Biology 5090/62 — May/June 2020

Cambridge O-Level · Alternative to Practical · worked solutions for every part, with the mark scheme

questions

marks

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Topics Experimental Contexts · Use of Techniques, Apparatus and Materials · Observations and Measurements · Microscopy and Biological Drawing · Planning Experiments and Investigations · Analysis, Conclusions and Evaluation

Q119MPlanning Experiments and InvestigationsUse of Techniques, Apparatus and MaterialsAnalysis, Conclusions and EvaluationExperimental ContextsObservations and MeasurementsFree sample

In the beetroot plant, cells in the root contain a red pigment. This pigment remains in the cells unless the cells are damaged. If beetroot tissue is placed in water and the cells are damaged, the pigment leaves the cells and colours the water.

Some students investigated the effect of temperature on the release of the red pigment from beetroot tissue.

They followed these instructions:

Cut four cylinders of beetroot tissue, each $30\text{ mm} \times 10\text{ mm}$ .
Wash the beetroot cylinders in the beaker of rinsing water.
Label four test-tubes A, B, C and D.
Place one beetroot cylinder in each test-tube.
Place test-tube A in a beaker of water at $20\,^\circ\text{C}$ .
Make three water-baths at initial temperatures of $40\,^\circ\text{C}$ , $60\,^\circ\text{C}$ and $80\,^\circ\text{C}$ .
Place test-tube B in the $40\,^\circ\text{C}$ water-bath, test-tube C in the $60\,^\circ\text{C}$ water-bath and test-tube D in the $80\,^\circ\text{C}$ water-bath.
Add water from each of the water-baths to the test-tube placed in it until the beetroot cylinder is just covered with the water.
Leave the beetroot cylinders for 5 minutes and then remove the cylinders from the test-tubes.
Place the test-tubes in the test-tube rack and observe the water in them.

(a)

The table shows what the students observed.

Table 1.1

(i)

Suggest why the beetroot cylinders were all cut to $30\text{ mm} \times 10\text{ mm}$ .

______

(ii)

Explain why the beetroot cylinders were washed before starting the investigation.

______

(iii)

Suggest what the students concluded from their observations and explain your answer.

conclusion ______

explanation ______

(iv)

State two possible sources of error in the method used. For each, explain how the method could be improved.

source of error 1 ______
improvement 1 ______

source of error 2 ______
improvement 2 ______

(b)

Another student used an instrument called a colorimeter to obtain a numerical value for the colour in each test-tube. She did the experiment twice.

(i)

Explain how repeating the experiment makes the observations of colour more reliable.

______

(ii)

Some of the readings from the colorimeter are shown in the table.

temperature / $^\circ\text{C}$	colorimeter reading / arbitrary units
	experiment 1	experiment 2	average
20	0.6	1.6
40	1.6	2.8
60	4.9	4.7
80		9.8

The colorimeter reading at $80\,^\circ\text{C}$ for experiment 1 was:

Fig. 1.2

Insert this reading into the table of results.

(iii)

Calculate the average reading for each temperature and complete the table.

(iv)

On the grid construct a line graph to show the relationship between temperature and average colorimeter readings. Join your points with ruled, straight lines.

Fig. 1.3

(v)

Use your graph to determine the average colorimeter reading for $55\,^\circ\text{C}$ .

Show your working on your graph.

______ $\text{arbitrary units}$

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