Biology 9700/35 — May/June 2019

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

questions

marks

120

minutes

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

Q1Manipulation, Measurement and ObservationPresentation of Data and ObservationsAnalysis, Conclusions and EvaluationFree sample

Blood plasma contains proteins. The concentration of protein in blood plasma may change according to the health of a person.

The concentration of protein in blood plasma can be measured to identify possible health problems.

In this investigation you will be using protein solutions, P and U, instead of blood plasma.

You will need to:

prepare a serial dilution of solution P
carry out the test for protein on each concentration of protein solution
carry out the test for protein on the unknown concentration of protein, U
estimate the concentration of protein in U.

You are provided with the materials shown in Table 1.1.

Table 1.1

labelled	contents	hazard	volume/ $\text{cm}^3$
P	1% protein solution	none	30
U	protein solution of unknown concentration	none	10
W	distilled water	none	100
K	5% potassium hydroxide solution	harmful irritant	20
C	0.15% copper sulfate solution	none	20

If any solution comes into contact with your skin, wash off immediately under cold water. It is recommended that you wear suitable eye protection.

(a)

You will need to:

make a serial dilution of 1.0% protein solution, P, which reduces the concentration by half between each successive dilution
prepare $10\ \text{cm}^3$ of each concentration of protein solution.

Fig. 1.1 shows the first two beakers you will use to make your serial dilution.

(i)

Complete Fig. 1.1 by drawing as many extra beakers as you need for your serial dilution.

For each beaker:

state, under the beaker, the volume and concentration of protein solution available for use in the investigation
use one arrow with a label, above the beaker, to show the volume and concentration of protein solution added to prepare the concentration
use another arrow with a label, above the beaker, to show the volume of W added to prepare the concentration.

Fig. 1.1

(ii)

Carry out the test for protein on the different concentrations of protein using step 1 to step 7.

Prepare the concentrations of protein solution as decided in (a)(i) and shown in Fig. 1.1. Use a glass rod to mix the protein solutions and water.
Label the test-tubes with the concentrations of the protein solutions prepared in step 1.
Put $1\ \text{cm}^3$ of each concentration into the appropriately labelled test-tube.
Label another test-tube 0.0% and put $1\ \text{cm}^3$ of W into this test-tube.
Put $1\ \text{cm}^3$ of K into each test-tube. Shake gently to mix.
Put $1\ \text{cm}^3$ of C into each test-tube. Shake gently to mix.
Leave the test-tubes for at least 2 minutes. Shake gently to mix.

You will see a range of colours depending on the concentration of protein present.

Table 1.2 shows the range of colours and the letters you will use to record your observations in (a)(ii).

Table 1.2

colour	letters to use
very pale blue/colourless	VP
pale blue	PB
blue	B
pale purple	PP
purple	P
dark purple	DP

After step 7 you will see some of the colours in Table 1.2.

Record the colours, in an appropriate table, by using the letters in Table 1.2.

You may use the same letters for more than one test-tube.

It may help to observe the colour with a piece of white card behind the test-tube.

(iii)

You now need to estimate the concentration of U using your results.

Label a test-tube U and put $1\ \text{cm}^3$ of U into this test-tube.
Repeat step 5 to step 7 then record the colour of U in (a)(iii).

State the colour of U after step 7.

colour of U = ______

(iv)

Complete Fig. 1.2 to show the position on the line of each of the percentage concentrations of protein solution in (a)(i).

Using your results in (a)(ii) and (a)(iii), put the label U on Fig. 1.2 to show an estimate of the concentration of protein in U.

Fig. 1.2

(v)

Suggest how you could change the independent variable to have more confidence in your estimate of the concentration of protein in U.

(vi)

Suggest the apparatus that could be used to measure the concentration of protein in U more accurately.

(b)

The concentration of protein in blood plasma from five people with the same infection was measured for 11 days.

The results are shown in Table 1.3.

Table 1.3

time / days	concentration of protein in blood plasma / $\text{g dm}^{-3}$
	person 1	person 2	person 3	person 4	person 5	mean
0	57	53	52	59	54	55
3	91	89	94	90	86	90
6	120	115	115	120	130	120
8	87	106	82	81	86
11	53	62	59	54	57	57

(i)

Complete Table 1.3 by calculating the mean at 8 days.

Space for working.

(ii)

Plot a graph of the mean values shown in Table 1.3 on the grid in Fig. 1.3.

Use a sharp pencil for drawing graphs.

Fig. 1.3

(iii)

Explain, using your knowledge of the immune system, the increase in the concentration of protein in blood plasma between day 0 and day 6.

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