diffusion

Question 1

why do cells need to receive raw material

Answer 1

for the biochemical reactions and processes that go on in cells to sustain life

Question 2

what do cells make when they respire

Answer 2

ATP

Question 3

what does ATP provide

Answer 3

cellular energy to drive biochemical reactions

Question 4

what do cells need to respire

Answer 4

they need oxygen and glucose and need to remove the toxic metabolic ewaste products such as carbon dioxide.

Question 5

what else do cells need to do apart from respiring

Answer 5

to export some of the molecules they make, such as enzymes, hormones or other signalling molecules

Question 6

what does active and passive transport refer to

Answer 6

the exchange of substances between cells and their environment, or between membrane bound compartments within cells and the cell cytosol

Question 7

what does all movement require

Answer 7

energy usually in the form of ATP

Question 8

what does passive movement utilise

Answer 8

passive transport utilises energy from the natural motion of particles rather than the energy from another source. they do not use ATP

Question 9

what is diffusion

Answer 9

the net movement of particles (atoms, molecules or ions) from a region of high concentration to a region of low concentration

Question 10

what kind of process is diffusion

Answer 10

a passive process

Question 11

at what point does diffusion continue to occur

Answer 11

until there is a concentration equilibrium between the two areas

Question 12

why does diffusion happen

Answer 12

the particles in a gas or liquid have kinetic energy. this movement is random and an unequal distribution of particles eventually becomes an equal distribution.

Question 13

what does equilibrium actually mean

Answer 13

it doesnt mean the particles stop moving, the movement is just equal in both directions

Question 14

why is diffusion fast over short distances

Answer 14

particles move at high speeds which are constantly colliding which slows down their overall movement. so diffusion is faster when the pathway is shorter. as diffusion distance increases, the rate of diffusion slows down because more collisions take place

Question 15

what is a concentration gradient

Answer 15

a difference in concentration. it goes from high to a low concentration

Question 16

where does diffusion take place along the concentration gradient

Answer 16

DOWN the concentration gradient

Question 17

what acts as a barrier in the membrane

Answer 17

the non polar, hydrophobic tails of phospholipid molecules.

Question 18

if a molecule is small and less polar what does this mean

Answer 18

it will diffuse across the membrane easier and faster

Question 19

when does simple diffusion take place

Answer 19

for small non polar molecules.

Question 20

what types of molecules can easily pass through the lipid bilayer

Answer 20

small non polar molecules in a high concentration on one side of the membrane can easily pass through the bilayer. lipid soluble molecules and very small molecules can diffuse directly through the bilayer

Question 21

give examples of molecules can pass through cell membranes in simple diffusion

Answer 21

oxygen and carbon dioxide

Question 22

how do fat soluble molecules such as steroid hormones diffuse through cell membrane

Answer 22

even if they are larger, they diffuse through cell membranes as they dissolve in the lipid bilayer. they still move down their concentration gradient.

Question 23

is water soluble or insoluble in lipids

Answer 23

insoluble because they are polar

Question 24

what is the name of the specific water channel protein

Answer 24

aquaporins

Question 25

what is the role of aquaporins

Answer 25

in membranes where a very high rate of water movements are required aquaporins allow water molecules to cross the membrane

Question 26

which molecules diffuse freely down the concentration gradient

Answer 26

non polar molecules

Question 27

what does the hydrophobic interior of the membrane do

Answer 27

repels substance with a positive or negative charge so they can't easily pass through.

Question 28

how fast do polar molecules diffuse through

Answer 28

polar molecules with a slightly negative or slightly positive charge diffuse through at a slow rate

Question 29

which size molecules diffuse through faster

Answer 29

smaller molecules diffuse faster than larger molecules

Question 30

how is the concentration gradient maintained

Answer 30

molecules entering cells pass into organelles and then used for metabolic reactions. this maintains the concentration gradient and keeps more of the molecules entering the cell.

Question 31

give examples of how the concentration gradient is maintained

Answer 31

oxygen diffusing into the cytoplasm of respiring cells then diffuse into mitochondria and used for aerobic respiration carbon dioxide diffusing into the palisade mesophyll cells of a plant leaf will then diffuse into chloroplasts and used for photosynthesis

Question 32

how is the rate of simple diffusion affecting

Answer 32

simple diffusion relies on the molecules own kinetic energy. so factors altering the kinetic energy will affect the rate of diffusion

Question 33

how does temperature affect the rate of diffusion

Answer 33

if temperature increases, molecules have more kinetic energy so rate of diffusion increases. as they lose heat, diffusion slows down

Question 34

how does the distance of diffusion affect the rate of diffusion

Answer 34

the thicker the membrane across which molecules diffuse, the slower the rate of diffusion

Question 35

how does surface area affect the rate of diffusion

Answer 35

more diffusion takes place across a larger surface area. cells specialised for absorption have extensions have microvilli which increase surface area

Question 36

how does the size of the diffusing molecules affect the rate of diffusion

Answer 36

smaller ions or molecules diffuse more rapidly than large molecules

Question 37

how does the concentration gradient affect the rate of diffusion

Answer 37

the steeper the gradient, the faster the diffusion down the gradient.

Question 38

what is the phospholipid bilayer a barrier to

Answer 38

polar molecules and ions

Question 39

what do membranes contain that allow polar substances to pass through

Answer 39

channel proteins

Question 40

what is facilitated diffusion

Answer 40

diffusion across a membrane which uses channel proteins

Question 41

how do small ions diffuse through facillitated diffusion

Answer 41

through channel proteins embedded within the cell membrane. some of these open or close in response to a specific messenger or a change in voltage across the membrane

Question 42

what is special about membranes with protein channels

Answer 42

they are selectively permeable as most protein channels are specific to one molecule or ion.

Question 43

what else can facilitated diffusion involve

Answer 43

carrier proteins

Question 44

what is special about carrier proteins

Answer 44

they can change shape when a specific molecule binds

Question 45

what is similar about simple and facilitated diffusion

Answer 45

they both occur down the concentration gradient

Question 46

what does the rate of facilitated diffusion depend on

Answer 46

temperature, concentration gradient, membrane surface area and thickness but also affected by the number of channel proteins present

Question 47

how does the number of channel proteins affect facilitated diffusion

Answer 47

the more protein channels, the higher the rate of diffusion

Question 48

what do cholesterol molecules within the membrane do

Answer 48

they reduce the permeability of the membranes to small water-soluble molecules.

Question 49

how do glucose molecules pass through the membrane

Answer 49

glucose molecules are too large to diffuse through the water filled protein channel in a membrane but they can bind to a transmembrane carrier protein which then opens to allow the glucose to pass out on the other side of the membrane

Question 50

how are cells able to control the types of molecules that pass in or out

Answer 50

different cell types have membranes with differing proportions of transmembrane protein channels and carrier proteins.

Question 51

describe the mechanism of diffusion for lipid soluble molecules

Answer 51

- lipid soluble molecules diffuse through the plasma membrane from a region of high concentration outside the cell to a region of low concentration in the cytoplasm until they reach equilibrium

Question 52

describe the mechanism of diffusion for lipid insoluble solutes

Answer 52

- lipid insoluble solutes (such as sugars or amino acids) can't diffuse freely through the lipid bilayer due to their size or polarity. the carrier molecule binds with a molecule, such as glucose on the outside of the cell membrane. the carrier molecules changes shape and releases the molecule on the inside of the cell membrane

Question 53

describe the mechanism for diffusion for small lipid insoluble molecules

Answer 53

they travel through channel proteins. these open or close in response to a specific messenger. these are gated channel proteins

Question 54

describe the mechanism of diffusion for the transport of water

Answer 54

through aquaporins which are channel proteins. they travel by diffusion or osmosis.

Question 55

how does diffusion occur in neurones

Answer 55

neurone plasma membranes have many channels specific to either sodium or potassium ions. the diffusion of these ions into and out of the neurone axon is crucial for the conduction of nerve impulses. at synapses, there are also calcium ion channels and chloride ion channels.

Question 56

how does diffusion occur in epithelial cells

Answer 56

the plasma membranes of epithelial cells that line your airways have chloride ion channels and these play a crucial role in regulating the composition of mucus to trap pathogens and particles.

Question 57

how is the rate of diffusion calculated

Answer 57

using Ficks law surface area x difference in concentration/length of diffusion path (membrane thickness)