AS & A Level Biology - 9700 Paper 3 2017 Summer Zone 2

(a) You are required to prepare a serial dilution of the 0.3% solution of $S$ which reduces the concentration by a \textbf{factor of 10} between each successive dilution.

You will need to prepare $9 \text{ cm}^3$ 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:
\begin{itemize}
\item state, under the beaker, the \textbf{volume} and \textbf{concentration} of the solution available for use in the investigation
\item use one arrow, with a label above the beaker, to show the \textbf{volume} and \textbf{concentration} of the solution of $S$ added to prepare the concentration
\item use another arrow, with a label above the beaker, to show the \textbf{volume} of $W$ added to prepare the concentration
\end{itemize>

[3]

(ii) Prepare the space below and record your results for:

\begin{itemize}
\item $W$, the control
\item all the concentrations of molecule $S$.
\end{itemize}
[5]

(iii) Using your knowledge of enzymes, suggest how molecule $S$ may have reduced the activity of the enzyme.
.........................................................................................................................................................................
.........................................................................................................................................................................
.........................................................................................................................................................................
.........................................................................................................................................................................
.........................................................................................................................................................................
[3]

(vi) Describe \textbf{one} significant source of error in this investigation.
.........................................................................................................................................................................
.........................................................................................................................................................................
[1]

(vii) Describe how you could use this procedure to produce a more accurate estimate of the concentration of molecule $S$ in solution $X$ than the one given in (a)(v).
.........................................................................................................................................................................
.........................................................................................................................................................................
.........................................................................................................................................................................
.........................................................................................................................................................................
.........................................................................................................................................................................
[3]

(b)(i) Plot a chart of the data shown in Table 1.1.
The bars should be separated for each type of organism.

[Table_1.1]
[4]

(ii) A scientist wanted to compare the mercury concentration in the contaminated water with the mean mercury concentration of the five organisms.
Calculate the mean mercury concentration in the five organisms.
answer = ..................................................... ppm [1]

M1 is a slide of a stained transverse section through a plant stem. You are not expected to be familiar with this specimen.
(a) Observe the different tissues on M1 and select a field of view that shows part of the epidermis and the vascular bundles.
Use a sharp pencil for drawing.
(i) Draw a large plan diagram from the selected field of view which shows:
• part of the epidermis
• only three vascular bundles
• any other observable tissues.
You are expected to draw the correct shape and proportions of the different tissues.
Use one ruled label line and label to identify the xylem in one vascular bundle.
(ii) Observe the central tissue in the stem on M1. These cells are not identical.
Select one group of four adjacent (touching) cells which show some of the differences between these cells. Each cell must touch at least two 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. 2.1 is a photomicrograph of a stained transverse section through a stem of a different type of plant. You are not expected to be familiar with this specimen.
(i) Prepare the space below so that it is suitable for you to record the observable differences between the stem on M1 and the stem in Fig. 2.1.
Record your observations in the space you have prepared.

Fig. 2.2 is a photomicrograph of a stained transverse section through a vascular bundle from Fig. 2.1. A grid has been placed over the photomicrograph to help you answer (b)(ii) and (b)(iii).
(ii) You are required to find the area of the xylem tissue and the area of the vascular bundle.
• Draw on Fig. 2.2 an outline around the xylem tissue.
• Draw on Fig. 2.2 an outline around the vascular bundle.
• Count the number of 1 cm × 1 cm squares within each 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'.
• Show on your grid all of the 1 cm × 1 cm squares that you have counted.
State the area of the xylem tissue and the area of the vascular bundle.
area of xylem tissue ...........................................................
area of vascular bundle ................................................... [2]
(iii) Calculate the area of the xylem tissue as a percentage of the area of the vascular bundle.
You may lose marks if you do not show your working.
answer = ........................................................... % [2]