Reauired Practical: Incestigating Rates Of Decay In Milj

Question 1

What do bacteria break down in milk and what do they produce ?( In anaerobic conditions)

Answer 1

They break down the lactose in milk to produce lactic acid in anaerobic conditions

Question 2

What can we therefore investigate if they reproduce lactic acid in anaerobic conditions ?

Answer 2

The rate of milk decay by observing the decrease in pH over time

Question 3

What is the method used ?

Answer 3

1. 150ml milks added to 3x beakers
2. Foil used to seal the top of the breaker to prevent oxygen from entering
3. Beakers left at 5C, 15C and 25*C for 5 days
4. pH recorded using pH probs and date logged for the five days

Question 4

Why was the milk never kept higher than 25?

Answer 4

Stoped harmful pathogens

Question 5

Over time what would happen and why ?

Answer 5

The lactic acid causes the milk to clump
- this is why off milk tastes sour
- also how yoghurt is made and it is heated afterwards to remove any bacteria

Question 6

Which temperature will the pH decreased the most at ?

Answer 6

25

Question 7

Which temperature will the milk decay the fastest ?

Answer 7

25

Question 8

How can the accuracy be improved ?

Answer 8

Test a wider variety of temperatures

Question 9

What are the independent, dependant and control variables

Answer 9

Independent: PH change
Dependant: Temperature
Control variables: time in days, volume of milk