All Free Biology MCQs with Answers

4531. The table shows some differences between glucose and a triglyceride. Which difference explains the fact that glucose is soluble in water, while the triglyceride is insoluble in water?

• A. Option A
• B. Option B
• C. Option C
• D. Option D

Explanation: The correct answer is Option A. Glucose is soluble in water because it contains many polar hydroxyl (-OH) groups that can form hydrogen bonds with water molecules, facilitating its dissolution. This is a characteristic of polar molecules, making them hydrophilic. On the other hand, triglycerides are composed of long non-polar hydrocarbon chains, which repel water, making them insoluble (hydrophobic). Although options B, C, and D mention other molecular properties, they do not directly explain the difference in solubility between glucose and triglycerides.

4532. Which feature is not characteristic of cellulose?

• A. β-glucose molecules
• B. Fibrillar structure
• C. 1-6 glycosidic bonds
• D. Hydrogen bonds

Explanation: The correct answer is Option C: 1-6 glycosidic bonds. Cellulose is composed of β-glucose molecules linked by 1-4 glycosidic bonds, forming straight chains. Unlike cellulose, polysaccharides like starch and glycogen contain 1-6 glycosidic bonds, which result in branching. Cellulose's structure includes hydrogen bonds that hold the chains together in a fibrillar arrangement, providing strength and rigidity. Therefore, the presence of 1-6 glycosidic bonds is not characteristic of cellulose.

4533. Compared to globular proteins, fibrous proteins are:

• A. Less regular in structure
• B. Less stable chemically
• C. More readily soluble
• D. More resistant to high temperatures

Explanation: Fibrous proteins, such as collagen and keratin, have highly ordered structures and are known for their mechanical strength and resistance to high temperatures. These proteins have extensive cross-linking, making them more stable under thermal stress. On the other hand, globular proteins, like enzymes and hemoglobin, are compact and typically more sensitive to temperature changes because they can denature easily. Therefore, fibrous proteins are more resistant to high temperatures, making Option D the correct answer. Options A, B, and C are incorrect because fibrous proteins are more regular in structure, chemically stable, and usually insoluble, respectively.

4534. Which feature is true of cellulose and accounts for its strength?

• A. It contains both α-1, 4 and α-1, 6 links between glucose units
• B. It has OH groups that form hydrogen bonds with adjacent cellulose molecules
• C. It is a fibrous molecule that is insoluble in water
• D. It is made up of long, branched and coiled chains of β-glucose units with 1, 4 links

Explanation: Cellulose is a polysaccharide consisting of β-glucose units linked by β-1, 4 glycosidic bonds. The hydroxyl (OH) groups on these glucose units form hydrogen bonds with OH groups on adjacent cellulose chains. This extensive hydrogen bonding network results in a rigid, strong structure capable of withstanding mechanical stress, which is why cellulose is a key structural component in plant cell walls.Option A is incorrect because α-1, 4 and α-1, 6 linkages are characteristics of starch, not cellulose. Option C correctly describes some properties of cellulose but does not explain the strength derived from hydrogen bonding. Option D incorrectly describes cellulose as branched and coiled; it is actually linear, and its strength arises from its linear nature and the hydrogen bonding between chains.

4535. Which formula is a carbohydrate?

• A. CH3CHO
• B. C2H5OH
• C. C3H6O3
• D. C15H31COOH

Explanation: Carbohydrates generally follow the formula Cn(H2O)m. Option C, C3H6O3, follows this formula (where n = 3 and m = 3), making it a carbohydrate. Option A, CH3CHO, is an aldehyde, not following the carbohydrate formula. Option B, C2H5OH, is ethanol, an alcohol. Option D, C15H31COOH, is a fatty acid, specifically palmitic acid, and does not fit the carbohydrate formula.

4536. The following statements describe the structure of a certain protein molecule.1-The molecule consists of two polypeptide chains which are folded around each other.2-In each chain, the amino acids are held in a helix by hydrogen bonds.Which orders of structure are described by these statements?

• A. Primary and Secondary
• B. Secondary and Tertiary
• C. Primary and Quaternary
• D. Secondary and Quaternary

Explanation: The correct answer is D) Secondary and Quaternary. The statements describe features of both the secondary and quaternary structures of proteins. The secondary structure involves the formation of helices in each chain due to hydrogen bonding, which is clearly mentioned. The quaternary structure involves the interaction and arrangement of multiple polypeptide chains, as indicated by the description of two chains folded around each other.Options A and C are incorrect because they do not account for the quaternary structure. Option B is incorrect because it doesn't fully address the quaternary structure, which involves multiple polypeptide chains interacting.

4537. The diagram represents a tripeptide.At which bonds does hydrolysis occur to release the amino acids from the tripeptide?

• A. 1 and 4
• B. 1 and 6
• C. 2 and 5
• D. 3 and 6

Explanation: The correct answer is Option C: 2 and 5. In a tripeptide, the amino acids are linked by peptide bonds. Hydrolysis specifically targets these peptide bonds to break them, releasing individual amino acids. Positions 2 and 5 in the diagram correspond to these peptide bonds. The other options do not represent these crucial peptide bond positions and thus are incorrect.

4538. Which of the following is the trace element _?

• A. Hydrogen
• B. Copper
• C. Oxygen
• D. Carbon

Explanation: Copper is needed in small amounts by living organisms for enzymatic activity, classifying it as a trace element.

4539. The branch of biology which deals with the study of chemical compounds and the chemical processes in the living organisms is called?

• A. Chemistry
• B. Molecular Biology
• C. Biochemistry
• D. Both a and b

Explanation: Biochemistry is the branch of science that explores the chemical processes within and related to living organisms. It is a laboratory-based science that combines biology and chemistry.

4540. What type of atom is a carbon atom?

• A. Divalent
• B. Monovalent
• C. Trivalent
• D. Tetravalent

Explanation: A tetravalent atom can form four bonds. Carbon is tetravalent because it has four valence electrons that can form bonds with other atoms.