the cell membrane & transport through the cell membrane

Question 1

why is the cell membrane called a fluid-mosaic model?

Answer 1

mixture + movement of phospholipids, proteins, glycoproteins & glycolipids

Question 2

how do the molecules in a membrane affect its permeability?

Answer 2

1. phospholipid bilayer allows diffusion of non-polar/ lipid-soluble substances
2. membrane proteins allow polar/H2O-soluble substances to pass through bilayer (otherwise cant pass through)
3. carrier proteins allow active transport
4. channel/carrier proteins allow facilitated diffusion
5. shapes of channels & proteins determine which molecules can pass through
6. cholesterol affects fluidity & ,therefore, permeability of a membrane

Question 3

phospholipids

Answer 3

• head has +ve charge bc of phosphate group –> hydrophilic
• fatty acid tail is uncharged –> hydrophobic
• align as bilayer

Question 4

function of cholesterols in the bilayer

Answer 4

• restricts lateral movement of other molecules in membrane
• makes membrane less fluid at high temps

Question 5

types of intrinsic proteins

Answer 5

• carrier proteins
• protein channels

Question 6

function of carrier proteins in the bilayer

Answer 6

• binds to a molecule & changes shape to export it
• used in facilitated diffusion & active transport (passive process during fac. diffusion but active process during active transport)

Question 7

function of protein channels in the bilayer

Answer 7

• form tubes that fill with water, allowing polar, H2O- soluble substances to diffuse across
• used in facilitated diffusion

Question 8

function of extrinsic proteins in the bilayer

Answer 8

• provide mechanical support
• can connect to proteins/lipids, forming glycoproteins/glycolipids –> act as receptors during cell recognition

Question 9

simple diffusion
(type of transport)

Answer 9

= net movement of small, non-polar molecules down a conc. gradient until dynamic equilibrium is reached
> passive

Question 10

Fick’s Law

Answer 10

rate of diffusion proportional to (S.A x conc. gradient)/thickness of exchange surface

Question 11

facilitated diffusion
(type of transport)

Answer 11

= net movement of molecules down conc. gradient through carrier proteins/protein channels
>passive (doesn’t req. ATP)

Question 12

osmosis
(type of transport)

Answer 12

= net movement of H2O molecules down water potential gradient through partially permeable membrane
> passive

Question 13

define ‘water potential’

Answer 13

= the pressure (KPa) created by H2O molecules & the ability of the sol. to give out H2O
–> w.p doesn’t go above 0
–> higher -ve no. = lower w.p

Question 14

define ‘hypertonic solution’

HIGHpertonic solution ;)

Answer 14

= solution w higher water potential than cell
–> water moves out solution, into cell
* animal cells –> shrivelled
* plant cells –> plasmolysed

Question 15

define ‘isotonic solution’

Answer 15

= solution with same water potential as cell
* animal cells –> remain same
* plant cells –> flaccid

Question 16

define ‘hypotonic solution’

hypOtonic solution

Answer 16

= solution with lower water potential than cell
–> water moves into solution, out of cell
* animal cells –> lysed (burst)
* plant cells –> turgid

Question 17

active transport
(type of transport)

Answer 17

= movement of molecules against a conc. gradient via a carrier protein using ATP

active process obviously

Question 18

process of active transport

Answer 18

1. certain molecules bind to receptor site on carrier proteins
2. ATP binds to the carrier protein on inner membrane –> hydrolysed into ADP + Pi
3. causes protein to change shape, opening towards inner membrane
4. molecules released –> protein reverts to og. shape

Question 19

nowhere near as complicated as u think lol, use ur brain

co - transport
(type of transport)

Answer 19

• done via symport proteins
• eg. sodium - potassium pump
  1. Na+ moves out cell –> generates conc. gradient for Na+ from ileum into cell
  2. Na+ moves into cell via facilitated diffusion, co-transporting glucose w it

Question 20

name every type of transport

decribe how substances can cross a cell-surface membrane (5)

Answer 20

1. simple diffusion down conc. gradient
2. non-polar molecules pass via phospholipid bilayer but polar molecules go through proteins
3. water moves by osmosis down water potential gradient
4. active transport = movement of molecules against a conc. gradient via carrier proteins
5. at req. ATP
6. ref. to Na+/glucose transport

Question 21

explain 3 features you would find in a cell specialised for absorption

Answer 21

1. folded membrane/microvilli –> larger S.A for absorption
2. large no. of mitochondria –> relaeases more energy for active transport
3. large no. of carrier proteins –> for active transport

Question 22

describe two ways in which simple and facilitated diffusion are similar

Answer 22

1. both passive
2. down conc. gradient

Question 23

give one way to ensure the temp remains constant in an exp.

Answer 23

use a thermometer to measure the water bath at specific time intervals

Question 24

independant variable in osmosis req. prac

Answer 24

concentration of sugar solution

Question 25

how to find water potential from values found from exp.

Answer 25

1. plot calibration curve
2. interpolate from ratio of 1
3. change conc. into w.p