Biology Practical

1-The effect of temperature on membrane permeability

1. The independent variable: Temperature of water

2. The dependent variable: % transmission of light through resulting solution

3. Control variables: a) volume of distilled water

b) Time left in water

c) Size of beetroot piece

4. Validity: a) The same diameter core is used to ensure the surface area of all the beetroot pieces are of the same size.

b) 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 results.

c) Distilled water should be used so that there will be a reliable substance to test with.

d) Beetroot must be raw, not cooked. Use a size 4 cork borer and cut with care using a cutting board. Leave the cores overnight in a beaker of distilled water. The pigment from any cells that have been cut by the cork borer will leak into the water. Rinse away any pigmented water in the morning and replace with fresh water.

5. Reliability: Repeat the experiment at least thrice and compare them.

Risk assessment

Risk Method to control the risk1. Cutting tool like knives and scalpels can be dangerous and cut the skin.

1. Always carry cutting tools like knives

and scalpels in a small tray. Replace the

cutting tool in the tray when not in use.

Take care while carrying scalpels or

knives around the laboratory.

2. Beetroot juice will stain clothing (and, 2. Students can wear lab coats to

temporarily, skin) but is not hazardous. protect their clothing from stains.

Method: Using a cork borer and knife, cut pieces of beetroot into 1 cm length cylinders. Place in distilled water overnight to remove any dye released on preparation. Wash and blot dry. Place 8 boiling tubes of distilled water into 8 water baths of different temperature. Then add a piece of beetroot to each and leave for 30 minutes. Remove the beetroot and shake tubes to disperse dye. Set colorimeter to % absorbance on blue/green filter. Calibrate using distilled water in a cuvette first then add 2cm3 of beetroot solution from the first temp to a new cuvette. Place into colorimeter to read % absorbance. Repeat for all other pieces.

Calculations & outcome: to calculate % transmission = 100-%absorbance. As temperature increased, % transmission slightly increased to a point at which it greatly increased due to membrane molecules gaining more heat energy, vibrating more to a point where the vibrations caused large gaps in the membrane enabling the release of dye also proteins in membrane denatured leaving large pores.

2- The effect of alcohol concentration on membrane permeability

1. The independent variable: Alcohol concentration

2. The dependant variable: % transmission of light through resulting solution

3. Control variable: a) Size of beetroot piece

4. Validity: a) The same diameter core is used to ensure the surface area of all the beetroot pieces are of the same size.

b) 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 results.

c) The volume of the alcohols should be the same.

d) Distilled water should be used so that there will be a reliable substance to test with.

e) Beetroot must be raw, not cooked. Use a size 4 cork borer and cut with care using a cutting board. Leave the cores overnight in a beaker of distilled water. The pigment from any cells that have been cut by the cork borer will leak into the water. Rinse away any pigmented water in the morning and replace with fresh water.

5. Reliability: Repeat the experiment at least thrice and compare them.

Risk Assessment

Risk Method to control the risk 1. The compounds used in this experiment are flammable and poisonous. Methanol, sometimes referred to as wood alcohol, can cause blindness and death. Propanol is fatal if consumed. One possible reason why they are so dangerous to living organisms is that they might damage cellular membranes.

1. The compounds used in this experiment are flammable and poisonous. Avoid inhaling vapours. Avoid contacting them with your skin or clothing.

2. Some alcohols are flammable. 2. Be sure there are no open flames in the lab during this experiment.

Method: In this experiment, you will test the effect of three different alcohols (methanol, ethanol, and 1-propanol) on membranes. Ethanol is found in alcoholic beverages. Methanol, sometimes referred to as wood alcohol, can cause blindness and death. Propanol is fatal if consumed. One possible reason why they are so dangerous to living organisms is that they might damage cellular membranes. Methanol, ethanol, and 1-propanol are very similar alcohols, differing by the number of carbon and hydrogen atoms within the molecule. Methanol, CH3OH, is the smallest, ethanol, CH3CH2OH, is intermediate in size, and 1-propanol, CH3CH2CH2OH, and is the largest of the three molecules.

If beet membranes are damaged, the red pigment will leak out into the surrounding environment. The intensity of colour in the environment should be proportional to the amount of cellular damage sustained by the beet.

To measure the colour intensity, you will be using a Colorimeter or Spectrometer. In this device, blue light from the LED light source will pass through the solution and strike a photocell. The alcohol solutions used in this experiment are clear. If the beet pigment leaks into the solution, it will colour the solution red. A higher concentration of coloured solution absorbs more light and transmits less light than a solution of lower concentration. The device monitors the light received by the photocell as either an absorbance or a percent transmittance value.

You are to prepare five solutions of differing alcohol concentrations (0%, 10%, 20%, 30%, and 40%) for each of the three alcohols. A small piece of beet is placed in each solution. After ten minutes, each alcohol solution is transferred to a cuvette that is placed into the Colorimeter or Spectrometer. The amount of light that penetrates the solution and strikes the photocell is used to compute the absorbance of each solution. The absorbance is directly related to the amount of red pigment in the solution. By plotting the percent alcohol vs. the amount of pigment (that is, the absorbance), you can assess the amount of damage various alcohols cause to cell membranes.