AS & A Level Biology - 9700 Paper 3 2013 Winter Zone 5

(a) (i) Decide which concentrations of hydrogen peroxide to make:
• using serial dilution,
• using 40 cm³ 6% hydrogen peroxide solution, H, to start the serial dilution,
• reducing the concentration by half between each concentration.
Complete Fig. 1.1 to show how you will make three further concentrations.


(a) (ii) Prepare the space below to record, for each concentration, the processed results only for the maximum height of foam.

(a) (iii) Identify two significant sources of error in this investigation.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................

(a) (iv) Describe how you would modify this procedure to investigate the effect of copper sulfate concentrations on the enzyme in the plant extract solution.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................

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


(b) (ii) Explain the effect of the copper sulfate solution on the enzymes in the plant extract.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................

L1 is a slide of a transverse section through a plant leaf. This plant species grows widely including tropical, sub-tropical and temperate regions.
(a) (i) Draw a large plan diagram of the part of the leaf on L1 indicated by the shaded sector in Fig. 2.1.

On your diagram, use a ruled label line and label to show the vascular bundle.

(a) (ii) Make a drawing of one group of adjacent (touching) cells, as observed on the specimen on K1, made up of:
- three epidermal cells
- three of the palisade cells touching these epidermal cells.
On your drawing use a label line and label to show one palisade cell.

Fig. 2.2 shows a stage micrometer viewed through a microscope with an eyepiece graticule scale.
The smallest measurement on this stage micrometer is 0.1 mm.

You are required to:
- find the area of the field of view, using Fig. 2.2
- count the number of stomata in a quarter of the field of view, using Fig. 2.3 (on page 14)
- calculate the number of stomata per mm².
(b) (i) Calculate the area of the field of view, using:
- the formula for the area of a circle $\pi r^2$
- $\pi = 3.14$
- $r = \text{radius of the field of view}$.
You will lose marks if you do not show your working or if you do not use appropriate units.
area of field of view .............................. mm²

Fig. 2.3 is a photomicrograph of the lower surface of a leaf, with the same field of view as in Fig. 2.2.

Fig. 2.3 shows stomata on a leaf surface. There are too many stomata to count so the technique of sampling may be used to estimate the number of stomata in the field of view.
A sample should be counted in a known smaller portion and then the result multiplied to obtain an estimate of the number of stomata in the whole field of view.
For example, if the number of stomata is counted in a quarter of the field of view then this number would be multiplied by 4 to obtain the estimate of the total number in the field of view.
(ii) Count and record the sample number of stomata in the quarter of the field of view shown in Fig. 2.3.
- Mark clearly on Fig. 2.3 each of the stomata counted.
- Estimate the total number in the whole field of view.
Calculate the number of stomata per mm².
You will lose marks if you do not show your working.
number of stomata .......................... mm⁻²

Fig. 2.4 is a photomicrograph of the lower surface of a different leaf, with the same field of view (using the same lenses) as Fig. 2.3.

(c) Prepare the space below so that it is suitable for you to record the observable differences between the surface of each leaf shown in Fig. 2.3 and Fig. 2.4.
Record your observations in the space you have prepared.