Biological Molecules
Each subtopic includes About section, revision page link, 10 preview questions, and practice CTAs.
Carbohydrates, lipids and proteins
SubtopicCarbohydrates, lipids and proteins under Biological Molecules for Grade 11 IGCSE.
Preview questions (no answers)
- 1.
Which of these elements is sometimes found in proteins (in the R-group of certain amino acids) but never in carbohydrates?
A.Carbon
B.Hydrogen
C.Oxygen
D.Sulfur
- 2.
What color is Benedict's solution before it is added to a food sample?
A.Orange
B.Blue
C.Colorless
D.Red
- 3.
Which molecule consists of many glucose units linked in a way that makes it indigestible for humans but provides fiber?
A.Starch
B.Glycogen
C.Cellulose
D.Sucrose
- 4.
When testing a food, why might you grind it up with water first?
A.To make the test change color faster
B.To release the molecules into solution
C.To remove all the oxygen
D.To make the sample more acidic
- 5.
Which of the following molecules has the most complex three-dimensional structure?
A.Glucose
B.Water
C.A globular protein
D.A fatty acid
- 6.
A sample turns DCPIP from blue to colorless. What does this indicate about the sample?
A.It contains protein
B.It contains reducing sugar
C.It contains Vitamin C
D.It contains lipids
- 7.
When testing for a non-reducing sugar, what is the purpose of adding sodium hydrogencarbonate after boiling the sample with acid?
A.To catalyze the Benedict's reaction
B.To neutralize the acid
C.To break the glycosidic bonds
D.To precipitate the sugar
- 8.
Which type of bond is formed when two monosaccharides are joined together?
A.Peptide bond
B.Ester bond
C.Glycosidic bond
D.Hydrogen bond
- 9.
Which of the following contains the highest concentration of lipids per unit mass?
A.A potato tuber
B.A lean piece of steak
C.A sunflower seed
D.An apple fruit
- 10.
If a solution contains a high concentration of glucose, what will be the final color of the Benedict’s test after heating?
A.Green
B.Yellow
C.Brick-red
D.Blue
Download the worksheet for Biological Molecules - Carbohydrates, lipids and proteins to practice offline. It includes additional chapter-level practice questions.
Structure of DNA
SubtopicStructure of DNA under Biological Molecules for Grade 11 IGCSE.
Preview questions (no answers)
- 1.
Which chemical base is complementary to Thymine?
A.Guanine
B.Cytosine
C.Adenine
D.Uracil
- 2.
What provides the vertical stability for a single strand of DNA?
A.Hydrogen bonds between bases
B.Covalent bonds in the sugar-phosphate backbone
C.Ionic bonds between strands
D.Weak physical contact
- 3.
Which component of the nucleotide contains the element Nitrogen?
A.Phosphate
B.Sugar
C.Base
D.Both sugar and phosphate
- 4.
If a DNA molecule is found to have 20% Guanine (), what percentage of the molecule is Cytosine ()?
A.10%
B.20%
C.30%
D.40%
- 5.
A student builds a model of DNA. If they use 20 phosphate 'beads', how many deoxyribose 'beads' should they use to make the model scientifically accurate?
A.10
B.20
C.40
D.5
- 6.
Which of the following is the largest structure?
A.A nitrogenous base
B.A DNA nucleotide
C.A phosphate group
D.A five-carbon sugar
- 7.
In a DNA molecule, what is the significance of the base pairing being 'specific' (A with T, C with G)?
A.It ensures that the two strands are identical to each other
B.It allows the DNA to be copied accurately during cell division
C.It makes the DNA molecule flexible enough to fold into a nucleus
D.It prevents the sugar-phosphate backbone from breaking
- 8.
What is the result of the 'Chargaff's Rules' application to a double-stranded DNA molecule?
A.The amount of equals the amount of
B.The amount of Purines () equals the amount of Pyrimidines ()
C.The amount of Adenine equals the amount of Guanine
D.The amount of Cytosine equals the amount of Thymine
- 9.
In a nucleotide, which carbon of the deoxyribose is NOT part of the five-membered ring itself but is still attached to the phosphate?
A.carbon
B.carbon
C.carbon
D.carbon
- 10.
Which of the following is true about the diameter of the DNA double helix?
A.It varies depending on the sequence of bases
B.It is constant because a purine always pairs with a pyrimidine
C.It decreases in regions with high Adenine content
D.It is determined by the length of the sugar-phosphate backbone
Download the worksheet for Biological Molecules - Structure of DNA to practice offline. It includes additional chapter-level practice questions.
Chemical tests for molecules
SubtopicChemical tests for molecules under Biological Molecules for Grade 11 IGCSE.
Preview questions (no answers)
- 1.
If iodine solution is dropped onto a sample of pure vegetable oil, what color will the iodine remain?
A.Blue-black
B.Orange-brown
C.Clear
D.Purple
- 2.
Which reagent should be selected to test for the presence of glucose ()?
A.Iodine solution
B.Benedict's solution
C.Biuret reagent
D.DCPIP
- 3.
In the emulsion test, what change occurs to the liquid once the ethanol extract is added to water?
A.It turns dark blue
B.It becomes a cloudy/milky emulsion
C.It turns bright purple
D.It stays completely clear
- 4.
What color is the precipitate formed in a Benedict's test when a very high amount of sugar is present?
A.Blue
B.Brick-red
C.Green
D.Light purple
- 5.
In an emulsion test, if a sample contains a very low concentration of lipids, how would the final mixture appear?
A.Transparent and blue
B.A faint hazy or cloudy appearance
C.A thick layer of white solid
D.The solution would be bright yellow
- 6.
Why does a solution of free amino acids (not linked in a chain) generally give a negative Biuret test?
A.Amino acids are too small to be seen
B.Biuret reagent only reacts with peptide bonds in polypeptides and proteins
C.Free amino acids are acidic and neutralize the reagent
D.Free amino acids are only soluble in ethanol
- 7.
Which of the following describes a positive Iodine test for starch?
A.The solution turns from brown to blue-black
B.The solution turns from blue to purple
C.A white cloud forms in the water
D.The solution turns from blue to orange
- 8.
Which of the following best explains why the emulsion test is a qualitative rather than a quantitative test?
A.Lipids do not react with the reagents at all.
B.The turbidity of the emulsion is difficult to measure and relate to a specific mass of lipid without specialized equipment.
C.Ethanol only dissolves a fixed amount of lipid regardless of the sample size.
D.The test depends on the temperature of the water added.
- 9.
A sample of honey is tested with Benedict's reagent and turns brick-red. After boiling another sample of honey with and neutralizing, it also turns brick-red with Benedict's. What does this tell you about the sugar content of honey?
A.It contains only non-reducing sugars.
B.It contains reducing sugars and may or may not contain non-reducing sugars.
C.It contains no sugars at all.
D.The destroyed the reducing sugars.
- 10.
What would be the effect of using a copper(II) sulfate solution instead of the standard solution in a Biuret test?
A.The test would be more sensitive and detect lower protein concentrations.
B.The deep blue color of the excess might mask the purple color of a positive result.
C.The protein would be hydrolyzed into amino acids, giving a negative result.
D.A brick-red precipitate would form instead of a purple solution.
Download the worksheet for Biological Molecules - Chemical tests for molecules to practice offline. It includes additional chapter-level practice questions.