Rucete ✏ AP Biology In a Nutshell
9. The Cell Cycle — Practice Questions
This chapter explores the sequence of stages that cells go through to grow, replicate DNA, divide, and how this cycle is regulated by molecular signals and checkpoints.
Need a quick review?
📘 Go to the Concept Summary
(Multiple Choice — Click to Reveal Answer)
1. A chemotherapy drug stops the replication of DNA. During which stage of the cell cycle would this drug have the greatest effect?
(A) G0
(B) G1
(C) G2
(D) S
Answer
(D) — DNA is replicated during the S phase, making it the most affected stage.
2. A cell has reached full maturity, is fully differentiated, and no longer divides. Which of the following describes this stage of the cell cycle?
(A) G0
(B) G1
(C) G2
(D) S
Answer
(A) — G0 is the non-dividing resting phase of the cycle.
3. Which stage of mitosis has twice as many chromosomes at its end as it had at its beginning?
(A) Prophase
(B) Metaphase
(C) Anaphase
(D) Telophase
Answer
(C) — Chromatids are pulled apart in anaphase, doubling the chromosome number temporarily.
4. During which stage of mitosis do the centromeres of chromosomes attach to spindle fibers and line up in a single column in the center of the cell?
(A) Prophase
(B) Metaphase
(C) Anaphase
(D) Telophase
Answer
(B) — Metaphase is when chromosomes align at the metaphase plate.
5. Approximately what percentage of cells are in interphase if G1 = 73, S = 89, G2 = 68, and M = 43?
(A) 16%
(B) 33%
(C) 52%
(D) 84%
Answer
(D) — Interphase includes G1, S, and G2. (73+89+68)/273 ≈ 84%.
6. Which process best describes what occurs when soft tissue between the fingers dies during embryonic development?
(A) Apoptosis
(B) DNA replication
(C) Mitosis
(D) Cytokinesis
Answer
(A) — Apoptosis is programmed cell death crucial during development.
7. During which process is the cytoplasm divided between daughter cells?
(A) Apoptosis
(B) DNA replication
(C) Mitosis
(D) Cytokinesis
Answer
(D) — Cytokinesis is responsible for dividing the cytoplasm after mitosis.
8. Which of the following is a correct statement?
(A) Cancer cells exhibit anchorage dependence.
(B) Somatic cells exhibit density-dependent inhibition.
(C) Somatic cells spend most of their time in mitosis.
(D) Cancer cells exhibit density-dependent inhibition.
Answer
(B) — Normal somatic cells stop dividing when overcrowded (density-dependent inhibition).
9. Which of the following best describes a role of mitosis?
(A) Mitosis distributes cytosol between the daughter cells.
(B) Replication of DNA occurs during mitosis.
(C) Replication of cell organelles occurs during mitosis.
(D) Mitosis distributes genetic material between the daughter cells.
Answer
(D) — Mitosis ensures equal distribution of genetic material into daughter nuclei.
10. During which phase of the cell cycle is a cleavage furrow or cell plate formed?
(A) Interphase
(B) Mitosis
(C) Cytokinesis
(D) G0
Answer
(C) — A cleavage furrow (in animals) or cell plate (in plants) forms during cytokinesis.
11. What occurs during the G1 phase of the cell cycle?
(A) Chromosomes condense and spindle fibers form.
(B) DNA is replicated.
(C) The cell grows and prepares for DNA replication.
(D) The cell divides into two daughter cells.
Answer
(C) — G1 is the first part of interphase where growth and preparation for DNA synthesis occurs.
12. What triggers the start of mitosis in a normal cell cycle?
(A) Breakdown of the nuclear membrane
(B) Activation of cyclin-dependent kinases by cyclins
(C) Completion of cytokinesis
(D) Activation of tumor suppressor genes
Answer
(B) — Cyclins bind to CDKs forming MPF, which triggers entry into mitosis.
13. Which molecule remains at a constant level throughout the cell cycle?
(A) Cyclin
(B) Cyclin-dependent kinase (CDK)
(C) MPF
(D) Tubulin
Answer
(B) — CDKs are always present; they are activated only when bound to cyclins.
14. What checkpoint ensures DNA is fully and correctly replicated before mitosis begins?
(A) G1 checkpoint
(B) G2 checkpoint
(C) M checkpoint
(D) S checkpoint
Answer
(B) — The G2 checkpoint ensures accurate DNA replication before entering mitosis.
15. During which stage of mitosis do sister chromatids separate and move toward opposite poles?
(A) Prophase
(B) Metaphase
(C) Anaphase
(D) Telophase
Answer
(C) — Anaphase is when spindle fibers pull sister chromatids apart.
16. What structure forms in animal cells to divide the cytoplasm during cytokinesis?
(A) Cell plate
(B) Spindle fiber
(C) Cleavage furrow
(D) Centromere
Answer
(C) — The cleavage furrow pinches the membrane to complete cell division in animals.
17. What best defines apoptosis?
(A) Uncontrolled cell growth
(B) Cell division
(C) Programmed cell death
(D) Nuclear envelope breakdown
Answer
(C) — Apoptosis is the process by which cells intentionally self-destruct when necessary.
18. Which checkpoint is directly responsible for preventing a cell with DNA damage from entering S phase?
(A) G0 checkpoint
(B) G1 checkpoint
(C) G2 checkpoint
(D) M checkpoint
Answer
(B) — The G1 checkpoint ensures the DNA is undamaged before replication in S phase.
19. Which type of gene, when mutated in only one allele, can cause cancer by promoting uncontrolled cell division?
(A) Tumor suppressor gene
(B) Proto-oncogene
(C) Apoptosis gene
(D) Cyclin gene
Answer
(B) — A mutated proto-oncogene (now oncogene) can stimulate excessive cell division.
20. Which statement is true regarding tumor suppressor genes?
(A) One mutated allele is enough to cause cancer.
(B) They promote mitosis.
(C) Both alleles must be mutated to disable the gene.
(D) They encode for MPF.
Answer
(C) — Tumor suppressor genes are recessive; both alleles must be mutated to lose function.
21. What does MPF stand for?
(A) Mitotic Proliferation Factor
(B) Metaphase Processing Force
(C) Mitosis Promoting Factor
(D) Molecular Protein Factor
Answer
(C) — MPF stands for Mitosis Promoting Factor and is crucial for cell cycle progression.
22. What happens to cyclin levels during the cell cycle?
(A) Remain constant
(B) Gradually decrease
(C) Spike before mitosis and then fall
(D) Increase continuously until cytokinesis
Answer
(C) — Cyclin levels rise before mitosis and fall rapidly after it begins.
23. What is the main function of spindle fibers during mitosis?
(A) Copy DNA
(B) Move chromosomes
(C) Form the nuclear envelope
(D) Divide the cytoplasm
Answer
(B) — Spindle fibers attach to centromeres and help move chromosomes during mitosis.
24. What happens if the M checkpoint is not properly regulated?
(A) Apoptosis will initiate during G0
(B) DNA will not replicate
(C) Chromosomes may not align properly and aneuploidy can occur
(D) Cell will skip G1 phase
Answer
(C) — If the M checkpoint fails, chromosome separation may be uneven, causing defects.
25. Which of the following is a correct pair?
(A) G1 – DNA replication
(B) S – Chromosome alignment
(C) G2 – Spindle fiber formation preparation
(D) M – Apoptosis
Answer
(C) — G2 involves preparation for mitosis, including spindle component production.
26. If a cell fails to form spindle fibers during mitosis, what stage will be directly impacted first?
(A) Prophase
(B) Metaphase
(C) Anaphase
(D) Telophase
Answer
(B) — Without spindle fibers, chromosomes cannot align at the metaphase plate.
27. What would be the likely consequence if a mutation caused constant high levels of cyclin in a cell?
(A) The cell would remain in G0 indefinitely.
(B) Mitosis would occur repeatedly and uncontrollably.
(C) DNA replication would cease.
(D) Cytokinesis would never begin.
Answer
(B) — Cyclin constantly activating MPF would force the cell into repeated mitosis.
28. A researcher blocks cyclin production in a cell. What is the most immediate expected result?
(A) The cell will skip cytokinesis.
(B) The nuclear envelope will disintegrate prematurely.
(C) MPF will not form, and the cell will not enter mitosis.
(D) Chromosomes will fail to replicate.
Answer
(C) — Without cyclin, MPF cannot be formed to trigger mitosis.
29. What distinguishes a cell in telophase from one in prophase?
(A) Chromatin is visible in telophase but not in prophase.
(B) Nuclear envelope dissolves in telophase but reforms in prophase.
(C) Spindle fibers attach in telophase.
(D) DNA replication occurs in telophase.
Answer
(A) — In telophase, chromosomes decondense back into chromatin; in prophase, they condense.
30. What would happen if a mutation caused a proto-oncogene to become permanently active?
(A) The cell would stop dividing.
(B) The cell would permanently enter G0.
(C) The cell would divide uncontrollably.
(D) The spindle apparatus would disassemble.
Answer
(C) — A proto-oncogene mutation leads to unregulated cell division, forming oncogenes.
31. Which of the following mechanisms contributes to the loss of contact inhibition in cancer cells?
(A) Enhanced DNA proofreading enzymes
(B) Hyperactivation of cyclin-dependent kinases
(C) Normal levels of tumor suppressor proteins
(D) Permanent entry into G0
Answer
(B) — Hyperactive CDKs can override growth signals and checkpoints, leading to uncontrolled growth.
32. Why does a cell need checkpoint regulation during the cell cycle?
(A) To speed up mitosis
(B) To prevent apoptosis
(C) To detect and repair DNA damage before division
(D) To ensure transcription occurs during mitosis
Answer
(C) — Checkpoints ensure the integrity of DNA and control the timing of progression.
33. What feature of mitosis ensures that daughter cells are genetically identical to the parent cell?
(A) Semi-conservative replication
(B) Equal distribution of duplicated chromosomes
(C) Apoptosis
(D) Anchoring of centromeres
Answer
(B) — Mitosis distributes exact copies of chromosomes to daughter cells.
34. In the absence of functional tumor suppressor genes, what is a likely cellular consequence?
(A) The cell will enter apoptosis immediately.
(B) The cell cycle will halt permanently.
(C) The cell may divide uncontrollably.
(D) Cyclins will no longer be produced.
Answer
(C) — Without tumor suppressors, there's no braking mechanism to stop cell division in faulty cells.
35. Which experimental result would suggest a molecule acts like a tumor suppressor gene?
(A) Its presence correlates with increased mitotic activity.
(B) It is always active in G0 phase.
(C) Cells lacking the molecule grow faster and form tumors.
(D) The molecule activates proto-oncogenes.
Answer
(C) — Loss of tumor suppressors leads to unchecked growth and tumor formation.
36. What is the primary role of cyclins in the cell cycle?
Answer
Cyclins regulate the cell cycle by binding to and activating cyclin-dependent kinases (CDKs), forming MPF to trigger progression into mitosis.
37. How do tumor suppressor genes help prevent cancer?
Answer
They code for proteins that inhibit cell division or trigger apoptosis in response to DNA damage. Both alleles must be mutated for loss of function.
38. Explain the difference between a proto-oncogene and an oncogene.
Answer
A proto-oncogene normally promotes controlled cell division, but a mutation can convert it into an oncogene, which promotes unregulated division.
39. What would be the likely result if apoptosis failed to occur during embryonic development?
Answer
Improper tissue development, such as webbed fingers or toes, due to failure to eliminate unnecessary cells.
40. Why is the G2 checkpoint important before a cell enters mitosis?
Answer
It ensures DNA is fully and accurately replicated before division, preventing errors from being passed to daughter cells.
41. Describe what happens during metaphase of mitosis.
Answer
Chromosomes align along the metaphase plate, attached to spindle fibers at their centromeres in preparation for separation.
42. How do plant and animal cells differ in cytokinesis?
Answer
Animal cells form a cleavage furrow, while plant cells form a cell plate to divide the cytoplasm and construct new cell walls.
43. What is the function of the mitotic spindle during mitosis?
Answer
It separates sister chromatids and ensures equal distribution of chromosomes to the daughter cells.
44. Why is uncontrolled activation of MPF harmful to the cell?
Answer
It can push the cell into mitosis without proper DNA checks, increasing the risk of mutations and cancer development.
45. How does density-dependent inhibition regulate cell growth?
Answer
It stops cells from dividing when they come into contact with other cells, maintaining tissue architecture and preventing overgrowth.
46. Describe the role of CDKs in the cell cycle.
Answer
CDKs are enzymes that, when activated by cyclins, phosphorylate target proteins to promote progression through cell cycle checkpoints.
47. How is the cell cycle related to cancer formation?
Answer
Mutations in genes regulating the cell cycle (e.g., oncogenes or tumor suppressors) can lead to uncontrolled cell division and tumor growth.
48. What happens to the nuclear envelope during prophase and telophase?
Answer
It breaks down in prophase to allow chromosome access and reforms in telophase to enclose the separated nuclei.
49. Why do some fully differentiated cells enter G0 and remain there?
Answer
These cells no longer divide (e.g., neurons or muscle cells) and stay in G0 permanently to maintain their specialized functions.
50. How could a BRCA gene mutation increase cancer risk?
Answer
BRCA is a tumor suppressor gene; a mutation in one allele increases the chance of losing both functional copies, leading to unregulated division and cancer.