What term describes the complete set of DNA in a cell?
Genome
✓
Karyotype
Chromatin
Nucleoid
Correct Answer
Genome
A genome is all of the DNA a cell carries, whether one circular molecule in a bacterium or many linear chromosomes in a eukaryote. A karyotype is an image of chromosomes arranged in pairs, not the DNA itself. Chromatin is the DNA-protein material that chromosomes are made of. A nucleoid is the region of a prokaryotic cell where the chromosome sits.
Category: The Genome
Question 2
How many chromosomes does a normal human sperm or egg cell contain?
46
23
✓
22
92
Correct Answer
23
Human gametes are haploid and carry one set of 23 chromosomes, so fertilization restores the diploid number. 46 is the number in a diploid body cell. 22 is the number of non-sex chromosomes in one set, leaving out the X or Y. 92 is double the diploid number, not a gamete number.
Category: The Genome
Question 3
Which statement correctly describes a pair of homologous chromosomes?
They carry different sets of genes
Both came from the mother
One came from each parent
✓
They are copies made in S phase
Correct Answer
One came from each parent
Homologous chromosomes match in length and carry genes for the same traits at the same positions, with one inherited from each parent. They carry different sets of genes is wrong because homologs carry the same genes, though possibly different versions. Both came from the mother is wrong because one homolog is maternal and one paternal. They are copies made in S phase describes sister chromatids, not homologs.
Category: The Genome
Question 4
In which stage of interphase is a cell's DNA replicated?
G1 phase
G2 phase
G0 phase
S phase
✓
Correct Answer
S phase
S stands for synthesis: during S phase the DNA is copied, so each chromosome becomes two sister chromatids. G1 phase is a period of growth and protein production before replication. G2 phase follows replication and prepares the cell for mitosis. G0 phase is a resting state in which the cell is not preparing to divide.
Category: Interphase and Checkpoints
Question 5
During which phase of mitosis does the nuclear envelope break apart and the chromosomes begin to condense?
Prophase
✓
Metaphase
Anaphase
Telophase
Correct Answer
Prophase
Prophase is the first phase of mitosis: the nuclear envelope breaks into vesicles, the nucleolus disappears, and chromosomes condense enough to be seen. Metaphase is when condensed chromosomes line up at the cell's center. Anaphase is when sister chromatids separate. Telophase is when new nuclear envelopes form.
Category: Mitosis
Question 6
How do plant cells divide their cytoplasm after mitosis?
By a contractile ring of actin
By a cell plate built from Golgi vesicles
✓
By an FtsZ ring forming a septum
By pinching the nuclear envelope
Correct Answer
By a cell plate built from Golgi vesicles
A rigid cell wall prevents a plant cell from pinching in two, so Golgi vesicles gather at the cell's center and fuse into a cell plate that grows outward into a new wall. By a contractile ring of actin describes animal cell cytokinesis. By an FtsZ ring forming a septum describes bacterial binary fission. By pinching the nuclear envelope is wrong because the nuclear envelope is not involved in dividing the cytoplasm.
Category: Cytokinesis
Question 7
Which human cells typically stay permanently in the G0 phase?
Bone marrow stem cells
Cells lining the intestine
Mature nerve cells
✓
Skin basal cells
Correct Answer
Mature nerve cells
Mature nerve cells, like mature cardiac muscle cells, leave the cell cycle and remain in G0 for good. Bone marrow stem cells divide continually to replace blood cells. Cells lining the intestine are replaced every few days. Skin basal cells divide often to renew the outer skin layers.
Category: Interphase and Checkpoints
Question 8
In which phase does a cell reach the checkpoint where it commits irreversibly to dividing, after checking its size, nutrient reserves and DNA?
G2 phase
S phase
Metaphase
G1 phase
✓
Correct Answer
G1 phase
The G1 checkpoint, also called the restriction point, falls in G1 phase and decides whether conditions favor division; a cell that passes it is committed to dividing. G2 phase holds the later checkpoint that confirms the DNA was fully and correctly replicated. S phase is when DNA is copied, after the commitment has already been made. Metaphase is where the M checkpoint checks spindle attachment.
Category: Interphase and Checkpoints
Question 9
What does the M checkpoint confirm before sister chromatids are pulled apart?
Each chromatid pair is attached to both spindle poles
✓
The cell has grown large enough
Enough nutrients are stored
The DNA has finished replicating
Correct Answer
Each chromatid pair is attached to both spindle poles
Separating sister chromatids cannot be undone, so the M checkpoint holds the cell at the end of metaphase until every pair is attached to spindle fibers from opposite poles. The cell has grown large enough and Enough nutrients are stored are conditions checked at the G1 checkpoint. The DNA has finished replicating is the main check of the G2 checkpoint.
Category: Interphase and Checkpoints
Question 10
What is the name for a normal gene that codes for a positive regulator of the cell cycle?
Oncogene
Proto-oncogene
✓
Tumor suppressor gene
Pseudogene
Correct Answer
Proto-oncogene
Proto-oncogenes are normal genes whose proteins push the cell cycle forward. An oncogene is a mutated proto-oncogene that can drive a cell toward cancer. A tumor suppressor gene codes for a negative regulator that can stop the cycle. A pseudogene is a nonfunctional gene copy and does not regulate the cell cycle.
Category: Cancer and Cell Cycle
Question 11
When normal p53 protein detects damaged DNA before replication begins, what does it do?
Pushes the cell into S phase
Builds the mitotic spindle
Halts the cycle so repair can occur
✓
Breaks down the nuclear envelope
Correct Answer
Halts the cycle so repair can occur
Normal p53 stops the cell cycle and activates repair genes, and if the damage cannot be fixed it triggers cell death. Pushes the cell into S phase is the opposite of what p53 does with damaged DNA. Builds the mitotic spindle is the work of centrosomes and microtubules. Breaks down the nuclear envelope happens in prophase and is not a p53 response.
Category: Cancer and Cell Cycle
Question 12
A mutation lets the regulatory protein Cdk become active too early. What can result?
The cell enters G0 permanently
The cell stops replicating DNA
The cell switches to binary fission
The cell passes a checkpoint too soon
✓
Correct Answer
The cell passes a checkpoint too soon
Cdk is a positive regulator, so activating it early can push a cell past a checkpoint before conditions are met, an early step toward cancer. The cell enters G0 permanently is wrong because an overactive positive regulator drives division rather than stopping it. The cell stops replicating DNA is wrong because the mutation speeds the cycle. The cell switches to binary fission is wrong because only prokaryotes divide that way.
Category: Cancer and Cell Cycle
Question 13
Which protein assembles into a ring at the middle of a dividing bacterium and directs formation of the septum?
FtsZ
✓
Tubulin
Actin
Cdk
Correct Answer
FtsZ
FtsZ proteins gather at the cell's midpoint to form a ring that directs the septum and recruits new membrane and wall material. Tubulin builds eukaryotic spindle microtubules, though it is related to FtsZ. Actin forms the contractile ring in dividing animal cells. Cdk is a eukaryotic cell cycle regulator, not a structural ring protein.
Category: Prokaryotic Division
Question 14
Where does DNA replication begin on a bacterial chromosome?
At the centromere
At the origin of replication
✓
At the kinetochore
At the telomere
Correct Answer
At the origin of replication
Bacterial replication starts at a single origin of replication, near where the chromosome attaches to the plasma membrane, and proceeds in both directions. At the centromere is wrong because centromeres join sister chromatids in eukaryotes. At the kinetochore is wrong because kinetochores are eukaryotic spindle attachment sites. At the telomere is wrong because telomeres cap the ends of linear chromosomes, and a circular bacterial chromosome has no ends.
Category: Prokaryotic Division
Question 15
Which feature of prokaryotes explains why they divide without a mitotic spindle?
They lack DNA
They lack ribosomes
They have one chromosome and no nucleus
✓
They have no plasma membrane
Correct Answer
They have one chromosome and no nucleus
With no nucleus and a single circular chromosome, a prokaryote can separate its DNA copies by binary fission without a spindle. They lack DNA is wrong because every cell has DNA. They lack ribosomes is wrong because prokaryotes have ribosomes. They have no plasma membrane is wrong because all cells have one, and the growing membrane helps move the chromosome copies apart.
Category: Prokaryotic Division
Question 16
Which structure gives rise to the mitotic spindle in an animal cell?
Nucleolus
Golgi apparatus
Lysosome
Centrosome
✓
Correct Answer
Centrosome
The centrosome, which in animal cells holds a pair of centrioles, organizes the microtubules of the mitotic spindle. The nucleolus makes ribosome parts and disappears during prophase. The Golgi apparatus packages proteins and, in plants, supplies vesicles for the cell plate. A lysosome digests worn-out materials.
Category: Mitosis
Question 17
Which description of cancer is accurate?
A group of diseases marked by uncontrolled cell division
✓
A single disease caused by one virus
Excess death of healthy cells
A failure of DNA to replicate
Correct Answer
A group of diseases marked by uncontrolled cell division
Cancer is a name for many diseases that share one mechanism: cells divide without normal control. A single disease caused by one virus is wrong because cancer has many forms and causes. Excess death of healthy cells is wrong because cancer cells tend to escape cell death. A failure of DNA to replicate is wrong because cancer cells keep replicating and dividing.
Category: Cancer and Cell Cycle
Question 18
Which interphase stage directly follows DNA synthesis and prepares the cell for mitosis?
G1 phase
G2 phase
✓
G0 phase
Prophase
Correct Answer
G2 phase
In G2 phase the cell replenishes energy, makes proteins needed to move chromosomes, and finishes duplicating its centrosome. G1 phase comes before DNA synthesis, not after. G0 phase is a resting state outside the active cycle. Prophase is the first phase of mitosis itself, not part of interphase.
Category: Interphase and Checkpoints
Question 19
During which phase of mitosis do sister chromatids separate and move toward opposite poles?
Prophase
Metaphase
Anaphase
✓
Telophase
Correct Answer
Anaphase
In anaphase the sister chromatids split apart at the centromere, and each one, now an individual chromosome, is pulled to a pole. Prophase is when chromosomes condense and the nuclear envelope breaks down. Metaphase is when the joined chromatids line up at the center. Telophase is when the separated chromosomes arrive at the poles and new nuclei form.
Category: Mitosis
Question 20
What is the role of tumor suppressor genes in a healthy cell?
They make proteins that build the spindle
They make proteins that copy DNA
They make proteins that split the cytoplasm
They make proteins that can halt the cell cycle
✓
Correct Answer
They make proteins that can halt the cell cycle
Tumor suppressor genes such as p53 and RB1 code for negative regulators that stop the cycle when something is wrong. They make proteins that build the spindle describes tubulin genes, not tumor suppressors. They make proteins that copy DNA describes genes for replication enzymes. They make proteins that split the cytoplasm describes proteins such as actin used in cytokinesis.
Category: Cancer and Cell Cycle