(d) sections of plant tissue showing the cell cycle and stages of mitosis

The idea

This specification point asks you to recognise the cell cycle and the stages of mitosis in prepared sections of plant tissue, typically a root tip. In a root tip squash or longitudinal section, cells are not synchronised, so a single field of view shows cells at different points in the cycle. You identify each stage from chromosome behaviour and nuclear appearance: in interphase the nucleus is intact with visible nucleolus and no distinct chromosomes; in prophase chromosomes condense and become visible; in metaphase they align at the equator (metaphase plate); in anaphase chromatids separate and move to opposite poles; in telophase two nuclei reform and the cell plate begins to form. You also relate the proportion of cells in each stage to the relative duration of that stage, since more cells are seen where the stage lasts longer.

What earns the marks

• Interphase cells show an intact nucleus with a visible nucleolus and no individually distinguishable chromosomes.
• Prophase cells show chromosomes condensing and becoming visible within the nucleus.
• Metaphase cells show chromosomes (or chromatids) aligned along the equator or metaphase plate of the cell.
• Anaphase cells show separated chromatids moving towards opposite poles of the cell.
• Telophase cells show two reforming nuclei and the beginnings of a cell plate between daughter cells.
• The relative number of cells observed in each stage reflects the relative duration of that stage in the cell cycle.

Common mistakes and how to put them right

• Confusing metaphase with anaphase.

  Put it right: In metaphase chromosomes line up at the equator, whereas in anaphase they are already separated and moving to the poles.

• Assuming all cells in a root tip section are at the same stage.

  Put it right: Cells divide asynchronously, so a field of view shows a mixture of stages.

• Treating interphase as a resting or inactive phase.

  Put it right: Interphase is an active period of growth and DNA replication, even though chromosomes are not individually visible.

Exam tips

• Learn a clear visual cue for each stage (nucleolus visible, chromosomes at equator, chromatids at poles, two nuclei plus cell plate) so you can match a diagram or description quickly.
• Remember that the frequency of a stage in a section relates to how long that stage lasts, not to how important it is.
• Read the whole option before choosing; distractors often swap the chromosome positions of two adjacent stages.