Required Practicals - Decay

Question 1

What is the goal of the decay practical?

Answer 1

To investigate the effect of temperature on the rate of decay of fresh milk by measuring pH change.

Question 2

What is the apparatus list of the decay practical?

Answer 2

-a small beaker of full fat milk or single cream
-a small beaker of sodium carbonate solution
-a small beaker of lipase solution
-250cm3 beaker
-boiling tubes
-marker pen
-10cm3 plastic syringes
-thermometer
-A kettle
-Cresol red
-ice

Question 3

What is the method for the decay practical?

Answer 3

-label a boiling tube ‘lipase’ and add 5cm3 of lipase solution
-label a boiling tube ‘milk’ and add five drops of Cresol red solution
-Use a calibrated dropping pipette to add 5cm3 of milk to the ‘milk’ boiling tube
-Use another pipette to add 7cm3 of sodium carbonate solution to the ‘milk’ tube. The solution should be purple
-Put a thermometer into the ‘milk’ tube.
-Set up a water bath.
-Put both boiling tubes into the water bath. Wait until the contents reach the same temperature as water bath.
-Use another dropping pipette to transfer 1cm3 of lipase from the ‘lipase’ tube to the ‘milk’ tube. Immediately start the stopclock.
-Stir the contents of the ‘milk’ boiling tube until the solution turns yellow.
-Record the time taken for the colour to change to yellow.
-Repeat the investifation for different temperatures of water bath.
-Record results in a table.
-

Question 4

What happens if milk is left at room temperature?

Answer 4

It goes sour

Question 5

Why does milk go sour at room temperature?

Answer 5

bacteria in the milk start the decay process.

the bacteria use enzymes to produce acidic molecules

Question 6

How do we model decay in the decay practical?

Answer 6

Using lipase enzyme

Question 7

What do we do first in the decay practical?

Answer 7

Measure 5cm3 of lipase solution into a test tube

Question 8

What do we do second in the decay practical?

Answer 8

Add 5 drops of cresol red indicator and add 5cm3 of milk and 7cm3 of sodium carbonate solution

Question 9

Which indicator is used in the decay practical?

Answer 9

Cresol red

Question 10

What colour is the milk test tube in the decay practical? Why is this?

Answer 10

Purple, as the solution is alkaline due to the sodium carbonate solution

Question 11

What is the third step of the decay practical?

Answer 11

Place a thermometer in the milk test tube and record the temperature after putting them in a beaker of water.

Question 12

What is the fourth step of the decay practical?

Answer 12

Use a pipette to transfer 1cm3 of lipase solution to the test tube containing milk.

Stir the solution and start a timer.

Question 13

What happens after lipase is added to the milk test tube in the decay practical?

Answer 13

Lipase enzyme will start to break down lipid molecules in the milk, releasing fatty acids, causing the solution to become acidic

Question 14

What happens to cresol red indicator when in acidic solution?

Answer 14

It changes to yellow

Question 15

What do we do when cresol red solution turns yellow in the decay practical?

Answer 15

Stop timing and record results

Question 16

How do we repeat the decay practical experiment?

Answer 16

Repeat at a range of different temperatures.

Question 17

What is the independent variable in the decay practical?

Answer 17

The temperature

Question 18

What is the dependent variable in the decay practical?

Answer 18

The time taken for milk solution to turn yellow

Question 19

What are the control variables in the decay practical?

Answer 19

The volumes of the different solutions

These include:
lipase
milk
sodium carbonate solution
cresol red

Question 20

What kind of test tube do we use in the decay practical?

Answer 20

A clean test tube

Question 21

Why do we need to use a clean test tube in the decay practical?

Answer 21

Any traces of lipase will trigger the reaction before we are ready

Question 22

What is the problem with the decay practical?

Answer 22

The point at which the cresol red has fully turned yellow is subjective so results may vary.

Question 23

How can we combat the problems with subjectivity in the decay practical?

Answer 23

Sharing data with other groups and calculating a mean

Question 24

Why is the time taken for the cresol red to turn yellow high at low temperatures in the decay practical?

Answer 24

Enzymes work slowly at lower temperatures.

Question 25

In the decay practical, what is the temperature at which rate is fastest called?

Answer 25

Optimum temperature

Question 26

In the decay practical, why is time taken high at very high temperatures?

Answer 26

The enzyme would have denatured.