# Explain how the spindle apparatus ensures that each daughter cell receives a complete set of chromosomes during mitosis.

> IB DP Biology Higher Level (2023 syllabus) — D2.1 Cell and nuclear division · Explain · 4 marks

## Mark scheme (4 marks)

1. Spindle fibres (microtubules) attach to chromosomes at the centromere via the kinetochore.
2. Sister chromatids of each chromosome are attached to spindle fibres from opposite poles (bi-orientation / amphitelic attachment), ensuring tension is generated.
3. At anaphase, cohesins holding sister chromatids together are cleaved, allowing the spindle fibres to pull one chromatid (now a chromosome) to each pole.
4. Because one chromatid from every chromosome is delivered to each pole, both daughter cells receive a full, identical set of chromosomes (same number as the parent cell).

## Key terms

- [spindle apparatus](https://www.gradenine.co.uk/glossary/spindle-apparatus)

## Related

- [Revision notes for IB DP Biology Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-spindle-apparatus-ensures-e64f43e4) · Published by Druglandscape Ltd.