Yeast cells make an enzyme named invertase. Invertase speeds up the breakdown of sucrose into reducing sugars. Sucrose is not itself a reducing sugar.
A student looked at how two different concentrations of invertase extract affected a sucrose solution.
The student carried out this procedure:
Step 1 Give the three test-tubes the labels A, B and W.
Step 2 Use a syringe to place 2 cm$^3$ of sucrose solution into each of the three test-tubes.
Step 3 With a fresh syringe, add 2 cm$^3$ of 100% invertase extract to test-tube A.
Step 4 With a fresh syringe, add 2 cm$^3$ of 10% invertase extract to test-tube B.
Step 5 With a fresh syringe, add 2 cm$^3$ of distilled water to test-tube W.
Step 6 Keep all three test-tubes in a warm water-bath at 40^{\circ}C for 15 minutes.
Step 7 Check the temperature of the liquid in the test-tubes.
Step 8 With a fresh syringe, add 4 cm$^3$ of Benedict’s solution to each test-tube.
Step 9 Put all three test-tubes into a hot water-bath for five minutes.
Step 10 After five minutes, note the colour of the liquid in each test-tube.
Fig. 1.1 shows the observations the student wrote down for step 10.
Fig. 1.1: the liquid in test-tube A is brick-red; the liquid in test-tube B is green; W stays blue.
(a)[1]
State the name of the apparatus used for measuring temperature.
(b)[3]
Prepare a table and use the information in Fig. 1.1 to show the results of this investigation.
(c)[1]
State a conclusion from the results shown in test-tube A and test-tube B.
(d)[2]
Explain the purpose of test-tube W.
(e)[1]
State the independent variable in this investigation.
(f)[1]
Explain why the test-tubes were placed in the warm water-bath in step 6.
(g)[1]
Explain why a clean syringe was used in steps 3, 4 and 5.
(h)[1]
State the reagent used to test for the presence of protein.
Worked solution & mark scheme
This 11-mark question has a full step-by-step worked solution and mark scheme. One marking point: “a thermometer” …