Biology 5090/31 — May/June 2010
Cambridge O-Level · Practical Test · worked solutions for every part, with the mark scheme
Topics Experimental Contexts · Analysis, Conclusions and Evaluation · Observations and Measurements · Use of Techniques, Apparatus and Materials · Planning Experiments and Investigations · Microscopy and Biological Drawing
Read through the whole question before starting.
Do not taste the fruit sections provided.
Fruits of banana, Musa spp, change as they ripen.
You are provided with two pieces from an unripe banana fruit, labelled S1, and two pieces from a ripe banana fruit, labelled S2.
Describe the observable differences between one piece of S1 and one piece of S2.
______
- Using forceps, dip the cut surface of one piece of S1 and one piece of S2 into the iodine solution for approximately 3 seconds.
Describe and explain the observable differences between S1 and S2 after this test.
______
Describe a food test that you could carry out to show that the ripe banana S2 contains more reducing sugar than the unripe banana S1, including at least one safety factor.
______
- Cut the other pieces of S1 and S2 each into three equal parts.
- Test one of these pieces of S1 and one of these pieces of S2 for reducing sugar.
Complete the table below by recording your observations and conclusions.
| S1 | S2 | |
|---|---|---|
| observations | ||
| conclusions |
One of the changes that takes place as a banana fruit ripens is the breakdown of starch to sugar.
How do your results in (a)(ii) and (b)(ii) support this statement?
______
- Put one piece of S1 into an empty beaker and leave this open to the air. Label the beaker S1.
- Put the other piece of S1 into one of the beakers labelled S3, which contains a dilute acid. Label this beaker S1.
- Put one piece of S2 into an empty beaker and leave this open to the air. Label the beaker S2.
- Put the other piece of S2 into one of the beakers labelled S3, which contains a dilute acid. Label this beaker S2.
- Leave these for at least 15 minutes.
While waiting for 15 minutes, begin Question 2.
- Observe the appearance of the pieces of S1 and S2 that were left.
Complete the table below by describing the appearance of the two pieces of S1 and S2.
| exposed to the air | in S3 | |
|---|---|---|
| S1 | ||
| S2 |
Suggest what may have caused any differences in appearance between the pieces of banana left open to the air and those immersed in dilute acid.
______
Outline, but do not carry out, an investigation to find out the effect of pH on the changes you observed.
______
The rest of this paper
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