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the parent cell."},{"text":"The chromatid number.","correct":false,"explanation":"Chromatid number changes when replicated sister chromatids separate. It is chromosome number that mitosis preserves because each daughter cell receives one chromosome from every sister-chromatid pair."},{"text":"The cell volume.","correct":false,"explanation":"Cytokinesis does not necessarily divide the cytoplasm into precisely equal volumes. Mitosis preserves chromosome number by distributing one copy of each chromosome to each daughter cell."},{"text":"The organelle number.","correct":false,"explanation":"Organelles are distributed during cell division but not necessarily in identical numbers. The quantity reliably maintained by mitosis is chromosome number through equal chromatid separation."}]},{"id":"44f8a677-59ab-4592-8a7a-5b4fd61cf12f","cardType":"basic","points":1,"front":"Why must DNA be copied before cell division?","back":"Each daughter cell needs a complete genome copy.","mcqOptions":[{"text":"Each daughter cell needs a complete genome copy.","correct":true,"explanation":"DNA replication produces two copies of every chromosome, allowing their subsequent separation so that each daughter cell inherits all the genetic information required for normal function."},{"text":"Each daughter cell needs a half genome copy.","correct":false,"explanation":"Confusing mitosis with reduction division suggests that each cell receives half a genome. Mitosis instead requires replication so each daughter cell inherits a complete genome copy."},{"text":"Each daughter cell needs a complete RNA copy.","correct":false,"explanation":"RNA is produced by transcription and does not constitute the inherited genome. DNA must be copied so that each daughter cell receives a complete genome copy."},{"text":"Each daughter cell needs a double genome copy.","correct":false,"explanation":"Replication temporarily doubles the DNA content, but sister chromatids are then separated. Consequently, each daughter cell receives one complete genome copy rather than two copies."}]},{"id":"fbd84f2b-58a6-4b41-bd46-e77c4e2134fb","cardType":"cloze","points":null,"front":"Human body cells are [ ], with [ ] in total.","back":"Human body cells are diploid, with 46 chromosomes in total.","mcqOptions":[{"text":"Human body cells are diploid, with 46 chromosomes in total.","correct":true,"explanation":"Most human body cells contain two sets of 23 chromosomes, one set inherited from each parent. They are therefore diploid and contain 46 chromosomes altogether."},{"text":"Human body cells are haploid, with 46 chromosomes in total.","correct":false,"explanation":"Haploid human cells contain only one set of 23 chromosomes and are normally gametes. Body cells are diploid, containing two sets and therefore 46 chromosomes."},{"text":"Human body cells are diploid, with 23 chromosomes in total.","correct":false,"explanation":"The value 23 counts one haploid set rather than both sets in a body cell. Human body cells are diploid and contain 46 chromosomes in total."},{"text":"Human body cells are haploid, with 23 pairs of chromosomes in total.","correct":false,"explanation":"Having 23 homologous pairs means possessing two chromosome sets, so the cell is diploid rather than haploid. Human body cells contain 46 individual chromosomes in total."}]},{"id":"2ae6c8ea-85e4-48ff-88f0-fe424126cccb","cardType":"basic","points":1,"front":"After DNA replication, what holds sister chromatids together?","back":"The centromere.","mcqOptions":[{"text":"The centromere.","correct":true,"explanation":"After replication, the two identical sister chromatids remain joined at a constricted chromosome region called the centromere until they separate during anaphase."},{"text":"The spindle fibre.","correct":false,"explanation":"Spindle fibres attach to kinetochores and move chromatids during mitosis; they do not join sister chromatids together. The sister chromatids are held together at the centromere."},{"text":"The centriole.","correct":false,"explanation":"Centrioles help organise the spindle at the cell poles and are not part of the replicated chromosome. Sister chromatids remain attached at the centromere."},{"text":"The chiasma.","correct":false,"explanation":"A chiasma forms between homologous chromosomes following crossing over in meiosis. Replicated sister chromatids are instead held together at their centromere."}]},{"id":"a5620966-7408-4eaa-a759-b6e2530977df","cardType":"basic","points":2,"front":"Why is chromosome number unchanged immediately after DNA replication?","back":"Chromosomes are counted by centromeres, not chromatids.","mcqOptions":[{"text":"Chromosomes are counted by centromeres, not chromatids.","correct":true,"explanation":"Each replicated chromosome has two sister chromatids but only one centromere region. It therefore still counts as one chromosome until the sister chromatids separate."},{"text":"Chromosomes are counted by chromatids, not centromeres.","correct":false,"explanation":"Counting chromatids would incorrectly double the chromosome number after DNA replication. Chromosomes are counted by centromeres, so a two-chromatid chromosome still counts as one chromosome."},{"text":"Chromosomes are counted by telomeres, not chromatids.","correct":false,"explanation":"Every linear chromosome has telomeres at both ends, making them unsuitable for counting chromosomes directly. Chromosome number is determined by the number of centromeres."},{"text":"Chromosomes are counted by genes, not chromatids.","correct":false,"explanation":"Each chromosome contains many genes, and different chromosomes carry different numbers of them. Chromosomes are counted by centromeres, not by genes or chromatids."}]},{"id":"e8a605cd-9631-4e00-9826-2b8e7c222592","cardType":"cloze","points":null,"front":"After DNA replication, a human skin cell has [ ] and [ ].","back":"After DNA replication, a human skin cell has 46 chromosomes and 92 chromatids.","mcqOptions":[{"text":"After DNA replication, a human skin cell has 46 chromosomes and 92 chromatids.","correct":true,"explanation":"Replication produces two sister chromatids for each of the cell’s 46 chromosomes. Chromatid number doubles to 92, but chromosome number remains 46 because centromeres have not divided."},{"text":"After DNA replication, a human skin cell has 92 chromosomes and 92 chromatids.","correct":false,"explanation":"This treats every newly formed chromatid as a separate chromosome before centromere division. The replicated cell has 46 chromosomes, each with two chromatids, giving 92 chromatids."},{"text":"After DNA replication, a human skin cell has 46 chromosomes and 46 chromatids.","correct":false,"explanation":"This overlooks the doubling of DNA during S phase. Chromosome number stays at 46, but each chromosome gains a sister chromatid, producing 92 chromatids."},{"text":"After DNA replication, a human skin cell has 23 chromosomes and 46 chromatids.","correct":false,"explanation":"This incorrectly treats a diploid skin cell as haploid. A human skin cell has 46 chromosomes, and replication gives each two chromatids, producing 92 chromatids."}]},{"id":"494b2c4d-12f7-4707-97d9-b03e3a2d13dc","cardType":"basic","points":1,"front":"Which cell-cycle stage involves cell growth and organelle production?","back":"G1 phase.","mcqOptions":[{"text":"G1 phase.","correct":true,"explanation":"During G1, the newly formed cell grows, synthesises proteins and produces or duplicates organelles, preparing the cellular resources needed before DNA replication begins."},{"text":"S phase.","correct":false,"explanation":"S phase is primarily when DNA is replicated, not the main stage associated with cell growth and organelle production. Those processes characterise G1 phase."},{"text":"G2 phase.","correct":false,"explanation":"G2 mainly involves final growth, DNA checks and synthesis of proteins needed for mitosis. The principal stage for general cell growth and organelle production is G1."},{"text":"M phase.","correct":false,"explanation":"M phase consists of nuclear division and usually cytokinesis rather than the main period of growth and organelle production. These activities occur principally during G1 phase."}]},{"id":"b44d5fc8-2b63-4e53-836b-6db2a907ed62","cardType":"basic","points":1,"front":"Which cell-cycle stage involves DNA replication?","back":"S phase.","mcqOptions":[{"text":"S phase.","correct":true,"explanation":"The S stands for synthesis because DNA is synthesised during this stage. Each chromosome is replicated to form two genetically identical sister chromatids."},{"text":"G1 phase.","correct":false,"explanation":"G1 is mainly associated with cell growth, protein synthesis and organelle production before replication. DNA itself is replicated during the following S phase."},{"text":"G2 phase.","correct":false,"explanation":"G2 follows DNA replication and includes checks and preparation for mitosis. The genome has already been copied during S phase before the cell enters G2."},{"text":"M phase.","correct":false,"explanation":"M phase separates the chromosomes that were previously replicated and then divides the cell. DNA replication occurs earlier in the cell cycle, during S phase."}]},{"id":"6df66bd0-5ece-403f-a952-15ea4bac79bd","cardType":"basic","points":1,"front":"Which cell-cycle stage checks copied DNA and makes proteins for division?","back":"G2 phase.","mcqOptions":[{"text":"G2 phase.","correct":true,"explanation":"G2 occurs after DNA replication. The cell checks the copied DNA for damage and synthesises proteins, including those needed for spindle formation and mitosis."},{"text":"G1 phase.","correct":false,"explanation":"G1 mainly involves cell growth and protein synthesis before DNA replication. G2 is the stage that checks copied DNA and prepares the cell for division."},{"text":"S phase.","correct":false,"explanation":"S phase is when DNA is replicated, rather than when the completed copies are checked. These checks and final preparations for division occur during G2."},{"text":"M phase.","correct":false,"explanation":"M phase is when mitosis and cytokinesis take place. The preceding G2 phase checks replicated DNA and produces proteins required for the division process."}]},{"id":"eeff0b69-1539-4b4b-97f1-058f42eb0df7","cardType":"cloze","points":null,"front":"[ ] includes mitosis and cytokinesis.","back":"M phase includes mitosis and cytokinesis.","mcqOptions":[{"text":"M phase","correct":true,"explanation":"M phase comprises mitosis, when the nucleus divides, and cytokinesis, when the cytoplasm separates to produce two daughter cells."},{"text":"G1 phase","correct":false,"explanation":"G1 phase is a period of cell growth before DNA replication, not nuclear and cytoplasmic division. M phase includes both mitosis and cytokinesis."},{"text":"S phase","correct":false,"explanation":"S phase is the part of interphase in which DNA is replicated. M phase follows interphase and includes both mitosis and cytokinesis."},{"text":"G2 phase","correct":false,"explanation":"G2 phase checks replicated DNA and prepares the cell for division, but division has not yet begun. M phase includes mitosis and cytokinesis."}]},{"id":"d56da0d6-19e0-4f80-9ad3-780e4aeb0c89","cardType":"basic","points":1,"front":"What can cell-cycle checkpoints pause the cycle in response to?","back":"DNA damage or incorrect chromosome attachment.","mcqOptions":[{"text":"DNA damage or incorrect chromosome attachment.","correct":true,"explanation":"Checkpoints detect problems such as damaged DNA and chromosomes not correctly attached to spindle fibres. Pausing allows repair or prevents faulty chromosomes being distributed."},{"text":"Complete DNA replication or correct chromosome attachment.","correct":false,"explanation":"Completed replication and correct attachment indicate that the cell may progress, rather than pause. Checkpoints halt the cycle when DNA is damaged or chromosome attachment is incorrect."},{"text":"ATP production or chromosome condensation.","correct":false,"explanation":"ATP production and chromosome condensation are normal cellular processes, not the faults targeted by these checkpoints. The cycle can pause for DNA damage or incorrect chromosome attachment."},{"text":"Protein synthesis or nuclear envelope breakdown.","correct":false,"explanation":"Protein synthesis and nuclear envelope breakdown are expected events during the cycle. Checkpoints instead pause progression when DNA is damaged or chromosomes are attached incorrectly."}]},{"id":"4c95338a-5ba2-4663-8159-731d33eafab5","cardType":"basic","points":2,"front":"How can mutations in cell-cycle control genes lead to cancer?","back":"Cells divide uncontrollably and form a tumour.","mcqOptions":[{"text":"Cells divide uncontrollably and form a tumour.","correct":true,"explanation":"Mutations can disable checkpoint proteins or activate growth-promoting proteins, allowing repeated cell division without normal regulation. The resulting mass of abnormal cells forms a tumour."},{"text":"Cells divide more slowly and form a tumour.","correct":false,"explanation":"Cancer results from excessive, unregulated division, not simply slower division. Mutated control genes can let cells divide uncontrollably, producing a growing mass called a tumour."},{"text":"Cells divide uncontrollably and undergo apoptosis.","correct":false,"explanation":"Apoptosis removes damaged cells and therefore limits tumour development. Cancer arises when abnormal cells evade such controls, divide uncontrollably and accumulate to form a tumour."},{"text":"Cells differentiate uncontrollably and form a tumour.","correct":false,"explanation":"A tumour forms through uncontrolled cell division, not uncontrolled differentiation. Mutations in cell-cycle control genes remove restraints on mitosis, causing abnormal cells to accumulate."}]},{"id":"b51c8f76-427b-4d5c-8077-1f58ede3d771","cardType":"basic","points":1,"front":"What happens to chromosomes during prophase?","back":"They condense, becoming shorter and thicker.","mcqOptions":[{"text":"They condense, becoming shorter and thicker.","correct":true,"explanation":"During prophase, chromatin coils tightly so each chromosome becomes shorter, thicker and visible. This compact form helps chromosomes move safely during mitosis."},{"text":"They decondense, becoming longer and thinner.","correct":false,"explanation":"Decondensation occurs as chromosomes return to chromatin after division, particularly during telophase. In prophase, chromosomes condense and become shorter and thicker."},{"text":"They replicate, becoming doubled and identical.","correct":false,"explanation":"DNA replication occurs during S phase before mitosis, so each chromosome already has two sister chromatids. During prophase, chromosomes condense, becoming shorter and thicker."},{"text":"They separate, becoming shorter and thinner.","correct":false,"explanation":"Sister chromatids separate during anaphase, not prophase. In prophase, the chromosomes coil and condense, making them shorter and thicker before their movement."}]},{"id":"df4c6735-7c9d-4a02-8d72-421be946d01f","cardType":"basic","points":1,"front":"What happens to the nuclear envelope during prophase?","back":"It breaks down.","mcqOptions":[{"text":"It breaks down.","correct":true,"explanation":"The nuclear envelope breaks down during prophase, allowing spindle fibres to reach the chromosomes and attach to their centromere regions."},{"text":"It reforms.","correct":false,"explanation":"Reformation of the nuclear envelope occurs during telophase around each chromosome set. During prophase, the existing nuclear envelope breaks down."},{"text":"It remains intact.","correct":false,"explanation":"The nuclear envelope does not remain intact throughout prophase. It breaks down so spindle fibres can interact with and move the chromosomes."},{"text":"It duplicates itself.","correct":false,"explanation":"The nuclear envelope is not duplicated during prophase. Instead, it breaks down, removing the barrier between the spindle fibres and the condensed chromosomes."}]},{"id":"b401f593-98f5-4f29-82c1-bc71f41bae7d","cardType":"basic","points":1,"front":"Where do chromosomes line up during metaphase?","back":"Along the cell equator.","mcqOptions":[{"text":"Along the cell equator.","correct":true,"explanation":"During metaphase, spindle fibres position chromosomes along the cell equator, forming the metaphase plate before sister chromatids separate."},{"text":"At opposite cell poles.","correct":false,"explanation":"Chromosomes move towards opposite poles during anaphase and reach them by telophase. During metaphase, they line up along the cell equator."},{"text":"Along the nuclear envelope.","correct":false,"explanation":"The nuclear envelope has broken down before metaphase, so chromosomes cannot line up along it. They align along the equator of the cell."},{"text":"Beside the cell membrane.","correct":false,"explanation":"Chromosomes are not positioned beside the cell membrane during metaphase. Spindle fibres arrange them centrally along the cell equator before separation."}]},{"id":"cbf2589c-5089-46ee-a424-a2a048be13aa","cardType":"cloze","points":null,"front":"In metaphase, spindle fibres attach to the [ ].","back":"In metaphase, spindle fibres attach to the centromeres.","mcqOptions":[{"text":"centromeres","correct":true,"explanation":"Spindle fibres attach at the centromere regions of chromosomes, enabling them to position the chromosomes and later pull sister chromatids towards opposite poles."},{"text":"telomeres","correct":false,"explanation":"Telomeres protect the ends of chromosomes but are not the spindle attachment sites. Spindle fibres attach at the centromere regions during metaphase."},{"text":"centrosomes","correct":false,"explanation":"Centrosomes organise the spindle and lie at opposite poles; they are not chromosome attachment sites. Spindle fibres connect to chromosomes at their centromere regions."},{"text":"nucleosomes","correct":false,"explanation":"Nucleosomes package DNA around histone proteins but do not provide spindle attachment sites. In metaphase, spindle fibres attach at the chromosomes’ centromere regions."}]},{"id":"800062af-e7b0-462e-8617-3d50e222acec","cardType":"basic","points":1,"front":"What happens to centromeres during anaphase?","back":"They split.","mcqOptions":[{"text":"They split.","correct":true,"explanation":"Centromeres divide during anaphase, allowing the sister chromatids to separate and be pulled towards opposite poles of the cell."},{"text":"They remain joined.","correct":false,"explanation":"Sister chromatids remain joined at their centromeres before anaphase. During anaphase, the centromeres split so the chromatids can move to opposite poles."},{"text":"They replicate.","correct":false,"explanation":"DNA, including the centromeric region, is replicated during interphase rather than anaphase. In anaphase, the centromeres split to separate sister chromatids."},{"text":"They re-form.","correct":false,"explanation":"Centromeres do not disappear and re-form during mitosis. They split during anaphase, enabling the two sister chromatids of each chromosome to separate."}]},{"id":"a90e8cca-e74b-4147-8f69-600b5bdf2eb9","cardType":"basic","points":1,"front":"What pulls sister chromatids to opposite poles in anaphase?","back":"Spindle fibres.","mcqOptions":[{"text":"Spindle fibres.","correct":true,"explanation":"Spindle fibres attached to the centromere regions shorten during anaphase, pulling sister chromatids towards opposite poles of the cell."},{"text":"Centrioles.","correct":false,"explanation":"Centrioles help organise the spindle in animal cells but do not directly pull chromatids. Spindle fibres shorten to move the sister chromatids apart."},{"text":"Centromeres.","correct":false,"explanation":"Centromeres are the regions where sister chromatids are joined and spindle fibres attach. The spindle fibres, not the centromeres themselves, pull chromatids apart."},{"text":"Nuclear envelopes.","correct":false,"explanation":"The nuclear envelope breaks down before metaphase and therefore cannot pull chromatids. Spindle fibres move the sister chromatids towards opposite poles during anaphase."}]},{"id":"29f8cae1-4b46-480f-ae64-c4ef504928e3","cardType":"basic","points":1,"front":"What forms around each chromosome set during telophase?","back":"New nuclear envelopes.","mcqOptions":[{"text":"New nuclear envelopes.","correct":true,"explanation":"During telophase, a new nuclear envelope forms around each set of chromosomes, producing two nuclei within the dividing cell."},{"text":"New spindle fibres.","correct":false,"explanation":"Spindle fibres disassemble during telophase rather than forming around the chromosomes. New nuclear envelopes develop around the two separated chromosome sets."},{"text":"New cell walls.","correct":false,"explanation":"In plant cytokinesis, a cell wall eventually forms between daughter cells, not around each chromosome set. Nuclear envelopes form around the separated sets during telophase."},{"text":"New centromeres.","correct":false,"explanation":"Centromeres are chromosome regions and are not newly formed around chromosome sets. During telophase, new nuclear envelopes enclose each separated set."}]},{"id":"e8ad463a-c2bb-4dec-9959-dcabf28bdc1b","cardType":"cloze","points":null,"front":"In animal cytokinesis, the cell membrane [ ].","back":"In animal cytokinesis, the cell membrane pinches inwards.","mcqOptions":[{"text":"pinches inwards","correct":true,"explanation":"A contractile ring causes the animal cell membrane to pinch inwards, forming a cleavage furrow that separates the cytoplasm into two daughter cells."},{"text":"moves outwards","correct":false,"explanation":"An animal cell does not divide by expanding its membrane outwards. Its membrane pinches inwards to form a cleavage furrow during cytokinesis."},{"text":"dissolves completely","correct":false,"explanation":"The cell membrane remains intact throughout animal cytokinesis rather than dissolving. It pinches inwards until the two daughter cells separate."},{"text":"forms a cell plate","correct":false,"explanation":"Cell-plate formation occurs in plant cells because their rigid walls prevent pinching. In animal cytokinesis, the cell membrane pinches inwards."}]},{"id":"58c6a64b-617b-4c72-96fb-7285e80c0278","cardType":"basic","points":1,"front":"Why are root tips useful for observing mitosis?","back":"They contain meristems where cells divide rapidly.","mcqOptions":[{"text":"They contain meristems where cells divide rapidly.","correct":true,"explanation":"Root tips contain meristematic tissue, whose cells undergo mitosis frequently for growth. This produces many cells in visible stages of mitosis."},{"text":"They contain root hairs where cells divide rapidly.","correct":false,"explanation":"Root hair cells are differentiated for absorbing water and mineral ions, so they do not divide rapidly. Rapid mitosis occurs in root-tip meristems."},{"text":"They contain xylem vessels where cells divide rapidly.","correct":false,"explanation":"Mature xylem vessels are dead, hollow cells specialised for transport and cannot undergo mitosis. Root tips are useful because their meristems divide rapidly."},{"text":"They contain phloem tubes where cells divide rapidly.","correct":false,"explanation":"Phloem tissue is specialised for translocation rather than rapid cell division. The root-tip meristems contain actively dividing cells suitable for observing mitosis."}]},{"id":"36eea80f-2ea1-4255-8631-b2972abae691","cardType":"basic","points":1,"front":"What is the mitotic index formula?","back":"$$\\text{mitotic index}=\\frac{\\text{number of cells in mitosis}}{\\text{total cells observed}}$","mcqOptions":[{"text":"$$\\text{mitotic index}=\\frac{\\text{number of cells in mitosis}}{\\text{total cells observed}}$","correct":true,"explanation":"The mitotic index is the proportion of observed cells undergoing mitosis, so the number in mitosis is divided by the total number examined."},{"text":"$$\\text{mitotic index}=\\frac{\\text{total cells observed}}{\\text{number of cells in mitosis}}$","correct":false,"explanation":"This reverses the numerator and denominator, producing a value that can exceed one. Mitotic index is cells in mitosis divided by total cells observed."},{"text":"$$\\text{mitotic index}=\\frac{\\text{number of cells not in mitosis}}{\\text{total cells observed}}$","correct":false,"explanation":"This calculates the proportion of cells outside mitosis, usually in interphase. Mitotic index uses the number of cells in mitosis as the numerator."},{"text":"$$\\text{mitotic index}=\\frac{\\text{number of cells in mitosis}}{\\text{number of cells not in mitosis}}$","correct":false,"explanation":"This compares mitotic cells only with non-mitotic cells rather than with the whole sample. The denominator must be the total number of cells observed."}]},{"id":"25eac20e-9387-49ee-87e4-d15219612c74","cardType":"basic","points":2,"front":"A field has 240 cells, 36 in mitosis. What is the mitotic index?","back":"0.150 or 15.0%.","mcqOptions":[{"text":"0.150 or 15.0%.","correct":true,"explanation":"Dividing the 36 cells in mitosis by all 240 observed cells gives $36/240=0.150$. Multiplying by 100 converts this to 15.0%."},{"text":"0.015 or 1.5%.","correct":false,"explanation":"This places the decimal point one position too far left. The calculation gives $36/240=0.150$, which is 15.0% rather than 1.5%."},{"text":"0.850 or 85.0%.","correct":false,"explanation":"This uses the proportion of cells not in mitosis: $204/240=0.850$. Mitotic index uses the 36 mitotic cells, giving 0.150 or 15.0%."},{"text":"6.67 or 667%.","correct":false,"explanation":"This reverses the division and calculates $240/36$ instead of $36/240$. The correct mitotic index is 0.150, equivalent to 15.0%."}]},{"id":"40e70512-f427-4fbb-bc15-39e4baaa1dca","cardType":"basic","points":2,"front":"Using mitotic index 0.150 and cycle time 86,400 s, estimate time in mitosis.","back":"12,960 s.","mcqOptions":[{"text":"12,960 s.","correct":true,"explanation":"The estimated time in mitosis is the mitotic index multiplied by total cycle time: $0.150\\times86{,}400=12{,}960\\text{ s}$."},{"text":"1,296 s.","correct":false,"explanation":"This result comes from an extra factor-of-ten reduction, equivalent to using 0.015. Using the stated index gives $0.150\\times86{,}400=12{,}960\\text{ s}$."},{"text":"73,440 s.","correct":false,"explanation":"This uses 0.850, the proportion of the cycle outside mitosis. The time in mitosis uses 0.150, giving $12{,}960\\text{ s}$."},{"text":"576,000 s.","correct":false,"explanation":"This divides the cycle time by the mitotic index instead of taking the stated proportion. Multiplying $86{,}400$ by 0.150 gives $12{,}960\\text{ s}$."}]},{"id":"286d93c5-7227-424f-964e-e00a24bdc186","cardType":"basic","points":1,"front":"What does a high mitotic index indicate?","back":"A large proportion of cells are dividing.","mcqOptions":[{"text":"A large proportion of cells are dividing.","correct":true,"explanation":"A high mitotic index means many cells are undergoing mitosis at the time of observation, so a large proportion of the cell population is dividing."},{"text":"A large proportion of cells are differentiating.","correct":false,"explanation":"Mitotic index measures the proportion of cells undergoing mitosis, not differentiation. A high value therefore indicates that a large proportion of cells are dividing."},{"text":"A small proportion of cells are dividing.","correct":false,"explanation":"This reverses the meaning of a high mitotic index. A high index shows that many cells are in mitosis, so a large proportion of cells are dividing."},{"text":"A large proportion of cells are dead.","correct":false,"explanation":"The mitotic index does not measure cell death. It measures the proportion of cells undergoing mitosis, so a high value indicates that many cells are dividing."}]},{"id":"ef38f591-a299-4f8b-bcde-736b5797ad46","cardType":"cloze","points":null,"front":"Stem cell differentiation depends on [ ].","back":"Stem cell differentiation depends on selective gene expression.","mcqOptions":[{"text":"selective gene expression","correct":true,"explanation":"Differentiation occurs when different genes are selectively expressed or repressed, causing cells with the same genome to produce different proteins and develop specialised functions."},{"text":"random gene mutation","correct":false,"explanation":"Differentiation normally results from selective gene expression, not random mutation. Different genes are switched on or off in cells, producing their specialised characteristics."},{"text":"continuous DNA replication","correct":false,"explanation":"DNA replication copies the genome before cell division but does not determine specialised cell function. Differentiation depends on selective gene expression in the cell."},{"text":"uncontrolled cell division","correct":false,"explanation":"Uncontrolled division is associated with tumour formation rather than normal differentiation. Stem cells become specialised through selective expression of particular genes."}]},{"id":"0c905df8-a751-4edc-ac1c-f227ea7d8c24","cardType":"basic","points":2,"front":"Why can cells with the same genome become different specialised cells?","back":"Different genes are switched on or off.","mcqOptions":[{"text":"Different genes are switched on or off.","correct":true,"explanation":"Cells can contain the same genome but express different genes. Switching particular genes on or off produces different proteins, giving cells specialised structures and functions."},{"text":"Different genes are mutated during mitosis.","correct":false,"explanation":"Normal mitosis preserves the genetic information rather than mutating different genes. Cell specialisation results from different genes being switched on or off."},{"text":"Different genes are removed from the genome.","correct":false,"explanation":"Specialised cells generally retain the same genome as other body cells. Their differences arise because different genes are switched on or off, not because genes are removed."},{"text":"Different genes are replicated in different numbers.","correct":false,"explanation":"DNA replication normally produces an identical copy of the genome before division. Specialisation is caused by selective gene expression, with different genes switched on or off."}]},{"id":"a936ccfe-0b2a-4f7f-81ff-80d52b62161e","cardType":"basic","points":1,"front":"What does stem cell potency describe?","back":"The range of cell types it can produce.","mcqOptions":[{"text":"The range of cell types it can produce.","correct":true,"explanation":"Stem cell potency describes how many different types of specialised cell a stem cell can form. Greater potency means the stem cell can produce a wider range."},{"text":"The rate of cell division it can achieve.","correct":false,"explanation":"Division rate describes how quickly a cell population increases, not potency. Potency refers to the range of specialised cell types the stem cell can produce."},{"text":"The number of chromosomes it contains.","correct":false,"explanation":"Chromosome number describes the cell’s genetic complement, not its developmental potential. Potency is the range of cell types that the stem cell can produce."},{"text":"The size of cells it can produce.","correct":false,"explanation":"Cell size is not the definition of potency. Stem cell potency describes the range of different specialised cell types that the stem cell can form."}]},{"id":"95db8bf1-4df6-40c2-851f-e10f3929094b","cardType":"basic","points":1,"front":"Which potency can form all cell types, including placenta?","back":"Totipotent.","mcqOptions":[{"text":"Totipotent.","correct":true,"explanation":"Totipotent stem cells can form every cell type in the body as well as extra-embryonic tissues such as the placenta, allowing development of a complete organism."},{"text":"Pluripotent.","correct":false,"explanation":"Pluripotent cells can form almost all body cell types but cannot form extra-embryonic tissues such as the placenta. The ability to form placenta is totipotency."},{"text":"Multipotent.","correct":false,"explanation":"Multipotent cells form a limited range of related cell types, such as different blood cells. Forming all body cell types and placenta requires totipotency."},{"text":"Unipotent.","correct":false,"explanation":"Unipotent cells can produce only one cell type, despite retaining some self-renewal ability. Cells capable of forming all body and extra-embryonic types are totipotent."}]},{"id":"4e544753-aa57-4f3b-a795-0b6f2d01d8bf","cardType":"basic","points":1,"front":"Which potency can form almost all body cell types, but not extra-embryonic tissues?","back":"Pluripotent.","mcqOptions":[{"text":"Pluripotent.","correct":true,"explanation":"Pluripotent stem cells can differentiate into almost all body cell types, but they cannot form extra-embryonic tissues such as the placenta."},{"text":"Totipotent.","correct":false,"explanation":"Totipotent cells have greater potential than described because they can form both all body cell types and extra-embryonic tissues. The limitation to body cells indicates pluripotency."},{"text":"Multipotent.","correct":false,"explanation":"Multipotent cells produce a restricted range of related cell types, not almost every body cell type. The broader potential described is pluripotency."},{"text":"Unipotent.","correct":false,"explanation":"Unipotent cells can form only one type of specialised cell. Producing almost all body cell types, while excluding extra-embryonic tissue, describes pluripotency."}]},{"id":"52d3e9de-935a-48d7-8dc0-b8f8364b0e62","cardType":"basic","points":1,"front":"Which potency forms a limited range of related cell types?","back":"Multipotent.","mcqOptions":[{"text":"Multipotent.","correct":true,"explanation":"Multipotent stem cells can differentiate into a limited range of related cell types, such as several types of blood cell from a blood stem cell."},{"text":"Totipotent.","correct":false,"explanation":"Totipotent cells can form all body and extra-embryonic cell types, which is much broader than a limited range of related cells. The correct potency is multipotent."},{"text":"Pluripotent.","correct":false,"explanation":"Pluripotent cells can form almost all body cell types, whereas multipotent cells are restricted to a limited range of related types."},{"text":"Unipotent.","correct":false,"explanation":"Unipotent cells produce one specialised cell type, not a limited range of several related types. That broader but restricted ability is characteristic of multipotent cells."}]},{"id":"d20d3e23-0068-4d01-8a35-10d6ddf5dcfd","cardType":"basic","points":2,"front":"Why are embryonic stem cells more flexible than most adult stem cells?","back":"They are pluripotent, so produce more cell types.","mcqOptions":[{"text":"They are pluripotent, so produce more cell types.","correct":true,"explanation":"Embryonic stem cells are pluripotent, meaning they can differentiate into almost all body cell types. Most adult stem cells are multipotent and have a narrower range."},{"text":"They are totipotent, so produce more cell types.","correct":false,"explanation":"Embryonic stem cells are generally described as pluripotent, not totipotent. Totipotency also includes forming extra-embryonic tissues, whereas embryonic stem cells mainly produce body cell types."},{"text":"They are multipotent, so produce more cell types.","correct":false,"explanation":"Multipotency gives adult stem cells a limited range of related cell types. Embryonic stem cells are more flexible because they are pluripotent."},{"text":"They are unipotent, so produce more cell types.","correct":false,"explanation":"Unipotent cells produce only one specialised cell type, so this would make them less flexible. Embryonic stem cells produce more types because they are pluripotent."}]},{"id":"28f4ff65-e55c-4911-9269-67373235ceb6","cardType":"basic","points":1,"front":"What ethical issue can embryonic stem cell use raise?","back":"Embryos may be destroyed.","mcqOptions":[{"text":"Embryos may be destroyed.","correct":true,"explanation":"Obtaining embryonic stem cells can destroy an early embryo. Some people consider this unethical because they regard the embryo as a potential human life."},{"text":"Embryos may be rejected.","correct":false,"explanation":"Rejection is an immune risk affecting transplanted cells, not the central ethical issue concerning the embryo. The ethical concern is that embryos may be destroyed."},{"text":"Embryos may be mutated.","correct":false,"explanation":"Mutation is a genetic change, but it is not the characteristic ethical objection to obtaining embryonic stem cells. The concern is that embryos may be destroyed."},{"text":"Embryos may be implanted.","correct":false,"explanation":"Implantation is a normal stage of pregnancy and is not caused by collecting embryonic stem cells. The ethical issue is that embryos may be destroyed."}]},{"id":"d2d070fe-2b2b-46a2-8fbe-f8624410c7de","cardType":"basic","points":1,"front":"What immune risk can transplanted stem cells have?","back":"They may be rejected.","mcqOptions":[{"text":"They may be rejected.","correct":true,"explanation":"The recipient’s immune system may recognise transplanted stem cells as foreign and attack them, causing the cells to be rejected and preventing successful treatment."},{"text":"They may be accepted.","correct":false,"explanation":"Acceptance means the immune system tolerates the transplanted cells, so it is the desired outcome rather than a risk. The immune risk is rejection."},{"text":"They may be matched.","correct":false,"explanation":"Tissue matching reduces the likelihood of an immune response rather than creating one. The relevant risk is that transplanted stem cells may be rejected."},{"text":"They may be differentiated.","correct":false,"explanation":"Differentiation is the process by which stem cells become specialised, not an immune response. The immune system may instead identify transplanted cells as foreign and reject them."}]},{"id":"6acc9e60-463f-482b-8d2f-9cd6efd9b34e","cardType":"basic","points":1,"front":"What tumour risk can stem cells have in therapy?","back":"They may divide uncontrollably.","mcqOptions":[{"text":"They may divide uncontrollably.","correct":true,"explanation":"Stem cells retain the ability to divide, so failure to regulate their cell cycle can cause uncontrolled proliferation and the formation of a tumour."},{"text":"They may divide slowly.","correct":false,"explanation":"Slow division could reduce the effectiveness of tissue repair, but it would not itself produce a tumour. Tumours arise when stem cells divide uncontrollably."},{"text":"They may divide symmetrically.","correct":false,"explanation":"Symmetrical division describes the types of daughter cells produced and can occur normally in stem cell populations. The tumour risk comes from uncontrolled division."},{"text":"They may divide infrequently.","correct":false,"explanation":"Infrequent division would limit cell production rather than generate an excessive mass of cells. The tumour risk is that stem cells may divide uncontrollably."}]}]}],"examCountdown":{"examDate":"2027-06-07","paperLabel":"Paper 1"},"heading":"Mitosis, cell cycle and stem cells","title":"Mitosis, cell cycle and stem cells Flashcards","topbar":{"backHref":"/a-level/biology/edexcel/a/flashcards"},"topicSidebar":"$L38"}]}],"topicId":"9a5a517e-069c-5189-84db-5ab1629ee0f4","walled":"$L39"}],"$L3a","$L3b"]