5: Food and Humans - Practical

Question 1

5.1: Detection of food substances by food tests

Do the amounts of the samples used in the food tests need to be measured very accurately and why?

Answer 1

No. This is because the food tests are qualitative tests to show the presence of certain food substances. They are not quantitative tests.

Question 2

5.1: Detection of food substances by food tests

Why is a boiling water bath preferred to a Bunsen flame for heating up the mixture of glucose solution and Benedict’s solution to conduct Benedict’s test?

Answer 2

The water bath provides a better control over the temperature and can prevent bumping of the mixture.

Question 3

5.1: Detection of food substances by food tests

How does the translucent spot faused by lipids differ from the one caused by distilled water in the translucent spot test?

Answer 3

The translucent spot caused by lipids is permanent. On the contrary, the translucent spot caused by water disappears when water evaporates.

Question 4

5.1: Detection of food substances by food tests

Explain the result after immersing the filter paper with the translucent spot caused by lipids into an organic solvent.

Answer 4

Lipids dissolve in the organic solvent. Therefore, the translucent spot caused by lipids disappear.

Question 5

5.1: Detection of food substances by food tests

List two possible ways of conducting Benedict’s test on a blood sample.

Answer 5

As the red colour of the blood will mask the results of the Benedict’s test, the blood sample should be diluted with distilled water first.
Alternatively, the blood sample should be centrifuged and the plasma collected is used to perform the Benedict’s test.