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Cambridge International Examinations

Cambridge International Advanced Level
* 3 2 5 5 9 4 4 2 1 1 *

BIOLOGY 9700/52
Paper 5 Planning, Analysis and Evaluation May/June 2015
1 hour 15 minutes
Candidates answer on the Question Paper.
No Additional Materials are required.

READ THESE INSTRUCTIONS FIRST

Write your Centre number, candidate number and name on all the work you hand in.
Write in dark blue or black pen.
You may use a soft pencil for any diagrams, graphs or rough working.
Do not use staples, paper clips, glue or correction fluid.
DO NOT WRITE IN ANY BARCODES.

Answer all questions.

Electronic calculators may be used.

At the end of the examination, fasten all your work securely together.
The number of marks is given in brackets [ ] at the end of each question or part question.

This document consists of 8 printed pages.

DC (ST/SW) 90190/5
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1 Many fungi are decomposer organisms which carry out extracellular digestion. To do this they
secrete a number of enzymes.

A group of students made a solution of enzyme extract from a fungus. The extract contained the
enzyme amylase. They wanted to find out the concentration of amylase in the extract.

They were provided with:

• 0.5 g dm–3 stock solution of amylase

• starch agar plates with wells into which enzyme solutions can be placed. Starch agar plates
are Petri dishes containing agar mixed with starch.

Fig. 1.1 shows how the students used the plates to find the concentration of amylase.

starch agar

well containing
enzyme solution

plates were incubated

plates were flooded with iodine solution

area stained blue

area stained brown

Fig. 1.1

The students thought that the area stained brown was proportional to the amylase concentration.

(a) Identify the independent and dependent variables in this investigation.

independent variable ................................................................................................................

dependent variable .............................................................................................................. [2]

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(b) Describe how the students could use the method outlined in Fig. 1.1 to find out the
concentration of the enzyme amylase in their extract.
Your method should be detailed enough for another person to follow.

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(c) There are different types of amylase enzyme. They hydrolyse starch in different ways.
Two of these enzymes are:

• β-amylase hydrolyses every second α-1,4 glycosidic bond in starch molecules

• γ-amylase hydrolyses all α-1,6 glycosidic bonds and all α-1,4 glycosidic bonds in starch
molecules.

In a second investigation, the students were provided with two beakers, A and B. One
contained β-amylase and the other contained γ-amylase. They used these solutions to
hydrolyse 25 cm3 samples of 0.5 g dm–3 starch solution.

Suggest and explain how the students could identify which beaker contained β-amylase and
which contained γ-amylase.

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(d) Humans produce the enzyme α-amylase in their salivary glands. There may be many copies
of the gene coding for α-amylase on chromosome 1. The concentration of the α-amylase in
the saliva is positively correlated with the number of copies of this gene.

In a third investigation, the students obtained saliva from six people, A to F. Equal volumes of
saliva were added to wells in agar plates similar to those shown in Fig. 1.1.
The plates were incubated for the same length of time and the area of the brown zone for
each sample of saliva was calculated.

Table 1.1 shows results of this investigation.

Table 1.1

area of brown zone / mm2

enzyme extract
plate 1 plate 2 plate 3 plate 4 plate 5 plate 6
A 3632 3848 3632 3632 3632 3848
B 2827 2827 2642 2463 1963 2827
C 2124 1963 1963 2124 1963 2124
D 1385 1257 1809 1257 1257 1385
E 656 707 707 656 707 656
F 298 298 314 314 298 298

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(i) Identify two results in Table 1.1 that may be anomalous. Show your answers by circling
the two values. [2]
(ii) State how the students should deal with these anomalies.

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(iii) The students decided to calculate the standard deviations of their results using the
formula:

/ (x - x ) 2
s=
n-1
Key to Symbols
s = standard deviation x = a result x = mean Σ = sum of n = sample size

Use Table 1.2 and the formula above to calculate the standard deviation for the results
for person F.
Table 1.2

plate x x-x (x - x ) 2
1 298
2 298
3 314
4 314
5 298
6 298
Σ

answer .......................................................... [2]

(iv) Suggest an explanation for the results shown in Table 1.1.

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[Total: 20]
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2 The speed at which an electrical impulse travels along a nerve can be determined by carrying out
a nerve conduction velocity (NCV) test.

Surface electrodes are placed on the skin over nerves at various locations. They produce a very
mild electrical charge, which stimulates the nerve.

The resulting electrical activity in the nerve is measured by a recording electrode. The distance
between the electrodes and the time it takes for electrical impulses to travel between them are
used to determine the nerve conduction velocity.

Fig. 2.1 shows how the NCV is measured in the ulnar nerve of the human forearm.

position of ulnar nerve

surface electrode

monitoring device

Fig. 2.1

An investigation to measure the NCV in the ulnar nerve in females of different ages was carried
out on 394 individuals.

(a) Suggest three variables which the investigators should have standardised.

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Table 2.1 shows the results of this investigation.

Table 2.1

age category / years mean conduction confidence limits

velocity ± SM
lower limit upper limit
30–39 54.3 ± 1.200 51.90 56.70
40–49 54.7 ± 0.645 53.41 55.99
50–59 52.4 ± 0.600 51.20 53.60
60–69 52.2 ± 0.675
70–79 49.0 ± 1.075 46.85 51.15

SM = standard error

(b) The confidence limit = mean ± 2 SM.

Use this formula to calculate the missing confidence limits. Use the space below for any
working and enter your answers in Table 2.1.

[1]

One conclusion from these data is that mean conduction velocity in the ulnar nerve varies
significantly with age.

(c) (i) Identify two age categories which appear to support this conclusion and give a reason
for your choice.

age categories ............................................................... and ............................................

reason ...............................................................................................................................

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(ii) State which statistical test could have been used to confirm this conclusion and give a
reason for your choice.

test ....................................................................................................................................

reason ...............................................................................................................................

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(iii) State a null hypothesis for this test.

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(d) State one reason why the results of the investigation were considered to be reliable.

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[Total: 10]

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