Biology 9700/34 — October/November 2017
Cambridge AS Level · Advanced Practical Skills · worked solutions for every part, with the mark scheme
Topics Manipulation, Measurement and Observation · Presentation of Data and Observations · Analysis, Conclusions and Evaluation · Use of the Light Microscope
Yeast cells contain enzymes that catalyse metabolic reactions. Some of these reactions release carbon dioxide.
You are required to investigate the progress of enzyme-catalysed reactions by testing for the release of carbon dioxide.
A sample of yeast cells in sucrose solution, Y, will be put into a piece of Visking tubing, V, as shown in Fig. 1.1.
The Visking tubing membrane is selectively permeable. The carbon dioxide molecules produced by the yeast cells will diffuse through the membrane of the tubing into the water surrounding the Visking tubing.
Fig. 1.1 shows the apparatus you will set up for this investigation.
To test for the release of carbon dioxide, a sample of the water surrounding the Visking tubing is added to drops of an indicator, B.
As the concentration of carbon dioxide increases, B changes from blue to green to yellow.
BLUE GREEN YELLOW
| BLUE | GREEN | YELLOW |
|---|---|---|
| no carbon dioxide | increasing concentration | highest concentration of carbon dioxide |
To follow the progress of this reaction you will need to take samples from the water surrounding the Visking tubing at different times for a total of 10 minutes.
Decide how often you will take these samples, including a final sample at 10 minutes.
State the times when you will remove the samples.
You are provided with:
| labelled | contents | hazard | volume / |
|---|---|---|---|
| Y | yeast cells in sucrose solution | none | 20 |
| B | bromothymol blue indicator solution | harmful | 10 |
| W | distilled water | none | 100 |
| labelled | details |
|---|---|
| V | length of Visking tubing in a beaker containing distilled water |
If any liquids come into contact with your skin, wash off immediately under cold water. It is recommended that you wear suitable eye protection.
Proceed as follows:
Read step 1 to step 18.
- Label the tile with the sampling times you decided in (a)(i) and 0 (zero) for a sample removed at the start of timing.
- Put one drop of B onto the tile for each of the sampling times.
- Tie a knot in the Visking tubing as close as possible to one end so that it seals the end.
- To open the other end, wet the Visking tubing and rub the tubing gently between your fingers.
- Stir Y and put approximately of Y into the open end of the Visking tubing.
note: remove the liquid not the froth.
- Rinse the outside of the Visking tubing by dipping it into the water in the container labelled V.
- Hold the Visking tubing close to the liquid so there is as little air in the tubing as possible. Twist the open end of the Visking tubing.
Look carefully at Fig. 1.1. This has been set up so that the volume of water is as small as possible to cover the Visking tubing. The part of the Visking tubing containing Y is on the bottom of the beaker.
- Put the Visking tubing into the beaker, labelled A, as shown in Fig. 1.1.
- Make sure the twisted end of the Visking tubing is held in place by a paperclip.
- Put W into the beaker up to the level shown on Fig. 1.1, using a syringe so that you can measure the volume of W.
State the volume of W you have decided to use.
volume of W = ______
- Start timing.
- Immediately remove a sample of the water with a glass rod.
- Mix the sample on the glass rod into the drop of B labelled 0 and record the colour in (a)(iii).
- Gently shake the beaker to mix the water. Repeat step 12 and step 13 at each of the sampling times, gently shaking the beaker before step 12 each time. Continue until the final sample is removed at 10 minutes.
- After the final sample at 10 minutes, clean off the tile and dry it. Repeat step 1 and step 2.
- Holding the twisted end of the Visking tubing, pour the water from the beaker into the container labelled for waste.
- Put the volume of fresh water stated in (a)(ii) into the beaker with the Visking tubing.
- Repeat step 11 to step 14.
Record your results in an appropriate table.
Describe and compare the results for the first 10 minutes with the results for the second 10 minutes.
A student set up the apparatus as in Fig. 1.1 to investigate the hydrolysis (breakdown) of sucrose into reducing sugar by yeast cells.
These reducing sugar molecules are able to pass through the Visking tubing into the surrounding water.
The student removed a sample of the surrounding water after 20 minutes and carried out a Benedict’s test on the sample. The time taken to the first colour change was measured.
Think about how the student would estimate the concentration of reducing sugar in this sample.
Describe how to prepare a range of concentrations of reducing sugar, using a 4% reducing sugar solution.
The student tested a range of concentrations of reducing sugar with Benedict’s solution and measured the time taken to the first colour change for each test.
Using the results the student collected, describe how you would estimate the concentration of reducing sugar in the sample removed after 20 minutes.
A student investigated the effect of different sugars on the metabolic reactions in yeast.
Yeast cells in different types of sugar solution were prepared. All other variables were standardised.
The rate of metabolic reactions was measured by a sensor which recorded the concentration of carbon dioxide released in 5 minutes.
Table 1.1 shows the results for this investigation.
Table 1.1
| type of sugar | rate of metabolic reactions / arbitrary units (au) |
|---|---|
| fructose (F) | 0.16 |
| glucose (G) | 0.31 |
| lactose (L) | 0.01 |
| maltose (M) | 0.17 |
| sucrose (S) | 0.20 |
Use a sharp pencil for drawing charts.
Draw a chart of the data shown in Table 1.1.
Describe the difference in the rate of metabolic reactions in yeast between sucrose and glucose. Using your knowledge of enzymes and carbohydrates, suggest an explanation for this difference.
description ______
explanation ______
The rest of this paper
1 more questions- Q2Use of the Light Microscope19M