Rucete ✏ AP Biology In a Nutshell
9. The Cell Cycle — Practice Questions 3
This chapter explores the stages of the cell cycle, including interphase and mitosis, the roles of checkpoint control mechanisms, and how disruptions in regulation can lead to diseases such as cancer.
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(Multiple Choice — Click to Reveal Answer)
1. What event occurs during the G2 phase of the cell cycle?
(A) Chromosomes are aligned
(B) DNA is replicated
(C) Spindle fibers begin to form
(D) Proteins are prepared for mitosis
Answer
(D) — G2 is when the cell produces the proteins and components needed for mitosis.
2. Which structure is responsible for separating sister chromatids during mitosis?
(A) Centrioles
(B) Centromere
(C) Spindle fibers
(D) Cell plate
Answer
(C) — Spindle fibers pull sister chromatids apart during anaphase.
3. During which stage of mitosis do chromosomes become visible under a light microscope?
(A) Anaphase
(B) Prophase
(C) Telophase
(D) Cytokinesis
Answer
(B) — Chromosomes condense and become visible during prophase.
4. What does the cell plate do in plant cells?
(A) Attaches chromosomes
(B) Forms the spindle
(C) Builds new cell wall material
(D) Separates chromatids
Answer
(C) — In plant cells, the cell plate eventually becomes the new cell wall between daughter cells.
5. Which term refers to cells permanently exiting the cell cycle?
(A) Apoptosis
(B) G0 phase
(C) Cytokinesis
(D) CDK inhibition
Answer
(B) — Cells that stop dividing and enter a resting state are said to be in G0.
6. When are sister chromatids considered individual chromosomes?
(A) During metaphase
(B) At the start of interphase
(C) When the centromere splits in anaphase
(D) After cytokinesis
Answer
(C) — When the centromere splits, each chromatid becomes an independent chromosome.
7. What is a key characteristic of the metaphase stage?
(A) Spindle fibers disassemble
(B) The nuclear envelope reforms
(C) Chromosomes align at the center
(D) Chromatids are pulled apart
Answer
(C) — Metaphase is defined by the alignment of chromosomes at the metaphase plate.
8. Which of the following is a regulatory protein that must bind with CDK to drive the cell cycle forward?
(A) Tubulin
(B) Cyclin
(C) ATPase
(D) Centromere
Answer
(B) — Cyclins bind with cyclin-dependent kinases to regulate the cell cycle.
9. Which cell structure anchors spindle fibers during cell division in animal cells?
(A) Cell wall
(B) Centrosome
(C) Nucleolus
(D) Ribosome
Answer
(B) — Centrosomes organize the mitotic spindle in animal cells.
10. What determines the rate of cell division in most somatic cells?
(A) Apoptotic signals
(B) ATP availability
(C) External growth factors and checkpoints
(D) mRNA transcription speed
Answer
(C) — Growth factors and internal checkpoints regulate how often a cell divides.
11. Which stage of the cell cycle includes both DNA replication and centrosome duplication?
(A) G1
(B) S
(C) G2
(D) M
Answer
(B) — The S (synthesis) phase includes DNA replication and centrosome duplication.
12. What distinguishes the telophase stage of mitosis?
(A) Chromosomes align
(B) Spindle fibers form
(C) Nuclear membranes reform
(D) DNA condenses
Answer
(C) — During telophase, two new nuclear envelopes form around the separated chromosomes.
13. What enzyme is responsible for adding phosphate groups to target proteins during the cell cycle?
(A) DNA polymerase
(B) RNA polymerase
(C) Cyclin-dependent kinase
(D) Ligase
Answer
(C) — Cyclin-dependent kinases (CDKs) phosphorylate target proteins to control cell cycle transitions.
14. What phase of the cell cycle follows mitosis in a continuously dividing cell?
(A) S phase
(B) G0
(C) Cytokinesis
(D) Interphase
Answer
(C) — After mitosis, cytokinesis physically divides the cytoplasm between the two daughter cells.
15. In which stage do centrioles begin to migrate toward opposite poles in animal cells?
(A) Metaphase
(B) Telophase
(C) Prophase
(D) Anaphase
Answer
(C) — In early prophase, centrioles move to opposite ends to organize spindle fiber formation.
16. Which structure forms in plant cells instead of a cleavage furrow?
(A) Centrosome
(B) Cell plate
(C) Nuclear pore
(D) Chromatin bridge
Answer
(B) — The cell plate forms during cytokinesis in plant cells to initiate a new cell wall.
17. What checkpoint assesses DNA integrity before replication begins?
(A) G0 checkpoint
(B) S checkpoint
(C) G1 checkpoint
(D) G2 checkpoint
Answer
(C) — The G1 checkpoint checks for DNA damage before S phase starts.
18. Which of the following best describes the purpose of interphase?
(A) To divide the nucleus
(B) To equally distribute cytoplasm
(C) To prepare the cell for mitosis
(D) To undergo apoptosis
Answer
(C) — Interphase prepares the cell by growing and duplicating its DNA and organelles.
19. What happens if the cell fails to complete DNA replication in the S phase?
(A) The cell skips mitosis
(B) The G2 checkpoint prevents mitosis
(C) Cytokinesis begins prematurely
(D) Spindle fibers form too early
Answer
(B) — The G2 checkpoint ensures DNA replication is complete before mitosis begins.
20. What is the function of the centromere during mitosis?
(A) It helps replicate DNA
(B) It protects the ends of chromosomes
(C) It attaches chromatids to spindle fibers
(D) It produces ribosomes
Answer
(C) — The centromere is where spindle fibers attach to move sister chromatids during anaphase.
21. Which factor can lead to cells bypassing normal cycle regulation and becoming cancerous?
(A) Reduced transcription
(B) Mutated cyclin or CDK genes
(C) Increased apoptosis
(D) Active anchorage dependence
Answer
(B) — Mutations in cyclins, CDKs, or checkpoint regulators can lead to uncontrolled division.
22. What typically triggers a cell to enter G0 permanently?
(A) DNA damage
(B) Differentiation into a specific function
(C) Attachment to a substrate
(D) Absence of ribosomes
Answer
(B) — Differentiated cells like neurons often exit the cycle and remain in G0.
23. Why is DNA in chromatin form during interphase?
(A) It is easier to distribute
(B) It is more stable
(C) It is accessible for transcription and replication
(D) It is easier to stain
Answer
(C) — Chromatin is a loosely packed form of DNA that allows access for necessary enzymes.
24. How does density-dependent inhibition work in normal somatic cells?
(A) Cells stop dividing when they lose contact with neighbors
(B) Cells continue dividing as long as glucose is present
(C) Cells stop dividing when overcrowded
(D) Cells divide when DNA is uncoiled
Answer
(C) — Normal cells stop dividing when they are in contact with other cells.
25. Which checkpoint ensures chromosomes are attached to spindle fibers before separation?
(A) G1
(B) S
(C) G2
(D) M
Answer
(D) — The M checkpoint ensures spindle fiber attachment before anaphase.
26. What would likely happen if cyclin levels failed to decrease after mitosis?
(A) The cell would re-enter interphase early
(B) The nucleus would remain intact
(C) The cell might immediately re-enter mitosis
(D) Cytokinesis would accelerate
Answer
(C) — Persistent high levels of cyclin could maintain MPF activity, pushing the cell repeatedly into mitosis.
27. A researcher observes a cell that fails to pass the G1 checkpoint. What would most likely happen next?
(A) The cell enters mitosis prematurely
(B) The cell initiates DNA replication
(C) The cell remains in G0
(D) The spindle fibers begin forming
Answer
(C) — If a cell does not pass the G1 checkpoint, it typically enters G0 or undergoes apoptosis.
28. Which molecular event leads to the activation of CDKs?
(A) Cyclin degradation
(B) Cyclin binding
(C) ATP hydrolysis
(D) Centrosome duplication
Answer
(B) — CDKs are activated only when bound to their regulatory partner, cyclin.
29. What is a key difference between mitosis and cytokinesis?
(A) Mitosis splits the cytoplasm; cytokinesis splits DNA
(B) Mitosis involves nuclear division; cytokinesis divides the cytoplasm
(C) Cytokinesis occurs before mitosis
(D) Both occur only in animal cells
Answer
(B) — Mitosis ensures equal DNA distribution; cytokinesis separates the cytoplasmic contents.
30. What would be the consequence if spindle fibers failed to attach to kinetochores?
(A) Cytokinesis would begin early
(B) Chromosomes wouldn’t condense
(C) Chromosomes would not separate properly
(D) DNA replication would stop
Answer
(C) — If kinetochores are not attached to spindle fibers, chromosomes cannot be pulled apart during anaphase.
31. Which mechanism most directly prevents a damaged cell from progressing past G2?
(A) Activation of telomerase
(B) DNA repair protein inhibition
(C) Tumor suppressor gene expression
(D) Spindle checkpoint failure
Answer
(C) — Tumor suppressor genes like p53 detect damage and can block the cycle at the G2 checkpoint.
32. Why are BRCA mutations associated with increased cancer risk?
(A) They activate oncogenes
(B) They inhibit cell membrane synthesis
(C) They impair tumor suppressor function
(D) They promote telophase failure
Answer
(C) — BRCA genes help suppress tumors. When mutated, they lose their ability to prevent uncontrolled growth.
33. Which observation would suggest a cell is in metaphase?
(A) Nuclear membrane is visible
(B) Chromosomes are lined up in the center
(C) Sister chromatids are separating
(D) Cleavage furrow is forming
Answer
(B) — In metaphase, chromosomes align along the metaphase plate at the cell’s equator.
34. Which of the following occurs during late telophase?
(A) DNA condenses
(B) Spindle fibers shorten
(C) Chromosomes decondense and nuclear envelopes re-form
(D) Sister chromatids separate
Answer
(C) — In telophase, chromosomes relax and nuclear envelopes form around each new nucleus.
35. If a proto-oncogene is mutated to remain permanently active, what is the result?
(A) Apoptosis is triggered
(B) Cyclin levels are suppressed
(C) Unregulated cell division begins
(D) DNA replication halts
Answer
(C) — Proto-oncogenes regulate normal growth; when mutated, they can drive continuous division.
36. How does a malfunction in the M checkpoint contribute to aneuploidy?
Answer
If the M checkpoint fails, cells may proceed to anaphase without ensuring that all chromosomes are properly attached to spindle fibers, leading to unequal chromosome distribution (aneuploidy).
37. Describe the relationship between cyclins, CDKs, and MPF in regulating mitosis.
Answer
Cyclins bind to CDKs to form MPF (mitosis-promoting factor), which activates proteins necessary to initiate mitosis.
38. What would happen if a cell entered mitosis with unreplicated or damaged DNA?
Answer
This could result in daughter cells with incomplete or damaged genomes, potentially causing mutations or cell death.
39. Explain the role of the centromere during chromosome segregation.
Answer
The centromere is the attachment site for spindle fibers, ensuring proper separation of sister chromatids during anaphase.
40. Why is the G1 checkpoint often considered the most critical in cell cycle control?
Answer
It determines whether the cell proceeds toward division or enters a resting (G0) phase; it prevents replication of damaged DNA.
41. What happens to cyclin levels at the end of mitosis and why is this important?
Answer
Cyclin levels drop rapidly, inactivating MPF and allowing the cell to exit mitosis and reset the cycle.
42. How do tumor suppressor genes function to prevent uncontrolled cell growth?
Answer
They monitor DNA integrity, halt the cycle if damage is detected, and can trigger apoptosis if damage is irreparable.
43. Compare and contrast plant and animal cytokinesis mechanisms.
Answer
Animal cells form a cleavage furrow using actin, while plant cells form a cell plate that develops into a new cell wall.
44. Why is it important for sister chromatids to remain joined until anaphase?
Answer
Joining ensures equal and coordinated distribution of genetic material; premature separation could cause genomic instability.
45. What is the primary function of apoptosis during embryonic development?
Answer
Apoptosis eliminates unnecessary cells (e.g., webbing between digits), shaping organs and structures properly.
46. What effect would a loss-of-function mutation in both BRCA alleles have on the cell?
Answer
The cell would lose critical tumor suppressor function, increasing the likelihood of uncontrolled division and cancer formation.
47. How do external growth factors influence the progression of the cell cycle?
Answer
Growth factors bind to cell surface receptors and trigger signaling pathways that promote progression past G1 checkpoint.
48. Why is mitosis necessary for asexual reproduction and tissue repair?
Answer
Mitosis creates genetically identical cells, allowing organisms to reproduce without gametes and repair damaged tissues accurately.
49. What would happen to a cell that lacked functional CDKs?
Answer
The cell would be unable to progress through the cycle, as CDKs are essential for phosphorylating proteins at key checkpoints.
50. How do mutations in proto-oncogenes differ from mutations in tumor suppressor genes in their contribution to cancer?
Answer
Proto-oncogenes cause cancer when overactive (dominant), while tumor suppressor genes cause cancer when both alleles are inactivated (recessive).