In some countries, certain plants have seasonal growth. During the summer plants transport sucrose from the leaves to store it as starch in the roots. Table 1.1 summarises the changes in the leaves and roots during the year. Table 1.1 season leaves roots --- --- --- summer leaves synthesize sucrose sucrose stored as starch winter no leaves starch stored spring leaves growing starch converted to glucose You are required to identify the source of four plant extracts. These…

Biology 9700/34 — May/June 2011

Cambridge AS Level · Advanced Practical Skills · worked solutions for every part, with the mark scheme

questions

marks

120

minutes

Topics Presentation of Data and Observations · Analysis, Conclusions and Evaluation · Manipulation, Measurement and Observation · Use of the Light Microscope

Q1Analysis, Conclusions and EvaluationManipulation, Measurement and ObservationPresentation of Data and ObservationsFree sample

In some countries, certain plants have seasonal growth. During the summer plants transport sucrose from the leaves to store it as starch in the roots.

Table 1.1 summarises the changes in the leaves and roots during the year.

Table 1.1

season	leaves	roots
summer	leaves synthesize sucrose	sucrose stored as starch
winter	no leaves	starch stored
spring	leaves growing	starch converted to glucose

You are required to identify the source of four plant extracts. These have been taken from

a root in winter
a root in spring
phloem sap in summer
phloem sap in winter

(a)

(i)

Use the information in Table 1.1 to predict which substances you would expect to be present in each of the four plant extracts, then complete Table 1.2.

Key: ✓ (tick) substance present in plant extract
✗ (cross) substance absent from plant extract

Table 1.2

source of plant extract	substances present in each of the plant extracts
	starch	sucrose	glucose
root in winter
root in spring
phloem sap in summer
phloem sap in winter

(ii)

One sample was taken from each of the four plant extracts shown in Table 1.2.

You are required to identify from which plant extract each of the four samples S1, S2, S3 and S4 was taken.

You are provided with:

Table 1.3

labelled	contents	hazard	volume / $\text{cm}^3$
Benedict’s solution	Benedict’s solution	harmful irritant	If you require more of any of these reagents, please ask the Invigilator.
Biuret	copper sulfate sodium hydroxide	harmful irritant
iodine	iodine in potassium iodide solution	irritant
hydrochloric acid	hydrochloric acid	irritant
sodium hydrogen carbonate	sodium hydrogen carbonate	none

Describe the tests that show that sucrose is present in a plant extract.

(iii)

Select the appropriate reagents from those provided in Table 1.3 and carry out tests to identify the samples S1, S2, S3 and S4.

Prepare the space below and record your results.

(iv)

Complete Table 1.4 to match the samples, S1, S2, S3 and S4, with each plant extract.

Table 1.4

source of plant extract	sample
a root in winter
a root in spring
phloem sap in summer
phloem sap in winter

(b)

A student investigated the effect of different concentrations of sodium chloride solution on root tissues. A separate sample of root tissue was put into a starting volume of each concentration of sodium chloride solution. After a set time the root tissue was removed and the final volume of each solution was recorded. The change in volume for each concentration was calculated.

(i)

State three variables which the student should keep the same in this investigation. Describe how the student would keep each of these variables the same.

(ii)

The results of the student’s investigation are shown in Table 1.5.

Table 1.5

concentration of sodium chloride / $\text{mol dm}^{-3}$	change in volume of solution / $\text{cm}^3$
0.00	$-6.0$
0.25	$+1.0$
0.50	$+4.5$
0.80	$+5.2$
1.00	$+5.2$

Plot a graph of the data shown in Table 1.5.

Fig. 1.1

(iii)

Show on your graph the sodium chloride concentration where there is no change in volume of solution. [1]

Use this information to estimate the sodium chloride concentration where there is no change in volume of solution.

concentration = ______ $\text{mol dm}^{-3}$

(iv)

Use your graph to explain the effect of the different concentrations of sodium chloride solution on the root cells.

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Q2Use of the Light Microscope · Presentation of Data and Observations18M

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