diffusion

Question 1

what are the two types of diffusion

Answer 1

-simple diffusion
-facilitated diffusion

Question 2

definition for diffusion

Answer 2

-the net movement of particles from a region of higher concentration to region of lower concentration

net movement of particles down a concentration gradient

Question 3

describe why diffusion is a passive transportation process

Answer 3

diffusion moves molecules/ions down a concentration gradient

-diffusion does not require a metabolic source of energy such as ATP to transport molecules across the membrane

it instead relies on the energy from the natural, random movement of particles

Question 4

explain why simple diffusion occurs and when it stops

Answer 4

-the particles of gas/liquid have kinetic energy
-their movement is random
-This creates an unequal distribution of particles between two areas
-This establishes a concentration gradient as substances diffuse from a region of higher concentration to a region of lower concentration

-Diffusion stops when an equilibrium is established, meaning that there is an equal distribution of particles between the two areas

Question 5

what does an equilibrium being reached mean in terms of the movement of particles

Answer 5

particles are still constantly moving, however they now move equally in both directions

Question 6

what factors affect the rate of diffusion

Answer 6

-steepness of concentration gradient
-surface area
-thickness of membrane
-temperature
-properties of molecules

Question 7

what is the rate of uptake dependent on for simple diffusion

Answer 7

• the concentration

Question 8

explain what is meant by the steepness of the concentration gradient

Answer 8

-firstly concentration gradient means the difference in the concentration of a substance between the two areas

-steepness-refers to the degree of a difference, the larger the difference between concentrations ,the steeper the concentration gradient

Question 9

how does the steepness of the concentration gradient affect the rate of diffusion.
Explain your answer

Answer 9

The bigger the difference in the concentration of a substance , between the two areas ,the higher the rate of diffusion will be.

This is because the overall movement of particles from a region of higher concentration to a region of lower concentration will be larger.

Question 10

explain how temperature effects the rate of diffusion

Answer 10

-as temperature increases, molecules have more kinetic energy thus move faster, this results in higher rate of diffusion

Question 11

how does the thickness of a membrane affect the rate of diffusion. Explain

Answer 11

-the thicker the membrane, the longer the diffusion distance will be ,meaning that particles will collide more ,decreasing the rate of diffusion

Question 12

describe how the surface area has an affect on the rate of diffusion

Answer 12

-the larger the surface area, the higher the number of molecules that can diffuse through at once, increasing the rate of dission

Question 13

how can we increase the surface area

Answer 13

-the folding of a membrane increases the SA.

-like cristae in mitochondria

Question 14

how does the SA:V ratio affect the rate of diffusion

Answer 14

-as the size of a cell increase, its SA:V ratio decreases.

This increases the diffusion distance of molecules and thus slows down the rate of diffusion

Question 15

why is the rate of diffusion faster over short distances and slower over long distances

Answer 15

-particles move at high speed and are constantly colliding

-over short distances particles collide less thus rate of diffusion is faster

-over longer distances ,particles collide more thus the rate of diffusion is slower

Question 16

what type of molecules are transported by facilitated diffusion and what by simple diffusion

Answer 16

-small, non-polar molecules such as oxygen are transported down a concentration gradient and across the membrane by simple diffusion

-larger and polar molecules like glucose are transported down a concentration gradient and across the membrane using carrier/channel proteins via facilitated diffusion

Question 17

definition of facilitated diffusion

Answer 17

diffusion across a membrane using channel/carrier proteins

Question 18

what are the two types of proteins involved in facilitated diffusion

Answer 18

-carrier proteins
-channel proteins

Question 19

why are channel ad carrier proteins said to be specific

Answer 19

they are specific to and thus only transport one type of ion/molecule

Question 20

difference between channel and carrier proteins

Answer 20

channel proteins do not change shape to transport substances across the membrane, whereas carrier proteins do

Question 21

how do channel proteins control the exchange of charged/polar molecules

Answer 21

-they are ‘‘gated’’, meaning that a part of them moves to open and close the pore as the substance is being transported across the membrane

Question 22

how do carrier proteins transport a polar molecule across the membrane

Answer 22

-the binding site of the carrier protein opens
-a molecules attaches to the binding site of the carrier protein which is embedded within the membrane

-this causes the carrier protein to change shape and release the molecule on the opposite end of the membrane

-the molecules are moved down a concentration gradient

Question 23

is facilitated diffusion passive

Answer 23

yes

Question 24

what other factors also affects the rate of facilitated diffusion

Answer 24

-the number of carrier/channel protein embedded in the cell membrane,

the higher the number of carrier/channel protein, the more molecules can be transported across at once, thus increasing the rate of diffusion

Question 25

when does facilitated diffusion stop?

Answer 25

when the carrier/channel protein become saturated

Question 26

describe a practical used to investigate the effect SA:V ratio has on the rate of diffusion

Answer 26

-cut the agar into required dimension, decresing the SA:V ratio with each agar cube
-the cubes contain an indicator which makes them pink
-place each agar cube into a test tube,containing equal volume of sodium hydroxide
-allow them to sit for 10 minutes
-Within that time the sodium hydroxide will diffuse into the agar cube turning the indicator colourless
-Remove the agar cubes
-Measure the distances travelled by the sodium hydroxide using a ruler

-Calculate the rate of diffusion

Question 27

what are the two formulas for calculating the rate of diffusion

Answer 27

-distance travelled/time

-volume filled/time

Question 28

which is affected by surface area and which is not

Answer 28

the volume filled is affected by the surface area, whereas the distance travelled is not

Question 29

What should the results of the investigation be

Answer 29

-we should find that with the increase of size of the agar cube and thus decrease of the SA:V ratio ,the rate of diffusion will decrease

Question 30

describe how to investigate what substances can diffuse across partially permeable membrane

Answer 30

-use something known as dialysis tubing-its used as a substitute membrane
-fill a section of the dialysis tubing with a mixture of glucose and a mixture of starch solution
-dialysis tubing has pores which prevent the passage of large molecules like starch and allow smaller molecules like glucose to diffuse across
-suspend the tubing in a beaker of water and place a lid on top so it doesn’t evaporate

-test the water outside the dialysis tubing for starch and glucose ,using a benedict test for glucose ad iodine test for starch

Results should indicate that only glucose has diffused across

Question 31

describe how you would use dialysis tubing to investigate how temperature affects the rate of diffusion

Answer 31

-use dialysis tubing, fill it with a set concentration of glucose solution
- submerge in a beaker with a set volume of water
-put the beaker in water bath set at different temperatures, e .g 20,30,40,50

-allow the beaker to sit in the water bath for the same amount of time, enough for the glucose to diffuse across and into the water

-remove the dialysis tubing from the beaker

-carry out a benedict test on the remaining solution, the bigger the colour change, the higher the concentration of glucose present and thus the faster the rate of diffusion

Question 32

how to investigate how concentration affects the rate of diffusion

Answer 32

use dialysis tubing, fill it with a set concentration of glucose solution

-fill each dialysis tube with an increasing concentration of glucose

-can create standard solutions of known concentration of glucose by carrying out serial dilutions of an existing stock solution

• submerge in a beaker with a set volume of water ,set at the same temperature each time

-allow the beaker to sit in the water bath for the same amount of time, enough for the glucose to diffuse across and into the water

-remove the dialysis tubing from the beaker

-carry out a benedict test on the remaining solution, the bigger the colour change, the higher the concentration of glucose present and thus the faster the rate of diffusion

Question 33

explain why oxygen and carbon dioxide can move freely through cell membrane via simple diffusion

Answer 33

-small and non-polar meaning that they can easily diffuse through the spaces between the phospholipids

-water molecules can diffuse across the cell membrane despite being polar as they are small enough to fit between the phospholipids

Question 34

describe relationship between concentration and rate of diffusion

Answer 34

as a concentration of a substance increases,the rate of diffusion also increases

,this is because the concentration gradient is higher/increased

Question 35

describe how astudent can carry out an experiment investigating how concentration gradient affects the rate of diffusion in model cells

Answer 35

-can prepare equal sized agar cubes ,each containing a ph indicator

-then prepare test tubes with an increasing concentration of sodium hydroxide

-submurge the agar cubes into the test tubes and time how long it takes for the the agar cube to turn colourless

-the faster it turns colourless the higher the rate of diffusion

Question 36

which is the dependent and independent variable in the experiment

Answer 36

the dependent variable is the time taken for the agar cube to turn colourless,

the independent variable is the concentration of sodium hydroxide

Question 37

how can the student make the results precise

Answer 37

can carry out 3 repeats at each concentration and calculate a mean time taken for the cube to turn colourless