diffusion Flashcards
what are the two types of diffusion
-simple diffusion
-facilitated diffusion
definition for diffusion
-the net movement of particles from a region of higher concentration to region of lower concentration
net movement of particles down a concentration gradient
describe why diffusion is a passive transportation process
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
explain why simple diffusion occurs and when it stops
-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
what does an equilibrium being reached mean in terms of the movement of particles
particles are still constantly moving, however they now move equally in both directions
what factors affect the rate of diffusion
-steepness of concentration gradient
-surface area
-thickness of membrane
-temperature
-properties of molecules
what is the rate of uptake dependent on for simple diffusion
- the concentration
explain what is meant by the steepness of the concentration gradient
-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
how does the steepness of the concentration gradient affect the rate of diffusion.
Explain your answer
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.
explain how temperature effects the rate of diffusion
-as temperature increases, molecules have more kinetic energy thus move faster, this results in higher rate of diffusion
how does the thickness of a membrane affect the rate of diffusion. Explain
-the thicker the membrane, the longer the diffusion distance will be ,meaning that particles will collide more ,decreasing the rate of diffusion
describe how the surface area has an affect on the rate of diffusion
-the larger the surface area, the higher the number of molecules that can diffuse through at once, increasing the rate of dission
how can we increase the surface area
-the folding of a membrane increases the SA.
-like cristae in mitochondria
how does the SA:V ratio affect the rate of diffusion
-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
why is the rate of diffusion faster over short distances and slower over long distances
-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
what type of molecules are transported by facilitated diffusion and what by simple diffusion
-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
definition of facilitated diffusion
diffusion across a membrane using channel/carrier proteins
what are the two types of proteins involved in facilitated diffusion
-carrier proteins
-channel proteins
why are channel ad carrier proteins said to be specific
they are specific to and thus only transport one type of ion/molecule
difference between channel and carrier proteins
channel proteins do not change shape to transport substances across the membrane, whereas carrier proteins do
how do channel proteins control the exchange of charged/polar molecules
-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
how do carrier proteins transport a polar molecule across the membrane
-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
is facilitated diffusion passive
yes
what other factors also affects the rate of facilitated diffusion
-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
when does facilitated diffusion stop?
when the carrier/channel protein become saturated
describe a practical used to investigate the effect SA:V ratio has on the rate of diffusion
-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
what are the two formulas for calculating the rate of diffusion
-distance travelled/time
-volume filled/time
which is affected by surface area and which is not
the volume filled is affected by the surface area, whereas the distance travelled is not
What should the results of the investigation be
-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
describe how to investigate what substances can diffuse across partially permeable membrane
-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
describe how you would use dialysis tubing to investigate how temperature affects the rate of diffusion
-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
how to investigate how concentration affects the rate of diffusion
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
explain why oxygen and carbon dioxide can move freely through cell membrane via simple diffusion
-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
describe relationship between concentration and rate of diffusion
as a concentration of a substance increases,the rate of diffusion also increases
,this is because the concentration gradient is higher/increased
describe how astudent can carry out an experiment investigating how concentration gradient affects the rate of diffusion in model cells
-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
which is the dependent and independent variable in the experiment
the dependent variable is the time taken for the agar cube to turn colourless,
the independent variable is the concentration of sodium hydroxide
how can the student make the results precise
can carry out 3 repeats at each concentration and calculate a mean time taken for the cube to turn colourless
