Biology 7.2.5

Question 1

Explain the ‘Decay Practical’: (10)

Answer 1

-Use a Syringe to Measure 5cm^3 of Milk & Pour into a Test Tube.

-Add 7cm^3 of 0.05mol/dm^3 of Sodium Carbonate to the Test Tube, to Ensure that the Milk is Alkaline.

-Add 5 Drops of Phenolphthalein Indicator to the Solution. It Produces a Pink-Purple Colour when in an Alkaline Solution (eg right now).

-Use a Syringe to Measure 5cm^3 of Lipase Enzyme & Pour it into a Separate Test Tube.

-Place Both Test Tubes into a Water Bath of 10’C. Wait Until the Milk Solution Test Tube Equilibrates to 10’C as well, Using a Thermometer.

-Once the Milk Solution Reaches 10’C, Add 1cm^3 of the Lipase Enzymes. You need to Constantly Mix the Solution.

-Use a Stopwatch to Measure the Time it Takes for the Milk Solution to Discolour, Due to the Production of Fatty Acids, Which Cause the Solution to be Acidic rather than Alkaline, Indicating Decay.

-Record the Time Taken for the Milk Solution to Discolour (Signifying that Decay has Taken Place, Acid > Alkali).

-Repeat the Experiment 2 More Times, at Temperatures 20’C, & 30’C.

-Repeat the Overall Experiment 2 More Times to Calculate an Average of the Overall Results, to Reduce the Negative Effect of Anomalous Results.