interpret photomicrographs, diagrams and microscope slides of cells in different stages of the mitotic cell cycle and identify the main stages of mitosis
Chromosome Behaviour in Mitosis – Cambridge A‑Level Biology 9700
Chromosome Behaviour in Mitosis
Learning Objective
Interpret photomicrographs, diagrams and microscope slides of cells in different stages of the mitotic cell cycle and accurately identify the main stages of mitosis.
Key Concepts
Mitotic phases: Prophase, Prometaphase, Metaphase, Anaphase, Telophase, and Cytokinesis.
Structural changes in chromosomes (condensation, alignment, segregation).
Role of the spindle apparatus and kinetochores.
Typical visual cues in photomicrographs that distinguish each stage.
Typical Features of Each Mitotic Stage
Stage
Chromosome Appearance
Spindle/Cellular Features
Key \cdot isual Cues in Photomicrographs
Prophase
Chromatin condenses into short, thickened chromosomes; each consists of two sister chromatids joined at the centromere.
Centrioles migrate to opposite poles; mitotic spindle begins to form.
Visible “fuzzy” chromosomes, nucleolus fading, nuclear envelope still intact.
Prometaphase
Chromosomes continue condensing; kinetochores become visible.
Nuclear envelope breaks down; spindle fibers attach to kinetochores.
Chromosomes appear scattered; spindle fibers can be seen extending toward them.
Metaphase
Chromosomes line up at the metaphase plate; sister chromatids are aligned side‑by‑side.
Spindle fibers are fully attached; tension is evident.
Clear, straight line of chromosomes across the centre of the cell; minimal movement.
Anaphase
Sister chromatids separate and are pulled toward opposite poles.
Spindle fibers shorten (anaphase A) and poles move apart (anaphase B).
Two distinct groups of chromosomes moving away from the centre; “V‑shaped” spindle.
Telophase
Chromatids reach opposite poles and begin de‑condensing into chromatin.
New nuclear envelopes form around each set; spindle disassembles.
Two nuclei visible; chromosomes appear less distinct, more diffuse.
Cytokinesis
Chromosomes are fully de‑condensed; cell division completes.
Cleavage furrow (animal cells) or cell plate (plant cells) forms.
Two separate daughter cells with distinct membranes; no mitotic spindle.
Interpreting Photomicrographs
Assess the nuclear envelope: intact = early stages; fragmented = prometaphase.
Locate the spindle fibers: visible as thin lines radiating from poles; their orientation helps identify anaphase vs. telophase.
Identify the metaphase plate: a straight line of chromosomes across the centre indicates metaphase.
Look for the cleavage furrow or cell plate: presence signals cytokinesis.
Common Mistakes and How to Avoid Them
Confusing prophase with prometaphase: remember that the nuclear envelope is still intact in prophase.
Missing the metaphase plate: ensure the cell is not tilted; a true metaphase plate appears as a single, sharp line.
Identifying anaphase too early: sister chromatids must be clearly separated; partial separation is still prometaphase.
Overlooking cytokinesis in plant cells: look for a developing cell plate rather than a furrow.
Suggested Diagrams and Photomicrographs
Suggested diagram: A labelled illustration of the spindle apparatus showing centrioles, microtubules, kinetochores and the metaphase plate.
Suggested photomicrograph: A high‑resolution image of a cell in metaphase with chromosomes aligned at the metaphase plate, suitable for student practice.
Understanding the visual characteristics of each mitotic stage enables accurate interpretation of photomicrographs and microscope slides. By systematically examining the nuclear envelope, chromosome morphology, spindle configuration, and cytokinetic structures, students can confidently identify prophase, prometaphase, metaphase, anaphase, telophase, and cytokinesis.