AP - Advanced Placement Biology MCQ 1

Question 1

In a signal transduction pathway, cAMP (cyclic AMP) functions as a:

Accepted Answer

Second messenger that relays the signal inside the cell

Answer

cAMP is synthesized inside the cell after a primary messenger (e.g., a hormone) binds to a G-protein-coupled receptor. It relays the extracellular signal to intracellular targets, classifying it as a second messenger.

Question 2

Competitive inhibition of an enzyme differs from noncompetitive inhibition in that competitive inhibition:

Accepted Answer

Can be overcome by increasing substrate concentration

Answer

A competitive inhibitor occupies the active site, but flooding the reaction with excess substrate out-competes the inhibitor for binding, restoring activity. Noncompetitive inhibition lowers Vmax regardless of substrate concentration because the inhibitor binds elsewhere.

Question 3

Crossing over between homologous chromosomes occurs during which phase of meiosis?

Accepted Answer

Prophase I

Answer

During Prophase I, homologous chromosomes synapse to form bivalents. Crossing over (exchange of segments at chiasmata) occurs at this stage, generating genetic recombination before chromosomes align on the metaphase plate.

Question 4

Which of the following conditions would violate Hardy-Weinberg equilibrium and cause allele frequencies to change over generations?

Accepted Answer

Gene flow due to migration into the population

Answer

Gene flow (migration of individuals carrying alleles into or out of a population) directly changes allele frequencies, violating one of the five Hardy-Weinberg assumptions and causing the population to deviate from equilibrium.

Question 5

In the E. coli lac operon, maximal transcription occurs when:

Accepted Answer

Lactose is present and glucose is absent

Answer

Lactose (via allolactose) inactivates the repressor, freeing the operator. Simultaneously, low glucose raises cAMP levels, activating the CAP-cAMP complex that greatly stimulates RNA polymerase binding. Both signals together produce maximal transcription.

AP Practice Test

AP Practice Test

AP - Advanced Placement Biology MCQ 1