Suggest a hypothesis and describe the procedure for an experiment investigating the effect of varying concentrations of stale milk on methylene blue decolorization.

Here is the hypothesis and the completed procedure for your experiment:

a. Suggest a Hypothesis for your experiment

• Hypothesis: As the percentage concentration of stale milk (or yeast suspension) increases, the activity of the dehydrogenase enzyme will increase, leading to a shorter time required for the methylene blue to decolorize.

b. Describe your procedure

Aim: To investigate the effect of varying concentrations of stale milk (or yeast suspension) on the rate of decolorization of methylene blue.

Materials:

• Stale milk (or yeast suspension)
• Distilled water
• Methylene blue solution (e.g., 0.005%)
• 5 clean test tubes
• Test tube rack
• Measuring cylinders or pipettes (e.g., 10 ml, 1 ml)
• Stopwatch
• Water bath (e.g., set at 37°C)
• Thermometer
• Marker pen for labelling

Method:

1. Preparation of Dilutions:

   • Five test tubes were labelled A, B, C, D, and E.
   • The following dilutions of the stale milk (or yeast suspension) were prepared using distilled water, ensuring a total volume of 10 ml for each dilution, and placed into the different test tubes:
     • Test Tube A (0%): 0 ml stale milk + 10 ml distilled water.
     • Test Tube B (25%): 2.5 ml stale milk + 7.5 ml distilled water.
     • Test Tube C (50%): 5 ml stale milk + 5 ml distilled water.
     • Test Tube D (75%): 7.5 ml stale milk + 2.5 ml distilled water.
     • Test Tube E (100%): 10 ml stale milk + 0 ml distilled water.

2. Addition of Methylene Blue:

   • To each test tube (A-E), 1 ml of methylene blue solution was added.
   • Immediately after adding the methylene blue, each test tube was gently shaken to obtain a uniform blue colour.

3. Incubation and Measurement:

   • All five test tubes were simultaneously placed into a water bath set at a constant temperature (e.g., 37°C).
   • A stopwatch was started immediately upon placing the test tubes in the water bath.
   • The time taken for the methylene blue to completely decolorize (turn colorless) in each test tube was observed and recorded.
   • If a test tube did not decolorize within a set time (e.g., 60 minutes), this was noted.

4. Controlled Variables:

   • The temperature of the water bath was kept constant throughout the experiment.
   • The volume of methylene blue solution added to each test tube was kept constant.
   • The total volume of the milk dilution in each test tube was kept constant.
   • The mixing procedure for each test tube was consistent.

5. Data Collection:

   • The percentage concentration of stale milk and the corresponding decolorization time for each test tube were recorded in a table.