Biology Plasmolysis Coursework

Topics: Cell wall, Cell, Osmotic pressure Pages: 5 (1696 words) Published: October 12, 2008
I am going to do an investigation into what concentration of sucrose solution would cause “Incipient Plasmolysis”.

Plasmolysis is the result of a (in particular) plant cell which has lost vast amounts of water. When this happens, turgor pressure within the cell has decreased to the point where the cytoplasm of the cell membrane peels away from the cell wall. When this begins to happen it is called Incipient Plasmolysis and when the cytoplasm is almost completely gone it is call “full/complete” Plasmolysis. Plasmolysis is only possible if the cell is placed in a hypertonic solution, which is a solution where the water external to the cell has more solutes than within the plant cell and because of that the water potential outside the cell would be lower than inside the cell. This would cause water (turgor pressure) to be lost by Osmosis. Osmosis is the net movement of water from high pressure to low pressure across a partially permiable membrane and it is that reason that it requires no energy for the movement. Osmosis eventually stops/slows down when water pressure has become balanced out between the “movements”.

Planning & Implementing
In this study I will use different solutions of sugar mixed in water (Sucrose solution) and I will be using sugar because it is known to be hypertonic. I will use red onion cells because the cell sap is coloured making the process of incipient plasmolysis easier to see. By that I mean it will be easier to see the cell membrane peeling away from the cell wall. If this is correct it will change the water from being hypotonic to being hypertonic in high enough sucrose concentrations.

Preliminary Results
Before I started this experiment I did a preliminary test, to test whether certain methods of conducting the experiment would work. This was important because it allowed myself to not only prepare but also detect any early onset problems that could occur. For the initial experiments I did a single test for each concentration of sucrose and as you can see below the results seem to be consistant with the theory. I used the information I obtained in the preliminary findings to rectify some things in methods, such as for example; the amount time for each experiment, list of concentrations etc.

The Method that was used to acquire the preliminary results seems to work, and I will use it to conduct the experiment with it. Also it is relatively easy to setup and analyse the results and we do have the equipment for it to be a usable method of conducting the experiment with.

The equipment list is as follows:
Light Microscope
Glass Slide/s
Cutting Tile
10ml Measuring Cylinder
Red Onion Pieces
Sucrose Solution
Cover Slip/s

Gather all the equipment
Setup microscope, cut out onion pieces & peel off the required amounts of skin. Place the “Onion skin” on the glass slide.
Prepare concentration of sucrose using the measuring cylinder. Mix in the amount of water & sucrose needed. Using the pipette to extract the solution from the measuring cylinder the mixture of sucrose. Place a drop of the liquid on the onion skin, start the timer & slowly close the cover slip using the scalpel. Wait the amount of time allocated (10mins) & then stop the Timer. Place the slide under the microscope, observe how many cells are plasmolysed, and write down the result. Repeat the process again if necessary, either using a different or same concentration of sucrose.

Procedure & Safety
It is important to do the same procedure throughout the practical, this would help reduce the likelihood of producing erroneous results. For example, it could produce results that are extremely different than to the other results taken, also making sure the method is the same throughout will also help save time as well. As a side note, the reason I will use the scalpel instead of my fingers to lower the glass slide is mainly because it would be...
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