chemical gradients
• protects cell components

Question 4

Define the term “partially permeable”.

Answer 4

Membrane that allows some substances to cross but not others.

Question 5

Define the term “cell signalling”. (F)

Answer 5

A complex system of intercellular communication.

Question 6

Define the term “phospholipid bilayer”. (F)

Answer 6

Arrangement of phospholipids found in cell membranes; the hydrophilic phosphate heads form both the inner and outer surface of a membrane, sandwiching the fatty acid tails to form a hydrophobic core.

Question 7

Explain what is meant by “fluid” in the “fluid mosaic model of membrane structure”. (F)

Answer 7

The phospholipids within the bilayer are free to move.

Question 8

Explain what is meant by “mosaic” in the “fluid mosaic model of membrane structure”. (F)

Answer 8

There are proteins of different shapes and sizes embedded in various positions.

Question 9

Define the term “glycoprotein”.

Answer 9

Extrinsic membrane proteins with attached carbohydrate molecules of varying lengths and shapes.

Question 10

Define the term “phospholipid”.

Answer 10

Modified triglycerides, where one fatty acid has been replaced with a phosphate group.

Question 11

Define the term “cholesterol”.

Answer 11

A lipid containing a hydrocarbon tail attached to a hydrocarbon ring and a hydroxyl group.

Question 12

Define the term “channel protein”.

Answer 12

Membrane proteins that provide a hydrophilic channel through a membrane.

Question 13

Define the term “carrier protein”.

Answer 13

Membrane proteins that play a part in the transport of substances through a membrane.

Question 14

Define the term “receptor protein/glycoprotein”.

Answer 14

Extrinsic glycoproteins that bind chemical signals, triggering a response by the cell.

Question 15

Define the term “intrinsic protein”.

Answer 15

Protein that is embedded in both layers of the membrane.

Question 16

Define the term “extrinsic protein”.

Answer 16

Protein that is embedded in one layer of the membrane.

Question 17

State the role of phospholipids in the membrane. (F)

Answer 17

-

Question 18

State the role of phospholipids in the membrane. (F)

Answer 18

• hydrophilic phosphate head can interact with water

- hydrophobic tails form a hydrophobic core

Question 19

State the role of cholesterol in the membrane. (F)

Answer 19

• regulates fluidity of membranes
• adds stability without being too rigid
• prevents rigidity

Question 20

State the role of glycoproteins in the membrane. (F)

Answer 20

• cell adhesion

- receptors for chemical signals

Question 21

State the role of glycolipids in the membrane. (F)

Answer 21

• cell markers/antigens

- cell recognition by immune system

Question 22

State the role of channel proteins in the membrane. (F)

Answer 22

• provide a hydrophilic channel to allow passive movement of polar molecules and ions

Question 23

State the role of carrier proteins in the membrane. (F)

Answer 23

• passive transport

- active transport

Question 24

Define the term “cell adhesion”.

Answer 24

When cells join together to form tight junctions in certain tissues.

Question 25

Explain how cholesterol affects the fluidity and stability of membranes.

Answer 25

- positioned between phospholipids - hydrophilic end interacts with heads - hydrophobic end interacts with tails - pulls them together - stop phospholipids from grouping too closely and crystallising

Question 26

Explain the importance of membrane bound proteins in chemical reactions.

Answer 26

They need to be in particular positions for chemical reactions to take place.

Question 27

Explain how the binding of a molecule to a membrane bound glycoprotein can cause effects within a cell.

Answer 27

- elicits a response from cell | - direct response or cascade of events

Question 28

Describe the effect of changing temperature on the permeability of cell membranes. (F)

Answer 28

- as temperature increases, the membrane becomes more permeable

Question 29

Explain the effect of changing temperature on the permeability of cell membranes.

Answer 29

- as temperature increases, the phospholipids will have more kinetic energy and will move more - loses structure, so becomes more permeable - channel and carrier proteins become denatured, increases permeability

Question 30

Describe the effect of solvent (e.g. ethanol) concentration on the permeability of cell membranes. (F)

Answer 30

- the higher the solvent concentration, the higher the permeability

Question 31

Explain the effect of solvent (e.g. ethanol) concentration on the permeability of cell membranes.

Answer 31

- organic solvents are less polar than water - can dissolve lipids - membrane becomes more fluid and more permeable

Question 32

Describe a method using a colorimeter to investigate the effect of temperature on the permeability of cell membranes.

Answer 32

1. Cut 5 equally sized pieces of beetroot and wash 2. Place in 100ml of distilled water 3. Place in water baths at different temperatures (10ºC intervals) 4. After 5 minutes, measure absorbance of each sample with a colorimeter with a blue filter 5. Repeat for each temperature and calculate the average.