AS & A Level Biology - 9700 Paper 3 2016 Winter Zone 6

(a) When carrying out a practical procedure the hazards of using the solutions need to be considered. Then the level of risk needs to be assessed as low or medium or high.

State the hazard with the greatest level of risk when using the solutions then state the level of risk of the procedure: low or medium or high.

hazard ...............................................................

level of risk ............................................................... [1]

(b) You are required to make a serial dilution of the 1% antibiotic solution, A, which reduces the concentration by half between each successive dilution.

You will need to prepare 20 cm³ of each concentration.

Fig. 1.1 shows the first two beakers you will use to make your serial dilution.
(i) Complete Fig. 1.1 by drawing as many extra beakers as you need for your serial dilution.
For each beaker:
• state, under the beaker, the volume and concentration of the antibiotic solution available for use in the investigation
• use one arrow, with a label above the beaker, to show the volume and concentration of antibiotic solution added to prepare the concentration
• use another arrow, with a label above the beaker, to show the volume of W added to prepare the concentration.



Proceed as follows:
1. Prepare the concentrations of antibiotic solution as decided in (b)(i) and as shown in Fig. 1.1.
2. Adjust the volumes so that there is 20 cm³ of antibiotic solution in each beaker.
3. Label a beaker as U and put 20 cm³ of U into this beaker.
You will need to cut the agar block, B, into smaller pieces as shown in Fig. 1.2.

To avoid staining your skin, try not to touch the agar. You may use the blunt forceps and paper towels to handle the agar.



4. Place the agar block, B, onto a white tile and cut into identical pieces, each 5 mm x 5 mm as shown in Fig. 1.2. You do not need to adjust the depth.
5. Put one piece of agar into each beaker containing the concentrations prepared in step 1 and start timing.
6. Gently stir the contents of each beaker at intervals.
7. Record in (b)(ii) the time taken for the pieces of agar to reach the end-point.
Note that the colour of the agar may change from blue to green and then to yellow.
If any piece of agar has not changed to yellow after 240 s, stop timing and record as 'more than 240'.
Note that the same concentrations of antibiotic solution can be used again.

(ii) Prepare the space below and record your results for the known concentrations of antibiotic solution.

(iii) Record the time taken for the piece of agar in U to change to reach the end-point.

time taken ................................................ [1]

(iv) Use your results in (b)(ii) and (b)(iii) to estimate the concentration of antibiotic solution in U.
.................................................................................................................................[1]

(v) Identify one significant source of error in this investigation.
.................................................................................................................................

(vi) This procedure investigated the effect of the concentration of the antibiotic solution (the independent variable) on its diffusion into stained agar blocks.

To modify this procedure for investigating the effect of another independent variable, the concentration of antibiotic solution would need to be standardised.

Describe how the concentration of antibiotic solution could be standardised.
.................................................................................................................................
.................................................................................................................................
Describe how you would modify this procedure to investigate the effect of the independent variable, temperature, on diffusion into stained agar blocks.
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................

(i) Plot a graph of the data shown in Table 1.1.



(ii) Use your graph to estimate the rate of glucose uptake by cells for an external concentration of glucose of 7 mmol dm^-3.
Show on your graph how you estimated the rate of glucose uptake.

rate of glucose uptake .............................. mmol cm^-3 h^-1 [1]

(iii) Using the graph, explain how the results of the investigation support the idea that glucose enters cells by facilitated diffusion.
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
................................................................................................................................. [2]

(a) When carrying out a practical procedure the hazards of using the solutions need to be considered. Then the level of risk needs to be assessed as low or medium or high.

State the hazard with the greatest level of risk when using the solutions then state the level of risk of the procedure: low or medium or high.

hazard ...............................................................

level of risk ............................................................... [1]

(b) You are required to make a serial dilution of the 1% antibiotic solution, A, which reduces the concentration by half between each successive dilution.

You will need to prepare 20 cm³ of each concentration.

Fig. 1.1 shows the first two beakers you will use to make your serial dilution.
(i) Complete Fig. 1.1 by drawing as many extra beakers as you need for your serial dilution.
For each beaker:
• state, under the beaker, the volume and concentration of the antibiotic solution available for use in the investigation
• use one arrow, with a label above the beaker, to show the volume and concentration of antibiotic solution added to prepare the concentration
• use another arrow, with a label above the beaker, to show the volume of W added to prepare the concentration.



Proceed as follows:
1. Prepare the concentrations of antibiotic solution as decided in (b)(i) and as shown in Fig. 1.1.
2. Adjust the volumes so that there is 20 cm³ of antibiotic solution in each beaker.
3. Label a beaker as U and put 20 cm³ of U into this beaker.
You will need to cut the agar block, B, into smaller pieces as shown in Fig. 1.2.

To avoid staining your skin, try not to touch the agar. You may use the blunt forceps and paper towels to handle the agar.



4. Place the agar block, B, onto a white tile and cut into identical pieces, each 5 mm x 5 mm as shown in Fig. 1.2. You do not need to adjust the depth.
5. Put one piece of agar into each beaker containing the concentrations prepared in step 1 and start timing.
6. Gently stir the contents of each beaker at intervals.
7. Record in (b)(ii) the time taken for the pieces of agar to reach the end-point.
Note that the colour of the agar may change from blue to green and then to yellow.
If any piece of agar has not changed to yellow after 240 s, stop timing and record as 'more than 240'.
Note that the same concentrations of antibiotic solution can be used again.

(ii) Prepare the space below and record your results for the known concentrations of antibiotic solution.

(iii) Record the time taken for the piece of agar in U to change to reach the end-point.

time taken ................................................ [1]

(iv) Use your results in (b)(ii) and (b)(iii) to estimate the concentration of antibiotic solution in U.
.................................................................................................................................[1]

(v) Identify one significant source of error in this investigation.
.................................................................................................................................

(vi) This procedure investigated the effect of the concentration of the antibiotic solution (the independent variable) on its diffusion into stained agar blocks.

To modify this procedure for investigating the effect of another independent variable, the concentration of antibiotic solution would need to be standardised.

Describe how the concentration of antibiotic solution could be standardised.
.................................................................................................................................
.................................................................................................................................
Describe how you would modify this procedure to investigate the effect of the independent variable, temperature, on diffusion into stained agar blocks.
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................

(i) Plot a graph of the data shown in Table 1.1.



(ii) Use your graph to estimate the rate of glucose uptake by cells for an external concentration of glucose of 7 mmol dm^-3.
Show on your graph how you estimated the rate of glucose uptake.

rate of glucose uptake .............................. mmol cm^-3 h^-1 [1]

(iii) Using the graph, explain how the results of the investigation support the idea that glucose enters cells by facilitated diffusion.
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
................................................................................................................................. [2]

M1 is a slide of a stained transverse section through a plant leaf. You are not expected to be familiar with this specimen. This leaf has several vascular bundles along its length.
(a) Select the central vascular bundle which is larger than the others.
You are required to use a sharp pencil for drawings.
(i) Draw a large plan diagram of the quarter of the midrib shown by the shaded area in Fig. 2.1.
Use one ruled label line and label to identify the phloem.

You are expected to draw the correct shape and proportions of the different tissues.
(ii) Observe the xylem tissue in the vascular bundle of the midrib on M1. Select one group of four adjacent (touching) cells in a chain. Each cell of the chain 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.

(b) Fig. 2.2 is a photomicrograph of a stained transverse section through a different type of leaf, including the midrib.
You are not expected to be familiar with this specimen.

(i) Use the line X–Y to determine the simplest ratio of the depth of the midrib to the length of the vascular bundle.
You may lose marks if you do not show your working.
simplest ratio ...............................................................
(ii) Suggest one observable feature, shown in Fig. 2.2, which supports the conclusion that this plant may grow in an aquatic habitat.
..................................................................................................................................................
..................................................................................................................................................

(c) Prepare the space below so that it is suitable for you to record observable differences between the leaf midrib on M1 and the leaf midrib in Fig. 2.2.
Record your observations in the space you have prepared.

M1 is a slide of a stained transverse section through a plant leaf. You are not expected to be familiar with this specimen. This leaf has several vascular bundles along its length.
(a) Select the central vascular bundle which is larger than the others.
You are required to use a sharp pencil for drawings.
(i) Draw a large plan diagram of the quarter of the midrib shown by the shaded area in Fig. 2.1.
Use one ruled label line and label to identify the phloem.

You are expected to draw the correct shape and proportions of the different tissues.
(ii) Observe the xylem tissue in the vascular bundle of the midrib on M1. Select one group of four adjacent (touching) cells in a chain. Each cell of the chain 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.

(b) Fig. 2.2 is a photomicrograph of a stained transverse section through a different type of leaf, including the midrib.
You are not expected to be familiar with this specimen.

(i) Use the line X–Y to determine the simplest ratio of the depth of the midrib to the length of the vascular bundle.
You may lose marks if you do not show your working.
simplest ratio ...............................................................
(ii) Suggest one observable feature, shown in Fig. 2.2, which supports the conclusion that this plant may grow in an aquatic habitat.
..................................................................................................................................................
..................................................................................................................................................

(c) Prepare the space below so that it is suitable for you to record observable differences between the leaf midrib on M1 and the leaf midrib in Fig. 2.2.
Record your observations in the space you have prepared.