Practise CAIE AS Biology 2.1 by interpreting reagent results, estimating reducing sugar concentration, and detecting non-reducing sugars after acid hydrolysis.
Many flowers produce a sweet solution called nectar. Bees provided with nectar use enzyme Q to change the nectar into honey.
After testing a sample of nectar for the presence of reducing sugar using standard laboratory reagents, the sample was blue. After testing a sample of honey in the same way, the sample was orange.
Which conclusion about the reaction catalysed by enzyme Q is consistent with these results?
type of reaction
substrate
product
condensation
maltose
glucose
condensation
sucrose
fructose
hydrolysis
sucrose
fructose
hydrolysis
maltose
glucose
Glucose is used in the synthesis of amylose. Glucose is first converted to glucose 1-phosphate (G 1-P).
Starch phosphorylase is an intracellular enzyme that can catalyse the synthesis of amylose from G 1-P, which is the substrate for the reaction:
n= a large number
Students used a colorimeter to investigate the progress of the reaction.
The students made a reaction mixture containing 1-P in a buffer solution at pH6.0. A very small quantity of amylose was added to initiate the reaction.
A solution of starch phosphorylase was added to the reaction mixture and samples were taken at 1-minute intervals. Each sample was added to a dilute iodine solution, stirred and then poured into a cuvette. The absorbance of each solution was recorded.
The results of the investigation are shown in Fig. 2.1.
Fig. 2.1
Explain why the absorbance increases, as shown in Fig. 2.1.
Which set of steps is the best method for conducting the emulsion test for lipids?
Add of water to the sample. Pour the water into a test-tube containing of ethanol. Lipids are present if the mixture becomes cloudy.
Add of ethanol to the sample and shake. Pour the ethanol into a test-tube containing of water and boil. Lipids are present if the mixture becomes clear.
Add of water to the sample and shake. Pour the water into a test-tube containing of ethanol and boil. Lipids are present if the mixture becomes cloudy.
Add of ethanol to the sample and shake. Pour the ethanol into a test-tube containing of water and shake again. Lipids are present if the mixture becomes cloudy.
Which tests will identify biological molecules that contain monomers with a carboxyl group?
The table shows some steps that can be made in carrying out the Benedict's test.
Which combination of steps is required to carry out a semi-quantitative test on a reducing sugar solution?
standardise volume of Benedict's solution and volume of test solution
boil with hydrochloric acid and then neutralise with alkali
standardise boiling time with Benedict's solution and compare final colour with numbered colour standards
✓
x
✓
✓
×
✓
×
✓
key
✓ = step made
step not made
Tests for biological molecules were carried out on three solutions. Each solution contained only one type of biological molecule.
The observations were as follows.
Which solutions would contain either sucrose or amylase?
1, 2 and 3
1 and 3 only
2 and 3 only
2 only