The Effect of Temperature on the Cell Membranes of Beetroot Cells
·Corer size 4
· White tile
· A Beetroot
· Automatic Water Bath
· Segregated knife
· A thermometer
· First take the white tile and the corer. Then collect a cylinder of
beetroot by pushing the corer into the beetroot and withdrawing it.
The cylinder remains inside the corer- so push it out with the end of
· Collect 3 cylinders, and then cut them into 6 pieces of 3 cm with a
· The beetroot was cut to 1cm. Because the beetroot has been cut some
of the cell membranes
had been broken, which means some anthocyanin
will leak out. This must be completely washed off in order to maintain
the reliability of the results.
· The water bath must then be heated to 20oC (the first temperature
for the experiment)
· Once the water bath is at the correct temperature (measured using
the thermometer), one piece of beetroot is placed into the hot water
directly and left for exactly1 minute (using a stopwatch).
· The beetroot piece is then placed into a tube of 5 cm of distilled
This procedure will be repeated with the other four pieces of beetroot
and the temperature should be changed accordingly. The temperatures
will be using are 20oC, 40oC , 60oC and 80oC
Each time a piece of beetroot is removed from the heated water, it
will be left in the distilled water for exactly 30 minutes, before
The fluid in each of the test tubes will be analysed using a
colorimeter and compared against the control, which is distilled water
to check for any variations in the colour of the water.
The variables kept constant
· The same diameter corer is used so to keep the surface area of each
beetroot piece the same size.
· When the beetroot has been cut some of the cell membranes are
broken, which means some anthocyanin will leak out. This must be
completely washed off in order to maintain the reliability of the
· I will use distilled water to so that I have a reliable substance to
test with a colourimeter.
To be added as I can't do one on my computer ( not good enough
software)- I will use a computer at school.
The reason why the amount of betalain pigment released (colourimeter
reading) from the vacuole increased directly proportionally to the
temperature of the water bath (from 20oC to 40oC) is because the
amount of random movement of betalain molecules out through the cell
membrane depends on the amount of heat energy the betalain molecules
are given to convert into kinetic energy- hence the higher the
temperature the more betalain lost from the vacuole.
This is because the betacyanin pigment of beet root cells is normally
sequestered in the vacuole and by means of the cell membrane which
maintains the integrity of the cell and the tonoplasts, it does not
leak into the cytosol or the extra-cellular sap of the beet root.
However when we increase the temperature the relatively weak forces
holding the different parts of the polypeptide chains together (like
hydrogen bonds, sulphur bridges and ionic bonds) can be disrupted very
easily- this damages the vacuole and makes holes in the cell membrane,
The cell membrane is also damaged and so diffusion of betalain occurs
through the partially permeable membrane by osmosis- the betalain
molecules move by diffusion from an area where they are more highly
concentrated to an area where they are at a lower concentration, along
a concentration gradient.
The reason why the amount of betalain pigment increases rapidly (from
40oC to 60oC) is because most mammalian protein's denature and
tertiary structure unravels (the strong covalent bonds between the R
groups of amino acids in the polypeptide chains are destroyed) at
temperatures over 40oC.
The reason why the curve starts to flattens out (between 60oC and
80oC), is because although the denaturing of the protein causes a
rapid rise in the amount of betalain released to start with, when the
temperatures begin to get higher still, the protein's tertiary
structure blocks some of the holes in the cell membrane and therefore
slows down the release of betalain.
There were a number of sources of error that may have affected the
accuracy of my results. Firstly I had one stopwatch and timed all the
water baths for fifteen minutes, so was a slight delay however between
the placing of the tubes in each water bath, as I had to walk to each
water bath so it would have affected my reults slightly. This would
only have had a small effect on my results, because the vacuole of the
beetroot would have only released slightly more betalain, as the
molecules would have only had a very small amount more heat energy to
convert into kinetic energy.
Secondly I when I washed each of the beetroot pieces I may not have
removed all of the red pigment on the outside, so this would have
affected my results very slightly. Again this would only have had a
small effect on my results, because a very slight increase in betalain
molecules would not have changed the reading on the colourimeter.
There were also limitations of my experiment. Firstly I only had an
hour in which to conduct my experiment- this did not give me time to
collect a suffient number of results. A larger number of results taken
at different temperatures between 20oC and 60oC would have allowed me
to find out more accurately where the point of denaturation occured.
It would also have been better to have had the time to repeat each
temperature more times to make the results more reliable and so I
could be sure the results were not gained through chance. This may
have eliminated my anomaly, but I did repeat the experiment twice and
the two results on each temperature were almost identical, so this
would have had very little effect on the accuracy of my results.
Another limitation was cutting the beetroot into pieces. The pieces
cut had roughly the same surface area to volume ratio- but not exactly
the same. This would have had a slight effect on my results because
the rate of diffusion of betalain particles across the plasma membrane
is increased, as the surface area of the beetroot increases. So the
slightly thinner and smaller pieces of beetroot I cut would have
released more betalain from their vacuole.
I only looked at one type of plant cell, so I can not be sure that
every plant cell and indeed eykaryote- which have different plasma
membranes, that may be adapted to cope with heat better or worse than
willl have the same results.
I can firmly conclude that there are no apparent anomalies in my
results and none of my sources of error or limitations of my
experiment are enough to deem my results unreliable. However the
sources of error and limitations in my results may have made my
results slightly less accurate, but other students in my class found
the same patterns occuring and roughly the same results- which would
vary slightly between each beetroot anyway.