OxfordAQA International A Level Biology
OxfordAQA International A Level Biology 3.2.10 Cells Divide by Binary Fission and Mitosis Exam Questions
Free OxfordAQA International A Level Biology revision for 3.2.10 Cells Divide by Binary Fission and Mitosis: what you need to know, common mistakes and exam-style questions with answers. Covers the cell cycle, the stages of mitosis, the mitotic index, binary fission and conjugation in bacteria.
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About OxfordAQA International A Level Biology 3.2.10 Cells Divide by Binary Fission and Mitosis
This Unit 2 topic covers how cells divide. You need to describe the cell cycle, including the G1, S and G2 phases of interphase, and explain the behaviour of chromosomes during prophase, metaphase, anaphase and telophase. You should be able to recognise each stage in drawings or photographs. You also need to describe binary fission in prokaryotes and conjugation as a form of horizontal gene transfer. Required practical 4, preparing a stained root tip squash and calculating a mitotic index, belongs here. It links to meiosis, cancer and gene mutations, and to the prokaryotic cell structure covered in Unit 1.
What you need to know
- The cell cycle Interphase includes G1 (cell growth and production of proteins and organelles), S (DNA replication) and G2 (rapid growth and protein synthesis). It is followed by mitosis and cytokinesis.
- Prophase and metaphase In prophase chromosomes condense and become visible as two sister chromatids joined at a centromere, and the nuclear envelope breaks down. In metaphase chromosomes line up on the equator, attached to spindle fibres by their centromeres.
- Anaphase and telophase In anaphase centromeres divide and spindle fibres pull the chromatids to opposite poles. In telophase nuclear envelopes reform, then the cytoplasm divides to form two genetically identical cells.
- Required practical 4 Root tips are treated with hydrochloric acid, stained, squashed and viewed under a microscope. Mitotic index = number of cells in mitosis / total number of cells observed.
- Binary fission In prokaryotes the circular DNA and plasmids replicate, then the cytoplasm divides. Each daughter cell gets one copy of the circular DNA but may get a variable number of plasmids.
- Conjugation Conjugation is horizontal gene transfer: a copy of a plasmid is passed from one bacterium to another, which can spread genes such as antibiotic resistance.
Common mistakes in 3.2.10 Cells Divide by Binary Fission and Mitosis
- Saying DNA replicates during prophase. DNA replicates in the S phase of interphase.
- Saying chromosomes separate in anaphase of mitosis. Sister chromatids separate.
- Saying prokaryotes divide by mitosis. They divide by binary fission.
- Forgetting why root tips are used. Root tips contain meristem cells that are actively dividing.
Try three 3.2.10 Cells Divide by Binary Fission and Mitosis exam-style questions
1. In a root tip squash, 24 cells out of 320 were in mitosis. Calculate the mitotic index. (1 mark)
Show the mark scheme answer
24 / 320 = 0.075 (or 7.5%).
2. Describe what happens to chromosomes during anaphase. (2 marks)
Show the mark scheme answer
Centromeres divide; spindle fibres shorten and pull sister chromatids to opposite poles.
3. Explain why hydrochloric acid is used when preparing a root tip squash. (2 marks)
Show the mark scheme answer
Breaks down the material holding cells together; so cells can be separated and spread into a single layer for viewing.
3.2.10 Cells Divide by Binary Fission and Mitosis FAQs
What does OxfordAQA International A Level Biology 3.2.10 Cells Divide by Binary Fission and Mitosis cover?
It covers the cell cycle, the stages of mitosis, the mitotic index, binary fission and conjugation in bacteria.
Which unit is 3.2.10 Cells Divide by Binary Fission and Mitosis examined in?
It is part of Unit 2, Biological systems and disease, which is examined at International AS. The Unit 5 synoptic paper at A2 can also draw on this content.
How do I calculate the mitotic index?
Count the cells in any stage of mitosis, then divide by the total number of cells in the field of view. Count enough cells to make the result representative.
