Regulation of Cell Cycle

Regulation of Cell Cycle is topic 4.6 of AP Biology, inside Cell Communication and Cell Cycle. This page works through three real practice questions on it, with the full reasoning behind each credited answer.

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24 questionsConcept Explanation50% with a figure
Worked examples

Three real regulation of cell cycle questions

From the practice pool, not the mock papers — each with the reasoning that produces the answer.

50% of them come with a figure. Reading the graph or diagram correctly is most of the work here before any content knowledge applies.

Questions and Methods · with figure

A researcher wants to test whether a growth factor increases the percentage of cells entering S phase. Which measurement would best serve as the dependent variable?

  1. AThe volume of medium added to each culture
  2. BThe concentration of growth factor added to the treatment group
  3. CThe brand of culture dish used for both groups
  4. DThe percentage of cells incorporating a DNA-synthesis labelcorrect
Why D is correct

The dependent variable is the measured outcome. Incorporation of a DNA-synthesis label indicates cells entering or undergoing S phase.

This prompt is testing design logic in the scenario "A researcher wants to test whether a growth factor increases the percentage of cells entering S phase. Which...". A complete explanation should name the changed factor, the measured response, and the evidence pattern "The dependent variable is the measured outcome" before interpreting the outcome. The item-specific reasoning is The dependent variable is the measured outcome. Incorporation of a DNA-synthesis label indicates cells entering or undergoing S phase

Argumentation

A damaged cell activates proteins that fragment its DNA and package cell contents for removal without releasing inflammatory contents. Which claim is best supported?

  1. AThe cell is using facilitated diffusion to import glucose.
  2. BThe cell is completing photosynthesis in its chloroplasts.
  3. CThe cell is undergoing apoptosis, a regulated cell-death process.correct
  4. DThe cell is increasing gene flow between populations.
Why C is correct

Apoptosis is regulated cell death that includes DNA fragmentation and controlled packaging of cell contents.

The stem asks students to explain a specific mechanism, not just recall a unit term: "A damaged cell activates proteins that fragment its DNA and package cell contents for removal without releasing...". The correct choice is supported by Apoptosis is regulated cell death that includes DNA fragmentation and controlled packaging of cell contents. The tempting alternatives such as cell is using facilitated diffusion to import glucose or cell is completing photosynthesis in its chloroplasts fail because they do not produce the same outcome described in the stem.

Concept Explanation

Cyclin proteins bind cyclin-dependent kinases, CDKs, to help regulate progression through cell-cycle checkpoints. Which statement best describes this role?

  1. ACyclins permanently stop all DNA replication in every healthy cell.
  2. BCyclins are sugars that form cellulose in plant cell walls.
  3. CCyclin-CDK complexes help regulate progression through cell-cycle stagescorrect
  4. DCyclins are DNA bases that replace chromosomes.
Why C is correct

Cyclin-CDK complexes regulate cell-cycle transitions and checkpoints by phosphorylating target proteins that help determine whether the cell proceeds.

The stem asks students to explain a specific mechanism, not just recall a unit term: "Cyclin proteins bind cyclin-dependent kinases, CDKs, to help regulate progression through cell-cycle checkpoints....". The correct choice is supported by Cyclin-CDK complexes regulate cell-cycle transitions and checkpoints by phosphorylating target proteins that help determine whether the cell proceeds. The tempting alternatives such as Cyclins permanently stop all DNA replication in every healthy cell or Cyclins are sugars that form cellulose in plant cell walls fail because they do not produce the same outcome described in the stem.

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Last reviewed 2026-08-28. Topic and unit names follow the College Board course framework. Question counts describe the PrepScore practice bank, not the exam.
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