Cell Membranes

Front 1

why is it important that the cell membrane is partially permeable

Back 1

they let the molecules that they need through and not the ones that may damage the cell

Front 2

name three ways in which substances can move across cell - surface membranes

Back 2

diffusion

osmosis

active transport

Front 3

what does partially permeable mean

Back 3

they let some molecules through but not others

Front 4

what are cell membranes and where are they found

Back 4

they are boundaries around a cell or some organelles in eukaryotic cells

Front 5

what do membranes around organelles do

Back 5

act as a barrier between the organelle and cytoplasm

Front 6

what is a cell membrane composed of

Back 6

(phospo) lipids, proteins, and carbohydrates

Front 7

what are the carbohydrates attached to

Back 7

proteins or lipids

Front 8

what year was the fluid mosaic model suggested

Back 8

1972

Front 9

why was the fluid mosaic model created

Back 9

to describe the arrangement of molecules in the membrane as it is very small to see

Front 10

describe the model

Back 10

phospholipid molecules form a continuous (doublle/) bilayer

it is 'fluid' because the phospholipids are always moving

proteins are scattered throughout like tiles in a mosaic

Front 11

what do channel proteins control

Back 11

the movement of charged particles through a membrane

Front 12

what do carrier proteins controll

Back 12

the movement of large particles through a membrane

Front 13

what do receptor proteins do and where are they found

Back 13

on the cell surface membrane

allow the cell to detect chemicals released from other cells

then signals the cell to respond in some way

Front 14

give an example of how a receptor protein would work

Back 14

the hormone insulin binds to the receptor protein on liver cells

it then tells the cell to absorb glucose

Front 15

protein + carbohydrate

Back 15

glycoproteins

Front 16

lipid + carbohydrate

Back 16

glycolipid

Front 17

what is the purpose of cholesterol in the bilayer

Back 17

gives the membrane stability

binds to hydrophobic tails of phospholipids, causing them to pack more closely together

making membrane less fluid and more rigid

Front 18

what creates a further barrier to polar substances moving through the membrane

Back 18

cholesterol

Front 19

what types of cells do cholesterol help maintain the shape of

Back 19

animal cells

Front 20

what is a solvent

Back 20

something that dissolves a substance (solute) in it

Front 21

what is a solute

Back 21

something that dissolves in a solvent

Front 22

3 factors affecting the rate of diffusion

Back 22

concentration gradient

thickness of exchange surface

surface area

Front 23

how does concentration gradient affect the rate of diffusion

Back 23

the higher it is the faster the rate

as diffusion takes place the difference in concentration between the two sides of the membrane decrease until it reaches equilibrium

Front 24

how does the thickness of the exchange surface affect the rate of diffusion

Back 24

the thinner the exchange surface the faster the rate

ie the shorter the distance the particles have to travel

Front 25

what is facilitated diffusion

Back 25

a type of diffusion that uses carrier and channel proteins to facilitate charged or larger molecules

Front 26

is facilitated diffusion passive or active and what does this mean

Back 26

it is a passive process

so it does not require energy to work

Front 27

how do carrier proteins work

Back 27

a large molecule attaches to the protein

the protein changes shape

this releases the molecule on the opposite side of the membrane

Front 28

how do channel proteins work

Back 28

form pores in the membrane for charged articles to diffuse through

different channel proteins facilitate the diffusion of different charged particles

Front 29

2 factors affecting the rate of facilitated diffusion

Back 29

concentration gradient

the number of channel or carrier proteins

Front 30

how does the number of channel or carrier proteins affect the rate of facilitated diffusion

Back 30

the more there are, the faster the rate

once all the proteins in a membrane are in use, the diffusion cannot happen any faster.

Front 31

how do you calculate the rate of diffustion

Back 31

gradient = change in y / change in x

Front 32

of the line on the graph is curved what do you have to draw

Back 32

a tangent

Front 33

what is osmosis

Back 33

the diffusion of water molecules across a partially permeable membrane

from an area of high water potential to an area of low water potential

Front 34

define water potential

Back 34

the likelihood of water molecules to diffuse out of or into a solution

Front 35

what is the water potential of pure water

Back 35

0 kPa

Front 36

what does adding solutes to pure water do to the water potential do

Back 36

it lowers it

becoming -ve

Front 37

isotonic

Back 37

water potential is the same between solutions

Front 38

hypertonic

Back 38

solutions with a higher water potential than the cell

Front 39

hypotonic

Back 39

solutions with a lower water potential than the cell

Front 40

3 factors affecting the rate of osmosis

Back 40

water potential

thickness of exchange surface

surface area

Front 41

how does water potential affect the rate of osmosis

Back 41

the higher the water potential the faster the rate

Front 42

what is a co-transporter

Back 42

a type of carrier protein

used in active transport

requires energy

Front 43

what type of movement occurs in (facilitated&) diffusion

Back 43

a net, over all, movement