AS & A Level Biology - 9700 Paper 3 2016 Summer Zone 2

Yeast cells use enzymes to hydrolyse (break down) glucose, releasing carbon dioxide. The release of carbon dioxide can be used to measure the activity of yeast cells.

You are required to investigate the effect of temperature (independent variable) on the activity of a yeast cell suspension.

You are provided with:

[Table_1]

(a) (i) You will need to test the activity of a yeast cell suspension at the temperature of the room.

Use the thermometer to measure the temperature of the room.

temperature .................................................... [1]

(ii) You will also need to test the activity of a yeast cell suspension at the maximum temperature of 60°C.

State the other temperatures you will use in your investigation.
.......................................... [1]

Proceed as follows:

Read step 1 to step 11.

1. Put 10 cm³ of the yeast cell suspension, Y, into a test-tube labelled with the temperature of the room you recorded in (a)(i).



2. Position the open end of the syringe so that it touches the side of the test-tube as shown in Fig. 1.1.
3. Gently press the plunger of the syringe so that the yeast cell suspension runs down the side of the test-tube to the bottom with as little foam as possible being formed.
4. Put this test-tube in the test-tube rack.
5. Repeat step 1 to step 4 for each of the other temperatures you will use in your investigation.
6. Label the beakers with the temperatures you will use in your investigation and set these up as water-baths ready for step 7.
7. Put the test-tube labelled 60°C into the water-bath at that temperature.
8. Repeat step 7 for each of the labelled test-tubes.
9. Maintain the temperatures of the water-baths for 15 minutes.
10. After 15 minutes, stop timing, take the test-tubes out of each water-bath and put them in the test-tube rack.
11. Measure the height of the foam above the level of the yeast cell suspension in each of the test-tubes.

Record your results in (a)(iii).

(iii) Prepare the space below and record your results. [5]

(iv) Identify two significant sources of error in this investigation.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................ [2]

(v) Describe how you could set up a control for this investigation.
........................................................................................................................
........................................................................................................................
........................................................................................................................ [1]

(vi) Explain how the temperature affected the enzymes in the yeast cell suspension.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................ [2]

(vii) This procedure investigated the effect of temperature on the activity of a yeast cell suspension.

To modify this procedure for investigating another variable, the independent variable (temperature), would need to be standardised.

Describe how the temperature could be standardised.
........................................................................................................................
........................................................................................................................
Now consider how you would modify this procedure to investigate the effect of pH on the activity of a yeast cell suspension.

Describe how this independent variable, pH, could be investigated.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................ [3]

(b) A student investigated the effect of concentration of glucose solution on the activity of a yeast cell suspension. The volume of carbon dioxide released was measured. All other variables were standardised.

The results of the student’s investigation are shown in Table 1.1.

[Table_2]

(i) Plot a graph of the data shown in Table 1.1.



[4]

(ii) Use your graph to estimate the volume of CO₂ released at 3.5% concentration of glucose solution.
volume ............................................................. cm³ [1]

Yeast cells use enzymes to hydrolyse (break down) glucose, releasing carbon dioxide. The release of carbon dioxide can be used to measure the activity of yeast cells.

You are required to investigate the effect of temperature (independent variable) on the activity of a yeast cell suspension.

You are provided with:

[Table_1]

(a) (i) You will need to test the activity of a yeast cell suspension at the temperature of the room.

Use the thermometer to measure the temperature of the room.

temperature .................................................... [1]

(ii) You will also need to test the activity of a yeast cell suspension at the maximum temperature of 60°C.

State the other temperatures you will use in your investigation.
.......................................... [1]

Proceed as follows:

Read step 1 to step 11.

1. Put 10 cm³ of the yeast cell suspension, Y, into a test-tube labelled with the temperature of the room you recorded in (a)(i).



2. Position the open end of the syringe so that it touches the side of the test-tube as shown in Fig. 1.1.
3. Gently press the plunger of the syringe so that the yeast cell suspension runs down the side of the test-tube to the bottom with as little foam as possible being formed.
4. Put this test-tube in the test-tube rack.
5. Repeat step 1 to step 4 for each of the other temperatures you will use in your investigation.
6. Label the beakers with the temperatures you will use in your investigation and set these up as water-baths ready for step 7.
7. Put the test-tube labelled 60°C into the water-bath at that temperature.
8. Repeat step 7 for each of the labelled test-tubes.
9. Maintain the temperatures of the water-baths for 15 minutes.
10. After 15 minutes, stop timing, take the test-tubes out of each water-bath and put them in the test-tube rack.
11. Measure the height of the foam above the level of the yeast cell suspension in each of the test-tubes.

Record your results in (a)(iii).

(iii) Prepare the space below and record your results. [5]

(iv) Identify two significant sources of error in this investigation.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................ [2]

(v) Describe how you could set up a control for this investigation.
........................................................................................................................
........................................................................................................................
........................................................................................................................ [1]

(vi) Explain how the temperature affected the enzymes in the yeast cell suspension.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................ [2]

(vii) This procedure investigated the effect of temperature on the activity of a yeast cell suspension.

To modify this procedure for investigating another variable, the independent variable (temperature), would need to be standardised.

Describe how the temperature could be standardised.
........................................................................................................................
........................................................................................................................
Now consider how you would modify this procedure to investigate the effect of pH on the activity of a yeast cell suspension.

Describe how this independent variable, pH, could be investigated.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................ [3]

(b) A student investigated the effect of concentration of glucose solution on the activity of a yeast cell suspension. The volume of carbon dioxide released was measured. All other variables were standardised.

The results of the student’s investigation are shown in Table 1.1.

[Table_2]

(i) Plot a graph of the data shown in Table 1.1.



[4]

(ii) Use your graph to estimate the volume of CO₂ released at 3.5% concentration of glucose solution.
volume ............................................................. cm³ [1]

M1 is a slide of a stained transverse section through a plant leaf.

You are not expected to be familiar with this specimen.

You are required to use a sharp pencil for drawings.

(a) (i) Draw a large plan diagram of the part of the leaf as shown by the shaded area in Fig. 2.1, to include observable features and two vascular bundles.
Use one ruled label line and label to identify the xylem.



You are expected to draw the correct shape and proportions of the different tissues.
[5]

(ii) Within this leaf on M1 canals are situated between the vascular bundles.
The canals are each made up of a circular group of cells surrounding a lumen.

Select one canal and observe the innermost ring of cells surrounding the lumen.

Select one group of four adjacent (touching) cells. Each cell of the group must touch at least one other cell.

Make a large drawing of this group of four cells.

Use one ruled label line and label to identify the cell wall of one cell.

[5]

(c) (i) Prepare the space below so that it is suitable for you to record observable differences between the leaf on M1 and the leaf in Fig. 2.2.

Record your observations in the space you have prepared.

[4]

(ii) The leaf on M1 and the leaf in Fig. 2.2 both grow in dry habitats.

Suggest one observable feature shown by both the leaf on M1 and the leaf in Fig. 2.2 which supports the conclusion that these plants grow in dry conditions.

Explain how this feature may help the plants grow in dry conditions.

feature .................................................
explanation ................................................

[2]

M1 is a slide of a stained transverse section through a plant leaf.

You are not expected to be familiar with this specimen.

You are required to use a sharp pencil for drawings.

(a) (i) Draw a large plan diagram of the part of the leaf as shown by the shaded area in Fig. 2.1, to include observable features and two vascular bundles.
Use one ruled label line and label to identify the xylem.



You are expected to draw the correct shape and proportions of the different tissues.
[5]

(ii) Within this leaf on M1 canals are situated between the vascular bundles.
The canals are each made up of a circular group of cells surrounding a lumen.

Select one canal and observe the innermost ring of cells surrounding the lumen.

Select one group of four adjacent (touching) cells. Each cell of the group must touch at least one other cell.

Make a large drawing of this group of four cells.

Use one ruled label line and label to identify the cell wall of one cell.

[5]

(c) (i) Prepare the space below so that it is suitable for you to record observable differences between the leaf on M1 and the leaf in Fig. 2.2.

Record your observations in the space you have prepared.

[4]

(ii) The leaf on M1 and the leaf in Fig. 2.2 both grow in dry habitats.

Suggest one observable feature shown by both the leaf on M1 and the leaf in Fig. 2.2 which supports the conclusion that these plants grow in dry conditions.

Explain how this feature may help the plants grow in dry conditions.

feature .................................................
explanation ................................................

[2]