Question 1
A diploid eukaryotic cell has chromosomes. What is the expected chromosome number in each daughter nucleus after mitosis?
A.
, because mitosis halves the chromosome number.
B.
, because chromosomes are replicated before mitosis.
C.
, because mitosis maintains the chromosome number.
D.
, because each chromosome forms four chromatids.
Question 2
A dividing root tip cell is undergoing cytokinesis. What process splits the cytoplasm in this plant cell?
A.
A contractile ring pulls the plasma membrane inward to form a cleavage furrow.
B.
Chromatids decondense and the nuclear membrane reforms around each group.
C.
Homologous chromosomes separate to opposite poles before the cell wall forms.
D.
Vesicles fuse at the cell equator to form new membrane and cell wall.
Question 3
Budding in yeast produces a small bud on the surface of a larger parent cell. What feature makes this an example of unequal cytokinesis?
A.
The parent cell produces genetically varied nuclei by crossing over before budding.
B.
The parent cell keeps its nucleus while only cytoplasm enters the bud.
C.
The bud receives a smaller share of cytoplasm but must receive a nucleus.
D.
The bud receives half the chromosomes but no mitochondria from the parent cell.
Question 4
The diagram shows a cell during mitosis. What phase is shown?
A.
Telophase
B.
Metaphase
C.
Prophase
D.
Anaphase
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Question 5
What process increases the number of mitochondria in a cell during interphase?
A.
Condensation of chromatin to form new mitochondrial membranes before mitosis
B.
Fusion of lysosomes with the nuclear envelope during the G2 phase
C.
Assembly of complete mitochondria from free phospholipids and enzymes in the cytosol
D.
Growth and division of mitochondria that already exist in the cell
Question 6
A primary tumour remains localized and its cells do not invade neighbouring tissues. How should this tumour be classified?
A.
Benign, because it does not invade or spread to distant sites
B.
Cancerous, because it cannot form secondary tumours
C.
Secondary, because it remains at the original site
D.
Malignant, because all primary tumours cause metastasis
Question 7
A chromosome has completed DNA replication but anaphase has not yet begun. What description is correct?
A.
It is one chromosome made of two sister chromatids.
B.
It is two chromosomes, each made of one chromatid.
C.
It is one chromatid made of two homologous chromosomes.
D.
It is two bivalents held together by cohesin proteins.
Question 8
A species has a haploid chromosome number of . How many chromosome combinations can random orientation of bivalents produce, before crossing over is considered?
A.
B.
C.
D.
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Question 9
The graph shows relative DNA content per nucleus during one cell cycle. At which labelled interval is the cell most likely in S phase?
A.
A
B.
B
C.
C
D.
D
Question 10
What role do cyclins have in control of the cell cycle?
A.
They form spindle microtubules that pull chromosomes toward opposite poles.
B.
They replicate nuclear DNA by adding nucleotides during the S phase.
C.
They rise and fall in concentration, allowing checkpoints to be passed at threshold levels.
D.
They cut cohesin proteins so that sister chromatids separate in anaphase.
Question 11
A mutation causes a normal gene that promotes cell-cycle progression to be permanently overactive. What term describes the mutated gene?
A.
Bivalent
B.
Chiasma
C.
Oncogene
D.
Tumour suppressor gene
Question 12
The diagrams show cytokinesis in an animal cell and in a plant cell.
State the process that divides the cytoplasm between daughter cells.
[1]
Distinguish cytokinesis in animal cells from cytokinesis in plant cells.
[2]
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Question 13
Unequal cytokinesis occurs in yeast budding and in human oogenesis.
Define unequal cytokinesis.
[1]
Explain why each daughter cell produced by unequal cytokinesis must receive at least one mitochondrion.
[2]
Question 14
Eukaryotic cells carry out nuclear division before the cytoplasm is divided.
State the effect of mitosis on chromosome number.
[1]
State the effect of meiosis on chromosome number.
[1]
Explain why nuclear division is needed before cytokinesis in eukaryotic cells.
[2]
Question 15
Cell proliferation occurs in plant meristems, early animal embryos and during repair of skin wounds.
Define cell proliferation.
[1]
Outline how proliferation in a shoot apical meristem contributes to plant growth.
[2]
Question 16
Interphase is sometimes described incorrectly as a resting stage.
State why interphase is metabolically active.
[1]
Explain why mitochondria and chloroplast numbers must be increased before division of cells that contain them.
[2]
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Question 17
The drawings show cytokinesis in two eukaryotic cells observed after nuclear division.
State which cell is undergoing cytokinesis by formation of a cell plate.
[1]
Describe two differences between the mechanisms of cytokinesis shown in Cell A and Cell B.
[2]
Explain why the mechanism shown in Cell A would not be effective in Cell B.
[1]
Question 18
The micrograph shows cells from a stained onion root tip squash. Four cells are labelled.
Identify the labelled cell that is in metaphase.
[1]
Describe two visible features that distinguish anaphase from metaphase in this micrograph.
[2]
State the phase in which nuclear membranes reform around the separated chromosomes.
[1]
Question 19
In a tumour sample, cells are observed in mitosis out of cells counted. What is the mitotic index?
A.
B.
C.
D.
Question 20
Before mitosis or meiosis begins, nuclear DNA has already been replicated.
State why DNA replication is required before nuclear division.
[1]
Outline the relationship between a replicated chromosome and sister chromatids.
[2]
State the role of spindle microtubules in nuclear division.
[1]
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Question 21
The diagram shows four cells from a root tip squash during mitosis.
Identify the phase of mitosis shown by cell B.
[1]
Identify the phase of mitosis shown by cell C.
[1]
Outline two features that would identify telophase in a plant cell.
[2]
Question 22
Down syndrome is usually caused by trisomy 21.
Define non-disjunction.
[1]
Explain how non-disjunction can lead to trisomy 21 after fertilization.
[2]
State one process in meiosis that increases genetic variation without changing chromosome number.
[1]
Question 23
The graph shows relative DNA content per nucleus during one cell cycle.
Identify the phase in which nuclear DNA is replicated.
[1]
Explain why cells in S phase can have DNA contents between the values for and .
[2]
State the sequence of events after in the cell cycle.
[1]
Question 24
The graph shows changes in the concentration of different cyclins during the cell cycle. Dashed lines show checkpoint thresholds.
Define a checkpoint in the cell cycle.
[1]
Explain how cyclins control progression through checkpoints.
[2]
Suggest one possible consequence if a mutation caused a cyclin signal promoting division to remain high.
[1]
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Question 25
A biopsy sample from a tumour contains 120 observed cells. Of these, 18 cells are in mitosis. Other observations indicate whether tumour cells have invaded neighbouring tissue.
Calculate the mitotic index of the biopsy sample.
[1]
Distinguish a benign tumour from a malignant tumour.
[2]
State what is meant by a secondary tumour.
[1]
Question 26
The table summarizes observations from two examples of cytokinesis: budding in yeast and oogenesis in humans.
Example | Cell | Cytoplasm share / % |
|---|---|---|
Yeast budding | mother cell | 85 |
Yeast budding | bud | 15 |
Human oogenesis | oocyte | 99 |
Human oogenesis | polar body | 1 |
Identify the example that shows the greater inequality in cytokinesis.
[1]
Outline the evidence from the data that cytokinesis in yeast budding is unequal.
[1]
Explain why the smaller daughter cell must still receive a nucleus and mitochondria.
[2]
Question 27
The diagram shows gametes produced after an error involving chromosome 21 during meiosis. These gametes may fuse with normal gametes during fertilization.
Identify the meiotic error shown in the diagram.
[1]
State the number of copies of chromosome 21 in the zygote formed when a gamete with two copies of chromosome 21 fuses with a normal gamete.
[1]
Explain how this error can result in Down syndrome.
[2]
Question 28
Cell proliferation was measured in a plant root and in mammalian skin after a small wound. Mitotic index was used as a measure of the fraction of cells in mitosis.
Tissue | Condition / position | Mitotic index |
|---|---|---|
Root | 0.0 mm from root tip | 0.18 |
Root | 1.0 mm from root tip | 0.15 |
Root | 2.0 mm from root tip | 0.11 |
Root | 3.0 mm from root tip | 0.06 |
Root | 4.0 mm from root tip | 0.03 |
Skin | Unwounded | 0.02 |
Skin | 24 h after wound | 0.10 |
Skin | 72 h after wound | 0.04 |
Identify the region of the root where cell proliferation is greatest.
[1]
Using the data, calculate the percentage decrease in mitotic index from the root tip to 4.0 mm from the root tip.
[1]
Explain why cells in a root apical meristem have a high mitotic index.
[2]
Suggest why the mitotic index of skin cells changes after wounding.
[1]
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Question 29
Researchers measured cell volume and organelle numbers in a population of algal cells at three stages of interphase before cell division.
Interphase stage | Mean cell volume / m | Mean DNA content / arbitrary units | Mean mitochondria per cell | Mean chloroplasts per cell |
|---|---|---|---|---|
G1 | 80 | 1.0 | 12 | 4 |
S | 100 | 1.6 | 15 | 5 |
G2 | 120 | 2.0 | 18 | 6 |
Describe two changes in the cells during interphase shown by the data.
[2]
Explain why mitochondria and chloroplast numbers must increase before cytokinesis.
[2]
Question 30
Mutations in genes that regulate the cell cycle can contribute to tumour formation.
Distinguish a proto-oncogene from an oncogene.
[2]
Explain how loss-of-function mutations in tumour suppressor genes can lead to uncontrolled cell division.
[2]
Question 31
A diploid organism has six chromosomes in each body cell. The diagram tracks chromosome number and DNA amount per nucleus through mitosis and meiosis after DNA replication.
Stage | Chromosome number per nucleus | DNA amount per nucleus |
|---|---|---|
Body cell before DNA replication | 6 | 6 |
After DNA replication | 6 | 12 |
Each daughter nucleus after mitosis | 6 | 6 |
Each nucleus after meiosis I | 3 | 6 |
Each nucleus after meiosis II | 3 | 3 |
State the chromosome number in each nucleus produced by mitosis.
[1]
Compare the effect of mitosis and meiosis on chromosome number in this organism.
[2]
Explain why DNA replication is required before mitosis and before meiosis.
[2]
Question 32
The stimulus shows two processes that occur during meiosis I and data for the number of possible chromosome combinations produced by random orientation of bivalents.
Calculate the number of possible chromosome combinations from random orientation when the haploid chromosome number is 5.
[1]
Describe the relationship between haploid chromosome number and possible chromosome combinations shown in the data.
[1]
Explain how random orientation of bivalents generates genetic diversity.
[2]
State how crossing over contributes to genetic variation.
[1]
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Question 33
DNA content was measured in a population of proliferating cells using fluorescence proportional to the amount of DNA per nucleus.
Identify the cell-cycle stage represented by nuclei with the lower DNA content peak.
[1]
Explain why cells in S phase have DNA contents between the two peaks.
[2]
Calculate the percentage of cells in S phase.
[1]
State the sequence of stages after G2 that produces two separate daughter cells.
[1]
Question 34
The graph shows changes in the concentration of three cyclins during one cell cycle. Horizontal lines indicate threshold concentrations required to pass checkpoints.
Identify the cyclin that reaches its threshold immediately before entry into mitosis.
[1]
Explain the effect on the cell cycle if a cyclin does not reach the threshold concentration for its checkpoint.
[2]
Suggest why different cyclins peak at different times in the cell cycle.
[2]
Question 35
The diagram shows cytokinesis in two eukaryotic cells, X and Y.
I.
Identify which cell, X or Y, is carrying out cytokinesis typical of an animal cell.
[1]
II.
State the function of cytokinesis in cell division.
[1]
Compare and contrast cytokinesis in cells X and Y.
[3]
Explain why unequal cytokinesis in human oogenesis can be biologically advantageous, whereas a daughter cell receiving no mitochondria would be unlikely to survive.
[2]
Question 36
The micrograph shows cells from an onion root tip squash. Three cells are labelled A, B and C.
I.
Identify the phase of mitosis shown by cell A.
[1]
II.
Identify the phase of mitosis shown by cell B.
[1]
III.
Identify the phase of mitosis shown by cell C.
[1]
Explain the chromosome behaviour that allowed you to identify cells B and C.
[2]
Discuss how mitosis produces two genetically identical daughter nuclei.
[2]
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Question 37
A unicellular eukaryote can reproduce asexually in favourable conditions but also has a sexual stage in its life cycle.
I.
State one role of mitosis in eukaryotes.
[1]
II.
State one role of meiosis in eukaryotes.
[1]
Explain why nuclear division is normally needed before cytokinesis in eukaryotic cells.
[2]
Evaluate the advantages of using mitosis for asexual reproduction and meiosis for the sexual stage of the life cycle.
[3]
Question 38
A researcher compares cell proliferation in a plant root apical meristem, an early animal embryo and skin tissue near a wound.
I.
Define cell proliferation.
[1]
II.
State the nuclear division process required for proliferation in these tissues.
[1]
Explain how cell proliferation contributes to growth in the root apical meristem and in an early animal embryo.
[2]
Discuss why cell proliferation is necessary but not sufficient by itself for growth and tissue repair.
[3]
Question 39
Cultured human cells were engineered with mutations affecting two genes involved in cell-cycle control. Cell number was recorded after seven days.
Genotype | Cell number after 7 days / cells | Cells in S phase / % |
|---|---|---|
Control | 1.0 | 14 |
Growth-promoting gene activated | 2.8 | 32 |
Division-inhibiting gene, 1 copy inactive | 1.1 | 15 |
Division-inhibiting gene, 2 copies inactive | 4.6 | 40 |
Compare the effect of activating the growth-promoting gene with the effect of inactivating one copy of the division-inhibiting gene.
[2]
Use the data to distinguish between an oncogene and a tumour suppressor gene.
[2]
Explain why tumour formation usually requires several mutations in the same cell lineage.
[1]
Question 40
Samples from three tumours were examined. Cells in mitosis were counted, and clinical observations were recorded.
Tumour sample | Cells in mitosis | Total cells counted | Clinical observations |
|---|---|---|---|
A | 36 | 300 | Localized; does not invade neighbouring tissue; no secondary tumours. |
B | 48 | 300 | Invades neighbouring tissue; no secondary tumours. |
C | 72 | 300 | Invades neighbouring tissue; secondary tumours in lungs. |
Calculate the mitotic index for tumour A.
[1]
Identify the tumour with the highest rate of cell division, using the mitotic index values.
[1]
Distinguish between benign and malignant tumours using the observations in the table.
[2]
Suggest one reason why a treatment that targets mitosis may also damage some normal tissues.
[1]
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Question 41
A diploid cell has four chromosomes at the start of interphase. It will undergo mitosis followed by cytokinesis.
I.
State the number of chromosomes in the cell at the start of interphase.
[1]
II.
State the number of chromatids in the nucleus immediately after DNA replication is complete.
[1]
Explain why a replicated chromosome is still counted as one chromosome until anaphase.
[2]
Discuss the importance of DNA replication and cohesin for accurate nuclear division.
[2]
Question 42
The diagram shows possible chromosome movements for chromosome pair 21 during meiosis in a human primary oocyte.
I.
State the chromosome movement that normally occurs in meiosis I.
[1]
II.
State the chromosome movement that normally occurs in meiosis II.
[1]
Explain why meiosis is described as a reduction division in a sexual life cycle.
[3]
Using chromosome 21 as an example, explain how non-disjunction can result in Down syndrome.
[3]
Question 43
A species of flowering plant has a haploid chromosome number of . During meiosis, bivalents form and align at metaphase I.
I.
Calculate the number of possible chromosome combinations in gametes produced by random orientation of bivalents alone.
[1]
II.
State the meiotic stage in which random orientation of bivalents occurs.
[1]
Explain how random orientation of bivalents generates genetic variation.
[2]
Discuss how crossing over and random orientation together contribute to evolution by natural selection.
[3]
Question 44
The graph shows relative DNA content per nucleus for cells sampled from a proliferating cell culture.
I.
Identify the cell-cycle stage represented by region P.
[1]
II.
Identify the cell-cycle stage represented by region Q.
[1]
III.
Identify one stage represented by region R.
[1]
Explain the sequence of events in the cell cycle that accounts for the DNA content pattern shown.
[3]
Discuss why interphase should not be described as a resting stage.
[2]
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Question 45
A drug is tested on proliferating cells. The graph shows the concentration of one cyclin during a cell cycle with and without the drug. A horizontal line marks the threshold needed to pass a checkpoint.
I.
State what is meant by a checkpoint in the cell cycle.
[1]
II.
State the effect of the drug on cyclin concentration relative to the threshold.
[1]
Explain how cyclins control progression through the cell cycle.
[3]
Evaluate the likely effect of the drug on cell proliferation and on tissue repair.
[3]
Question 46
Two biopsy samples, A and B, were taken from different tumours. Cells were examined in microscope fields and classified as either in mitosis or not in mitosis.
Sample | Cells in mitosis | Cells not in mitosis | Total cells observed | Capsule | Neighbouring tissue invaded | Distant cells detected |
|---|---|---|---|---|---|---|
A | 12 | 88 | 100 | no | yes | yes |
B | 30 | 70 | 100 | yes | no | no |
I.
Calculate the mitotic index for sample A.
[1]
II.
Calculate the mitotic index for sample B.
[1]
III.
State what a higher mitotic index indicates about a tumour sample.
[1]
Distinguish between benign and malignant tumours using the observations in the table.
[2]
Evaluate why mitotic index alone is not sufficient to decide whether a tumour is cancerous.
[3]
Question 47
Cells from a tissue sample contain mutations in two genes involved in cell-cycle control. Gene A normally stimulates cell-cycle progression when growth signals are present. Gene B normally inhibits division when DNA damage is detected.
I.
Identify the class of normal gene represented by gene A.
[1]
II.
Identify the class of normal gene represented by gene B.
[1]
Explain how mutations in gene A and gene B could each contribute to uncontrolled cell division.
[3]
Discuss why tumour formation usually requires several mutations accumulating in the same cell lineage.
[3]
Question 48
A chemotherapy drug disrupts spindle microtubules. It is given to a patient with a malignant primary tumour. The patient develops side effects in tissues with rapid routine cell replacement.
I.
State the role of spindle microtubules during mitosis.
[1]
II.
State why cancer cells are often affected by drugs that target mitosis.
[1]
Explain how disruption of spindle microtubules could reduce growth of the primary tumour.
[2]
Discuss why the same drug can cause side effects in normal tissues and why it may not prevent metastasis completely.
[3]
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