Decay

Question 1

Write a method for this practical

Answer 1

1. Label a boiling tube ‘lipase’ and add 5 cm3 of the lipase solution.
2. Label another boiling tube ‘milk’ and add five drops of the Cresol red solution.
3. Use a calibrated dropping pipette to add 5 cm3 of milk to the ‘milk’ boiling tube.
4. Use another pipette to add 7 cm3 of sodium carbonate solution to the ‘milk’ boiling tube. The solution should be purple.
5. Put a thermometer into the ‘milk’ boiling tube.
6. Set up a water bath to your first chosen temperature.
7. Put both boiling tubes into the water bath. Wait until the contents reach the same temperature as the water bath.
8. Use another dropping pipette to transfer 1 cm3 of lipase from the ‘lipase’ tube to the ‘milk’ tube.
   Immediately start the stopclock.
9. Stir the contents of the ‘milk’ boiling tube until the solution turns yellow.
10. Record the time taken for the colour to change to yellow, in seconds.
11. Then repeat the investigation for different temperatures of water bath.
12. Record your results in a table

Question 2

What is meant by the term decay?

Answer 2

To rot or decompose through the action of bacteria or fungi

Question 3

Why is milk used?

Answer 3

Milk was used as it contains a lipids that are broken down into fatty acids and glycerol which creates an acidic
condition that can be measured

Question 4

What is the independent variable?

Answer 4

Temperature

Question 5

What is the dependant variable?

Answer 5

Time taken for the indicator to show acidic conditions

Question 6

What are some control variable?

Answer 6

Same volumes of milk, lipase, sodium
carbonate and cresol red.
Same type of milk.
Same person looking at the colour
change.

Question 7

Why is sodium carbonate solution added to the milk?

Answer 7

The sodium carbonate solution was
added to create an alkaline solution so
that the initial pH is the same and a
change to acidic pH is more easily
detected.

Question 8

Why is a water bath used?

Answer 8

The water bath was used to ensure the
temperature of the solutions used in
each investigation remained constant.

Question 9

Why did a colour change occur?

Answer 9

As the lipase broke down the lipids in
the milk into fatty acids and glycerol
this created a more acidic environment. Cresol red is an
indicator that will change from red to
yellow in acidic condition

Question 10

What is meant by a model?

Answer 10

Simpler representation of something