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The enzyme E catalyses the hydrolysis of sucrose to produce fructose and glucose.
You are required to investigate the progress of this enzyme-catalysed reaction by finding the time taken for the decolourization of potassium permanganate.
The products of the hydrolysis of sucrose will change the colour of potassium permanganate as follows:
purple $
ightarrow$ colourless
Test-tube Z shows the colourless end-point.
To follow the time course of this reaction take samples from the reaction mixture and test them with potassium permanganate.
(a) (i) Decide how often you will take these samples. You should not sample for longer than 20 minutes.
Write your sampling times in the space below. [2]
(ii) Prepare the space below to record
• the time you remove each sample and
• the time at which the end-point is reached and
• the time taken to reach the end-point. [5]
You are provided with
• 1% enzyme solution, labelled E
• 10% sucrose solution, labelled S
• 1 mol dm$^{-3}$ sulfuric acid, labelled A
• 0.01% potassium permanganate solution, labelled P.
The sulfuric acid and potassium permanganate are harmful.
If any comes into contact with your skin wash immediately under cold water.
It is recommended that you wear safety goggles/glasses.
Proceed as follows:
1. Label the test-tubes with the sampling times that you have decided to use.
2. Put 2.5cm$^{3}$ of A into each test-tube.
3. Put 1cm$^{3}$ of P into each test-tube. Gently shake each test-tube.
4. Put 30cm$^{3}$ of S into a beaker.
5. Put 4cm$^{3}$ of E into the beaker containing S.
6. Immediately stir the reaction mixture in the beaker and start timing.
7. At each of your sampling times, remove 5cm$^{3}$ of the reaction mixture and add to the appropriate test-tube, mixing well.
8. Immediately start timing and record the time taken to reach the end-point.
(b) Describe a suitable control for this investigation. [1]
(c) (i) Identify two significant sources of error in this investigation. [2]
(ii) State one variable which was not controlled in this investigation and how it could have been controlled. [1]
Table 1.1 shows the results for a similar investigation which measured the mass of reducing sugars produced over a period of 400 seconds.
\[ \begin{array}{|c|c|} \hline \text{time / s} & \text{mass of reducing sugars / mg} \\ \hline 60 & 0.32 \\ 120 & 0.64 \\ 180 & 0.95 \\ 300 & 1.55 \\ 400 & 2.05 \\ \hline \end{array} \]
(d) (i) Plot a graph of the data shown in Table 1.1. [4]
(ii) Use your graph to find the rate of hydrolysis of the sucrose by finding the gradient of the line.
Show on your graph where you took the readings to calculate the gradient.
Show all the steps in your calculation.
rate of enzyme activity ................................. mg s$^{-1}$ [2]
(iii) The student repeated the investigation for 600 seconds and found that the results for the enzyme-catalysed reaction between 60 and 400 seconds were similar to the results in Table 1.1 but after 400 seconds the mass of reducing sugars produced remained the same.
Explain why the mass of reducing sugars increased and then remained the same. [2]
567
581
527
J1 is a slide of a stained transverse section showing a tubular part of the digestive system of a mammal.
You are not expected to have studied this material.
Fig. 2.1
(a) Draw a large plan diagram of a quarter of the tube as shown in Fig. 2.1.
Labels are not required.
(b) Fig. 2.2 is a photomicrograph showing a transverse section through a different part of the digestive system in the same mammal, showing a number of similar structures.
Fig. 2.2
(i) Calculate the actual length, shown by line X, of one of the structures.
Show all the steps in your calculation.
...........................................................μm [2]
(ii) Explain how you would find the mean length of the structures shown in Fig. 2.2.
........................................................... [2]
(iii) Prepare the space below so that it is suitable for you to compare and contrast the specimen on J1 and that in Fig. 2.2.
Record your observations in the space you have prepared.
........................................................... [5]
(iv) Suggest how the structures in Fig. 2.2 are adapted for absorption.
........................................................... [1]
(c) Fig. 2.3 is a photomicrograph showing some cells from the lining of the digestive system.
Fig. 2.3
Make a large, labelled drawing of the complete cells shown in the sector on Fig. 2.3.
........................................................... [5]
540
509
530
