Testing for Biological Molecules (Cambridge (CIE) AS Biology)

A solution is mixed with dilute hydrochloric acid, heated and then cooled before being neutralised with sodium hydrogencarbonate until the solution is slightly alkaline. The mixture is then heated gently with Benedict’s reagent. 

The final observation of the solution is a blue colour. This is the same as the observation of the solution when it was gently heated with Benedict’s solution without treatment with acid and subsequent neutralisation. 

What can be determined about the composition of the solution? 

A starch solution was mixed with amylase.

Which of the following reagents could be used to confirm that a reaction had occurred and what observation would be made?

A group of students carry out several tests on a sample of a solution. 

The table below shows the results.

Which of the following molecules would be present in the sample tested based on the student’s observations?

A group of students tested three solutions for sugars. The colours observed after testing are shown in the table below.  

Which solutions may contain reducing sugars?

A group of students tested four solutions by heating them with Benedict’s reagent. The table below shows the students’ observations after testing. 

Which solution contains a non-reducing sugar?

A group of students carried out a series of tests on a liquid solution obtained from a plant. The table below shows the results of their tests:

Which of the following biological molecules were found in the plant liquid solution?

A group of students tested four solutions for sugars. The colours observed after testing are shown in the table below. 

Which solution may contain non-reducing sugars?

Using a large number of aphids, a solution from the sieve tube elements of a tomato plant was extracted. 

The following tests and observations were made:

Which row correctly shows the molecules found in the solution?

Key: ✓ = present, X = absent

A teacher demonstrated several food tests on a sample solution with an unknown composition of biological molecules. 

Which row of the table below correctly identifies the molecules present in the sample?

Key: ✓ = present, X = absent

The diagram below shows a biological molecule. 

Which of the following tests would give a positive result for this molecule?

Four tests were conducted to determine the types of biological molecules present in a sample solution. Observations from these tests are shown in the table below. 

Which molecules are present in this solution? 

Four sugar solutions were tested with Benedict’s solution. The observed colour of each solution is given in the table below. 

Which of the following options would be the best interpretation of the observed results?

Four tests were conducted to determine the types of biological molecules present in a sample solution. Observations from these tests are shown in the table below. 

Which molecules are present in this solution?

Samples of four different fruit juices (A, B, C and D), were heated with Benedict’s solution. 

A second sample of the same four juices was heated with dilute hydrochloric acid and then neutralised before being heated with Benedict’s solution. 

The table below shows the masses of precipitates formed in each test. 

Which juice contains the highest mass of non-reducing sugar?     

A teacher demonstrates the following biological tests on four food samples:

• starch

• reducing sugar

• protein

• lipids

One of the food samples, a banana milkshake, was found to contain reducing sugar, protein and lipid. 

Which of the food samples shown in the table below could be banana milkshake?

A teacher demonstrates several biological tests on two food samples to her class.

• Sample 1 was a mixture of phospholipids and starch. 

• Sample 2 tested positive for lipids and protein, but negative for reducing sugars.  

Which of the following options would be correct?

Birch trees can be tapped to extract a solution from their sieve tube elements. 

Different samples of the solution extracted from several birch trees were tested.

Which of the following would be the correct result?

Using a large number of aphids, the solution from the sieve tube elements of a strawberry plant was extracted, as shown in the image below. 

Different samples of the extracted solution were tested in the lab. 

Which of the following would be the correct result?

A sample solution underwent a series of biological tests to determine the substances present in the solution. 

When the biuret test was carried out a pale blue colour was observed; the same observation was made when the sample was heated with Benedict’s solution. 

When the sample was shaken in an organic solvent and then added to water, a milky emulsion was observed. 

Based on the information given, which of the following molecules are not present in this solution? 

Two solutions, one containing glucose and amylase, the other containing starch and sucrose, were tested with a variety of reagents to confirm their identity.

The table below shows the results recorded following the outcome of the biological tests. 

Which row correctly identifies the two solutions?

Key: + = biological molecule present, ー = biological molecule absent