Cell Membrane

Question 1

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

Answer 1

1. Membranes around organelles divide the cells into different compartments- acting as a barrier between the organelle and the cytoplasm
2. Membranes can form vesicles to transport substances between different areas of the cell.
3. Membranes within cells are also partially permeable so they can control which substances enter and the leave the organelle.
4. Membranes within organelles act as barriers between the membrane contents and the rest of the organelle
5. Membranes within cells can be the site of chemical reactions. the membranes of some organelles are folded, increasing their surface area and making chemical reactions more efficient.

Question 2

Define the term “compartmentalisation” and explain why compartmentalisation is useful to cells.

Answer 2

1. The formation of separate membrane-bound areas in a cell is called compartmentalisation.
2. It is vital to a cell as metabolism includes many different and often incompatible reactions.
3. Containing reactions in separate parts of the cell allows the specific conditions required for cellular reactions.

Question 3

Define the term “partially permeable”.

Answer 3

Membranes that allow some substances to cross but not others

Question 4

Define the term “cell signalling”.

Answer 4

A complex system of inter cellular communication.

Question 5

Define the term “phospholipid bilayer”.

Answer 5

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

Question 6

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

Answer 6

Fluid- all phospholipids and membrane proteins can move around because they are not bonded to each other
Mosaic- The phospholipids and the proteins form a pattern
Fluid-Mosaic Model- model of the structure of a cell membrane in which phospholipids within the phospholipid bilayer are free to move and proteins o various shapes and sizes are embedded in various positions

Question 7

Define the term “glycoprotein”.

Answer 7

Intrinsic membrane proteins with attaches carbohydrate molecules varying in lengths and shapes

Question 8

Define the term “phospholipid”,

Answer 8

Modified triglyceride where one fatty acid has been replaces by a phosphate group.

Question 9

Define the term “cholesterol”,

Answer 9

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

Question 10

Define the term “glycolipid”,

Answer 10

Cell surface membrane lipids with attached carbohydrate molecules of varying lengths and shapes.

Question 11

Define the term “channel protein”

Answer 11

Membrane proteins that provide a hydrophillic channel through a membrane that allows passive movement of polar molecules and ions down a conc. gradient.

Question 12

Define the terms “carrier protein”,

Answer 12

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

Question 13

Define the term “intrinsic protein”

Answer 13

1. Transmembrane proteins are embedded through both layers of a membrane e.g channel and carrier proteins.
2. They have amino acids with hydrophobic R-groups on their external surfaces, which interact with the hydrophobic core of the membrane keeping them in place.

Question 14

Define the term “extrinsic protein”

Answer 14

1, Peripheral proteins that are present in one side of the bilayer. e.g. Enzymes, proteins that bind cytoskeleton to membrane.
2. They normally have hydrophillic R-groups on their outer surfaces and interact with the polar heads of the phospholipids or with intrinsic proteins

Question 15

Define the terms “receptor protein”.

Answer 15

Usually glycoproteins, they detect the presence of an extra-cellular chemical and cause a response in the cell

Question 16

Draw a diagram of a phospholipid, label its components and annotate with their properties.

Answer 16

• Two hydrophobic fatty acid tails

- one hydrophillic (polar) phosphate head

Question 17

State the role of phospholipids in the membrane.

Answer 17

Forms the phospholipid bilayer. the phospholipid bi-layers are perfectly suited as membranes because the outer surface of the hydrophillic phosphate heads can interact with water.

Question 18

State the role of cholesterol in the membrane.

Answer 18

1. Regulates the fluidity of membranes.
2. They are positioned between phospholipids in a membrane bilayer, with hydrophillic end interacting with the heads and the hydrophobic end interacting with the tails, pulling them together.

Question 19

State the role of glycoproteins in the membrane.

Answer 19

Are intrinsic proteins.

1. Play a role in cell adhesion to hold cells together
2. Act as receptors for chemicals and hormones when chemicals bind ti the receptor it elicits a response from the cell. this may cause a direct response or set off a cascade of events inside the cell- cell communication or signalling
3. Act as antigens for cell recognition for non-self
4. Stabilises membrane structure by forming hydrogen bonds with water molecules

Question 20

State the role of glycolipids in the membrane.

Answer 20

Cell markers or antigens and can be recognised by the cells of the immune system as self or non-self.
Also stabilise the cell by forming hydrogen bonds with surrounding water molecules

Question 21

Define the term “cell adhesion”.

Answer 21

Glycoproteins play a role in cell adhesion, when cells join together to form tight junctions in certain tissues.

Question 22

Explain the importance of membrane bound proteins in chemical reactions.

Answer 22

Because they have to be in particular positions fr chemical reactions to take place.

Question 23

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

Answer 23

1. Higher temp- more permeable
2. Phospholipids have more kinetic energy and will move more- making membrane more fluid and lose its structure- this increases the permeability of the membrane making it easier for particles to cross.
3. If temp continues to increase the cell will break down completely.
4. Channel and carrier proteins will be denatured at higher temps- as they denature membrane permeability will be affected.

Question 24

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

Answer 24

1. Higher solvent concentration- more permeable
2. The non-polar alcohol molecules can enter the cell membrane and the presence of these molecules between the phospholipids disrupts the membrane.
3. When the membrane is disrupted it becomes more fluid and permeable.

Question 25

5. Describe a method using a colorimeter to investigate the effect of temperature (or ethanol concentration) on the permeability of cell membranes.

Answer 25

1. place 5 equally sized pieces of beetroot into a 100ml water bath of distilled water. 2. Increase the temperature of the bath by 10c intervals 3. Take samples of the water containing the beetroot five minutes after each temperature is reached 4. Measure the absorbance of each sample using a colorimeter using a blue filter. 5. Repeat with fresh beetroot pieces and calculate the mean.