You will be investigating the effect of salt concentration on the movement of water in potatoes. You are provided with the materials shown in Table 1.1. Table 1.1 labelled contents hazard volume / $\text{cm}^3$ :--- :--- :--- :--- P 5 lengths of potato none — W distilled water none 150 S $1\ \text{mol dm}^{-3}$ salt solution none 150 It is recommended that you wear suitable eye protection. (a) You will need to make different concentrations of salt solution using proportional…

Biology 9700/35 — May/June 2023

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

questions

marks

120

minutes

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

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

You will be investigating the effect of salt concentration on the movement of water in potatoes.

You are provided with the materials shown in Table 1.1.

Table 1.1

labelled	contents	hazard	volume / $\text{cm}^3$
P	5 lengths of potato	none	—
W	distilled water	none	150
S	$1\ \text{mol dm}^{-3}$ salt solution	none	150

It is recommended that you wear suitable eye protection.

(a)

You will need to make different concentrations of salt solution using proportional dilution of the $1.00\ \text{mol dm}^{-3}$ salt solution, S.

You will need to prepare $40\ \text{cm}^3$ of each concentration.

Table 1.2 shows two of the concentrations you will use.

Decide which other concentrations of salt solution you will use.

(i)

Complete Table 1.2 to show how you will prepare the other concentrations.

Table 1.2

final concentration of salt solution / $\text{mol dm}^{-3}$	volume of S / $\text{cm}^3$	volume of distilled water, W / $\text{cm}^3$
1.00	40	0



0.00	0	40

(ii)

Carry out step 1 to step 11.

step 1 Prepare the concentrations of salt solution, as shown in Table 1.2, in the beakers provided.

step 2 Cut 10 discs of potato for each of the concentrations prepared in step 1.

Each disc should be approximately $3\ \text{mm}$ thick.

step 3 Place 10 discs in a line as shown in Fig. 1.1.

Fig. 1.1

step 4 Measure the total length of the 10 discs and record this value in 1(a)(ii).

step 5 Put the 10 discs into the beaker containing $1\ \text{mol dm}^{-3}$ salt solution.

step 6 Repeat step 3 to step 5 with the other discs and the salt solutions you prepared in step 1.

step 7 Start timing and leave for 30 minutes.

Use this time to continue with other parts of Question 1.

step 8 After 30 minutes (step 7), discard the $1\ \text{mol dm}^{-3}$ salt solution from around the discs and tip the discs onto some paper towel.

step 9 Place the 10 discs in a line as in Fig. 1.1 and measure their total length. Record this value in 1(a)(ii).

step 10 Repeat step 8 and step 9 for the other salt concentrations.

step 11 Calculate the change in length for each line of 10 discs.

Record your results in an appropriate table, including raw results and processed results.

(iii)

Explain your results for the $0.0\ \text{mol dm}^{-3}$ salt solution (distilled water).

(iv)

Suggest why a line of 10 discs was measured instead of a single disc.

(v)

Identify one significant source of error in this investigation.

(vi)

Use your results to estimate a salt concentration where there is no net movement of water into or out of the potato.

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

(vii)

Describe two improvements to your procedure that would make the estimate in 1(a)(vi) more accurate.

1 ______

2 ______

(b)

The salt content of unprocessed food was measured.

The values are shown in Table 1.3.

Table 1.3

food type	salt content of unprocessed food / mg per 100 g food
potatoes (P)	10.0
tuna (T)	40.0
bran (B)	25.0
chicken (C)	50.0
salmon (S)	95.0

(i)

Plot a bar chart of the data shown in Table 1.3 on the grid in Fig. 1.2.

Use a sharp pencil.

Fig. 1.2

(ii)

The salt content of the same foods that had been processed was also measured.

The values are shown in Table 1.4.

Table 1.4

food type	salt content of processed food / mg per 100 g food
potatoes (P)	200.0
tuna (T)	300.0
bran (B)	1000.5
chicken (C)	350.5
salmon (S)	1800.0

Calculate the percentage increase in salt content when salmon is processed.

Show your working and write your answer to two significant figures.

increase in salt content = ______ $\%$

(iii)

State the independent variable in this study.

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Q2Use of the Light Microscope19M

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