Analysis, Conclusions and Evaluation

As you carry out each test to identify the presence or absence of the biological molecule in S1, S2 and S3, complete the following:

Decide which biological molecule to identify in the first test.

First test: Test for ______

Describe how you used the reagents to carry out this test.

Carry out the first test and record your observations.

Use these observations to complete the sentence.

Solution(s) ______ contain(s) the biological molecule ______ .

Decide which biological molecule to identify in the second test.

Second test: Test for ______

Describe how you used the reagents to carry out this test.

Carry out the second test and record your observations.

Use these observations to complete the sentence.

Solution(s) ______ contain(s) the biological molecule ______ .

Decide which test you will use to check the identity of the third biological molecule.

Third test: Test for ______

Describe how you used the reagents to carry out this test.

Carry out the third test and record your observation.

Use this observation to complete one of the following sentences.

Solution(s) ______ contain(s) the biological molecule ______ .

OR

Solution ______ does not contain any of these biological molecules, glucose, starch or sucrose.

State which of the biological molecules, glucose, starch or sucrose cannot be hydrolysed by the enzyme, E.

From your observations, state which of the solutions (S1, S2, S3) is hydrolysed by the enzyme, E. Explain the reason for your answer.

solution ______

reason ______

Describe how you would modify this procedure to investigate the effect of temperature on the enzyme, E.

Use your results to complete the following statement.

The sodium chloride concentration of the unknown sample, S4, is between

______ $\text{mol dm}^{-3}$ and ______ $\text{mol dm}^{-3}$.

Identify one significant source of error in using Fig. 1.1 to obtain your results.

Suggest how you would make three improvements to this investigation.

State the sodium chloride concentration at which 50% of the red blood cells are destroyed.

Show on the graph how you obtained the concentration.

Sodium chloride concentration = ______ $\times 10^{-2}\ \text{mol dm}^{-3}$

Explain what is happening between the red blood cells and the external solutions when 0 and 100% of red blood cells are destroyed.

0% red blood cells destroyed

100% red blood cells destroyed

During the investigation you will be sampling at intervals and using iodine solution to test for the presence of starch. The end-point is reached when the iodine solution is a dark yellow-brown. There may also be some specks of blue-black present in the iodine solution. These specks can be ignored.

Carry out step 1 to step 14.

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

step 2 Label test-tubes with the concentrations of amylase solution prepared in step 1.

step 3 Label the white tile with the numbers shown in Fig. 1.1.

The numbers indicate the sampling times in seconds.

step 4 Put one drop of iodine on the white tile at each sampling time, as shown in Fig. 1.1.

step 5 Put $3\ \text{cm}^3$ of S into each of the test-tubes labelled in step 2.

step 6 Put $1\ \text{cm}^3$ of the 2.0% amylase solution, E, into the test-tube labelled 2.0%. Use a glass rod to mix.

step 7 Start timing.

step 8 After 15 seconds, use the glass rod to transfer a drop of the mixture from the test-tube onto the drop of iodine that is labelled 15, on the white tile.

step 9 Clean the glass rod with a paper towel.

step 10 Repeat step 8 to step 9 at 15-second intervals until the end-point is reached.

step 11 Record in (a)(iii) the time when the end-point is first observed.

If the end-point is not reached at 180 seconds, record as 'more than 180'.

step 12 Clean the white tile with a damp paper towel and then dry the white tile. Make sure all the numbers are still visible.

step 13 Put one drop of iodine on the white tile at each sampling time, as shown in Fig. 1.1.

step 14 Repeat step 6 to step 13 using the other concentrations of amylase solution you prepared in step 1.

Record your results in an appropriate table.

Using your results in (a)(iii) and (a)(v), estimate the concentration of amylase in U.

Suggest one source of error in the procedure described in step 10 of this investigation.

Suggest how you could make one improvement to reduce the source of error stated in (a)(vii).

Use your graph in Fig. 1.2 to determine the rate of reaction when the concentration of substrate is $0.45\ \text{mol dm}^{-3}$.

rate of reaction = ______ arbitrary units

The $V_{\text{max}}$ of this enzyme is 2.250 arbitrary units.

Using this information and the graph in Fig. 1.2, state whether the inhibitor is a competitive inhibitor or a non-competitive inhibitor.

Explain your answer.

Using your results in (a) and (b)(iii), estimate the concentration of reducing sugar for the highest concentration of invertase solution ($1\%$) and for the lowest concentration of invertase solution, including appropriate units.

highest concentration ($1\%$) = ______

lowest concentration = ______

Describe how changing the concentration of invertase affects the concentration of reducing sugar produced.

Suggest and explain how increasing the temperature by $10\,^{\circ}\text{C}$ above room temperature would affect the results you obtained in (b)(iii).

Complete Table 1.4 by identifying two significant sources of error in this investigation.

Suggest how you would improve the procedure to reduce the effect of these errors.

Table 1.4

This investigation used colour to indicate the concentration of carbon dioxide in the sample.

Suggest three improvements to this investigation that would increase the accuracy of the results.

A student repeated the investigation using the same procedure but with starch as the substrate instead of glucose.

Suggest why it took much longer to reach the end-point when starch was used as the substrate.

Describe the trend shown by the graph in Fig. 1.4.

Use the graph in Fig. 1.4 to find the time required for the rate of carbon dioxide production to be 1.75au when the yeast was incubated at 35°C.

______

Complete the sentences by using two of the following words.

$\text{gain} \quad \text{less} \quad \text{lose} \quad \text{more}$

If the potato cells ..................... water then the sucrose solution will become more dilute.

This will change the sucrose solution so that it becomes ..................... dense.

A piece of potato is left in a sucrose solution for 15 minutes, to allow time for osmosis to take place.

The concentration of the sucrose solution after 15 minutes may be different from the original concentration.

After 15 minutes a blue dye is added to the sucrose solution to make a blue solution. The blue dye does not affect the concentration of the sucrose solution.

A small volume of this blue solution is then released into a known concentration of sucrose solution as shown in Fig. 1.2.

Fig. 1.2

The pipette is removed immediately after the blue solution is released.

The blue solution may move up, move down or remain at the same level depending on the difference in the concentration between the blue solution and the known concentration of sucrose solution.

Think about how the blue solution will move in the known concentration of sucrose in the test-tubes shown in Fig. 1.3.

Fig. 1.3

Complete Fig. 1.3 by drawing an arrow on each test-tube, using the key, to show how you expect the blue solution to move.

key:

• $\uparrow$ blue solution moves up
• $\downarrow$ blue solution moves down
• $\rightarrow$ blue solution remains at the same level

Using your results in (b)(iii) estimate the concentration of sucrose solution with a water potential equal to the water potential of the potato tissue.

Identify one significant source of error in this investigation.

Describe how you would use this procedure to produce a more accurate estimate of the concentration of sucrose solution with a water potential equal to the water potential of the potato tissue.

Describe the movement of water when the concentration of the sucrose solution surrounding the piece of potato has a water potential equal to the water potential in the potato tissue.

Using the same procedure a student observed that the blue solution stayed in the same position (did not move up or down) in a concentration of sucrose solution of $0.3\ \text{mol dm}^{-3}$.

Fig. 1.6 shows the relationship between the concentration of sucrose solution and the water potential of the sucrose solution.

Fig. 1.6

Use the graph in Fig. 1.6 to estimate the water potential of a $0.3\ \text{mol dm}^{-3}$ sucrose solution. Show on the graph how you estimated the water potential.

water potential = ______ $\text{kPa} \times 10^2$

The student’s hypothesis was:

“the time taken for the Benedict's solution to show the first appearance of a colour change will decrease as the temperature increases.”

State whether your results support this hypothesis.

Use your results to explain your answer.

You are required to:

• select one temperature from $70\ ^{\circ}\text{C}$, $80\ ^{\circ}\text{C}$, $90\ ^{\circ}\text{C}$ or $100\ ^{\circ}\text{C}$ to carry out the Benedict’s test
• make different concentrations of glucose from the solution G
• estimate the glucose concentrations of solutions S1 and S2 at the selected temperature.

You are provided with:

To compare the concentrations of glucose you will need to standardise the temperature using your results from (a)(ii).

State the temperature you will use.
State a reason for the temperature you have chosen.

temperature = ______ $^{\circ}\text{C}$
reason = ______

Complete Fig. 1.2 below to show:

• each percentage concentration of glucose solution (the concentration of G is shown)
• where the samples S1 and S2 fit in the series of concentrations.

Describe three modifications to this investigation which would improve the confidence in your results.

A systematic error occurs when apparatus with scales are used, since the scales may be slightly different.
For example, when measuring the same line, two rulers may give different lengths. However, as long as the same ruler is used for all the measurements, the trend is not affected because the error is consistent.

State one piece of apparatus used in this investigation that may have a systematic error. Suggest whether this affected your results and give a reason for your answer.

apparatus = ______
reason = ______

Complete the sentence by selecting the correct word from: least or most or same.

The piece of potato soaked in the lowest concentration of sodium chloride solution will have the ______ angle of bend when compared to the other concentrations of sodium chloride solution.

Using your results in (a)(iv) state the concentration of sodium chloride solution in S1, S2 and S3.

S1 = ______ $\text{mol dm}^{-3}$
S2 = ______ $\text{mol dm}^{-3}$
S3 = ______ $\text{mol dm}^{-3}$

Estimate the concentration of the sodium chloride solution in S4 using your results in (a)(iv), (a)(v) and (a)(vi).

A more accurate estimate for the concentration of sodium chloride solution in S4 can be found by using this graph.

Use your graph to estimate the concentration of sodium chloride solution in S4 using your answer to (a)(vi).
Show on the graph how you estimated the concentration of sodium chloride solution.

concentration in S4 = ______

Suggest how you would improve this procedure to have more confidence in your estimate of S4.

A student puts a piece of the potato from S1 into water.
Explain, in terms of water potential, the effect this would have on the potato cells.

Calculate the ratio of the total width of the stem compared to the width of the central air space.

Show all the steps in your working and use appropriate units.

ratio = ______

Describe how to improve the accuracy of this ratio.

Identify observable differences between the stem on K1 and the stem in Fig. 2.2.

Record the observable differences in Table 2.1.

Table 2.1

Show clearly on the diagrams below, using the key, how you would expect to see the drop or small volume of P move if:

Key:

• $\uparrow$ a drop or small volume of P moves up
• $\downarrow$ a drop or small volume of P moves down
• $\rightarrow$ a drop or small volume of P remains at same level

Complete the following by using one of the words ‘more’ or ‘less’.

You may use each word once or more than once.

P is ______ concentrated than $0.1\ \text{mol dm}^{-3}$ (S1).

P is ______ concentrated than $1.0\ \text{mol dm}^{-3}$ (S2).

Use your results to estimate the concentration of sucrose in P.

estimate of concentration of sucrose in P = ______

State which solution, S1 or S2, you will dilute to prepare further concentrations.

Use your results to explain the reason for your decision.

Using these additional results from (vi) state a more accurate estimate of the concentration of sucrose in P than in (iii).

Describe how you would modify this procedure to investigate the concentration of sucrose in P, using Benedict’s solution.