Rates Of Decay Practical 2 Flashcards
Why will milk turn sour ?
Bacteria start decay process using enzymes which produce acidic molecules- hence sour tase
Why do we use the enzyme lipase ?
To model decay as decay takes very long
What is the method ?
- 5cm3 lipase solution placed into test tube
- Add five drops of cresol red to another tube and add 5cm3 of milk and 7cm 3 of sodium carbonate to milk (solution should be purple)
- Place thermometer in milk test tube then place both into water bath at 20*c
- Wait until solution reach temp of bath then use pipette to add 1cm3 to milk solution- now start a timer
Once it’s yellow take time and repeat with different temperature
Why is the milk and sodium carbonate solution red ?
Because it’s an alkaline solution and cresol reed is purple in alkaline conditions
What happens when we add the lipase to the milk solution ?
It breaks down the milk causes fatty acids and causes the milk to become acidic
Why will cresol red change colour
Changes to yellow due to relapse of fatty acids
And cresol red is yellow in acidic conditions
Once it’s yellow we stop timing
What is the independent variable ?
Temperature
What is the dependant variable ?
Time taken for milk to turn yellow
What are the control variables ?
Volume of solutions
Why is it important to use a clean test tube ?
Any trace of lipase will trigger the reaction from cresol red
And therefore it can be difficult to decide the exact point to stop the timer
How could we negate the issue of being unsure as too when to stop the timer/ variation in results ?
Sharing data with other groups and calculating a mean
What would low temperature react like ?
Slowly as enzymes work slowly at lower temperatures
Where would the fastest rate of reaction be ?
At the lowest point on the Y axis (time taken) as it’s very quick
This is called the optimum temperature
Why will the reaction slow down in warmer temperatures ?
Enzymes denature at higher temperatures
