You are required to investigate the effect of three different concentrations of a solution on strips of potato tissue. (a) - Remove the potato tissue from the solution and blot it gently with the paper towel to remove excess liquid. - Cut six strips of potato exactly $70\text{ mm}$ long by approximately $10\text{ mm}$ wide. - Label three dishes A , B and C , then place two potato strips in each. - Add solutions A , B and C to the appropriate labelled dish, ensuring that the…

Biology 5090/32 — October/November 2010

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

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marks

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

Q120MPlanning Experiments and InvestigationsAnalysis, Conclusions and EvaluationObservations and MeasurementsExperimental ContextsUse of Techniques, Apparatus and MaterialsFree sample

You are required to investigate the effect of three different concentrations of a solution on strips of potato tissue.

(a)

Remove the potato tissue from the solution and blot it gently with the paper towel to remove excess liquid.
Cut six strips of potato exactly $70\text{ mm}$ long by approximately $10\text{ mm}$ wide.
Label three dishes A, B and C, then place two potato strips in each.
Add solutions A, B and C to the appropriate labelled dish, ensuring that the potato strips in each dish are covered by the solution.
Note, in Table 1.1, the time when the solutions were added.

Leave at least 30 minutes before returning to complete this question.

Carry on with Question 2 while you wait.

Then:

(i)

Remove the strips from solution A, blot them gently.
Note the time in Table 1.1.
Measure their lengths and record them in Table 1.1.
Repeat this procedure for the strips in B and C.

(ii)

Suggest why two strips were used, rather than one, in each solution.

______

(iii)

Explain how your observations do, or do not, support this suggestion.

______

(iv)

Complete Table 1.1.

Table 1.1

solution	concentration / $\text{mol per dm}^3$	initial lengths / $\text{mm}$	mean length / $\text{mm}$	final lengths / $\text{mm}$
A	0.8	70 and 70	70	and
B	0.4	70 and 70	70	and
C	0.1	70 and 70	70	and

(b)

(i)

Using the information in Table 1.1 draw a graph, on the axes provided, of mean change in length against concentration of solution.

Fig. 1.1

(ii)

From your graph, determine the concentration of the solution at which there would be no change in mean length of potato strip.

______

(iii)

Explain the significance of this concentration.

______

(c)

Suggest three ways in which this investigation could be improved.

______
______
______

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