No questions found
1. You are required to dilute the 0.10% ascorbic acid, A, to provide a range of known concentrations using simple dilution.
(a) (i) Decide which concentrations of ascorbic acid to make, then complete Table 1.1.
• The difference between each concentration should be 0.02%.
• You will need to make up 20 cm³ of each concentration.
Table 1.1
[Table_1]
(ii) Prepare the space below and record your results.
(iii) Identify two significant sources of error in this investigation.
.........................................................................................................................
.........................................................................................................................
(iv) Describe three modifications to this investigation which would improve the confidence in your results.
.........................................................................................................................
.........................................................................................................................
.........................................................................................................................
2. Prepare all the concentrations of ascorbic acid as in Table 1.1 in the beakers or containers provided.
You will need to cut the agar block, U, into smaller pieces as shown in Fig. 1.1.
3. Place the agar block onto a damp paper towel and cut the block into identical pieces of 5 mm × 5 mm × 5 mm as shown in Fig. 1.1.
Fig. 1.1 shows the measurement of the agar pieces that you need.
4. Put the prepared agar pieces into each of the concentrations of ascorbic acid. Immediately start timing.
5. Gently stir the contents of each beaker or container at regular intervals.
6. Record the time taken for the pieces to decolourise. After 15 minutes, if any agar piece has not decolourised, stop timing, and record ‘more than 900’.
(b) (i) Plot a graph of the data shown in Table 1.3.
[Table_2]
(ii) Use your graph to estimate the concentration of ascorbic acid present in a solution that required 0.875 cm³ of indicator.
Show clearly on your graph how you obtained the ascorbic acid concentration.
concentration of ascorbic acid ..........................................................
501
587
578
J1 is a slide of a transverse section through a tubular organ which is involved in transport.
(a) (i) Draw a large plan diagram of the part of the tube on J1 indicated by the shaded sector in Fig. 2.1.
On your diagram, use a label line and label to show the muscle tissue.
[5]
(ii) State one observable feature of the tube on J1 which supports the conclusion that the tube is involved in transport.
Explain how this feature supports the conclusion.
..............................................................................................................................
..............................................................................................................................
..............................................................................................................................
..............................................................................................................................
[2]
Fig. 2.2 is a photomicrograph of blood cells in a field of view.
Fig. 2.2 shows many blood cells. There are too many red blood cells to count, so the technique of sampling may be used to estimate the number of red blood cells in the field of view.
A sample should be counted in a known smaller area and then the result multiplied to obtain an estimate of the number of red blood cells in the whole field of view.
For example, if the number of red blood cells is counted in an eighth of the area of the field of view then this number would be multiplied by 8 to obtain the total number in the area of the field of view.
(b) (i) Count and record the sample number of red blood cells in the eighth of the area of the field of view.
• Mark clearly on Fig. 2.2 each of the red blood cells counted.
• Estimate the number of red blood cells in the whole field of view.
You will lose marks if you do not show your working.
number of red blood cells in the field of view ...................................................... [2]
(ii) Use the magnification on Fig. 2.2 to calculate the actual length of line r in mm.
actual length ........................................... mm
Use the actual length of line r to calculate the area of the field of view using the formula for the area of a circle:
$\text{area of a circle} = \pi r^2$
$\pi = 3.14$
$r =$ radius of field of view
area of field of view .......................................... mm$^2$ [2]
(iii) Calculate the number of red blood cells per mm$^2$ using your answers in (b)(i) and (b)(ii).
You will lose marks if you do not show your working.
number of red blood cells .......................................... mm$^{-2}$ [2]
A group of people climbed a mountain. They started at sea level (0.0km) and reached a height of 6km above sea level in 60 days.
The average number of red blood cells per cm$^3$ of blood was calculated for the group of people at the start of the climb and at 20 day intervals. The data is shown in Table 2.1.
[Table_1]
(iv) Describe the trend in the average number of red blood cells with height above sea level and explain the advantages of this trend.
..............................................................................................................................
..............................................................................................................................
..............................................................................................................................
..............................................................................................................................
[3]
Fig. 2.3 is a photomicrograph of blood from a different organism.
(c) Make a drawing of white blood cells as observed in Fig. 2.3 made up of:
• two cells of one type of white blood cell
• two cells of a different type of white blood cell.
The drawings should show any differences in size (linear magnification) observed between each type of cell.
On your drawing, use a label line and label to show one nucleus.
[5]
500
582
582
