Bio Prac Flashcards
1
Q
2 ways in your METHOD of using syringes that made measurements accurate
A
- Remove air bubbles by inverting syringe. Air bubbles will rise to the top and push the piston to remove air bubbles
—— - Use 5cm3 syringe to measure volumes 5cm3 and below. Use 10cm3 to measure volumes 10cm3 and below
2
Q
All possible sources of error.
(Effect & improvements)
A
- 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).
——— - There are no repeats. NON-DIRECTIONAL
- Eff: Time recorded May be unreliable as it may include outliers
- Impr: DO REPEATS
——— - Temp loss / gain
- Eff:
- Impr: Use a thermostatically controlled water bath
—— - Enzyme & substrate left in same beaker of a certain temp b4 mixing
- To ensure they are the same temp b4 mixing
——— - (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
——— - (FOR DETERMINING WATER POTENTIAL) Use a narrower range of water potentials to get precise WP
3
Q
Why was the Enzyme & substrate left in same beaker of a certain temp b4 mixing
A
To ensure that they were both at the same temp at the start
4
Q
Test for Reducing Sugars
A
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
——
R.S Absent: Solution remains blue
R.S present: Solution turns for blue to green, yellow, orange or forms red precipitate
5
Q
Test for fat. Ethanol emulsion test
A
- Add 2cm3 of ethanol to a drop of food sample in test tube
- Shake well
- Add 2cm3 of water
- shake again
——
Fat absent: solution remains Colourless
Fat present: A white emulsion formed
