No questions found
(a) (i) State three other temperatures that you will use to show the effect of temperature on the activity of E. ............................................................................................................... [1]
(ii) Record in (a)(ii) the time taken for the mixture to become clear (the end-point). You may find it easier to judge the end-point if the black card is held behind the mixture.
If the end-point is not reached by 180 seconds, record ‘more than 180’.
....................................................................................................... [5]
(iii) A student carried out the same procedure at 80°C and recorded the time taken to reach the end-point as 75 seconds.
Calculate the rate of enzyme activity at 80°C. Show your working.
rate of enzyme activity = ....................... s^{-1} [2]
(iv) The student identified two significant sources of error in the investigation as shown in Table 1.2.
Complete Table 1.2 to suggest how to make an improvement to reduce each of the sources of error the student identified.
Table 1.2
| significant source of error | how to make an improvement |
|---|---|
| difficult to judge when the end-point is reached | |
| difficult to maintain the temperature of the water-bath |
(v) Suggest how the student could set up an appropriate control for this investigation.
....................................................................................................... [1]
(b) A scientist carried out an experiment to investigate the effect of pH on the activity of a different enzyme that hydrolyses the protein in milk. Buffer solutions were used to change the pH and the investigation was carried out at the optimum temperature for this enzyme. All other variables were kept constant. The results are shown in Table 1.3.
Table 1.3
| pH | activity of enzyme /arbitrary units |
|---|---|
| 1.5 | 78 |
| 2.0 | 95 |
| 3.0 | 91 |
| 4.5 | 36 |
| 6.0 | 13 |
(i) State the independent variable in this investigation. ....................................................................................................... [1]
(ii) Plot a graph of the data shown in Table 1.3 on the grid in Fig. 1.1. Use a sharp pencil for drawing graphs. [4]
(iii) With reference to Fig. 1.1 describe the effect of pH on the activity of the enzyme. ....................................................................................................... [2]
(iv) Explain why the activity of the enzyme at pH 6 is different from the activity at pH 3. ....................................................................................................... [2]
(v) The scientist decided that the optimum pH for this enzyme had not been identified accurately. Suggest how the experiment could be modified to find a more accurate value for the optimum pH.
....................................................................................................... [2]
527
501
503
(a) (i) State three other temperatures that you will use to show the effect of temperature on the activity of E. ............................................................................................................... [1]
(ii) Record in (a)(ii) the time taken for the mixture to become clear (the end-point). You may find it easier to judge the end-point if the black card is held behind the mixture.
If the end-point is not reached by 180 seconds, record ‘more than 180’.
....................................................................................................... [5]
(iii) A student carried out the same procedure at 80°C and recorded the time taken to reach the end-point as 75 seconds.
Calculate the rate of enzyme activity at 80°C. Show your working.
rate of enzyme activity = ....................... s^{-1} [2]
(iv) The student identified two significant sources of error in the investigation as shown in Table 1.2.
Complete Table 1.2 to suggest how to make an improvement to reduce each of the sources of error the student identified.
Table 1.2
| significant source of error | how to make an improvement |
|---|---|
| difficult to judge when the end-point is reached | |
| difficult to maintain the temperature of the water-bath |
(v) Suggest how the student could set up an appropriate control for this investigation.
....................................................................................................... [1]
(b) A scientist carried out an experiment to investigate the effect of pH on the activity of a different enzyme that hydrolyses the protein in milk. Buffer solutions were used to change the pH and the investigation was carried out at the optimum temperature for this enzyme. All other variables were kept constant. The results are shown in Table 1.3.
Table 1.3
| pH | activity of enzyme /arbitrary units |
|---|---|
| 1.5 | 78 |
| 2.0 | 95 |
| 3.0 | 91 |
| 4.5 | 36 |
| 6.0 | 13 |
(i) State the independent variable in this investigation. ....................................................................................................... [1]
(ii) Plot a graph of the data shown in Table 1.3 on the grid in Fig. 1.1. Use a sharp pencil for drawing graphs. [4]
(iii) With reference to Fig. 1.1 describe the effect of pH on the activity of the enzyme. ....................................................................................................... [2]
(iv) Explain why the activity of the enzyme at pH 6 is different from the activity at pH 3. ....................................................................................................... [2]
(v) The scientist decided that the optimum pH for this enzyme had not been identified accurately. Suggest how the experiment could be modified to find a more accurate value for the optimum pH.
....................................................................................................... [2]
513
525
512
L1 is a slide of a stained transverse section through a plant stem.
You are not expected to be familiar with this specimen.
Use a sharp pencil for drawing.
(a) (i) Select a field of view so that you can observe the epidermis and the vascular bundles.
Draw a large plan diagram from the selected field of view which has:
• part of the epidermis
• only two smaller outer vascular bundles
• only one larger inner vascular bundle
• any other observable tissues.
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) Observe the cells of the epidermis on L1.
Select one group of four adjacent, touching epidermal cells. Each cell must touch at least one of the other cells.
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.
You are expected to draw the correct shape and proportions of the different cells.
[5]
(iii) The presence of air spaces supports the conclusion that the plant grows in water.
Suggest why the plant on L1 contains many air spaces.
..................................................................................................................
..................................................................................................................
[1]
Fig. 2.1 is a photomicrograph of a stained transverse section through a stem of a different type of plant.
You are not expected to be familiar with this specimen.
[Image_1: Fig. 2.1 showing a transverse section of a plant stem with labels J1, J2, J3]
(b) Determine the simplest whole number ratio of the total length of J1 and J2 (the cortex) to the length of J3 (vascular tissue).
Show your working and use appropriate units.
ratio .......................... [4]
(c) Observe the stem on L1 and the stem in Fig. 2.1 and identify the differences between them.
Record the observable differences in Table 2.1.
[Table_1: Table 2.1 with columns 'feature', 'L1', 'Fig. 2.1']
569
527
577
L1 is a slide of a stained transverse section through a plant stem.
You are not expected to be familiar with this specimen.
Use a sharp pencil for drawing.
(a) (i) Select a field of view so that you can observe the epidermis and the vascular bundles.
Draw a large plan diagram from the selected field of view which has:
• part of the epidermis
• only two smaller outer vascular bundles
• only one larger inner vascular bundle
• any other observable tissues.
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) Observe the cells of the epidermis on L1.
Select one group of four adjacent, touching epidermal cells. Each cell must touch at least one of the other cells.
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.
You are expected to draw the correct shape and proportions of the different cells.
[5]
(iii) The presence of air spaces supports the conclusion that the plant grows in water.
Suggest why the plant on L1 contains many air spaces.
..................................................................................................................
..................................................................................................................
[1]
Fig. 2.1 is a photomicrograph of a stained transverse section through a stem of a different type of plant.
You are not expected to be familiar with this specimen.
[Image_1: Fig. 2.1 showing a transverse section of a plant stem with labels J1, J2, J3]
(b) Determine the simplest whole number ratio of the total length of J1 and J2 (the cortex) to the length of J3 (vascular tissue).
Show your working and use appropriate units.
ratio .......................... [4]
(c) Observe the stem on L1 and the stem in Fig. 2.1 and identify the differences between them.
Record the observable differences in Table 2.1.
[Table_1: Table 2.1 with columns 'feature', 'L1', 'Fig. 2.1']
542
563
533
