Explain why cells in the meristem of a plant root tip have a higher proportion of cells in mitosis compared with cells taken from a mature leaf of the same plant.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Meristem cells are undifferentiated, rapidly dividing cells found at the growing tips of plant roots. Cells in a mature leaf are differentiated and perform specialised functions such as photosynthesis.
Model answer (4 marks)
Meristem cells are undifferentiated and retain the ability to divide by mitosis.
Mature leaf cells are differentiated and have permanently lost the ability to divide by mitosis.
Differentiation involves permanent changes to gene expression, so genes required for cell‑cycle control are no longer expressed in mature leaf cells.
The root‑tip meristem produces new cells needed for growth/elongation of the root, so a high rate of mitosis is required in that region.
Mature leaf cells are differentiated and have permanently lost the ability to divide by mitosis.
Differentiation involves permanent changes to gene expression, so genes required for cell‑cycle control are no longer expressed in mature leaf cells.
The root‑tip meristem produces new cells needed for growth/elongation of the root, so a high rate of mitosis is required in that region.
Examiner tips
- Use the word ‘undifferentiated’ and ‘differentiated’ to show understanding of cell types.
- Explain the link between differentiation and loss of mitotic ability.
- Mention the functional need for growth in the root tip.
- Keep each point short and to the point to hit all 4 marks.
Common mistakes
- Confusing ‘mitosis’ with ‘meiosis’ or not recognising that mature cells are post‑mitotic.
- Failing to mention the permanent change in gene expression during differentiation.
- Giving extra detail about cell size or shape that is not required for the 4‑mark answer.
Mark scheme (4 marks)
- Meristem cells are undifferentiated and retain the ability to divide by mitosis
- Mature leaf cells are differentiated and have permanently lost the ability to divide by mitosis
- Differentiation involves permanent changes to gene expression, so genes required for cell cycle control are no longer expressed in mature leaf cells
- The root tip meristem produces new cells needed for growth / elongation of the root, so a high rate of mitosis is required in that region
Key terms in this question
Related
- All OCR A-Level Biology A (H420) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More Cell division, diversity and organisation questions
- Explain why a cell in the metaphase of mitosis has twice the DNA content of a ce…
- Explain why cells in the meristem of a plant root tip divide by mitosis rather t…
- Explain why cells in the same organism can have very different structures even t…
- Explain why cells in the meristem of a plant root tip are able to divide repeate…