Membranes

Question 1

Components of a phospholipid bilayer

Answer 1

• Glycoproteins/Glycolipids
• Cholesterol
• Hydrophobic tails
• Hydrophillic heads
• Surface/Intrinsic/extrinsic proteins

Question 2

Nature of a phospholipid bilayer

Answer 2

• Negative charge on surface and no charge on tails
• Permeable to small non-polar molecules
• Impermeable to small polar molecules, ions and large molecules
• 7nm thickness

Question 3

Role of channel proteins

Answer 3

Allow the movement of large molecules and hydrophillic molecules across a membrane

Question 4

Role of ion channels

Answer 4

Transporting ions e.g. sodium and chloride ions

Question 5

Role of carrier proteins

Answer 5

Transport large water insoluble molecules and ions against their concentration gradient using ATP

Question 6

Role of protein receptors

Answer 6

• Detect specific hormones and nerve transmitter and allow them to bind to corresponding cells
• Allows drugs to bind to affect cell metabolism
• Activates enzymes within a cell

Question 7

Role of glycoproteins and glycolipids

Answer 7

Involved in cell signalling to allow recognition by the immune system
Bind tissues together
Can act as hormone receptors

Question 8

Role of cholesterol

Answer 8

• Cholesterol gives eukaryotic cell membranes mechanical stability and maintains fluidity
• Helps make the barrier more complete against water molecules trying to pass straight through

Question 9

Effect of temperature on a cell membrane

Answer 9

• As temperature rises, KE increases
• This causes the phospholipid molecules to vibrate more
• The molecules will gain enough KE to cause leakages in the membrane, making the membrane fully permeable

Question 10

Types of transport across membranes

Answer 10

• Simple diffusion
• Osmosis
• Facilitated diffusion
• Active transport
• Cytosis

Question 11

Functions of membranes

Answer 11

• Divides cell content into different compartments to make different functions more efficiently
• Regulates movement of substances in and out of the cells or organism
• Recognises specific molecules and other cells
• Membranes can allow electrical signals to pass along them (e.g. axon of a motor neurone)
• Membranes provide attachment sites for enzymes and other molecules involved in metabolism

Question 12

Fluid mosaic

Answer 12

Description of the arrangement of molecules in membranes.

Question 13

Antigen

Answer 13

Complementary to messenger molecule like hormones which bind to them and bring about a change in the cell

Question 14

Cell signalling

Answer 14

The molecule mechanism by which cells detect and respond to external stimuli and send messages to other cells

Question 15

Membrane proteins

Answer 15

• An enzyme that is built into the membrane with the active site sticking out into the adjacent solution
• Several enzymes are ordered as a team to carry out sequential steps of a metablic pathway

Question 16

Organelles with 2 membranes surrounding them

Answer 16

• Chloroplasts
• Mitochondria
• Lysosomes

Question 17

Term used to describe membranes that only allow some molecules through

Answer 17

Partially permeable

Question 18

Types of transport across membranes

Answer 18

• Osmosis
• Facilitated diffusion
• Diffusion
• Active Transport
• Cytosis

Question 19

Active transport

Answer 19

• Against a concentration gradient
• Requires ATP
• Uses specific carrier proteins to transport specific molecules
• Carry molecules at a faster rate than diffusion
• Carrier proteins change shape
• Can accumulate content outside cell or inside cell

Question 20

Endocytosis

Answer 20

Phagocytosis – organic matter or bacterium is engulfed

Pinocytosis – liquid mass

Question 21

Exocytosis

Answer 21

• Movement out of cell
• Vesicles moved by cytoskeleton
• Requires ATP

Question 22

Osmosis

Answer 22

• Small water moelcules fit between gaps in the phospholipid bilayer
• Water moves down the concentration gradient
• The movement of water will reach a dynamic equilibrium
• Water diffuses across both ways

Question 23

Diffusion

Answer 23

• Passive process (use their own KE)
• Down a diffusion gradient
• Will reach a dynamic equilibrium
• Diffusion will keep occuring in both directions
• Will transport the lipid soluble, non-polar and small molecules
• No proteins used
• Phospholipid layer must have gaps for this to occur

Question 24

Facilitated diffusion

Answer 24

• Requires ATP
• Ion channels are specific to certain ions/molecules
• Will transport large non-polar molecules and small charged particles
• Utilise channel or carrier proteins
• Down a concentration gradient

Question 25

Factors afftecting the rate of diffusion

Answer 25

• Surface area
• Concentration gradient
• Temperature
• Diffusion distance

Question 26

Why does an increase in surface area increase the rate of diffusion

Answer 26

There are more points of contact and potential gaps that the molecules can fit through

Question 27

Why does an increase in the concentration gradient lead to an increase in the rate of diffusion

Answer 27

If there is a greater concentration gradient, there will be a greater net movement of molecules across the membrane

Question 28

Why does an increase in temperature result in a increase in the diffusion rate

Answer 28

The phospholipid molecules will move more vigorously causing more gaps to appear for diffusion

Question 29

Why does a decrease in diffusion distance increase the rate of diffusion

Answer 29

The molecules will have to travel a shorter distance

Question 30

Water potential

Answer 30

0 is the highest water potential and kPa is used as the unit

Question 31

What will happen to a plant and animal cell when placed in pure water

Answer 31

The plant cell will become turgid

The animal cell will haemolyse

Question 32

What will happen to a plant and animal cell when placed in saline solution

Answer 32

The plant cell will become plasmolysed

The animal cell will become crenated