A student observes cells from a root tip under a microscope. Most cells are in interphase, but some are in different stages of mitosis. Explain why uncontrolled mitosis in these cells could lead to cancer, and describe what happens during metaphase and anaphase to produce two genetically identical daughter cells.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Root tip meristem tissue contains actively dividing cells. The cell cycle involves interphase followed by mitosis and cytokinesis.
Model answer (5 marks)
Uncontrolled mitosis allows cells to divide without the normal checks, so the number of cells increases abnormally, a hallmark of cancer.
During metaphase the duplicated chromosomes line up at the cell equator (the metaphase plate).
During anaphase the sister chromatids are pulled apart by spindle fibres to opposite poles of the cell.
Each pole therefore receives a complete set of chromosomes, so the two daughter cells contain the same genetic information as the parent.
Cytokinesis then divides the cytoplasm, producing two genetically identical daughter cells.
During metaphase the duplicated chromosomes line up at the cell equator (the metaphase plate).
During anaphase the sister chromatids are pulled apart by spindle fibres to opposite poles of the cell.
Each pole therefore receives a complete set of chromosomes, so the two daughter cells contain the same genetic information as the parent.
Cytokinesis then divides the cytoplasm, producing two genetically identical daughter cells.
Examiner tips
- Use the term ‘uncontrolled mitosis’ to link to cancer; mention loss of regulatory control. Explain the key events of metaphase and anaphase with correct terminology. Show that each daughter receives a complete chromosome set. Remember to state that cytokinesis follows to give two cells.
Common mistakes
- Confusing mitosis with meiosis; using ‘meiosis’ instead of ‘mitosis’. Failing to mention that each daughter cell has the same chromosome number as the parent. Omitting the role of spindle fibres in anaphase.
Mark scheme (5 marks)
- Cancer is caused by uncontrolled cell growth and division
- During metaphase, chromosomes align at the cell equator
- During anaphase, chromatids are pulled to opposite poles of the cell by spindle fibres
- Each set of chromatids at the poles contains an identical copy of the genetic information / same number of chromosomes as the parent cell
- Cytokinesis divides the cytoplasm to produce two genetically identical daughter cells
Key terms in this question
cancer · metaphase · anaphase · mitosis
Related
- All Edexcel A-Level Biology A: Salters-Nuffield (9BN0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More Cell cycle and mitosis questions
- Explain what happens during the cell cycle, including the stages of mitosis, to …
- A tumour forms when cells in the body divide in an uncontrolled way. Explain how…
- During the cell cycle, a cell undergoes interphase before entering mitosis. Desc…
- A student cuts a small piece of skin after an accident. New skin cells are produ…