2.5: Biological membranes

Question 1

What does it means by fluid?

Answer 1

Components can move freely along the membrane

Question 2

What are the functions of the plasma membrane?

Answer 2

• Compartmentalisation
  Provides specific conditions for certain reactions to occur
• Site of chemical reaction
  Holds proteins/enzymes that are involved in certain chemical reactions
• Acts as a barrier
  Partially permeable membrane, only allows small, lipid-soluble/non polar substances to diffuse across (phospholipid bilayer)

Question 3

What is a carrier protein?

Answer 3

It is a protein on the inside that is able to change its shape using energy to face outwards.
Used to transport moleules across membrane

• Involved in active transport mainly sometimes passive (facilitated diffusion)
  Because it uses energy to change shape

Question 4

What is a channel protein?

Answer 4

Allows faciltated diffusion
Because polar molecules cannot pass through the phospholipid bilayer

Question 5

What are the similarities of channel and carrier protein?

Answer 5

They are both selective so they have specific channels for specific molecules

E.g aquaporins are channel proteins that only allow water to go through

Question 6

What is a glycolipid and glycoprotein?

Answer 6

Glycolipid - carbohydrate chain attached to a phospholipid
Glycoprotein - carbohydrate chain attached to a protein
They can be receptors or antigens

Question 7

What is the role of cholesterol?

Answer 7

regulates fluidity

Question 8

What makes up the fluid mosaic model?

Answer 8

Carrier and channel proteins
glycolipids and glycoprotiens
cholesterol

Question 9

What is inbetween different phospholipids?

Answer 9

Weak intermolecular forces that stabilise the structure

Question 10

What are the factors affecting membrane structure?

Answer 10

• Temperature
• Solvent

Question 11

What does an increase in temperature do?

Answer 11

• Gain kinetic energy
• The weak intermolecular forces inbetween the phospholipids break
• Denatures protein channel/carriers
• There are more gaps for simple diffusion to take place
• Affects permeability

Question 12

What does a non polar solvent do?

Answer 12

A non polar solvent can insert themselves within the bilayer which causes some of the fatty acid tails to bend. This is because the head is hydrophilic (polar) and the tails are hydrophobic(non polar).

• This disrupts the weak intermolecular forces
• This disrupts the bilayer
• There are bigger gaps which increases permeability

Question 13

What is diffusion?

Answer 13

Net movement of particles down concentration gradient

Question 14

What is facilitated diffusion?

Answer 14

Diffusion across protein channel on plasma membrane
(has selective permeability)

Question 15

What are the factors increasing the rate of diffusion?

Answer 15

• Temperature
• Concentration difference
• Surface area to volume ratio
• Thickness of membrane (diffusion distance)

Question 16

What does an increase in temperature do?

Answer 16

Increasing temp increases kinetic energy. Particles vibrate more quicker

Question 17

What does an increase in concentration difference do?

Answer 17

The steeper the concentration gradient, the quicker the concentration difference

Question 18

What does an increase in surface area to volume ratio do?

Answer 18

Larger ratio the quicker the diffusion rate

Question 19

What does the increase thickness of membrane do?

Answer 19

Thinner the membrane, shorter the distance, quicker diffusion rate

Question 20

What is osmosis?

Answer 20

Net movement of water molecules down a water potential gradient

Question 21

What happens when there is a lower concentration of water molecules

Answer 21

There is a higher concentration of solute molecules

Question 22

What happens when there a higher concentration of water molecules?

Answer 22

There is a lower concentration of solute molecules

Question 23

What happens when plant cells are in a low solute concentration?

Answer 23

Water moves in by osmosis down a water potential gradient. Then the cell wall prevents bursting and a membrane pushes against the wall. The cell is turgid.

Question 24

What happens when a plant cell is in a high solute concentration?

Answer 24

Water moves out of cells by osmosis down a water potential gradient. Plant cell membrane pulls away from cel wall as water leaves. The cell is plasmolysed

Question 25

What happens when an animal cell is in a low solute concentration?

Answer 25

Water moves in by osmosis by down a water potential gradient, animal cell bursts open. It is cytolysed

Question 26

What happens when an animal cell is in a high solute concentration?

Answer 26

Water moves in by osmosis down a water potential concentration gradient. Animal cell shrinks and appears wrinkled. It is crenated

Question 27

What is water potential?

Answer 27

The tendency of water to move from one region to another by osmosis

• In pure water the WP is the highest
• Ad more solute moelecules are added the WP decreases

cell potential = solute potential + pressure potential

Question 28

What is pressure potential?

Answer 28

The hydrostatic pressure to which water is subjected.

• Usually positive and is 0 when cells are in equilibrium

sometimes referred to as turgor or water pressure

Question 29

What is solute potential?

Answer 29

A measure of reduction in the water potential due to the presence of solute molecules

• It is the negative component of water potential

sometimes referred to as the osmotic potential or osmotic pressure

Question 30

What is Active transport?

Answer 30

The movement of particles against the concentration gradient using eneregy/ATP involving carrier proteins

Question 31

What do protein carriers do?

Answer 31

Change their shape to transport (or exchange) substances acrosss a membrane

Question 32

What is conformational change?

Answer 32

Structural/shape change

Question 33

What is bulk transport?

Answer 33

Active transport of large molecules

Question 34

What is endocytosis?

Answer 34

The bulk transport of molecules, too large to pass through a cell membrane even via channel or carrier proteins, into a cell
Phagocytosis = solids
Pinocytosis = liquids

Question 35

What is exocytosis?

Answer 35

The bulk transport of molecules, too large to pass through a cell membrane even via channel or carrier proteins, out of a cell

involves the fusion of vesicles with plasma membrane

Question 36

What is the process of active transport?

Answer 36

1. Molecule or ion binds to the carrier protein on receptor site
2. ATP binds to carrier protein on the inside
3. Hydrolysis of ATP to ADP and phosphate (Pi) causes the carrier protein to change shape. This releases the molecule or ion on the opposite side of the membrane.
4. The phosphate (Pi) is released from the carrier protein, causing the carrier protein to return to its original shape, ready to be used again.

Question 37

What are the factors affecting active transport?

Answer 37

• Temperature - At higher temperatures, particles have more kinetic energy and travel faster. Respiration also increases with temperature. Very high temperatures denature carrier proteins, decreasing the rate of active transport.
• Thickness of membrane - Particles travel shorter distances through thin exchange surfaces, so travel faster
• Number of carrier proteins - The more of these proteins, the faster the rate of active transport
• Rate of respiration - The more respiration, the more ATP available for active transport