HSC Exam Practice

Sample response. Mitosis is a type of cell division that produces two daughter cells with the same chromosome number and hereditary information as the parent cell. It occurs in somatic (body) cells, not in cells producing gametes.

Marking notes. 1 mark for identifying mitosis as cell division producing two daughter cells with the same chromosome number as the parent; 1 mark for identifying somatic cells as the site of mitosis.

Sample response. In prophase the chromosomes condense and the nuclear envelope begins to break down. In metaphase the chromosomes line up at the equator of the cell. In anaphase the sister chromatids separate and move to opposite poles. In telophase new nuclei re-form around each chromosome set. Cytokinesis then divides the cytoplasm to form two separate daughter cells, completing the division.

Marking notes. 1 mark for naming all four stages in the correct order (prophase, metaphase, anaphase, telophase); 1 mark for a correct event at metaphase OR anaphase; 1 mark for a correct event at prophase OR telophase; 1 mark for stating that cytokinesis divides the cytoplasm to produce two separate daughter cells.

Sample response. DNA replication must occur before mitosis begins. This produces two identical sister chromatids for each chromosome, ensuring that when the cell divides each daughter cell receives a full and complete set of chromosomes.

Marking notes. 1 mark for identifying DNA replication; 1 mark for explaining that it ensures each daughter cell inherits a full set of hereditary information.

Sample response. Before mitosis, DNA replication produces two identical sister chromatids for every chromosome. During mitosis the replicated chromosomes line up at the cell equator (metaphase) and then the sister chromatids are separated to opposite poles (anaphase). New nuclei re-form around each set, and cytokinesis divides the cytoplasm. Because each daughter cell receives exactly one chromatid for each original chromosome, both daughter cells end with the same chromosome number as the parent somatic cell — chromosome number is maintained.

Marking notes. 1 mark for DNA replication producing sister chromatids before division; 1 mark for separation of sister chromatids during anaphase; 1 mark for each new nucleus / daughter cell receiving one complete chromosome set; 1 mark for explicit statement that the daughter cells have the same chromosome number as the parent.

Sample response. Mitosis occurs in somatic cells and maintains chromosome number; it supports growth, tissue repair and some asexual reproduction by producing genetically identical daughter cells. Meiosis occurs in the formation of gametes and reduces chromosome number by half; it supports sexual reproduction by producing gametes that combine at fertilisation to restore the chromosome number while contributing to genetic variation. The two processes therefore have different purposes (stability vs reduction) and different outcomes (identical somatic cells vs variable gametes).

Marking notes. 1 mark for site / cell type (somatic vs gamete formation); 1 mark for chromosome-number outcome (maintained vs halved); 1 mark for purpose (growth/repair/asexual reproduction vs sexual reproduction/variation).

Sample response (a). The mitotic-cell density rises sharply from a baseline of ~3 per mm² on day 0 to a peak of ~78 per mm² at day 3. From day 3 onwards the density falls steadily, reaching ~22 per mm² by day 7 — still above baseline but well below the day-3 peak. The curve is therefore unimodal: a rapid rise to a clear maximum at day 3 followed by a decline back toward baseline.

Sample response (b). Mitosis is the cell division that produces new somatic cells with the same chromosome number as the cells being replaced. Wounding removes a patch of skin cells, so the basal layer at the wound edge ramps up mitosis to generate new, genetically identical skin cells to repopulate the lost area. The day-0-to-day-3 rise reflects this upregulation of repair-driven mitosis, peaking when demand for new cells is greatest.

Marking notes. Part (a) — 1 mark for identifying the rise from baseline to a peak at day 3; 1 mark for identifying the decline after day 3; 1 mark for at least one quoted value from the figure. Part (b) — 1 mark for linking mitosis to repair / replacement of lost somatic cells; 1 mark for explaining that the rise reflects increased demand for new genetically identical cells at the wound edge.

Sample response. Each daughter cell will contain 24 chromosomes. Mitosis maintains chromosome number: before division, DNA replication doubles each chromosome to two sister chromatids, and during anaphase those chromatids are separated to opposite poles so that each daughter cell ends up with one chromatid (now counted as a chromosome) for every chromosome the parent cell had. The daughter cells therefore have the same chromosome number (24) as the parent somatic cell.

Marking notes. 1 mark for the correct answer of 24 chromosomes per daughter cell; 1 mark for explicit justification that mitosis maintains (does not halve) chromosome number; 1 mark for a correct mechanistic reference to DNA replication producing sister chromatids that are then separated during mitosis.

Sample response. The claim is well supported. In the lesson framing, mitosis is the cell division of somatic cells whose central function is to maintain stability — the same chromosome number and the same hereditary information — across daughter cells, not to generate variation. Mechanistically this is built into the process: DNA replication first produces two identical sister chromatids for every chromosome, so the cell entering prophase carries a complete copy ready to be shared. In metaphase the replicated chromosomes line up at the equator, and in anaphase the sister chromatids are separated equally to opposite poles. New nuclei re-form during telophase and cytokinesis divides the cytoplasm, producing two daughter cells each carrying one complete chromosome set identical to the parent's. The chromosome number is therefore maintained, not reduced. This stability is essential to organism-level continuity. In the human skin epidermis, basal-layer cells continually divide by mitosis to replace cells lost from the surface and to repair wounds; without mitosis maintaining chromosome number and hereditary information in those new cells, the replacement cells could not function as skin. The same is true in the gut lining and in bone marrow's production of new blood cells, and in asexual reproduction in some organisms where mitosis alone generates new individuals genetically equivalent to the parent. By contrast, mitosis does not routinely generate variation — that role belongs to meiosis, which reduces chromosome number for gamete formation and contributes to genetic variation. Therefore the claim is correct: mitosis is more important for stability and continuity within an organism than for creating variation; its very design (replication → even separation → cytokinesis) is geared to preserving, not changing, the hereditary information passed to daughter somatic cells.

Marking notes. 1 mark — explicit evaluative judgement that the claim is correct / well supported and explains why (stability vs variation). 1 mark — correct identification that DNA replication occurs before mitosis and produces sister chromatids. 1 mark — correct sequencing of mitotic events (prophase / metaphase / anaphase / telophase) including separation of sister chromatids in anaphase. 1 mark — explicit statement that daughter cells have the same chromosome number as the parent somatic cell. 1 mark — at least one named example of a tissue or organism where mitosis-driven stability is essential (skin, gut lining, bone marrow, wound healing, asexual reproduction in a named organism). 1 mark — explicit contrast with meiosis (chromosome reduction; gamete formation; site of routine variation), making clear that variation is not the role of mitosis. 1 mark — overall integration that links mechanism + example + contrast into a coherent argument in precise lesson terminology (continuity, genetic stability, somatic cells, hereditary information).