Rucete ✏ AP Biology In a Nutshell
9. The Cell Cycle — Practice Questions 2
This chapter explores the stages of the cell cycle, the regulation of cellular division, and mechanisms such as apoptosis that maintain healthy growth and development.
Need a quick review?
📘 Go to the Concept Summary
(Multiple Choice — Click to Reveal Answer)
1. Which phase of the cell cycle is primarily responsible for synthesizing DNA?
(A) G1
(B) G2
(C) S
(D) M
Answer
(C) — The S phase (Synthesis phase) is when DNA replication occurs.
2. What structure forms in animal cells during cytokinesis to divide the cytoplasm?
(A) Cell plate
(B) Spindle fiber
(C) Cleavage furrow
(D) Centromere
Answer
(C) — A cleavage furrow forms to split the cytoplasm in animal cells.
3. During which stage of mitosis do chromosomes condense and spindle fibers begin to form?
(A) Prophase
(B) Metaphase
(C) Anaphase
(D) Telophase
Answer
(A) — In prophase, chromosomes condense and spindle fibers assemble.
4. Which part of the cell cycle involves preparation for mitosis after DNA replication?
(A) G1
(B) G2
(C) S
(D) M
Answer
(B) — G2 is the final preparation phase before entering mitosis.
5. Which of the following cells is most likely to remain in G0 permanently?
(A) Skin cell
(B) Muscle cell
(C) Bone marrow cell
(D) Intestinal cell
Answer
(B) — Muscle cells are terminally differentiated and typically remain in G0.
6. What ensures chromosomes are properly aligned before they are separated in mitosis?
(A) S checkpoint
(B) G1 checkpoint
(C) M checkpoint
(D) Cytokinesis checkpoint
Answer
(C) — The M checkpoint ensures chromosomes are correctly attached to spindle fibers before separation.
7. What is the role of cyclins in the cell cycle?
(A) They break down spindle fibers
(B) They form chromosomes
(C) They activate CDKs to regulate progression
(D) They dissolve the nuclear membrane
Answer
(C) — Cyclins bind to CDKs to activate processes at specific checkpoints.
8. Which phase includes the alignment of chromosomes along the cell’s equator?
(A) Prophase
(B) Metaphase
(C) Anaphase
(D) Telophase
Answer
(B) — In metaphase, chromosomes align at the metaphase plate.
9. What triggers a cell to enter mitosis from G2 phase?
(A) High ATP levels
(B) Formation of MPF
(C) Completion of transcription
(D) Activation of lysosomes
Answer
(B) — MPF (Mitosis-Promoting Factor) initiates entry into mitosis.
10. Which of the following statements about apoptosis is correct?
(A) It occurs only during mitosis
(B) It causes uncontrolled cell growth
(C) It is programmed cell death to eliminate damaged cells
(D) It repairs DNA mutations
Answer
(C) — Apoptosis eliminates potentially harmful or unnecessary cells in a controlled manner.
11. Which of the following is true about the G1 phase of the cell cycle?
(A) DNA replication occurs
(B) Chromosomes condense
(C) The cell grows and synthesizes proteins
(D) The nucleus divides
Answer
(C) — G1 is the phase where the cell grows and prepares for DNA replication by making proteins and organelles.
12. What happens to the nuclear envelope during prophase?
(A) It doubles
(B) It strengthens
(C) It dissolves
(D) It replicates
Answer
(C) — During prophase, the nuclear envelope dissolves to allow chromosome movement.
13. What is the term for the identical copies of DNA held together at the centromere after replication?
(A) Homologous chromosomes
(B) Sister chromatids
(C) Chromatin
(D) Ribosomes
Answer
(B) — Sister chromatids are identical copies of a chromosome connected by a centromere after S phase.
14. What structure forms in plant cells to divide the cytoplasm during cytokinesis?
(A) Cleavage furrow
(B) Cell plate
(C) Centrosome
(D) Peroxisome
Answer
(B) — Plant cells build a cell plate to form new cell walls between daughter cells.
15. Which of the following is a hallmark of telophase?
(A) Chromosomes align at the equator
(B) Sister chromatids are pulled apart
(C) Two new nuclear membranes form
(D) DNA replicates
Answer
(C) — During telophase, chromosomes reach opposite poles and nuclear membranes reform.
16. Which component is essential for forming the mitotic spindle?
(A) Lysosomes
(B) Microtubules
(C) Ribosomes
(D) Nucleotides
Answer
(B) — Microtubules are structural components that form the mitotic spindle.
17. Which of the following best defines interphase?
(A) Division of the nucleus
(B) Phase where DNA is not duplicated
(C) Period of cell growth and DNA replication
(D) Programmed cell death
Answer
(C) — Interphase includes G1, S, and G2 phases, where the cell grows and prepares for division.
18. Why do some cells enter the G0 phase?
(A) They are cancerous
(B) They are preparing for cytokinesis
(C) They are fully differentiated and no longer divide
(D) They are undergoing mitosis
Answer
(C) — Cells in G0 are often mature and do not divide unless reactivated.
19. What would be the result if a cell skipped the S phase?
(A) It would have double the normal DNA
(B) It would undergo apoptosis
(C) It would divide without replicating DNA
(D) It would form extra nuclei
Answer
(C) — Skipping S phase means DNA wouldn’t be duplicated, leading to daughter cells missing genetic material.
20. When during the cell cycle does DNA appear as loosely packed chromatin?
(A) Prophase
(B) Metaphase
(C) Interphase
(D) Anaphase
Answer
(C) — In interphase, DNA remains as chromatin to allow transcription and replication.
21. What event is unique to anaphase during mitosis?
(A) Chromosomes align
(B) Sister chromatids separate
(C) Cytoplasm divides
(D) Chromosomes condense
Answer
(B) — Anaphase is characterized by the separation of sister chromatids toward opposite poles.
22. Why is cytokinesis important?
(A) It ensures that sister chromatids replicate
(B) It forms centrioles for spindle assembly
(C) It divides the cytoplasm and completes cell division
(D) It stops the cycle at the M checkpoint
Answer
(C) — Cytokinesis physically separates the daughter cells at the end of mitosis.
23. What is the name of the region where two sister chromatids are joined?
(A) Centrosome
(B) Cell plate
(C) Centromere
(D) Spindle pole
Answer
(C) — The centromere holds the sister chromatids together.
24. What happens if the M checkpoint fails?
(A) DNA will replicate again
(B) The cell will skip metaphase
(C) Chromosomes might not be evenly distributed
(D) The nuclear envelope reforms early
Answer
(C) — A failed M checkpoint could lead to unequal chromosome separation and cell defects.
25. What phase follows telophase in the cell cycle?
(A) Interphase
(B) G1
(C) Prophase
(D) Anaphase
Answer
(A) — After telophase and cytokinesis, the cell returns to interphase.
26. What would be the result if a mutation caused cyclin levels to remain constantly high?
(A) The cell would remain in G0
(B) DNA replication would be blocked
(C) The cell would continuously enter mitosis
(D) The spindle fibers would not form
Answer
(C) — High cyclin levels would keep CDKs active, repeatedly pushing the cell into mitosis.
27. Which of the following is a direct role of mitosis-promoting factor (MPF)?
(A) Stimulates spindle fiber disassembly
(B) Triggers DNA repair enzymes
(C) Pushes the cell from G2 into mitosis
(D) Promotes apoptosis in damaged cells
Answer
(C) — MPF activates processes required for the cell to begin mitosis.
28. A proto-oncogene becomes an oncogene when:
(A) It becomes underexpressed
(B) It mutates to promote uncontrolled cell division
(C) It repairs DNA faster than usual
(D) It undergoes apoptosis
Answer
(B) — When mutated, proto-oncogenes become oncogenes that drive uncontrolled proliferation.
29. What is the main reason cells use checkpoints during the cell cycle?
(A) To determine when to undergo apoptosis
(B) To ensure organelles are evenly distributed
(C) To verify conditions are safe for DNA replication and division
(D) To slow down protein synthesis
Answer
(C) — Checkpoints verify DNA integrity and cellular conditions before progression.
30. A cell is observed with chromosomes condensed, spindle fibers forming, but nuclear envelope still intact. Which specific point of mitosis is this?
(A) Early prophase
(B) Late prophase
(C) Telophase
(D) Anaphase
Answer
(A) — Early prophase is characterized by condensed chromosomes and early spindle formation, with envelope still intact.
31. Which of the following would most likely cause a cell to arrest at the G1 checkpoint?
(A) Incomplete chromosome alignment
(B) Insufficient nutrients or growth signals
(C) Delayed spindle attachment
(D) Mitochondrial division
Answer
(B) — The G1 checkpoint ensures the cell has proper resources and signals before DNA replication begins.
32. A scientist removes spindle fibers during mitosis. What phase would be immediately disrupted?
(A) Metaphase
(B) Prophase
(C) Telophase
(D) Cytokinesis
Answer
(A) — Without spindle fibers, chromosomes cannot align at the metaphase plate.
33. Which of the following best explains how tumor suppressor genes prevent cancer?
(A) They enhance DNA replication rate
(B) They promote telomerase activity
(C) They detect damage and pause the cell cycle or initiate apoptosis
(D) They form cyclin-CDK complexes
Answer
(C) — Tumor suppressors halt the cycle or trigger apoptosis if abnormalities are found.
34. What would happen if both alleles of a tumor suppressor gene are mutated?
(A) Cell division is permanently halted
(B) The gene can no longer suppress uncontrolled division
(C) The cell enters senescence
(D) MPF cannot form
Answer
(B) — Loss of both alleles means the “brakes” on cell division are gone, leading to tumor formation.
35. What feature of cancer cells allows them to continue dividing even when crowded?
(A) Overproduction of ribosomes
(B) Enhanced ATP production
(C) Loss of density-dependent inhibition
(D) Increased mitochondrial fusion
Answer
(C) — Cancer cells ignore signals to stop dividing in crowded environments.
36. What is the consequence of a nonfunctional M checkpoint in a dividing cell?
Answer
If the M checkpoint fails, the cell may proceed with mitosis even when chromosomes are not properly attached to the spindle, leading to unequal chromosome separation and potential aneuploidy.
37. Explain how MPF is formed and what its function is.
Answer
MPF (Mitosis-Promoting Factor) forms when cyclin binds to CDK. It triggers the transition from G2 into mitosis by activating proteins required for mitotic entry.
38. How does the loss of function in both alleles of a tumor suppressor gene affect the cell cycle?
Answer
Without functional tumor suppressor genes, the cell cannot properly regulate division, increasing the risk of unchecked proliferation and tumor formation.
39. Describe what occurs during anaphase of mitosis.
Answer
In anaphase, sister chromatids separate at the centromere and are pulled to opposite poles of the cell by shortening spindle fibers.
40. What role does apoptosis play in preventing cancer?
Answer
Apoptosis eliminates damaged or abnormal cells before they can divide uncontrollably, acting as a safeguard against tumor development.
41. Why is the G2 checkpoint important before mitosis begins?
Answer
The G2 checkpoint ensures that DNA has been fully and accurately replicated, preventing damaged or incomplete DNA from being passed to daughter cells.
42. How does anchorage dependence regulate the cell cycle in normal cells?
Answer
Normal cells require attachment to a substrate to proceed with division. If detached, they stop dividing—a mechanism that cancer cells ignore.
43. What happens to a cell with constant activation of a proto-oncogene?
Answer
The proto-oncogene becomes an oncogene, driving excessive cell division and potentially leading to cancer formation.
44. What is the function of the spindle apparatus in mitosis?
Answer
The spindle apparatus organizes and separates chromosomes during mitosis to ensure each daughter cell receives an identical set.
45. Why do neurons and some muscle cells permanently exit the cell cycle?
Answer
They are terminally differentiated and enter G0, where they perform specialized functions without dividing again.
46. Describe how cyclin levels fluctuate during the cell cycle.
Answer
Cyclin levels gradually rise during interphase, peak before mitosis, and drop sharply as the cell completes mitosis.
47. How do density-dependent inhibition and anchorage dependence prevent overgrowth?
Answer
They signal cells to stop dividing when space is limited or attachment is lost, preventing overcrowding and disorganized growth.
48. What role does the centromere play in chromosome movement?
Answer
The centromere is the region where sister chromatids are held together and where spindle fibers attach to move chromosomes during mitosis.
49. How does BRCA gene mutation increase cancer risk?
Answer
A BRCA mutation impairs tumor suppressor function, increasing the chance of uncontrolled cell division and cancer development, especially if both alleles are mutated.
50. Why is proper regulation of the cell cycle essential for multicellular organisms?
Answer
It ensures that growth, repair, and reproduction occur in a controlled manner, preventing mutations, tissue damage, and cancer.