A-Level · Biology · AQA · Mark scheme decoded

AQA A-Level Biology: The Cell Cycle and Mitosis — mark scheme explained

Machine-verifiedchecked against the AQA A-Level Biology specificationlast verified 3 July 2026

The short answer

In multicellular organisms, not all cells retain the ability to divide. However, those that do follow a specific sequence of events known as the cell cycle. This cycle is crucial for growth, development, and tissue repair. The cell cycle consists of two main phases: interphase and mitosis (M phase).

The question

Describe the stages of mitosis in a eukaryotic cell, including the key events that occur during each stage.

[Paraphrased for study — not reproduced from any exam paper.]

4 marks

Mark scheme, decoded

How the examiner actually awards the marks on this topic.

Gradora's own decode of the marking approach — not the exam board's published mark scheme.

How marks are awarded

For descriptive questions, marks are typically awarded for accurately identifying and describing key events and stages. For explanatory questions, marks are given for providing clear reasons and mechanisms. Comparisons should highlight both similarities and differences, while summaries should be concise and cover the main points.

What the command words demand

Describe: Provide a detailed account of the process, including key events and stages.
Explain: Give reasons for why something happens, including relevant mechanisms and principles.
Compare: Identify similarities and differences between two or more processes or concepts.
Summarize: Briefly outline the main points or steps in a process.

Model answer

A full-mark response to the question above, worked through step by step.

Timing: Allocate approximately 5-7 minutes per question to ensure you have enough time to carefully read the problem, provide detailed answers, and check your work.

Identify the four main stages of mitosis.0 marks
The four main stages are prophase, metaphase, anaphase, and telophase.
Describe the key events in prophase.1 mark
During prophase, chromosomes condense and become visible. The nuclear envelope breaks down, and spindle fibers form.
Describe the key events in metaphase.1 mark
In metaphase, chromosomes align at the equatorial plane of the cell, attached to spindle fibers via their centromeres.
Describe the key events in anaphase.1 mark
During anaphase, sister chromatids separate and are pulled to opposite poles of the cell by the spindle fibers.
Describe the key events in telophase.1 mark
In telophase, chromosomes decondense, nuclear envelopes re-form around the separated sets of chromosomes, and the cell prepares for cytokinesis.

Final answer: Prophase: Chromosomes condense, nuclear envelope breaks down, spindle fibers form. Metaphase: Chromosomes align at the equatorial plane, attached to spindle fibers via centromeres. Anaphase: Sister chromatids separate and are pulled to opposite poles by spindle fibers. Telophase: Chromosomes decondense, nuclear envelopes re-form, cell prepares for cytokinesis.

Work through every step correctly and you earn all 4 marks.

Another worked example

Explain the role of spindle fibers during mitosis.

3 marks

Identify when spindle fibers form and their attachment point.1 mark
Spindle fibers form during prophase and attach to the centromeres of chromosomes during metaphase.
Describe the function of spindle fibers in anaphase.1 mark
During anaphase, spindle fibers pull sister chromatids to opposite poles of the cell, ensuring equal distribution of genetic material.
Summarize the importance of spindle fibers in mitosis.1 mark
Spindle fibers are crucial for the proper separation of chromosomes during anaphase, ensuring that each daughter cell receives an identical set of genetic material.

Final answer: Spindle fibers form during prophase and attach to the centromeres of chromosomes during metaphase. During anaphase, they pull sister chromatids to opposite poles of the cell, ensuring equal distribution of genetic material.

Work through every step correctly and you earn all 3 marks.

Common mistakes

Misidentifying stages of mitosis.
Why it happens: Students may confuse the events that occur during different stages, leading to incorrect descriptions.
Fix: Practice identifying and describing the key events in each stage of mitosis. Use diagrams and labels to reinforce understanding.
Forgetting the role of spindle fibers.
Why it happens: The importance of spindle fibers can be overlooked, leading to incomplete explanations of anaphase.
Fix: Always include the role of spindle fibers in your descriptions of mitosis, especially during anaphase. Spindle fibers are crucial for separating sister chromatids.
Confusing cytokinesis in animal and plant cells.
Why it happens: Students may not fully understand the differences between how cytokinesis occurs in different types of cells.
Fix: Practice comparing and contrasting cytokinesis in animal and plant cells. Animal cells use a cleavage furrow, while plant cells form a cell plate.
Misunderstanding the process of binary fission in prokaryotes.
Why it happens: Students may confuse binary fission with mitosis or other forms of cell division.
Fix: Review the specific steps involved in binary fission, including DNA replication and cytoplasmic division. Use diagrams to help visualize the process.
Failing to explain how uncontrolled cell division leads to cancer.
Why it happens: Students may not fully grasp the relationship between regulatory mechanisms and cancer development.
Fix: Practice explaining the normal regulation of cell division and what happens when these mechanisms fail. Emphasize the consequences of uncontrolled cell division, such as tumour formation and metastasis.
Confusing the roles of different phases in interphase.
Why it happens: Students may mix up the events that occur during G1, S, and G2 phases, leading to incorrect descriptions.
Fix: Review the specific events that occur during each phase of interphase. Use a timeline or flowchart to help organize the information.

Where the marks go

The question types you’ll meet on this topic and the marks each one carries — so you know what to expect and where to focus.

Question type	What you’re asked to do	Marks
Describe Mitosis Stages	Describe the key events occurring during each of the four stages of mitosis.	4
Explain Spindle Function	Explain how spindle fibres attach to and separate chromosomes during mitosis.	3
Describe Biological Process	Describe the sequential stages of binary fission by which prokaryotic cells replicate and divide.	3
Explain Cancer Development	Describe how mutations cause uncontrolled cell division that leads to tumour formation and cancer.	4
Total across these question types		14

Question types and mark tariffs are Gradora’s guidance based on how this topic is typically examined — not the board’s official paper structure.