A blank nine-step write-up with the correct table headings. Print it for a real lesson and fill it in by hand. See the specimen lab book
Blank write-up: Decay
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Study Hack Lab
RP 10 · Biology
Decay
Write-up template
Name
Date
Course
GCSE Biology
Board and specification
AQA GCSE Biology (8461), 4.7.2.3Apparatus and techniques: AT 1, AT 3, AT 4, AT 5
Class and teacher
Aim
Investigate the effect of temperature on the rate of decay of fresh milk, by timing how long lipase takes to lower its pH and by following its pH over four days.
Contents
Plan and risk assessment
Apparatus
Method
Results
Graph
Analysis
Conclusion and evaluation
Make safe and clear up
A blank write-up for use in a real lesson. The headings follow the AQA required practical; the readings are yours to take. Layout v1, practical v2. Original material; not affiliated with AQA, which has not reviewed it.
1 Plan and risk assessment
Decay is the breakdown of dead material by microorganisms and their enzymes. In the lipase test, added lipase breaks fat into fatty acids and glycerol; the fatty acids lower the pH. In souring milk, bacteria ferment lactose to lactic acid, lowering the pH. Temperature affects these processes.
rate = 1 ÷ time
Variables
Independent (you change)
Dependent (you measure)
Control (you keep the same)
Prediction
How will the time for the pink colour to disappear change as the temperature goes up from 10 °C to 50 °C?
What will happen in the tube at 60 °C?
Three beakers of the same fresh milk are kept at 5 °C, 15 °C and 25 °C for 4 days. Which one’s pH will fall fastest?
Risk assessment
Hazard
Harm it could cause
Control
2 Apparatus
Safety goggles Protect your eyes from sodium carbonate and phenolphthalein.
Fresh full-fat milk (not UHT) Its fat is broken down by added lipase in the tube test; its lactose can be fermented by bacteria in the souring test.
0.05 mol/dm³ sodium carbonate solution Makes the milk alkaline (about pH 10) at the start.
Phenolphthalein in a dropping bottle Pink in alkali; colourless below about pH 8.3.
5 % lipase solution The enzyme that breaks down fat into fatty acids and glycerol.
Three 10 cm³ syringes, one labelled for each liquid (resolution 0.2 cm³) Measure the same volumes for every tube.
Test tubes, labelled, with glass rods Hold the pink milk mixture and the lipase; the rods stir them.
Six 250 cm³ beakers as water baths, a kettle and ice Keep each tube at its temperature: the independent variable.
Thermometers (resolution 1 °C) Check each bath, and the milk in the tube, are at the right temperature.
White tile Hold the tube against it to see when the last of the pink has gone.
Stopclock (resolution 1 s) Times each tube from the moment the lipase goes in.
Three beakers of 25 cm³ of milk The souring milk, one at each storage temperature.
Cling film Covers the souring milk.
A fridge (5 °C) and two incubators (15 °C and 25 °C) Keep the souring milk at a constant temperature for four days.
pH meter with a glass electrode (resolution 0.1) Measures the pH of the souring milk each day.
pH 7 buffer and a wash bottle of distilled water Calibrate the meter and rinse the electrode between beakers.
3 Method
Write numbered steps someone else could follow. Say what you measure, with which instrument, and how you keep it a fair test.
4 Results
The table is drawn before you measure. Record each reading to the resolution of the instrument, then work out the mean of your repeats, leaving out any anomaly.
Time for the pink colour to disappear · 5 cm³ milk, 7 cm³ sodium carbonate and 5 drops of phenolphthalein in each tube; 1 cm³ of 5 % lipase added. Leave any anomalous time out of the mean.
Temperature of the milk in °C
Time, trial 1 in s
Time, trial 2 in s
Time, trial 3 in s
Mean time in s
Rate (1 ÷ mean time) in /s
10
20
30
40
50
60
pH of the souring milk · 25 cm³ of the same fresh milk in each beaker, covered. pH read with the pH meter once a day.
Time in days
pH at 5 °C
pH at 15 °C
pH at 25 °C
0
1
2
3
4
Anomalies
Ring any anomalous result. Say what probably went wrong and whether you repeated it.
5 Graph
Rate against temperature · Choose your axes: the independent variable goes on the x-axis. Label each axis with the quantity and unit.pH of the milk against time · Choose your axes: the independent variable goes on the x-axis. Label each axis with the quantity and unit.
6 Analysis
Rate from the time
rate = 1 ÷ mean time
Answer
The optimum temperature
Read the temperature below the highest point of your curve.
Answer
Inside the tube
Answer
Gradient of your tangent at day 2 (15 °C)
Answer
Mean rate at 5 °C
mean rate of pH change = change in pH ÷ time
Answer
How many times faster
number of times faster = faster rate ÷ slower rate
Answer
7 Conclusion and evaluation
Conclusion
Conclusion: what do your results show? Use your own numbers.
Sources of error
For each, say whether it is systematic or random, and how it affected your results.
Judging by eye when the pink has gone
Stopping the clock when the tube first looks paler
Adding the lipase before the tubes reach the bath temperature
Not stirring the lipase in
Beakers of water as water baths
A pH meter that was not calibrated
Reading the pH at different times of day
One beaker at each temperature, read once a day
Improvement
How could you improve the method? Say why it would help.
8 Make safe and clear up
Switch off and unplug the kettle; let the hot baths cool before you pour them away
Pour the milk mixtures down the sink with plenty of water and rinse the tubes and syringes
After day 4, pour the sour milk down the sink with plenty of water, rinse the beakers and put the electrode back in its storage solution