chapter 5 - membranes

Question 1

roles of cell surface membrane

Answer 1

• selectively permeable barrier
• cell signalling
• cell recognition
• cell to cell adhesion to form tissues

Question 2

roles of membranes inside cells

Answer 2

• compartmentalisation
• sites of chemical reactions
• provide an internal transport system
• controls the movement of substances into/out of organelles

Question 3

functions of phospholipids in membranes

Answer 3

• gives the membrane fluidity
• barrier to large water soluble molecules and ions (polar molecules)
• allowes lipid soluble (hydrophobic/non-polar) molecules to pass through
• unsaturated fatty acid tails have kinks in them which prevents close packing allowing movement of phospholipids within the bilayer, making the membrane more fluid and permeable

Question 4

function of proteins in membranes

Answer 4

• structural support
• transport (channel proteins, carrier proteins)
• receptors for hormones (have specific shapes)

Question 5

function of cholesterol in membranes

Answer 5

• fits between the phospholipids
• regulates the fluiditiy of membranes
• reduces lateral movement of phospholipids, giving the membrane stability and flexibility

Question 6

function of glycocalyx in membranes

Answer 6

• receptor sites for hormones/neurotransmitters
• act as antigens, allowing cells to recognise “self”
• help cells adhere to one another, forming tissues

Question 7

effect of temperature on membranes

Answer 7

increase in temperature means an increase in kinetic energy, phospholipids vibrate causing them to become further apart; the bigger gaps allow larger molecules to pass through; the phospholipid bilayer is therefore more permeable

Question 8

effect of organic solvents on membranes

Answer 8

ethanol dissolves the lipids in the cell membrane which means the membrane loses its structure; increasing the concentration will increase permeability of membranes. very strong alcohol solutions will destroy cells

Question 9

diffusion

Answer 9

the net movement of molecules or ions from a region of their higher concentration to a region of their lower concentration (down a concentration gradient)

Question 10

affect of temperature on rate of diffusion

Answer 10

higher temperatures give molecules or ions more kinetic energy so rate of diffusion is faster

Question 11

affect of surface area on rate of diffusion

Answer 11

the greater the surface area the more molecules or ions that can cross the membrane so diffusion is faster

Question 12

affect of concentration gradient on rate of diffusion

Answer 12

the steeper the concentration gradient the quicker the rate of diffusion

Question 13

affect of stirring/moving on rate of diffusion

Answer 13

stirring/moving gives molecules or ions more kinetic energy which increases the rate of diffusion

Question 14

affect of distance on rate of diffusion

Answer 14

the shorter the distance, the faster the rate of diffusion

Question 15

affect of type of molecule or ion on rate of diffusion

Answer 15

larger molecules need more energy to move so they tend to diffuse more slowly. non-polar molecules diffuse more quickly because they can dissolve in the phospholipid bilayer

Question 16

simple diffusion

Answer 16

the net movement of molecules directly through the phospholipid bilayer between phosholipids down the concentration gradient eg small molecules (CO2, H2O) and non-polar molecules (steroids, fat-soluble vitamins)

Question 17

facilitated diffusion

Answer 17

passive movement of molecules or ions through a channel or carrier protein from a higher to a lower concentration

Question 18

channel proteins

Answer 18

channel proteins are specific for certain ions eg sodium ion channels; ions are charged and therefore need transport proteins

Question 19

carrier proteins

Answer 19

carrier proteins are for specific larger polar molecules like glucose and amino acids, when the specific molecule binds to the protein, it changed shape and allows the molecule across the membrane

Question 20

osmosis

Answer 20

the net movement of water from a region of higher water potential to a region of lower water potential across a partially permeable membrane

Question 21

water potential (ψ)

Answer 21

the tendancy of water molecules to leave a solution

Question 22

when would osmosis stop?

Answer 22

when water potential is equal or there is a physical barrier like a cell wall

Question 23

cell placed in low water potential (concentrated sugar solution)

Answer 23

water moves from a higher water potential inside the cell to a lower water potential outside the cell by osmosis through the partially permeable cell surface membrane

Question 24

cells placed in high water potential (pure water)

Answer 24

water moves from a higher water potential outside the cell to a lower water potential inside the cell by osmosis through the partially permeable cell surface membrane

Question 25

affect of low water potential on animal cells

Answer 25

- reduction in cell volume - cell becomes crenated - cells in tissue pull away from other cells - cytoplasm becomes concentrated - enzymes require aqueous conditions so cells may die

Question 26

affect of high water potential on animal cells

Answer 26

- pressure inside cell increases - plasma membrane fragile and cannot withstand pressure - no cell wall to prevent bursting and lysis occurs

Question 27

lysis

Answer 27

cell bursting

Question 28

affect of low water potential on plant cells

Answer 28

- volume of cytoplasm and vacuole decreases - cell is flaccid - plasma membrane eventually pulls away from cell wall in places - cell is plasmolysed - cell can die if membrane rips

Question 29

affect of high water potential on plant cells

Answer 29

- volume of cytoplasm and vacuole increases - contents push out on cell walls - wall pushes back on contents - cell is turgid

Question 30

active transport

Answer 30

the movement of molecules or ions through carrier proteins across membranes, against their concentration gradient, using energy from ATP

Question 31

affect of oxygen concentration on active transport

Answer 31

oxygen is required for aerobic respiration which results in more ATP so more active transport

Question 32

affect of glucose concentration on active transport

Answer 32

glucose is a substrate for respiration and will provide ATP so more active transport

Question 33

affect of temperature on active transport

Answer 33

increase in temperature will increase enzyme activity in aerobic respiration for more ATP too high a temperature will denature proteins preventing active transport

Question 34

affect of number of carrier proteins on active transport

Answer 34

more carrier proteins means more molecules can move at the same time so more active transport

Question 35

bulk transport

Answer 35

large molecules that are too large to move through carrier proteins or channel proteins enter or leave cells with the use of vesicles. this is an active process

Question 36

endocytosis

Answer 36

the cell surface membrane folds around the substance to engulf it the membrane pinches off to form a vesicle

Question 37

exocytosis

Answer 37

the vesicle fuses with the cell surface membrane the vesicle membrane becomes part of the cell surface membrane the contents of the vesicle are released outside the cell

Question 38

cell signalling

Answer 38

communication between cells using chemicals, triggering a response inside cells