Beetroot Cell Membrane Permeability Experiment

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Practical Assessment

Planning

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...
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