Effect of SA on diffusion of Beetroot Membranes
AIM
Beetroot cells contain a red pigment, which is stored in the cell vacuole and a vacuole membrane
to prevent this leaking out of the cell surrounds it. The outer of the cell is also surrounded by a
membrane, which again helps contain the pigment inside the cell. In this experiment I aim to find
out the relationship between the leakage of red pigment from a beetroot cell and the surface area.
To do this successfully I will need to alter the surface area of the beetroot cells accurately and
then measure if any and how much dye is let out. I can hopefully then look at my results and then
find a relationship between the two factors and be able to explain exactly why any changes took
place.
PREDICTION
For this experiment I would expect the leakage of dye to increase as the surface area increases
and this is based on the knowledge of the formation of membranes. Membranes are made of two
main types of chemical, lipids and proteins. The main type of membrane is known as a
phospholipid membrane. The purpose of partially permeable membranes is to selectively allow
the passage of materials in and out of the cell. Substances pass through via diffusion, osmosis or
active transport.
As surface area increases the rate of reaction which in turn would cause an increase in the rate of
diffusion causing more dye to be given out. This is due to the fact that more particles of
membrane in contact with the substance allowing more passage out of the cell and an increased
rate of this.
I would expect the rate to level off after a certain point and this would be the top amount of dye
leakage that could be achieved by any change to surface area. The graph of the results would
look like this: OUTLINE
To carry out this experiment I could perform it in several different manners, however all will
have to follow out the first basic step: ·Cut out several discs of beetroot of varying surface area. Treat all discs by washing with water
so that any excess dye that will be leaked out due to damage caused by the knife will not affect
the results.
Once this has been completed then the methods in which I perform the procedure can vary and I
could either: -
·I could cut two pieces of beetroot of different surface area and see how much the results of the
leakage varies between these two to find out exactly how many different surface areas I should
test in this experiment.
·I could leave two separate samples of beetroot of the same surface area in water for different
length periods e.g. 10 and 20 minutes and see which length shows the highest level of dye
leakage and this will be the length I will leave my samples in the water in the actual experiment.
·I could also test to see if the leakage of dye worked better in different temperature, e.g if at
lower temperatures no dye leaked out I could use higher temperatures from then on. However I
am unsure if this will be an applicable method as above 40C the membrane becomes damaged.
The method I have decided to use is the first one described, as this will give the most accurate
results.
VARIABLES
There are several variables involved in this experiment and these can either be altered by myself
or be measured as a result of the experiment. The variables, which will be altered, are known as
independent variables. The variables, which will be measure, are known as dependant variables.
In this experiment the independent variable is the surface area, which will be changed. The
dependant variable is the leakage of dye, which will be measured to find a relationship between
the two.
There are also other variables in this experiment, which will need to be controlled to prevent it
becoming an unfair test, these are: Temperature - Due to the fact that membranes are made of proteins, temperature is a very
important factor. At temperatures above approximately 50°C proteins begin to get destroyed; this
would therefore increase the permeability of both the cell wall and the vacuole wall. This would
make it impossible for us to distinguish as to whether it was the change in surface area or the
temperature that caused any change in dye leakage.
For this reason the water used will be at room temperature (23° approx) and will be performed
on the same day to allow no margin for any discrepancies.
Time - Time is an important factor. When leaving the beetroot in the test tubes it must be
ensured that they are in the water for exactly 20 minutes each. This will make sure that the same
period of time is given for dye leakage to occur. To control this, putting the beetroot into each
test tube two minutes apart will give enough time for them to be removed before the next test
tube is ready to have its contents removed.
pH - pH can affect the structure of a membrane and therefore cause it to be unable to function
efficiently. The pH's, which cause this affect, would be those that are acid or alkaline. Therefore
we must use water as our substance as it has a pH 7 and this is neutral and will have no affect on
the leakage of pigment.
APPARARATUS
·Safety goggles
·Cutting mat
·Test tube holder
·5 test tubes
·2 x 25 ml beaker
·Raw beetroot
·Mounted needle
·Cork borer or scalpel
·Stop watch
·Colorimeter
METHOD
1.Collect all the equipment required.
2.Use a cork borer to cut cylinders of raw beetroot. Ensure that all cuts made are at a vertical
angle and that each individual slice of beetroot is exactly 3mm in thickness. Cut five discs, as
this will provide a good enough range of results to draw a graph and also to make conclusions as
to why the results took a certain pattern. If a cut is made of the wrong thickness or the beetroot is
not cut at a vertical angle, discard this disk and take another one.
3.Place all the discs into a beaker and wash with water until no more pigment is washed from the
slices.
4.Take one disc and place it to the side without further cutting. Now take another disc and cut it
precisely in two pieces. Now take another disc and cut this into four pieces. Next take disc and
cut it into eight. Repeat this until each disc has been cut into a different number of pieces
(doubling each time).
5.Again wash all the pieces until no more pigment is washed out and this ensures that any
leakage gained in the next step is caused solely by the change in surface area.
6.Now take a 25ml beaker and fill with distilled water. Then place each of the varying surface
areas into a separate test tube of 6cm3 distilled water and time exactly twenty minutes each using
a stopwatch to allow time for pigment leakage.
7.Remove pieces of beetroot from test tubes using a mounted need with a wooden handle and
then discard them. However be careful not to spill any of the liquid in the test tubes.
8.Set the light transmission level of a colorimeter to 0% using pure water being careful not to get
fingerprints onto the tube, as this will affect the amount of light that can pass through.
9.Pour the coloured liquid for the first test tube into a small tube provided with a colorimeter and
then place this into the colorimeter. Measure the percentage transmission and then record the
results. Repeat this for all of the test tubes.
RISK ASSESSMENT
In every experiment there are certain dangers, which may be encountered and taking certain
precautions can prevent these: ·Pipettes need to be used with precision when being set up. If not used carefully enough when
putting the pipette in place it could smash causing you to cut your finger. However this can be
prevented if when doing this action you take it slowly and ease it in place without being too
hasty.
·Using a scalpel blade to cut the beetroot accurately also gives the problem of cutting yourself
with the blade. To prevent this keep your free hand as far away from the blade as possible.
Wearing rubber gloves may also help this purpose as they give an extra layer. Also remember to
use a cutting mat as this prevents causing damage to the table.
·When utilising the mounted needle be careful to keep your fingers away from the point of it so
that it doesn't end up causing any harm to your fingers.