A student investigated the effect of glucose concentration on the rate of anaerobic respiration in yeast. Anaerobic respiration in yeast breaks down glucose to form ethanol and carbon dioxide. Anaerobic respiration in yeast causes the blue dye, methylene blue, to become colourless. The time taken for the blue colour to disappear can be used as a measure of the rate of anaerobic respiration in yeast. The student used this method: Step 1 Label one test-tube $$$0.0 \%$$$, one test-tube $$$0.5 \%$$$ and one test-tube $$$1.0 \%$$$. Step 2 Put $$$5.0 \mathrm{~cm}^{3}$$$ of water into the test-tube labelled $$$0.0 \%$$$. Step 3 Put $$$2.5 \mathrm{~cm}^{3}$$$ of $$$1.0 \%$$$ glucose solution and $$$2.5 \mathrm{~cm}^{3}$$$ of water into the test-tube labelled $$$0.5 \%$$$. Step 4 Put $$$5.0 \mathrm{~cm}^{3}$$$ of $$$1.0 \%$$$ glucose solution into the test-tube labelled $$$1.0 \%$$$. Step 5 Stir the contents of the beaker containing the yeast suspension with the glass rod. Step 6 Add $$$5.0 \mathrm{~cm}^{3}$$$ of the yeast suspension to each of the test-tubes labelled $$$0.0 \%, 0.5 \%$$$ and $$$1.0 \%$$$. Step 7 Put all three test-tubes into a water-bath at $$$40^{\circ} \mathrm{C}$$$. Step 8 Start the stop-clock and wait for three minutes. Step 9 After three minutes, remove the test-tubes from the water-bath and place them in a test-tube rack. Step 10 Use a pipette to add one drop of methylene blue dye to each of the test-tubes. Carefully mix the contents of each test-tube with the glass rod. Step 11 Use a second pipette to slowly add a layer of oil to each of the test-tubes. The layer of oil will float on top of the yeast suspension and methylene blue mixture, as shown in Fig. 1.1. Fig. 1.1 Step 12 Put the test-tubes back into the water-bath and restart the stop-clock. Step 13 Measure the time taken for the blue colour in each of the test-tubes to disappear. Record the time taken in seconds for each test-tube. The student stopped timing if the blue colour had not disappeared after 10 minutes. They recorded this result as $$$> 600$$$ in their table. The stop-clocks from step 13 are shown in Fig. 1.2. $$$0.0 \%$$$ $$$0.5 \%$$$ $$$1.0 \%$$$ Fig. 1.2 One way to improve this investigation would be to use an increased number of different concentrations of glucose. (i) Suggest two other ways to improve this investigation. 1 .................................................................................................................................... ....................................................................................................................................... . ....................................................................................................................................... . 2 .................................................................................................................................... ....................................................................................................................................... . ....................................................................................................................................... . (ii) Describe how you would make $$$5.0 \mathrm{~cm}^{3}$$$ of $$$0.25 \%$$$ glucose solution using a $$$0.50 \%$$$ glucose solution and distilled water. ....................................................................................................................................... . ....................................................................................................................................... . ....................................................................................................................................... . ....................................................................................................................................... . ................................................................................................................................. (iii) Describe the method you would use to test a solution for the presence of glucose. ....................................................................................................................................... . ....................................................................................................................................... . ....................................................................................................................................... . ....................................................................................................................................... . .................................................................................................................................

Biology

IGCSE&ALevel

CAIE

Exam No：0610_m24_qp_62 Year：2024 Question No：1(b)

Answer:

Knowledge points:

4.1.1 List the chemical elements that make up: – carbohydrates – fats – proteins

4.1.10 Describe the roles of water as a solvent in organisms with respect to digestion, excretion and transport

4.1.2 State that large molecules are made from smaller molecules, limited to: – starch and glycogen from glucose – cellulose from glucose – proteins from amino acids – fats and oils from fatty acids and glycerol

4.1.3 Describe the use of: – iodine solution to test for starch – Benedict’s solution to test for reducing sugars – biuret test for proteins – ethanol emulsion test for fats and oils – DCPIP test for vitamin C

4.1.4 Describe the use of: – iodine solution to test for starch – Benedict’s solution to test for reducing sugars – biuret test for proteins – ethanol emulsion test for fats and oils – DCPIP test for vitamin C

4.1.5 Describe the use of: – iodine solution to test for starch – Benedict’s solution to test for reducing sugars – biuret test for proteins – ethanol emulsion test for fats and oils – DCPIP test for vitamin C

4.1.6 State that water is important as a solvent

4.1.7 Explain that different sequences of amino acids give different shapes to protein molecules

4.1.8 Relate the shape and structure of protein molecules to their function, limited to the active site of enzymes and the binding site of antibodies

4.1.9 Describe the structure of DNA as: – two strands coiled together to form a double helix – each strand contains chemicals called bases – cross-links between the strands are formed by pairs of bases – the bases always pair up in the same way: A with T, and C with G (full names are not required)

Answer:

Knowledge points:

Solution:

Related Question