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You are required to investigate the effect of surface area (independent variable) on the diffusion of solution E into agar blocks with different surface areas.
- agar block, S, contains starch which has been stained blue by iodine solution
- agar block, U, contains starch only
As solution E diffuses into the agar block it hydrolyses (breaks down) the starch and the iodine loses its colour.
You are provided with:
[Table_1]
You will need to cut three different sizes of agar block from each of the large agar blocks (block S and block U).
Fig. 1.1 shows you the measurements of the largest size of block you will cut (block 1).
You may use the space on Fig. 1.1 to work out how to cut the two further sizes of blocks, smaller than block 1, with different surface areas (blocks 2 and 3).
(a) (i) Complete Table 1.1.
[Table_1.1][3]
You must not touch the agar blocks with your hands.
You can use the mounted needle, blunt forceps and paper towel to handle the blocks.
Proceed as follows:
1. Prepare the different sized blocks 1, 2 and 3 as you decided in (a)(i) so that you have one stained and one unstained block of each size.
2. Cover the blocks with damp paper towel to prevent evaporation.
3. Put the beaker or container provided on to a piece of black card and put hot water between 50°C and 55°C into the beaker.
4. Put 5 $cm^3$ of solution E into six test-tubes and put them into the water-bath. Leave for 5 minutes.
5. Use a mounted needle to put block 1 from S and block 1 from U into two separate test-tubes in the water-bath as shown in Fig. 1.2. Be careful not to break up the blocks as you lower them into the solution E.
6. Observe the coloured surface of the block from S. Record the time taken for the colour to disappear. Use block U as a standard colour. If the colour does not disappear by 360 seconds, record ‘more than 360’.
7. Repeat steps 5 and 6 with blocks 2 and 3 from S and U.
8. Record the temperature of the water in the water-bath.
temperature of water ................................................... °C
(ii) Prepare the space below and record your results.
(iii) Identify two significant sources of error in this investigation.
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(iv) Describe three modifications to this investigation which would improve the confidence in your results.
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A student investigated the time course of an enzyme-catalysed reaction using the hydrolysis of starch by an enzyme.
Fig. 1.3 shows the apparatus used.
To measure the progress of the enzyme-catalysed reaction a bubble was released into the mixture. As the concentration of starch decreases the bubble rises faster.
Other variables were considered and kept to a standard.
The data from the student's investigation are shown in Table 1.2.
[Table_1.2]
(b) (i) Plot a graph of the data shown in Table 1.2.[4]
(ii) If a bubble was released at 10 seconds, use your graph to estimate the speed of the bubble.
Show on the graph how you estimated the speed of the bubble.
speed of bubble ............................[2]
(iii) Explain the reason for the results:
between 12 seconds and 17 seconds
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between 25 seconds and 30 seconds.
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585
530
508
N1 is a slide of a transverse section through a plant organ.
(a) (i) Draw a large plan diagram of a sector of the organ, as shown by the shaded area in Fig. 2.1, to include one complete vascular bundle.
On your diagram, use a label line and label to show the phloem. [5]
(ii) From the specimen on N1, choose one group made up of two large xylem vessels and the smaller xylem cells between them.
Make a large drawing of this group.
On your drawing, use a label line and label to show a lumen. [4]
Fig. 2.2 is a photomicrograph showing a longitudinal section of a root from a different plant species.
(b) (i) Calculate the ratio of the mean length to the mean width of cells in the cortex. [4]
(ii) Prepare the space below so that it is suitable for you to record observable differences between the cortex and xylem tissues in Fig. 2.2. [5]
542
529
529
