1 markStarfish can regenerate lost arms through rapid cell division. During which phase of the cell cycle does DNA replication occur, ensuring that each daughter cell receives a diploid set of chromosomes?
G1 phase
S phase
G2 phase
Mitosis
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1 markAfter liver damage, liver cells can divide to replace lost tissue. However, many liver cells are normally in a resting phase where they do not divide.
Which phase of the cell cycle do non-dividing cells enter when they are not actively progressing through the cycle?
G0 phase
G1 phase
S phase
Cytokinesis
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1 markThe outer layer of human skin is constantly being replaced by new cells produced through mitosis.
Which of the following best describes the purpose of mitosis in multicellular organisms?
To produce genetically identical daughter cells for growth and repair.
To increase genetic diversity through recombination.
To create gametes for reproduction.
To eliminate damaged or unnecessary cells through apoptosis.
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1 markCells must pass checkpoints to ensure they are ready to proceed through the cell cycle.
What is the primary role of checkpoints in the cell cycle?
To increase the rate of cell division under normal conditions
To ensure proper cell size, DNA replication, and nutrient availability before progression
To trigger apoptosis in all dividing cells with more than one set of chromosomes
To prevent any cell from entering mitosis and reduce the risk of tumor formation
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1 markDuring wound healing in human skin, fibroblast cells rapidly divide to help repair damaged tissue. The regulation of this healing process is crucial for preventing excessive scarring.
Which of the following best describes how cyclins control this process at the molecular level?
Cyclins bind to DNA in order to trigger DNA replication to create new cells to repair the damaged tissue.
Cyclins form complexes with kinases that remove phosphate groups from target proteins.
Cyclins bind to cyclin-dependent kinases to form complexes that phosphorylate target proteins.
Cyclins break down target proteins to signal the next phase of the cell cycle.
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Scientists studying intestinal epithelial cells in mammals observed that these cells typically divide every 10 hours under normal conditions. Figure 1 shows the distribution of time spent in each of the phases of the cell cycle.
Which of the following best explains the process occurring during G1 phase of the cell cycle?
Increased protein synthesis to separate sister chromatids during mitosis.
Increased protein synthesis to produce enzymes and proteins needed for cell growth.
Increased protein synthesis to create new DNA during replication.
Increased protein synthesis to form the nuclear envelope after cell division.
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1 markThe death rate from malignant brain tumors was investigated in the UK. The graph in Figure 2 shows the results for women in different age groups.
Which of the following conclusions are supported by this data?
Rate of brain tumor diagnosis increases with age.
Death rate of people with brain tumors is increases with age.
Brain tumors do not occur in the under 20's.
Brain tumor death rate differs between men and women.
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1 markA researcher studying cell division in onion root tips adds a chemical that prevents the formation of spindle fibers. Predict the affect that this would have on the chromosomes observed in these cells?
Chromosomes would fail to align at the metaphase plate.
DNA would not replicate during S phase.
Cytokinesis would occur before nuclear division.
Sister chromatids would fail to separate during prophase.
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1 markA cancer researcher studied the effects of a potential chemotherapy drug on cell division in three different cell lines. The table shows the percentage of cells in each phase of the cell cycle after 24 hours of treatment.
Cell type | Percentage of cells at each cell cycle stage (%) | |||
|---|---|---|---|---|
G1 | S | G2 | M | |
Control | 40 | 25 | 20 | 15 |
Cancer | 15 | 15 | 20 | 45 |
Treated cancer | 65 | 10 | 15 | 5 |
Which of the following best explains the drug's likely mechanism of action based on the cell cycle distribution data?
The drug causes cells to accumulate in G1 phase by preventing entry into S phase.
The drug accelerates progression through all phases of the cell cycle.
The drug causes cells to skip G1 phase entirely.
The drug promotes rapid progression through the G1 phase into the S phase.
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1 markResearchers investigating a particular form of lung cancer discovered that affected cells continue past the G1 checkpoint despite the presence of DNA damage. Genetic analysis revealed a mutation in the TP53 gene, which encodes a checkpoint regulator that normally activates DNA repair or apoptosis in damaged cells.
Which of the following best explains how a mutation in TP53 leads to uncontrolled cell growth?
A mutation in TP53 leads to production of a non-functional protein which disrupts the signal transduction pathway at the end of G1.
A mutation in TP53 leads to a reduction in cyclin production which increases the transition of cells from the G1 to the S phase.
A mutation in TP53 leads to excessive DNA repair activity, slowing down the cell cycle and reducing the rate of cell division.
A mutation in TP53 deactivates cyclin-dependent kinases to increase the rate of the cell cycle, resulting in tumor formation.
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1 markScientists examined early frog embryo development by measuring cyclin levels and mitotic activity over time. The results are seen in the table below:
Time (min post-fertilization) | Cyclin Concentration (AU) | Mitotic Divisions per Minute |
|---|---|---|
0 | 1 | 0 |
30 | 3 | 1 |
60 | 7 | 4 |
90 | 10 | 6 |
120 | 5 | 9 |
150 | 2 | 3 |
Which of the following conclusions is best supported by this data?
Cyclins are responsible for triggering movement of cells from G1 to S phase when present in high concentrations.
As cyclin levels decrease, cells remain permanently in the G0 phase and do not divide again.
A peak in cyclin levels at 90 minutes, is followed by a peak in cell differentiation after a slight delay.
A time lag between peak cyclin levels and peak mitotic division could be due to the time taken in formation of cyclin-CdK complexes.
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1 markCertain amphibians can regenerate lost limbs. Studies show that cells near the injury site re-enter the cell cycle from G0 and begin increasing in number, allowing tissue regeneration to occur. Scientists are investigating the cellular mechanisms that enable this process.
Which of the following is most likely an evolutionary adaptation that enables this regeneration?
Increased activation of signaling pathways that stimulate cyclin-CdK complex formation, promoting cell cycle re-entry.
Enhanced apoptosis rates, ensuring that damaged cells are rapidly removed before regeneration begins.
Changes in cell cycle regulation that reduce checkpoint control, allowing cells to re-enter the cell cycle and proliferate in response to injury.
Increased reliance on meiosis instead of mitosis, producing genetically diverse regenerative cells.
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1 markStem cells undergo frequent mitotic divisions to support tissue growth and repair. A group of researchers investigated chromosome transmission accuracy during mitosis in stem cells by introducing a fluorescent label onto centromeres. This allowed the researchers to track chromosome movement throughout cell division.
To assess the accuracy of chromosome segregation, the researchers analyzed 200 mitotic cells. They recorded the percentage of cells that successfully inherited an equal number of chromosomes, compared to those exhibiting chromosomal missegregation. This is a condition in which chromosomes are not properly separated during cell division, resulting in a cell with an abnormal number of chromosomes (aneuploidy). The results are summarized in the table below:
Cell type | Total cells analyzed | Cells with accurate chromosome transmission (%) | Cells with chromosome missegregation (%) |
|---|---|---|---|
Healthy stem cells | 100 | 98% | 2% |
Aged stem cells | 100 | 85% | 15% |
The researchers concluded that chromosome transmission becomes less reliable as stem cells age, leading to an increased risk of aneuploidy.
Which of the following best explains the higher rate of chromosome missegregation observed in aged stem cells?
Aged stem cells accumulate mutations in their mitochondrial DNA, resulting in uneven chromosome numbers being inherited by daughter cells.
A longer G1 phase in aged stem cells increases DNA replication errors, which disrupts chromosome number during mitosis.
Errors in spindle fiber attachment to centromeres during metaphase increase the likelihood of incorrect chromosome segregation in anaphase, leading to aneuploidy in aged stem cells.
Disruptions in the cell cycle checkpoints of aged stem cells allow mitotic errors to persist, increasing uncontrolled cell division.
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