A cell in the root tip of a pea plant completes the cell cycle and produces two daughter cells. Explain the roles of interphase and mitosis in ensuring that each daughter cell is diploid and genetically identical to the original parent cell.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
During interphase the cell grows and the genome is duplicated. DNA replication in S‑phase produces two identical sister chromatids for each chromosome, so the genetic material is present in duplicate.
In mitosis the duplicated chromosomes are separated. In metaphase the chromosomes line up at the metaphase plate. In anaphase the sister chromatids are pulled apart by spindle fibres to opposite poles. Thus each pole receives one copy of every chromosome.
Cytokinesis then divides the cytoplasm, forming two nuclei. Each new nucleus contains one complete set of chromosomes, so the daughter cells are diploid and genetically identical to the parent cell.
In mitosis the duplicated chromosomes are separated. In metaphase the chromosomes line up at the metaphase plate. In anaphase the sister chromatids are pulled apart by spindle fibres to opposite poles. Thus each pole receives one copy of every chromosome.
Cytokinesis then divides the cytoplasm, forming two nuclei. Each new nucleus contains one complete set of chromosomes, so the daughter cells are diploid and genetically identical to the parent cell.
Examiner tips
- Mention DNA replication in S‑phase, the formation of sister chromatids, alignment in metaphase, separation in anaphase, and cytokinesis.
- Use the terms interphase, mitosis, metaphase, anaphase, cytokinesis, diploid, genetically identical.
- Show the flow: interphase → mitosis → cytokinesis.
- Include that each daughter receives one copy of every chromosome.
Common mistakes
- Confusing mitosis with meiosis or omitting the role of interphase.
- Failing to state that each daughter receives one copy of every chromosome.
- Using incorrect terminology such as ‘chromosome’ instead of ‘chromatid’ for the duplicated units.
Mark scheme (5 marks)
- During interphase, DNA replication occurs so that each chromosome is copied
- This produces two chromatids per chromosome, so all the genetic information is present in duplicate
- During metaphase, chromosomes align at the cell equator, and during anaphase, chromatids are pulled to opposite poles by spindle fibres
- Each new nucleus therefore receives one copy of every chromatid / chromosome, giving the same genetic information as the parent cell
- Cytokinesis then divides the cytoplasm to produce two diploid daughter cells, each with two copies of every chromosome
Key terms in this question
interphase · mitosis · diploid
Related
- All Pearson Edexcel A-Level Biology A (9BI0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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