CIE A Level Biology

Topic Questions

Syllabus Edition

First teaching 2020

Last exams 2024

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2.1 Testing for Biological Molecules

11 mark

Which carbohydrate would form a brick-red solution when heated gently with Benedict’s solution?

  • sucrose

  • cellulose

  • starch

  • glucose

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21 mark

Which of the following biological molecules would not form a purple colour when added to biuret solution?

  • amylase

  • amylose

  • haemoglobin

  • lipase

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31 mark

Which of the following sequences correctly shows the colour change in precipitates formed when a solution with a high concentration of reducing sugar is heated with Benedict’s solution?

  • blue → yellow → orange → green → brick-red

  • blue → green → yellow → orange → brick-red

  • blue → brick-red → green → yellow → orange

  • green → blue → yellow → orange → brick-red

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41 mark

The diagram below shows a biological molecule.

qn-4-

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

  • mixing with Biuret solution 

  • heating gently with Benedict's solution

  • shaking with ethanol then pouring into water

  • adding iodine in potassium iodide solution

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51 mark

A sample of food was blended and several drops were decanted into a test tube with an equal volume of ethanol solution. The test tube was shaken vigorously for a minute before the mixture was poured into a test tube of water. 

A milky emulsion was observed. Which of the following biological molecules must have been present in the food?

  • carbohydrates

  • lipids

  • proteins

  • reducing sugars

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61 mark

Which of the following steps would not be involved in testing a sample for the presence of a non-reducing sugar? 

  • mixing with copper (II) sulfate

  • heating with copper (II) sulfate

  • acid hydrolysis

  • neutralisation

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71 mark

Samples of a mixture of biological molecules underwent a series of biological tests. 

When the biuret test was carried out on a sample of the mixture, the mixture turned lilac. 

When iodine in potassium iodide was added to a sample, the mixture turned black.

  • cellulose and phospholipid

  • starch and amylase

  • phospholipid and starch

  • cellulose and starch

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81 mark

The diagram below shows a biological molecule.

qn-8

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

  • heating gently with Benedict's solution

  • mixing with solutions of sodium hydroxide and copper (II) sulfate

  • shaking with ethanol then pouring into water

  • adding iodine in potassium iodide solution

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91 mark

Which carbohydrate would test positive for the Benedict’s test after acid hydrolysis, but negative before acid hydrolysis, has occurred? 

  • sucrose

  • galactose

  • fructose

  • glucose

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101 mark

The diagram below shows part of a biological molecule. 

qn-10

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

  • heating gently with Benedict's solution

  • mixing with solutions of sodium hydroxide and copper (II) sulfate

  • shaking with ethanol then pouring into water

  • adding iodine in potassium iodide solution

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11 mark

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. 

test observation
emulsion
iodine
Benedict’s
biuret
clear
orange
brick-red
purple

Which molecules are present in this solution? 

q21-1-bio-molecules-1

  • 1 and 3 only

  • 1 and 2 only

  • 2 and 3 only

  • 1, 3 and 4 

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21 mark

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

solution

colour

1

2

3

4

yellow

green

blue

brick-red

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

  solution 1 solution 2 solution 3 solution 4
A 0.1% reducing sugar 0.05% reducing sugar 0.5% non-reducing sugar   1.0% reducing sugar
B 0.5% reducing sugar 1.0% reducing sugar 1.0% non-reducing sugar 1.5% reducing sugar 
C 0.05% reducing sugar 0.1% reducing sugar 1.0% reducing sugar 0.5% reducing sugar
D 1.5% reducing sugar 1.0% non-reducing sugar 1.5% reducing sugar  1.0% non-reducing sugar

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31 mark

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. 

test observation

emulsion

iodine

Benedict’s

biuret

cloudy

blue-black

green

blue

Which molecules are present in this solution? q23-1-bio-molecules-3

  • 1 and 3 only

  • 1 and 4 only

  • 2 and 3 only

  • 1, 3 and 4

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41 mark

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

A second sample of the same four juices were 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?     

 

mass of precipitate before acid hydrolysis /mg

mass of precipitate after acid hydrolysis /mg

A

B

C

D

60

20

55

40

70

45

75

40

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51 mark

Question 25 - CIE IAS 2.1 Testing for Biological Molecules - HARD

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

  • 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 a banana milkshake?

Food observation
adding Biuret reagent heating with Benedict’s solution adding iodine in potassium iodide solution mixing with ethanol and adding to water 
A purple blue orange clear
B pale blue orange precipitate blue-black clear
C purple orange precipitate orange milky emulsion
D pale blue blue blue-black milky emulsion

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61 mark

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.  
food observation
adding Biuret reagent heating with Benedict’s solution adding iodine in potassium iodide solution mixing with ethanol and adding to water  hydrolysed and heated with Benedict’s
1 purple orange blue-black clear  blue
2 purple blue  orange milky brick-red
3 pale blue orange  orange milky  blue
4 pale blue blue blue-black milky brick-red

Which of the following options would be correct?

 

sample 1

sample 2

A

B

C

D

1

4

2

4

3

2

3

1

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71 mark

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?

  observation iodine in KI
before hydrolysis after hydrolysis
A blue red blue-black
B green  blue  brown
C blue red  brown
D red yellow blue-black

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81 mark

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. 

qn8

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

Which of the following would be the correct result?

  observation iodine in KI
before hydrolysis after hydrolysis
A blue red blue-black
B red  blue  blue-black
C red blue brown
D blue red brown

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91 mark

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? 

q-29

  • 1 and 3

  • 2 and 4

  • 1, 2 and 4

  • 3 only

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101 mark

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 conclusions recorded following the outcome of the biological tests. 

Which row correctly identifies the two solutions?

  add biuret add iodine in KI boil with Benedict’s solution boil with Benedict’s solution after acid hydrolysis
1 2 1 2 1 2 1 2
A + + + +
B + + + +
C + + + +
D + + + + +

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

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11 mark

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 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 reducing sugar is present

  • a non-reducing sugar is present

  • both reducing and non-reducing sugars are present

  • no sugar (reducing or non-reducing) is present

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21 mark

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?

  reagent observation of mixture
A iodine in potassium iodide solution blue-black
B Benedict’s solution blue
C iodine in potassium iodide solution orange
D Benedict’s solution brick-red

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31 mark

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

The table below shows the results.

test observations
Benedict’s yellow
Biuret lilac
Ethanol clear
iodine in potassium iodide solution orange


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

  • protein and reducing sugar

  • protein and lipids

  • protein and non-reducing sugar

  • protein and starch

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41 mark

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

  test 1 test 2
solution heated with Benedict’s solution  boiled with hydrochloric acid, neutralised, then heated with Benedict’s solution  
1
2
3
brown
blue
yellow
blue
red
orange

Which solution may contain reducing sugars?

  • 1 and 3 only 

  • 1 and 2 only

  • 2 and 3 only

  • 1, 2 and 3

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51 mark

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?

  heated with Benedict’s reagent boiled with hydrochloric acid, neutralised and then heated with Benedict’s reagent 
A orange blue
B orange orange
C blue orange
D blue blue

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61 mark

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:

reagent observation
Benedict's solution
biurets
ethanol and water
orange
lilac
clear

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

  • fatty acids and reducing sugars

  • non-reducing sugars and protein

  • reducing sugars and fatty acids

  • protein and reducing sugars

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71 mark

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

  test 1  test 2
solution heated with Benedict’s solution  hydrolysed, then heated with Benedict’s solution  
1
2
3
4
brown
blue
yellow
brown
blue
red
green
orange

 

Which solution may contain non-reducing sugars?

  • 1 and 2 only

  • 2 only

  • 3 and 4 only

  • 2, 3 and 4

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81 mark

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:

reagent observation
Benedict’s solution

Biuret
ethanol and water

brown precipitate
lilac colour

clear

Which row correctly shows the molecules found in the solution?

  fatty acids protein reducing sugar
A X X
B X X
C X
D X

Key: ✓ = present, X = absent

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91 mark

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

test observation
non-reducing sugar
lipid
starch
protein
blue
cloudy
orange
lilac

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

  fatty acids starch protein non-reducing sugar
A X X
B X
C X X
D X

Key: ✓ = present, X = absent

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101 mark

The diagram below shows a biological molecule. 

qn-20

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

  • heating gently with Benedict's solution

  • mixing with solutions of sodium hydroxide and copper (II) sulfate

  • shaking with an organic solvent then adding into water

  • adding iodine in potassium iodide solution

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