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Factors affecting cell membrane permeability.

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Factors affecting cell membrane permeability Aim: to investigate the factors affecting cell membrane permeability of red cabbage, using absolute alcohol (10 cm3), 1 M hydrochloric acid (10 cm3), 1M sodium hydroxide (10 cm3), and distilled water (10 cm3), and change of temperature (40 oC, 65 oC, 100 oC) Hypotheses: If the leaf discs are not rinsed, the distilled water will change colour, because the pigments can escape from the cell destroyed by cutting the cabbage. If the temperature increases, the solution will become more and more coloured, because the membrane becomes more and more permeable. Independent variables: for tubes 1-2: rinsing or not rinsing the leaf discs, for tube 3-5: the environment, (for tubes 4-5: pH), for tubes 6-8: temperature Dependent variable: for tubes 1-2: change of colour of the solution, for tubes 3-5: change of colour of the solution, for tubes 6-8: intensity of colour of the solution Controlled variables: for all tubes: species, size of leaf discs, amount of solution, for tubes 1-2: pH, for tubes 1-5: temperature, for tubes 6-8: pH Materials: absolute alcohol, 1 M hydrochloric acid, 1 M sodium hydroxide, distilled water, red cabbage Equipments: test tubes, test tube ...read more.


Observations of testing the cell membrane permeability of red cabbage when the independent variable is the environment Test tube number / - Environment / - Change of colours of solution / - 3 alcoholic slight purple 4 acidic strong red 5 basic strong yellow Colour of chemicals used: absolute alcohol, hydrochloric acid and sodium hydroxide are colourless Drawing 2. Observations of testing the cell membrane permeability of red cabbage when the independent variable is the alcoholic, acidic, and basic environment Table 3. Observations of testing the cell membrane permeability of red cabbage when the independent variable is temperature Test tube number / - Temperature / oC Intensity of purple colour / - 6 40 0.5 slight purple 7 65 0.5 medium purple 8 100 0.5 strong purple Drawing 3. Observations of testing the cell membrane permeability of red cabbage when the independent variable is temperature Table 3. Observations of leaf discs Test tube number / - Drawing of a leaf disc / - 1 2 3 4 5 6 7 8 Random error: - the difference between the diameter of the leaf and the test tubes was very small, therefore the sinking or floating of ...read more.


The more pigment releases, the more the membrane is broken down. For temperature being the independent variable, test tube 2 was the contol test, beacuse it showed what happens (the disitlled water will not change colour) at room temperature, beacuse the hydrophilic heads face the water, and the hydrophobic tails face each other. The carbohydrate legs of the hydrophilic part of the membrane kick out under certain conditions, e.g at certain pH levels. Red cabbage is used as a pH indicator, because for different pH levels, it results a different colour - for acidic the shades of red, for basic the shades of yellow, presuming after this experiment. Therefore another experiment should be done, in which the change of colour at different pH levels is examined. Alcohol showed that it cannot break down the membrane as much as e.g. high temperature did, but it causes damage, resulting in a slight purple colour. For more accurate results, the experiment should be repeated more times, or results of other students should be examined. To avoid the random error, the implement for cutting the red cabbage into discs should have a smaller diameter, or the diameter of the test tubes should be greater in order to examine the sinking of the leaf discs. 1 ...read more.

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