All Free Biology MCQs with Answers

901. Which factor does NOT affect enzyme activity?

• A. Temperature
• B. pH
• C. Substrate concentration
• D. Color of the solution

Explanation: Enzyme activity is affected by temperature, pH, substrate concentration, and presence of inhibitors/activators, but not by color.

902. The Michaelis constant (Km) represents

• A. Maximum reaction velocity
• B. Substrate concentration at half Vmax
• C. Enzyme concentration
• D. Inhibitor concentration

Explanation: Km is the substrate concentration at which the reaction velocity is half of Vmax. It indicates enzyme-substrate affinity.

903. Allosteric enzymes

• A. Follow Michaelis-Menten kinetics strictly
• B. Have multiple subunits and regulatory sites
• C. Are not affected by feedback inhibition
• D. Always show competitive inhibition

Explanation: Allosteric enzymes have multiple subunits with regulatory (allosteric) sites where activators or inhibitors bind, affecting enzyme conformation.

904. Which enzyme is involved in DNA replication?

• A. RNA polymerase
• B. DNA ligase
• C. Peptidase
• D. Lipase

Explanation: DNA ligase joins Okazaki fragments by forming phosphodiester bonds between adjacent nucleotides.

905. Zymogens are

• A. Active enzymes
• B. Inactive enzyme precursors
• C. Coenzymes
• D. Enzyme inhibitors

Explanation: Zymogens (proenzymes) are inactive precursors that are activated by cleavage, e.g., pepsinogen → pepsin, trypsinogen → trypsin.

906. The enzyme carbonic anhydrase is found in

• A. Stomach
• B. Red blood cells
• C. Pancreas
• D. Liver

Explanation: Carbonic anhydrase in RBCs catalyzes CO2 + H2O ↔ H2CO3, facilitating CO2 transport in blood.

907. Natural selection was proposed by

• A. Lamarck
• B. Darwin
• C. Mendel
• D. Wallace

Explanation: Charles Darwin proposed the theory of natural selection in 'On the Origin of Species' (1859).

908. Industrial melanism in peppered moth is an example of

• A. Directional selection
• B. Stabilizing selection
• C. Disruptive selection
• D. Genetic drift

Explanation: Industrial melanism demonstrates directional selection, where the dark phenotype became favored in polluted environments.

909. Homologous structures indicate

• A. Convergent evolution
• B. Divergent evolution
• C. No evolutionary relationship
• D. Analogous functions

Explanation: Homologous structures (same origin, different function) indicate divergent evolution from a common ancestor.

910. The bottleneck effect is a type of

• A. Natural selection
• B. Genetic drift
• C. Gene flow
• D. Mutation

Explanation: The bottleneck effect is genetic drift caused by a drastic reduction in population size, reducing genetic diversity.