Explain why cells in the meristem of a plant root tip divide by mitosis rather than meiosis, and describe one feature of the cell cycle that ensures each daughter cell receives the correct number of chromosomes.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Plant roots grow by producing new cells at the root tip. A region called the meristem contains rapidly dividing cells that are responsible for this growth. These cells are diploid and must remain genetically identical to the parent cell.
Model answer (4 marks)
Mitosis is used because the cells must remain genetically identical to the parent cell and to provide growth and repair, not sexual reproduction. Meiosis would produce haploid cells, so the daughter cells would no longer be diploid and would have the wrong chromosome number for somatic cells.
During the cell cycle, DNA is replicated in the S phase of interphase. This ensures that each chromosome is copied so that there is sufficient genetic material to be distributed equally. In mitosis, spindle fibres attach to the centromeres of the sister chromatids and pull them to opposite poles, guaranteeing that each daughter cell receives one copy of each chromosome.
During the cell cycle, DNA is replicated in the S phase of interphase. This ensures that each chromosome is copied so that there is sufficient genetic material to be distributed equally. In mitosis, spindle fibres attach to the centromeres of the sister chromatids and pull them to opposite poles, guaranteeing that each daughter cell receives one copy of each chromosome.
Examiner tips
- State that mitosis keeps cells diploid and identical – this earns the first point.
- Explain that meiosis would give haploid cells – this earns the second point.
- Mention S phase DNA replication – third point.
- Describe spindle fibre attachment to centromeres – fourth point.
Common mistakes
- Confusing mitosis with meiosis as the process used for growth.
- Forgetting to mention that meiosis produces haploid cells.
- Lacking detail about the spindle fibres and centromeres.
Mark scheme (4 marks)
- Mitosis is used because the daughter cells must be genetically identical to the parent cell / for growth and repair, not sexual reproduction
- Meiosis would produce haploid cells, so the daughter cells would no longer be diploid / would have the wrong chromosome number for somatic cells
- DNA replication (during S phase / interphase) ensures each chromosome is copied so there is sufficient genetic material to be distributed equally
- During mitosis, spindle fibres attach to centromeres and pull sister chromatids to opposite poles, ensuring each daughter cell receives one copy of each chromosome
Key terms in this question
meristem · cell cycle · daughter cell
Related
- All OCR A-Level Biology A (H420) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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