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 12 IGCSE.
Preview questions (no answers)
- 1.
What color is iodine solution when no starch is present?
A.Blue-black
B.Pale blue
C.Yellow-brown
D.Violet
- 2.
Which of these functional groups is found in every amino acid?
A.Phosphate group
B.Carboxyl group ()
C.Glucose group
D.Iron group
- 3.
Which form of carbohydrate is typically transported through the phloem of a plant?
A.Starch
B.Glucose
C.Sucrose
D.Glycogen
- 4.
What primarily determines the specific three-dimensional shape of a protein?
A.The number of carbon atoms
B.The sequence of amino acids
C.The amount of water present
D.The type of lipid attached
- 5.
If a sample turns blue-black upon addition of iodine, what can be concluded?
A.Proteins are present.
B.Reducing sugars are present.
C.Starch is present.
D.Lipids are present.
- 6.
What is the primary storage polysaccharide in plants?
A.Glucose
B.Cellulose
C.Amylopectin and Amylose
D.Glycogen
- 7.
Which of the following describes the function of an enzyme in terms of biological molecules?
A.A lipid that stores information.
B.A carbohydrate that provides structure.
C.A globular protein that acts as a biological catalyst.
D.A fibrous protein that provides tensile strength.
- 8.
What type of bond maintains the triple helix of a collagen molecule?
A.Peptide bonds between chains.
B.Hydrogen bonds between the peptide backbones of different chains.
C.Ester bonds between R-groups.
D.Glycosidic bonds between glucose residues.
- 9.
Which of the following molecules is the most highly branched?
A.Amylose
B.Amylopectin
C.Glycogen
D.Cellulose
- 10.
In protein tertiary structure, where are hydrophobic interactions most likely to occur?
A.On the surface of the protein in contact with water.
B.In the interior of the protein, away from water.
C.Between the amino group and the carboxyl group of the backbone.
D.Only in the quaternary structure between different subunits.
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 12 IGCSE.
Preview questions (no answers)
- 1.
Which molecule provides the template for the synthesis of proteins, based on its own sequence?
A.Lipid
B.DNA
C.Glucose
D.Starch
- 2.
What is the result of the twisting of the two polynucleotide chains around each other?
A.A straight ladder
B.A single strand
C.A double helix
D.A triple helix
- 3.
The genetic information is stored in which of the following?
A.The sugar molecules
B.The phosphate groups
C.The order of the nitrogenous bases
D.The thickness of the helix
- 4.
Which part of the DNA molecule is responsible for the negative charge often associated with it?
A.Nitrogenous bases
B.Deoxyribose sugar
C.Phosphate group
D.Hydrogen bonds
- 5.
If a sample of DNA has Adenine, what is the percentage of Cytosine?
A.B.C.D. - 6.
What is the total number of carbon atoms present in a single deoxyribose sugar molecule?
A.B.C.D. - 7.
The stability of the DNA double helix is maintained by hydrogen bonds and which other significant interaction?
A.Ionic bonds between the sugars
B.Hydrophobic stacking interactions between the bases
C.Disulfide bridges between the phosphates
D.Metallic bonding between nitrogen atoms
- 8.
A DNA strand has the sequence . Which of the following represents the correct mRNA sequence if this strand acts as the template?
A.B.C.D. - 9.
Identify the chemical bond that connects the of deoxyribose to the Nitrogen-9 of a purine base.
A.Phosphodiester bond
B.Hydrogen bond
C.-glycosidic bond
D.Peptide bond
- 10.
A mutation that changes a base pair to an base pair would result in:
A.An increase in the melting temperature of the DNA.
B.A decrease in the melting temperature of the DNA.
C.An increase in the width of the DNA helix.
D.No change in the physical properties of the DNA.
Download the worksheet for Biological Molecules - Structure of DNA to practice offline. It includes additional chapter-level practice questions.
Chemical tests for nutrients
SubtopicChemical tests for nutrients under Biological Molecules for Grade 12 IGCSE.
Preview questions (no answers)
- 1.
Which of the following results indicates the presence of a reducing sugar after heating with Benedict's solution?
A.A violet solution
B.An orange-brown precipitate
C.A blue-black solid
D.A milky-white emulsion
- 2.
A student tests a sample of vegetable oil. Which test should they use and what is the observation?
A.Iodine test; blue-black color
B.Biuret test; purple color
C.Emulsion test; cloudy white layer
D.Benedict's test; brick-red precipitate
- 3.
Why is it necessary to use a clear extract of food when performing the DCPIP test?
A.To prevent the food from reacting with the DCPIP
B.To ensure the fat is removed first
C.To clearly see the disappearance of the blue color
D.To make sure the Vitamin C is not destroyed
- 4.
Which reagent is used to test for the presence of peptide bonds in a molecule?
A.Benedict's reagent
B.Iodine solution
C.Biuret reagent
D.Ethanol
- 5.
Which observation would be seen if a solution of pure lipase enzyme was tested with the Biuret reagent?
A.A blue-black color
B.A purple color
C.A milky-white emulsion
D.A brick-red precipitate
- 6.
Which of the following sugars will NOT react with Benedict's reagent even after heating, unless it is first hydrolyzed?
A.Glucose
B.Galactose
C.Sucrose
D.Lactose
- 7.
Why is it important to use a water bath when heating the Benedict's reagent instead of a direct flame?
A.To ensure the sample is heated evenly and safely.
B.Because the Benedict's reagent is highly flammable.
C.Because the sugar will evaporate if heated over a flame.
D.To prevent the copper ions from reacting with the glass.
- 8.
Which molecular feature of Vitamin C (ascorbic acid) is responsible for the decolorization of DCPIP?
A.The presence of a carboxyl group that lowers the pH.
B.The presence of an ene-diol group that acts as a reducing agent.
C.The six-carbon ring structure that absorbs the blue light.
D.The oxygen atoms that form hydrogen bonds with the DCPIP molecule.
- 9.
A student finds that of a glucose solution takes 3 minutes to turn green in a Benedict's test at . If they repeat the test at , what is the most likely outcome?
A.The solution will take longer than 3 minutes to change color.
B.The solution will change color in less than 3 minutes.
C.The solution will remain blue regardless of the time.
D.The solution will turn brick-red immediately without passing through green.
- 10.
Which of the following would produce a purple color with Biuret reagent and a blue-black color with iodine?
A.A piece of bread
B.A solution of pure amylopectin
C.A mixture of albumin and starch
D.A suspension of lipid droplets in water
Download the worksheet for Biological Molecules - Chemical tests for nutrients to practice offline. It includes additional chapter-level practice questions.