No questions found
You are required to investigate the hypothesis that:
The rate of release of carbon dioxide from yeast cells will decrease with time.
Carbon dioxide reacts with water to form a weak acid. The indicator, P, can be used to show the change in pH.
The pink indicator, P, will become colourless when carbon dioxide is added. This is the end-point as shown in Fig. 1.1.
You are provided with:
[Table_1]
You will need to standardise the pink colour before you start the readings.
Proceed as follows:
1. Put 5 cm³ of W into a test-tube.
For steps 2 and 3, you must use one pipette to add the drops of P and a different pipette to add the drops of A.
2. Put 2 drops of P into the same test-tube. The solution should remain colourless. Insert the bung and with your finger holding the bung in place, mix the solution.
3. You are required to put drops of A into the solution until it becomes a pink colour. The colour should not be darker than the pink colour shown in Fig. 1.1.
(a)
(i) Decide how you will use this test-tube to standardise the five other test-tubes you require.
State the variables which you will standardise when setting up these test-tubes to take the readings.
......................................................................................................................... [1]
4. Set up the five test-tubes as you have described in (i).
(ii) Describe how you standardised the colour in these five test-tubes.
......................................................................................................................... [1]
Fig. 1.2 shows how to use the apparatus provided.
The tubing from the syringe needs to reach into the test-tube so that it is below the surface of the indicator solution as shown in Fig. 1.2.
(iii) Decide how you will standardise the position of the tubing in each test-tube, without cutting the tubing. You may find Fig. 1.2 helpful.
Describe how you standardised the position of the tubing.
......................................................................................................................... [1]
You are required to:
• take five readings as shown in Fig. 1.3
• leave Y in the syringe for 10 minutes
• take another five readings as shown in Fig. 1.3.
The tubing must be transferred from one test-tube to the next as quickly as possible, after reaching the end-point.
To avoid the time delay in stopping and starting the timing, you must not stop the timer at any of the end-points, just record the time.
From your readings you will be required to calculate the time taken to reach the end-point in each test-tube.
(iv) Consider the units of the values recorded on your timer or clock.
State the:
• smallest value which your timer shows ..........................................................
• smallest unit of time you have decided to record .............................................. [1]
(v) Complete Table 1.1 with the raw data, recording the time when the tubing is put into the indicator and the time when the end-point is reached. Repeat for each test-tube.
After 10 minutes, complete Table 1.2 with the second set of raw data.
[Table_1.1]
[Table_1.2]
Depending on the timer or clock which you have used you may find the following examples helpful, so that you can process your results to find the time taken to reach the end-point.
[Example 1]
[Example 2]
(vi) Using your results from Table 1.1, complete Table 1.3 below to show the calculation to find the time taken to reach the end-point in your first test-tube.
[Table_1.3]
......................................................................................................................... [1]
(vii) Combining the processed results from Table 1.1 and Table 1.2, prepare the space below to record only the processed results. This will enable the trend to be observed.
......................................................................................................................... [4]
(b) Identify three significant sources of error in this investigation.
......................................................................................................................... [3]
(c) Describe three modifications to this investigation which would improve the confidence in your results.
......................................................................................................................... [3]
The original hypothesis was:
The rate of release of carbon dioxide from yeast cells will decrease with time.
(d) State whether your results support this hypothesis.
Use your results to explain your answer.
......................................................................................................................... [2]
574
529
535
N1 is a slide of a transverse section through a plant leaf. This plant grows mainly in Spain.
(a) Draw a large plan diagram of the whole section of the plant leaf on N1.
On your diagram, use a ruled label line and label to show the epidermis.
(b) Make a large drawing of one group of adjacent (touching) cells, as observed on the specimen on N1, made up of four whole cells from this ring of large cells.
(c) Use the eyepiece graticule scale to measure the:
• diameter of the vascular bundle including the ring of cells
• width of the xylem tissue.
State the ratio of the diameter of the vascular bundle to the width of the xylem.
Note: You are not required to calibrate the eyepiece graticule scale with a stage micrometer.
You will lose marks if you do not show all the steps in finding the ratio.
Fig. 2.1 shows a photomicrograph of a transverse section through a leaf from a different species. This plant grows mainly in China.
[Image_1: Fig. 2.1]
(d) Prepare the space below so that it is suitable for you to record observable differences between the specimens on slide N1 and in Fig. 2.1.
Both the specimen on N1 and Fig. 2.1 are from plants which are adapted to survive in dry conditions.
Some scientists investigated the water potential in the leaf cells of a tree living in dry conditions over a period of 22 hours.
The results are shown in Table 2.1.
[Table_1: Table 2.1]
(e) (i) Plot a graph of the data shown in Table 2.1.
(ii) Suggest how transpiration may explain the difference in the water potential in the leaf cells between 12:00 hours and 22:00 hours.
..............................................................................................................................
..............................................................................................................................
.........................................................................................................................
503
590
511
