Explain why cells in the meristem of a plant root tip are able to divide repeatedly, whilst cells in the surrounding root cap are not.

OCR A-Level Biology A (H420) — 2.6 Cell division, diversity and organisation · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

The root tip of a plant contains two distinct regions: the meristem, a zone of actively dividing undifferentiated cells, and the root cap, a zone of differentiated cells that protect the tip as it pushes through soil. Both regions contain cells that were originally produced from the same parent cells and therefore contain identical DNA.

Model answer (4 marks)

Meristem cells are undifferentiated stem cells, so they retain the ability to undergo mitosis. In contrast, root‑cap cells are differentiated; only a limited set of genes are expressed. Although both cell types contain the same full genome, the genes required for cell division are not expressed in the root‑cap cells. Because differentiation of the root‑cap cells is permanent under normal conditions, they cannot revert to a dividing state.

Examiner tips

Use the terms ‘undifferentiated’ and ‘differentiated’ clearly; link differentiation to loss of mitotic ability.
Show that the genome is the same but gene expression differs – this is key to the answer.
Mention that the loss of division is irreversible in normal conditions.
Keep the answer concise – 4 marks only.

Common mistakes

Confusing ‘stem cells’ with ‘differentiated cells’; not recognising that both have the same DNA.
Failing to state that the loss of division is due to gene expression changes, not DNA loss.
Over‑expanding the answer with irrelevant details such as cell size or location.

Mark scheme (4 marks)

Meristem cells remain undifferentiated / are stem cells, so retain the ability to divide by mitosis
Root cap cells are differentiated, meaning only specific genes are expressed
Both cell types contain the same genes / full genome, but root cap cells do not express the genes required for cell division
Differentiation of root cap cells is permanent / irreversible in plants under normal conditions, so they cannot revert to a dividing state

Key terms in this question

meristem · root cap

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