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(a) (i) Select two cells from the epidermis which show the effect of sodium chloride solution from S1.
Make a large drawing of these two cells.
On your drawing use a ruled label line and label to identify the cell wall of one cell.
(a) (ii) Make a large drawing of the cell that you have selected.
Annotate your drawing to describe one feature that is different between this cell and the cells drawn in (a)(i).
(b) (i) State the magnification of the objective lens you will use.
magnification x .......................................................
(b) (ii) State the total number of cells you decided to count.
total number of cells ...............................................
(b) (iii) Using your results calculate the percentage of cells that are plasmolysed.
You may lose marks if you do not show your working.
(b) (iv) Prepare the space below and record the number of cells showing any degree of plasmolysis and the number of cells showing no plasmolysis (raw results) and record processed results for the percentage of cells that are plasmolysed in the onion tissue.
(v) Identify one significant source of error in measuring the dependent variable.
(vi) Explain, in terms of the movement of water and water potential, the effect of water replacing the sodium chloride solution on the cells of the epidermis.
(vii) Suggest how you would modify this investigation to find the sodium chloride concentration of an unknown solution.
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(a) (i) Calculate the total surface area of the exposed lower epidermis in the rolled leaf using the shape you have cut out:
• Count the number of 1 cm × 1 cm squares within the outline.
• Count any ‘half square’ or ‘more than half square’ as one square.
• Do not count any square that is less than half a square.
• Indicate on your grid all of the 1 cm × 1 cm squares that you have included in your surface area.
[Image_1 for Grid 2.1]
total surface area of the exposed lower epidermis in the rolled leaf .................................
(a) (ii) A student determined the ratio of the length of the unrolled leaf compared to the width of the unrolled leaf as shown below.
length of the unrolled leaf = 15 cm
width of the unrolled leaf = 6 cm
Ratio is the length of the unrolled leaf compared to the width of the unrolled leaf.
Ratio is 15:6
However, a ratio may be simplified to the smallest possible whole number on each side.
In this example, both sides of the ratio 15:6 are divisible by 3, so the simplest ratio is 5:2.
The surface area of the exposed lower epidermis of the unrolled leaf was found to be 60 cm2.
Determine the simplest ratio of the surface area of the unrolled leaf to the surface area of the rolled leaf (from page 15) using your answer from (a)(i).
You will lose marks if you do not show your working.
ratio ..................................................................................................
(b) A scientist investigated the effect of the number of leaves on a tomato plant on the rate of transpiration.
A tomato plant had 14 leaves at the start of the investigation. The transpiration rate of this tomato plant was recorded. At regular intervals leaves were removed and the transpiration rate recorded. All other variables were standardised.
The results of the investigation are shown in [Table_1].
[Table_1]
number of leaves | transpiration rate / μl min–1
14 | 9.5
10 | 4.3
8 | 3.9
5 | 3.5
2 | 1.8
You are required to use a sharp pencil for graphs.
(i) Plot a graph of the data shown in Table 2.1.
[Image_1 for the graph]
(ii) Estimate the transpiration rate of the plant with 12 leaves.
Show on the graph how you estimated the transpiration rate.
transpiration rate .............................................................
(d) Fig. 2.3 is a photomicrograph showing a stained transverse section of a mid-rib of a different plant species.
You are not expected to be familiar with this specimen.
Prepare the space below so that it is suitable for you to record observable differences between the mid-rib of Fig. 2.2 and the mid-rib of Fig. 2.3.
Record your observations in the space you have prepared.
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