Required Practical 10 - Investigate the effects of temperature on the rate of decay of fresh milk by measuring pH change.

Question 1

Method to investigate the effects of temperature on the rate of decay of fresh milk by measuring pH change:

Answer 1

1. Make a solution of milk and phenolphthalein indicator
2. Add sodium carbonate which will cause the solution to become alkaline and therefore appear pink
3. Place the tube in a water bath as a specific temperature
4. Add the lipase enzyme and begin stopwatch
5. Time how long it takes for the pink colour to disappear (i.e. when the pH has decreased) using stopwatch
6. Repeat this at different temperatures to see at which temperature the pink colour disappears the quickest, indiciating the quickest decomposition

Question 2

Decay:

Answer 2

process where decomposers such as microorganisms or insects eat, digest and break down edible materials

Question 3

What is decay necessary for?

Answer 3

• necessary for nutrients in edible materials to be recycled and returned to earth to be used again my different materials

Question 4

Factors affecting rate of decay:

Answer 4

• temperature - decomposers work faster in warm conditions, slow down to stop if too cold or hot
• moisture - makes it easier for decomposers to digest food and stops them from drying out
• oxygen -most decomposers respire aerobic ally so need oxygen to respire and release energy to fuel living processes

Question 5

Method for rate of decomposition:

Answer 5

1. Have 6 test tubes and partly fill them with 5cm3 fresh full fat milk
2. Have another 6 test tubes and partly full them with 3cm3 lipase - set aside for time being
3. add 5 drops of phenolphthalein to milk followed by adding 7cm3 sodium carbonate solution which is an alkaline solution - will make solution pink as phenolphthalein turns pink in presence of alkalis and colourless in presence of acids (or carry out with pH probe with gives quantitative data)
4. Place one pair of milk solution and lipase together in own water both and other pairs in different water baths (each water bath has different temp)
5. Leave them to reach equilibrium with temp of water bath
6. Once the temperatures have reached equilibrium add the lipase milk solution together and time how long it takes for colour to go from pink yo colourless

Question 6

Results:

Answer 6

• general trend showing specific set of temperatures
• 30 degrees C most effective
• enzymes found in decomposers and work best in certain conditions - too hot or cold results in lack of effectiveness