Asia-Pacific Forum on Science Learning and Teaching, Volume 18, Issue 2, Article 7 (Dec., 2017) Kwok-chi LAU Teaching about nature of science through short lab activities in Hong Kong classroom Previous Contents

Appendix

 

Name: ______________  Class: ________________  Date : ___________________
Lab task sheet

Question
Why does an apple turn brown after being cut?

 

Hypothesis (only one is provided in each task sheet)
Cutting an apple exposes it to air. The oxygen in air oxidizes the iron–containing compounds in the apple to produce a brown colour substance. OR

 

The apple turns brown because of an enzyme. When exposed to air, this enzyme catalyzes the formation of a brown colour product at the cut surface.

 

Prediction (only one is provided in each task sheet)
Dip the apple into a solution of ascorbic acid will slow down the browning. It is because ascorbic acid is an anti–oxidant, which would prevent the oxidation process on the cut surface. OR

 

If the enzyme is inactivated by acid, there will be no or less browning.

 

Procedure

1. Prepare three beakers containing 0.5% ascorbic acid, 2% ascorbic acid, and water respectively.
2. Cut an apple to obtain three slices of similar size.
3. Immediately dip the apple slices into the three beakers of solutions for one minute.
4. Take the apple slices out and place them on three watch glasses.
5. Take a photo of the three apple slices at the start and every 10 minutes thereafter for a period of 30 minutes.
6. Compare the browning of the three apple slices with the help of the photos.

Result

	Degree of browning (relative units)
Time (min)	Water	0.5% Ascorbic acid	2% Ascorbic acid
0
10
20
30

Discussion

1. Describe the results.
2. Do the results support the hypothesis? Explain your answer.

Conclusion