Bio Prac

Question 1

2 ways in your METHOD of using syringes that made measurements accurate

Answer 1

1. Remove air bubbles by inverting syringe. Air bubbles will rise to the top and push the piston to remove air bubbles
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2. Use 5cm3 syringe to measure volumes 5cm3 and below. Use 10cm3 to measure volumes 10cm3 and below

Question 2

All possible sources of error.
(Effect & improvements)

Answer 2

1. Difficult to see time when indicator 1st changes colour. DIRECTIONAL (FOR COLOUR CHANGE DVS)
   - Eff: Results may be inconsistent & variable. Time recorded May be higher than actual value
   - Impr 1: Use a colour chart for comparison
   - Impr 2: Slow the reaction using lower conc of reactant (state) (or by using more substrate).
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2. There are no repeats. NON-DIRECTIONAL
   - Eff: Time recorded May be unreliable as it may include outliers
   - Impr: DO REPEATS
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3. Temp loss / gain
   - Eff:
   - Impr: Use a thermostatically controlled water bath
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4. Enzyme & substrate left in same beaker of a certain temp b4 mixing
   - To ensure they are the same temp b4 mixing
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5. (FOR YEAST) Yeast suspension left for some time b4 experiment
   - Eff: ROR lower than expected as yeast will use up some glucose for aerobic res
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6. (FOR DETERMINING WATER POTENTIAL) Use a narrower range of water potentials to get precise WP

Question 3

Why was the Enzyme & substrate left in same beaker of a certain temp b4 mixing

Answer 3

To ensure that they were both at the same temp at the start

Question 4

Test for Reducing Sugars

Answer 4

For SOLID samples, crush it with mortar and pestle
1. Add 2cm of sample into 2cm3 of Benedict’s Solution
2. Shake well
3. Place test tube in a heated water bath for a few minutes
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R.S Absent: Solution remains blue
R.S present: Solution turns for blue to green, yellow, orange or forms red precipitate

Question 5

Test for fat. Ethanol emulsion test

Answer 5

1. Add 2cm3 of ethanol to a drop of food sample in test tube
2. Shake well
3. Add 2cm3 of water
4. shake again
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   Fat absent: solution remains Colourless
   Fat present: A white emulsion formed