The big idea: To name the phase of a cell in a diagram or micrograph, look at where the chromosomes are and whether there is a nucleus.
The points to remember
- Interphase: a round nucleus; no separate chromosomes visible.
- Prophase: thick, visible chromosomes; the nucleus is breaking down.
- Metaphase: chromosomes in a line across the middle.
- Anaphase: two groups moving apart, often V-shaped.
- Telophase: two groups at the ends; new nuclei forming.
Remember it as: Look where the chromosomes are.
Real example: a root-tip squash. Garlic or onion bulbs grown on water for a few days make fast-growing roots. Their tips, stained and squashed on a slide, show cells in every phase of mitosis under a light microscope.
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Making and reading a root-tip squash: Root tips are used because their cells divide often. The tip is softened, stained so the chromosomes show up dark, and squashed flat so the cells form a single layer.
| You see | Phase |
|---|---|
| Nucleus, no separate chromosomes | Interphase |
| Thick chromosomes, nuclear membrane fading | Prophase |
| Chromosomes lined up across the middle | Metaphase |
| Two groups pulled apart towards the ends | Anaphase |
| Two groups at the ends, new nuclei, cell dividing | Telophase |
Ordering cells: Asked to put labelled cells in order? Start with interphase if it is there, then prophase, metaphase, anaphase, telophase. Older (2016) SL papers also ask about the proportion of cells that are dividing: a high proportion means the tissue is growing fast.
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How it is asked: Almost always with a micrograph or diagram: identify the phase of a labelled cell, put labelled cells in order, name a phase that is missing, or predict what happens next.
In a micrograph of an onion root tip, cell X has two groups of chromosomes moving towards opposite ends of the cell. Identify the phase of mitosis in cell X.
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