AP Biology Unit 4: Cell Communication and Cell Cycle

Positive feedback amplifies the original stimulus. Oxytocin increases contractions, which increases cervical pressure and further oxytocin release.

The stem asks students to explain a specific mechanism, not just recall a unit term: "During childbirth, pressure on the cervix stimulates release of oxytocin. Oxytocin increases uterine contractions,...". The correct choice is supported by Oxytocin increases contractions, which increases cervical pressure and further oxytocin release. The tempting alternatives such as Hydrolysis because water breaks a polymer bond or Negative feedback because the response cancels the stimulus fail because they do not produce the same outcome described in the stem.

Cells lacking the checkpoint protein enter mitosis much more often after damage, supporting that the normal checkpoint helps block mitosis when DNA is damaged.

The evidence in the prompt matters before the topic label: "Cells are exposed to DNA-damaging radiation. Which conclusion is best supported by the data". The supported answer is "checkpoint protein helps prevent damaged cells from entering mitosis" because Cells lacking the checkpoint protein enter mitosis much more often after damage, supporting that the normal checkpoint helps block mitosis when DNA is damaged. Distractors such as checkpoint protein eliminates all cell division in healthy cells or checkpoint protein is required for photosynthesis either ignore the stated pattern or name a related concept without matching the evidence.

Receptors bind specific signaling molecules and trigger intracellular responses through signal transduction pathways.

The stem asks for a numerical or quantitative judgment: "A hormone binds to a receptor on the surface of a target cell. What is the most direct role of the receptor". The safe route is to identify the counted event, use the full denominator, and then interpret the number biologically. Here the worked reasoning is Receptors bind specific signaling molecules and trigger intracellular responses through signal transduction pathways, so choices based on To replicate the hormone's DNA sequence or To digest the plasma membrane completely lose the required setup.