Required Practical 10: Decay PAPER 2 Flashcards
In the required practical decay what do you investigate.
Describe how to investigate the effect of temperature on the rate of decay of fresh milk by measuring the pH change.
Decay is —- process so it is very hard to observe.
very slow
Decay is very slow process so it is very hard to …
observe.
Decay is very slow process so it is very hard to observe. This means that we use …
the enzyme lipase to model decay.
Decay is very slow process so it is very hard to observe. This means that we use the enzyme lipase to model decay.
What we are looking at is not strictly decay but it should …
give results that approximate to what we would see with decay.
Firstly, we start by labelling a test tube …
‘lipase’
Secondly, use pipette to place —— of lipase solution into the test tube.
5cm3
Thirdly, we label another test tube …
milk
Fourthly, add ———– in the milk labeled test tube.
five drops of the indicator cresol red.
Fifthly, we now add ———- and 7cm3 of sodium carbonate to the milk test tube.
5cm3 of milk
Fifthly, we now add 5cm3 of milk and ———- to the milk test tube.
7cm3 of sodium carbonate
Fifthly, we now add 5cm3 of milk and 7cm3 of sodium carbonate to the milk test tube. At this point the solution should be —– because carbonate solution is alkaline.
purple
Fifthly, we now add 5cm3 of milk and 7cm3 of sodium carbonate to the milk test tube. At this point the solution should be purple because …
carbonate solution is alkaline
—— is purple in alkaline conditions.
Cresol red
Sixthly, we place a ——- in the milk labeled test tube.
thermometer
Seventhly, place both test tubes in a ——— at the first chosen temperature usually 20c which is around room temperature.
water bath
Eighthly, use a pipette to transfer ———— to the test tube containing milk and stir well.
1cm3 of lipase solution
Ninthly, we start a …
timer
Ninthly, we start a timer. The enzyme lipase will start to …
break down the fat molecules in the milk.
Ninthly, we start a timer. The enzyme lipase will start to break down the fat molecules in the milk. This releases ——- and this causes the milk solution to become acidic.
fatty acids
Ninthly, we start a timer. The enzyme lipase will start to break down the fat molecules in the milk. This releases fatty acids and this causes the milk solution to become …
acidic
In acidic solutions, the indicator cresol red changes to …
yellow
Once the solution turns yellow …
stop timing and record the results.
Now repeat the experiment at a …
range of different temperature
The independent variable is the …
temperature.
The dependent variable is the …
time taken for the milk solution to turn yellow.
You must —— the test tubes for the milk solution for each experiment.
clean
Because we are looking for a change in colour, it may be difficult to …
decide the exact point to stop the timer.
After the experiment we should plot a …
graph
