Title: The Effect of Vinigar on Plasma Membranes
Name: Kathleen Morwood
Introduction:
A component of every biological cell, the selectively permeable cell membrane/plasma membrane is a thin and structured bilayer of phospholipid and protein molecules that encloses the cell. The cell membrane seperates the inside of a cell from the surounding matter. It is a selectivly permiable membrane whith imbedded protines to allow transfer of larger molecules. The affect of PH and thus vinigar on cell membranes is best explained by Ian White a secondary school Biology teacher who's statement can be found in its entirity at http://www.madsci.org/posts/archives/2004-03/1080223472.Cb.r.html.
"pH affects membranes by affecting the proteins that make up about 70% of
most cell membranes (less in inactive cells, such as red blood cells, more
in others, such as those of mitochondria). proteins are made of amino-
acids and each amino-acid has a variable number of nitrogen and oxygen
atoms in it. These can form HYDROGEN bonds with the many hydrogen atoms
found in the molecule. The clever thing is, that the protein folds up to
ensure that the MAXIMUM number of these hydrogen bonds is made.
When the pH of a solution changes, the position of some of these hydrogen
atoms also changes. This is because amino-acids are AMPHOTERIC, and tend
to stabilise pH. Thus, they can lose an H+ ion at the COOH [or 'acid']
part of the molecule at higher pHs, or gain an H+ ion at the NH2
[or 'amino'] end of the molecule at lower pHs.
This, in turn, causes the overall shape of the protein to change with pH.
This is the reason why most enzymes (which need a precisely-shaped 'ACTIVE
SITE') can only work well at a certain pH. Unlike heat, the denaturing of
a protein by changing pH is (normally) REVERSIBLE.
The dye in beetroot (betalain - see notes below) diffuses out of the cell
when the membrane proteins are damged."
It is therefore hypothesised that the vinigar used in the experiment will break down the protines and destroy the cell membranes causing a colour change proportional to the concentration of the vinigar in the solution. Higher concentrations will alter the PH more and thus there will be more diffusion of the betroot colour into the vinigar solution.
Materials:
x2 Burets; 10ml
x12 Petrie Dish
x96 Peices of Beetroot; aprox 1cm^3
x5 Beakers
x1 Marking Pen
x1 Twesers
Vinigar
Distilled Water
Method:
1. Equipment was collected.
2. Eight betroot peices were placed in each petrie dish.
3. Dishes 1 & 2 were filled with straight white vinigar and labeled.
4. Step three was repeated for each other pair of petrie dishes at vinigar concentrations of:
3 & 4; 75% vinigar
5 & 6; 50% vinigar
7 & 8; 25% vinigar
9 & 10; 10% vinigar
11 & 12; 0% vinigar
5. The pretrie dishes were left to sit for 35min.
6. Betroot peices were removed with tweasers and discarded.
7. The richness of colour of the liquid was noted and the dishes were aranged from darkest colour to least saturated and the order was recorded.
Results:
Darkest colour ----->
2(100%) 5(50%) 8(25%) 3(75%) 4(75%) 1(100%) 6(50%) 7(25%) 9(10%) 10(10%) 12(0%) 11(0%)
-----> Lightest colour
Discussion:
The results tho they did show a trend in colour change, were anomolous in some places. Such as the arrangment of the second, third and sixth placed dishes(5, 8, 1). The beetroot used in the experiment had originated from two differant beakers and thus two differant beetroots. It is also possible one was sitting pre cut longer than the other. The natural variation of vegetables will also have had a part to play, it is evident the experiment should have been repeated more than once for the gradient so as to reinforce trends and to discover if the results that seem out of place were infact anomolous. If we were to however disreguard these varients and look at the other results it is evident that as the concentration of vinigar in the solution decreses, as does the amout of colour in the solution. It is then evident that yes vinigar does destroy cell membranes. It could be hypothesised that vinigar does this due to its acidity as PH does affect cell membranes.
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