Chapter 5 - Plasma Membrane

Question 1

What is the purpose of plasma membranes ?

Answer 1

• Compartmentalisation
• Regulate transport of materials
• Involved in cell signalling

Question 2

What does the fluid mosaic model state ?

Answer 2

• Membranes are made of free to move phospholipids hence fluid
• Proteins are embedded within the membrane varying in size hence flexible

Question 3

What is the structure of a phospholipid ?

Answer 3

Question 4

What are the two structures formed by phospholipids ?

Answer 4

• Micelle
• Bilayer

Question 5

Why are Micelles formed ?

Answer 5

Helps body absorb lipids, fats, and soluble vitamins
Encapsulates water

Question 6

Why are Bilayers formed ?

Answer 6

Fatty acids are big and hurry to fit into interior of micelle

Question 7

What are the factors that affect plasma membrane permeability ?

Answer 7

Temperature and solvents

Question 8

How does temperature affect plasma membrane ?

Answer 8

As temp increases theres more kinetic energy, phospholipids move more.
This breaks structure

As temp decreases membrane stiffens, causes membrane to crack. This decreases fluidity which reduces permeability

Question 9

What is put in place to prevent the effects of increase and decrease of temp on plasma membrane ?

Answer 9

[Increase]
Cholesterol helps prevent this as it holds bilayer together hence maintaining fluidity
[Decrease]
Unsaturated fatty acid tails have a kink that pushes away other phospholipids
Cholesterol also pushes through the phospholipids to prevent crunching

Question 10

How do solvents affect plasma membranes ?

Answer 10

Some solvents such as ethanol can dissolve lipids which reduces bilayer stability and increases permeability

Question 11

What is cholesterol ?

Answer 11

A lipid (sterol) with hydrophillic end and hydrophobic end positioned inbetween phopholipids

Question 12

What is the function of cholesterol ?

Answer 12

• Adds stability by pulling phospholipids together; maintaining fluidity

Question 13

What are the two types of membrane proteins ?

Answer 13

1) Intrinsic proteins
- Proteins that span the whole width of membrane
- Embedded within membrane
2) Extrinsic proteins
- Proteins confined to outer surface of membrane

Question 14

What are the features of extrinsic proteins ?

Answer 14

• Act as receptors
• Involved in cell recognition
• Can dissociate from membrane

Question 15

What are the examples of intrinsic proteins ?

Answer 15

• Channels proteins
  (Act as a pore)
• Carrier proteins
  (Carry substances across membrane)
• Glycoproteins
  (Act as receptors)
• Glycolipids
  (Key in cell signalling, act as receptors for viruses)

Question 16

What factors affect passive diffusion ?

Answer 16

1) Temperature
- More kinetic energy
2) Concentration gradient
3) Surface area
4) Thickness of membrane

Question 17

What molecules are transported via facilitated diffusion ?

Answer 17

Molecules that are too large or are polar

Question 18

How does active transport occur ?

Answer 18

1) Molecule to be transported binds to receptor in channel of carrier protein
2) ATP binds to carrier protein and is hydrolysed into ADP and phosphate
3) Phosphate binds to carrier protein - changing its shape
4) Molecule or ion is released into the cell

Question 19

What is bulk transport ?

Answer 19

A form of active transport
- Used to move large molecules such as enzymes, hormones and whole cells

Question 20

What are the two types of bulk transport mechanisms ?

Answer 20

1) Endocytosis
- Bulk tranport into the cell
2) Exocytosis
- Bulk transport out of the cell

Question 21

What are the features of Endocytosis ?

Answer 21

Phagocytosis = Solids
Pinocytosis = Liquids
1- Plasma membrane invaginates
2 - Membrane enfolds the material until eventually the membrane fuses; forming a vesicle
3- Vesicle pinch off, and move into the cell

Question 22

What are the features of Exocytosis ?

Answer 22

• Reverse process of Endocytosis
  1 - Vesicle moves towards and fuses with cell surface membrane
  2 - Contents in vesicle are removed

Question 23

What is water potential ?

Answer 23

Pressure exerted by water molecules as they collide with a membrane or container

Question 24

What is osmosis ?

Answer 24

Movement of water from an area of high water potential to an area of low water potential across a partially permeable membrane

Question 25

How does water potential correlate to solute conc. ?

Answer 25

Increased solute conc. = Lower water potential

Question 26

What are the effects of osmosis on animal cells ?

Answer 26

If solution has a higher water potential : Cytolysis
- Water moves into the cell which increases hydrostatic pressure causing the cell to swell and burst

If solution has a lower water potential : Crenation
- Water moves out of cell causing a decrease in water volume of cell

Question 27

What are the effects of osmosis on plant cells ?

Answer 27