No questions found
Urea reacts with water to form ammonium carbonate.
$$\text{urea + water} \rightarrow \text{ammonium carbonate}$$
Enzyme $E$ catalyses this reaction.
Aqueous ammonium carbonate produces ammonium ions. This forms an alkaline solution which causes red litmus paper to turn blue. This will be used to indicate the end-point of the reaction.
Animals release urea into the soil in urine and ammonium carbonate is produced as part of the nitrogen cycle.
You are provided with:
[Table_1]
[Table_2]
You are required to investigate the independent variable, enzyme $E$ concentration on the formation of ammonium carbonate.
You are required to carry out a serial dilution of enzyme $E$, to reduce the concentration of the enzyme solution by half between each successive dilution.
Fig. 1.1 shows how to make the first concentration of 5% enzyme $E$ solution.
(a) (i) Complete Fig. 1.1 to show how you will make three further concentrations of enzyme $E$ solution. [3]
As part of this investigation you are required to set up a suitable control.
(ii) Describe how you will set up this control using the apparatus provided.
.................................................................[1]
Proceed as follows:
1. Prepare the concentrations of $E$ as shown in Fig. 1.1 in the containers provided.
2. Label test-tubes with the concentrations of $E$ and the control.
3. Cut the red litmus paper into lengths of 0.5 cm. Add one piece of litmus paper to each test-tube.
4. Put $2 \text{ cm}^3$ of $U$ into each test-tube.
5. Put $2 \text{ cm}^3$ of the lowest concentration of $E$ into the labelled test-tube and mix well.
6. Repeat step 5 with each of the other concentrations of $E$ and the control. Immediately start timing.
7. Record the time taken for the first appearance of blue colour in each piece of litmus paper. This is the end-point of the reaction. If a piece of litmus paper does not reach the end-point in ten minutes, record 'more than 600' for that dilution as your result.
(iii) Prepare the space below and record your results.
.................................................................[5]
(iv) Calculate the rate of reaction for the 10% $E$ concentration.
rate of reaction .................................................[1]
(v) Identify one significant error in your investigation.
.................................................................[1]
(vi) Suggest how you would make two improvements to this investigation.
.................................................................[2]
An investigation on global nitrogen fixation, from 1990 to 2000, studied the quantities of nitrogen fixed by different methods.
The results are shown in Table 1.1.
[Table_3]
(b) (i) Plot a chart of the data shown in Table 1.1.
[4]
Natural fixation in the years 1840–1850 was 123 million tonnes per year. Natural fixation in the years 1990–2000 was 108 million tonnes per year.
(ii) Calculate the percentage decrease from 1840–1850 to 1990–2000.
You may lose marks if you do not show your working.
.................................................................% [2]
(iii) Suggest one reason for the difference in the natural fixation between 1840–1850 and 1990–2000.
.................................................................[1]
509
550
571
K1 is a slide of a stained transverse section through a leaf.
Fig. 2.1
(a) (i) Draw a large plan diagram of the part of the leaf indicated by the shaded area in Fig. 2.1.
Label the vascular bundle and the palisade layer.
[5]
(ii) From K1, make a large drawing of one epidermal cell with one attached, whole trichome (hair).
Label the trichome (hair) and the epidermal cell.
[5]
(iii) State two observable features of K1 which support the conclusion that this is a leaf from a plant growing in a dry habitat.
Explain how these features reduce water loss.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
.........................................................................................................................
[2]
Fig. 2.2 is a photomicrograph of a transverse section of a leaf from a different plant species.
magnification · 350
Fig. 2.2
(b) (i) Use the magnification to calculate the actual length of line Y in \( \mu \text{m} \).
You may lose marks if you do not show your working or if you do not use appropriate units.
.......................................................... \text{\mu m} [3]
(ii) Prepare the space below so that it is suitable for you to record the observable similarities and differences between the specimens on K1 and in Fig. 2.2.
Record your observations in the space you have prepared.
[5]
521
544
573
