AS & A Level Biology - 9700 Paper 3 2014 Winter Zone 1

An enzyme, E, catalyses the hydrolysis (breakdown) of triglycerides into fatty acids and glycerol.
The substrate for E will be the triglycerides present in milk, labelled M.
The end-point of this hydrolysis can be determined by using an indicator, I, which changes colour when the fatty acids are produced, as shown in Fig. 1.1.

You are required to:
• prepare different concentrations of the enzyme solution, E
• investigate the effect of different concentrations of E (independent variable) on the hydrolysis of triglycerides in milk.
You are provided with:
[Table_1]
You are required to dilute the 5% enzyme solution, E, to provide a range of known concentrations using simple dilution.
Decide on the further concentrations of enzyme solution you will use in your investigation in addition to the 5% solution.
You will need to use 10cm³ of each enzyme solution.
(a) (i) Prepare the space below to show:
• the concentration of each enzyme solution
• the volumes of E
• the volumes of W. [3]
(ii) Describe the expected trend in the time taken to reach the end-point as the concentration of enzyme solution increases.
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(iii) State one reason for the expected trend described in (a)(ii).
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(iv) As part of this investigation you are required to set up a control using the apparatus provided. Describe how you will set up this control.
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Read step 1 to step 10 before proceeding.
Proceed as follows:
1. Prepare all the concentrations of enzyme solutions you have listed in (a)(i) in the containers provided.
You are required to investigate the effect of different concentrations of enzyme solutions on the hydrolysis of triglycerides in milk. The appearance of fatty acids can be detected by using the indicator solution I.
2. Put 2 cm³ of M into each of six separate test-tubes.
3. Put 2 cm³ of I into each test-tube containing M and gently shake.
4. Put 3 cm³ of A into each test-tube containing M and I and gently shake so that all the mixture turns orange.
Note that the mixtures might be different shades of orange.
The reaction will start as soon as you add enzyme solution, so read steps 5 to 10 before proceeding.
5. Set up your control as described in (a)(iv).
6. Put 2 cm³ of the lowest concentration of enzyme solution into one of the test-tubes from step 4 and mix well.
7. Repeat step 6 with two other concentrations of enzyme solution.
8. Start timing.
9. Record the time when each end-point (yellow) is reached, as shown in Fig. 1.1.
10. Repeat steps 6, 8 and 9 with the remaining concentrations of enzyme solution.
If the time taken to reach the end-point for any one concentration is longer than 300 seconds (5 minutes) record as ‘more than 300’.
(v) Prepare the space below to record your results. [5]
(vi) Calculate the rate of hydrolysis for the 5% E.
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(vii) Identify one significant source of error in measuring the dependent variable in the investigation you have just carried out.
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(viii) You used a syringe to measure the volumes of M.
State the volume of the smallest division on the syringe ..................
State the actual error of the syringe.
actual error .............................................................[1]
(b) Suggest how you would modify this investigation to obtain an accurate optimum temperature for the activity of E.
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(a) (i) Draw a large plan diagram of the part of the specimen on J1 indicated by the shaded sector in Fig. 2.1. Your plan diagram should include:
• the part of the specimen indicated by the shaded sector
• the four vascular bundles which you selected from the sector.
Use one ruled label line and label to show one vascular bundle.
(ii) Observe the tissue in the central pith.
Select one group of three whole cells, which includes:
• one large cell
• two smaller cells which touch each other and also touch the large cell.
Make a large drawing of the group of cells which you have selected.
Use one ruled label line and label to show one cell wall.

(b) Fig. 2.2 is a photomicrograph of a stained transverse section through a stem of a different plant species.
This plant species is found globally.

(i) Calculate the magnification of Fig. 2.2 using the scale bar.
You may lose marks if you do not show your working or if you do not use appropriate units.
magnification x ...........................................

(b) (ii) Prepare the space below so that it is suitable for you to show the observable differences between the specimens shown on J1 and on Fig 2.2.
Record your observations in the space you have prepared.

(c) A student investigated the effect of different concentrations of sucrose solutions on 5 pieces of plant stem.
At the start, each piece of plant stem was cut along part of its length as shown in Fig. 2.3.

Each piece of cut plant stem curved as shown in Fig. 2.4. The distance between the cut ends was 10 mm for each piece of plant stem.
Each piece of plant stem was placed in a separate dish as shown in Fig. 2.4 and covered with the same volume of one of the concentrations of sucrose solution. A different concentration of sucrose solution was used in each of the five dishes.
After a set time the distance between the cut ends was measured for each piece of plant stem.
The student calculated the change in distance between the cut ends for each plant stem.
The processed results of the student's investigation are shown in Table 2.1.
[Table_1]
(i) Plot a graph of the data in Table 2.1.
[Graph_1]
(ii) Explain the trend shown in the graph.