Biology 9700/35 — May/June 2014
Cambridge AS Level · Advanced Practical Skills · worked solutions for every part, with the mark scheme
Topics Analysis, Conclusions and Evaluation · Presentation of Data and Observations · Manipulation, Measurement and Observation · Use of the Light Microscope
During the summer, certain plants translocate sucrose from the leaves to the roots to be stored as starch.
In the spring, this starch is hydrolysed to produce glucose which will provide energy for new growth.
You are provided with three samples, S1, S2 and S3 from plant root extracts, removed at different times of the year:
- the middle of winter, when there was no plant growth
- the beginning of spring, when plant growth begins
- the middle of spring, during active growth.
These extracts were tested for starch. Predict the colour that was observed and complete the table.
| time of year extract was taken | predicted colour |
|---|---|
| middle of winter | |
| beginning of spring | |
| middle of spring |
State the reagent you will use to compare the concentrations of starch and describe how you will standardise the starch test for each sample.
reagent ______
description ______
Proceed as follows:
- Carry out the starch test as described in (a)(ii).
Prepare the space below and record your observations.
Complete the table to match the samples S1, S2 and S3 with the time of year that each extract was taken from the root.
| time of year extract was taken | sample |
|---|---|
| middle of winter | |
| beginning of spring | |
| middle of spring |
You are required to estimate the concentration of glucose in S3 using G1 and G2.
You are provided with:
| labelled | hazard | percentage concentration of glucose | volume / |
|---|---|---|---|
| G1 | none | 0.1 | 20 |
| G2 | none | 1.0 | 20 |
Proceed as follows:
- Carry out tests to compare the concentration of glucose in S3, G1 and G2 using the apparatus and reagents provided.
You will need to record the time taken for the first appearance of a colour change at the top of the mixture of the sample with the selected reagent(s).
If no colour change occurs after 5 minutes, stop the experiment and record 'more than 300'.
Prepare the space below and record your results.
Use the results you obtained to estimate the concentration of glucose found in S3.
Suggest how you would modify this investigation to obtain a more accurate estimate of the glucose concentration in S3.
A systematic error occurs when apparatus with scales are used, since the scales may be slightly different.
For example, when measuring the same line, two rulers may give different lengths. However, as long as the same ruler is used for all the measurements, the trend is not affected because the error is consistent.
State one piece of apparatus used in this investigation that may have a systematic error. Suggest whether this affected your results and give a reason for your answer.
apparatus ______
effect and reason ______
Certain plants translocate sucrose from the leaves to the roots to be stored as sucrose rather than as starch. These roots can be harvested and kept in storage until they are sold. However, water loss during storage reduces their value.
A scientist investigated how water loss from these roots was affected by the time in storage. Constant temperature and humidity were maintained during storage.
Ten roots were weighed at five day intervals. The mean percentage change in water content was calculated. It was found that all the roots had lost water.
The results are shown in Table 1.1.
Table 1.1
| time in storage / days | mean percentage change in water content |
|---|---|
| 5 | -6.25 |
| 10 | -11.00 |
| 15 | -15.50 |
| 20 | -17.25 |
| 25 | -17.50 |
Plot a graph of the data in Table 1.1.
Ten roots were stored for 5 days, and another ten roots were stored for 20 days. Pieces of root from the sample at 5 days and from the sample at 20 days were removed, weighed and soaked in dilute sucrose solution for 24 hours. The pieces were then reweighed.
State which sample would have the highest percentage gain in mass after soaking in the dilute sucrose solution.
Explain your answer using your knowledge of water potential.
sample ______
explanation ______
The rest of this paper
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