plasma membranes

Question 1

what holds the bilayer together?

Answer 1

weak hydrophobic interactions

Question 2

properties of the phospholipid bilayer

Answer 2

• hydrophobic tails helps to form a bilayer and separate two aqueous regions
• contains cholesterol to regulate fluidity

Question 3

how does the fluid mosaic model describe the structure of plasma membranes?

Answer 3

• proteins are randomly spread through the membrane
• bilayer has hydrophobic tails facing inwards and hydrophilic heads facing outwards

Question 4

what component of the plasma membrane acts as a barrier for mineral ions entering the cell?

Answer 4

phospholipid bilayer

Question 5

outline the role of membranes within cells

Answer 5

• compartmentalise areas which require specific conditions
• site of chemical reactions

Question 6

why is fluidity necessary?

Answer 6

allows spontaneous breaking and reforming for endo+exocytosis

Question 7

how might a variation in saturated and unsaturated fatty acid tails affect membrane properties?

Answer 7

• less stable
• increased fluidity

Question 8

what are channel proteins?

Answer 8

hydrophilic channel that allows movement of polar molecules down a concentration gradient

Question 9

what are carrier proteins?

Answer 9

they change shape for passive and active transport

Question 10

what are glycoproteins and what are they used for?

Answer 10

• proteins with a carb chain attached
• cell adhesion and as receptors for chemical signals

Question 11

what are glycolipids and what are they used for?

Answer 11

• lipid chain
• cell markers or antigens which are recognised by the immune system

Question 12

what is cholesterol?

Answer 12

lipid with a hydrophobic ad hydrophilic end

Question 13

what is the role of cholesterol in the plasma membrane

Answer 13

• binds to phospholipid fatty acid tails
• this increases the packing of the membrane
• reduces fluidity

Question 14

why cant glucose pass through a membrane via simple diffusion?

Answer 14

glucose is too large so the phospholipids act as a barrier

Question 15

why can progesterone move through membranes?

Answer 15

fat soluble so it can diffuse through

Question 16

what is diffusion?

Answer 16

the net movement of particles down a concentration gradient

Question 17

why does diffusion take longer over a larger distance?

Answer 17

particles have more chance to collide and slow the movement

Question 18

what are the factors affecting rate of diffusion?

Answer 18

• temperature
• concentration gradient
• distance travelled

Question 19

what is simple diffusion?

Answer 19

diffusion without the help of membrane proteins

Question 20

what is osmosis?

Answer 20

diffusion of water along a water potential gradient across a partially permeable membrane

Question 21

what is water potential?

Answer 21

the tendency of water to move from one place to another

Question 22

what is the highest water pressure?

Answer 22

0kPa

Question 23

what affects water potential?

Answer 23

presence of solutes

Question 24

what is a hypertonic solution?

Answer 24

higher solute conc than another solution

Question 25

what is a hypotonic solution?

Answer 25

lower solute conc than another solution

Question 26

what is an isotonic solution?

Answer 26

equal solute conc to another solution

Question 27

what is cytolysis?

Answer 27

cell bursting due to too much hydrostatic pressure

Question 28

what is crenation?

Answer 28

cell shrinking

Question 29

how does a cell prevent cytolysis or crenation?

Answer 29

surrounds itself with an aqueous solution

Question 30

what is a protoplast?

Answer 30

cell with cell wall removed

Question 31

what does the tonoplast do?

Answer 31

adjust turgor pressure

Question 32

what is turgor pressure?

Answer 32

force of water on cell wall due to osmosis

Question 33

what is plasmolysis?

Answer 33

when cells lose water in a hypertonic solution and contract

Question 34

active transport method

Answer 34

- transported ions bind to receptors on carrier proteins - ATP binds to carrier protein and is hydrolysed into ADP and phosphate ions - binding of phosphate ions to carrier protein causes it to change shape and open - ion enters and ATP reforms

Question 35

what is endocytosis?

Answer 35

bulk transport of molecules into a cell

Question 36

what is the effect of high temperatures on membranes?

Answer 36

- phospholipids have more kinetic energy and move apart - bilayer becomes more fluid - proteins denature

Question 37

how can root hair cells absorb water via osmosis when soil has a low water potential?

Answer 37

- uptake solutes via active transport to lower water potential until its lower than soil - creates a water potential gradient

Question 38

what happens to a membrane between 20 and 70 degrees using knowledge of the structure and properties of a bilayer?

Answer 38

- at 20 the membrane is impermeable so stability is high - as temp increases, kinetic energy increases and the membrane becomes more fluid and lets more liquid out - at 70 the membrane is disrupted and very permeable - all this is due to the structure of phospholipids - hydrophilic phosphate heads facing outwards and hydrophobic fatty acid tails facing inwards - the bilayer is a barrier to water