Safety and evidence boundary
Use prepared images, paper models, supplied datasets, or teacher-approved classroom microscopy. Do not culture unknown cells or microbes, collect human tissue, handle stains or preservatives without qualified supervision, or use personal medical records. This course does not diagnose growth disorders or disease.
Explicit science instruction
Mitosis is nuclear division that distributes replicated chromosomes so daughter nuclei receive corresponding chromosome sets. In prophase, chromosomes condense and the mitotic spindle begins organizing. By metaphase, replicated chromosomes align so sister kinetochores attach to opposite spindle poles. During anaphase, sister chromatids separate; after separation, each chromatid is considered an individual chromosome. During telophase, chromosome sets reach opposite ends and nuclei reorganize.
The named stages are useful models, but mitosis is continuous. Real cells do not pause to become textbook diagrams. Structures change progressively, and images captured between stages can be ambiguous.
Vocabulary: prophase; metaphase; anaphase; telophase; spindle; kinetochore; metaphase plate; chromosome segregation.
Worked example with reasoning
Suppose a replicated chromosome has two sister chromatids. At metaphase it counts as one replicated chromosome. When the sisters separate at anaphase, the cell temporarily contains two independently moving chromosomes derived from that replicated chromosome. Each daughter nucleus ultimately receives one.
Guided question
What observable chromosome behaviors are more reliable for classifying a mitotic image than simply matching its overall shape to a memorized stage picture?
Independent work
- Create a sequence diagram showing spindle attachment, alignment, separation, and nuclear re-formation.
- Write one observable criterion for each major stage.
- Explain why a cell between stages may be difficult to classify.
- For a 4-chromosome cell, model what each daughter nucleus receives.
Misconception check
Mitosis does not “make two identical cells” by itself. Cytokinesis, subsequent gene expression, mutation, unequal cytoplasmic contents, and environmental conditions can produce differences even when daughter nuclei receive corresponding chromosome sets.
Formative understanding check
Why does chromosome number appear to increase inside one cell at anaphase?
Show the worked response
Once sister chromatids separate, each is counted as an individual chromosome. The temporary whole-cell count rises before cytokinesis divides the cell into two daughter cells.
Open-book formative practice only; not an official mastery attempt or grade.
Mentor evidence conference
Ask Archaemenes to test your chromosome-counting logic, cell-cycle model, evidence classification, and stated limitations. The mentor may challenge reasoning but does not provide protected assessment answers.
Open Archaemenes for this lessonTeacher guidance
Foundation: sort prepared stage cards using one observable feature at a time. Core: justify stage classification from chromosome and spindle behavior. Extended: analyze transition images and explain where stage labels become model-dependent.
Preserve learning evidence
Keep the model, calculation or image analysis, correction note, and explanation in the matching Week 15 evidence field.
Return to tuesday Evidence Workspace