AS & A Level Biology - 9700 Paper 3 2014 Winter Zone 6

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, E. You will need to use 20 cm^3 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.

Read step 1 to step 13 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 using the indicator solution B.
Every 30 seconds, for a total of 180 seconds, a sample of milk will be removed from the test-tube and placed on a tile. You will need to have prepared this tile before you add the enzyme solutions.
Wipe the tile clean with a damp paper towel and then dry the tile. Label the tile as shown in Fig. 1.1. The numbers indicate the sampling times in seconds. Put two drops of indicator solution, B, on the tile above each sampling time, as shown in Fig. 1.1.
[Image_1: Fig. 1.1]
3. Prepare a water-bath between 35 °C and 40 °C. You will need to add hot water/cold water to maintain the temperature of the water-bath between 35 °C and 40 °C for steps 7 to 12.
4. Put 2.5 cm^3 of M into a test-tube.
5. Put 2.5 cm^3 of A into the same test-tube.
6. Repeat steps 4 and 5 for each of the concentrations of enzyme solution you are going to investigate, including the 5\% concentration, E.
7. Put all the test-tubes into the water-bath. Allow 2 minutes for the contents of the test-tubes to reach the same temperature as the water-bath.
The reaction will start as soon as you add the enzyme solutions so read steps 8 to 13 before proceeding.
8. Put 2.5 cm^3 of the 5\% concentration, E, into one of the test-tubes, leaving the test-tube in the water-bath. Stir the contents of the test-tube and start timing.
9. After 30 seconds use the pipette to transfer two drops of the contents of the test-tube to the drop of B, labelled 30.
10. Repeat step 9, at 30 second intervals, until a drop changes to yellow (end-point).
11. Record the time taken to reach the end-point.

If the drop at 180 seconds does not reach the end-point, record ‘more than 180’ as your result.
Once you have recorded a time for the end-point remove this test-tube from the water-bath and proceed to step 12.
12. Wipe the tile clean with a damp paper towel and then dry the tile. Label the tile again as shown in Fig. 1.1.
13. Repeat steps 8 to 12 with the remaining concentrations of enzyme solutions.
(ii) Prepare the space below to record your results.

(iii) Identify one significant source of error in measuring the dependent variable in this investigation.
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(iv) Describe one improvement to this investigation which would increase the confidence in your results.
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(b) A student investigated an enzyme which hydrolyses starch to glucose over a period of 20 minutes. The student measured the mass of glucose present at four minute intervals.
The volumes and concentrations of starch and enzyme were kept the same (standardised).
(i) State two other variables that need to be standardised in this investigation. Describe how you would standardise each of these variables.
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The results are shown in Table 1.1.
[Table_1]
time / min | mass of glucose / mg
4 | 1.90
8 | 3.15
12 | 3.90
16 | 4.00
20 | 4.05

(ii) Using the results in Table 1.1, calculate the rate of production of glucose between:
• 4 and 12 minutes .................................................. mg min^{-1}
• 12 and 20 minutes. .................................................. mg min^{-1}

(iii) Plot a graph of the data in Table 1.1.
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[Graph Paper Image]

(iv) Explain the reasons for the change in mass of glucose between:
• 0 and 12 minutes
• 12 and 20 minutes.
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M1 is a slide of a stained transverse section through a plant root. This plant species grows worldwide. You are not expected to be familiar with this specimen.
To help draw a plan diagram with the correct shape and proportions of the tissues, an eyepiece graticule can be used to measure the layers of tissues, without the need to calibrate the eyepiece graticule scale.
(a) (i) Explain how one observable feature on M1 identifies this specimen as a root.
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(ii) Draw a large plan diagram of the part of the specimen on M1 indicated by the shaded sector in Fig. 2.1.

Use one ruled label line and label to show the xylem. [5]
(iii) Observe the xylem and the cortex of the specimen on M1.
Select:
• one group of three whole touching xylem vessels
• one group of three whole touching cortex cells.
Make a large drawing of each of these two groups of three cells.
Use one ruled label line and label to show one lumen on one of your drawings.
xylem vessels
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cortex cells..........................................................................................................[5]

(b) Use the lines Y and Z shown on Fig. 2.2 to calculate the ratio of Y to Z.
You may lose marks if you do not show your working or if you do not use appropriate units.

ratio .......................................... [3]

(c) Prepare the space below so that it is suitable for you to record observable differences between the specimen on M1 and Fig. 2.2.
Record your observations in the space you have prepared. [5]