1. The Cell Cycle & Mitosis

In brief:All cells come from pre-existing cells. The cell cycle describes the stages a cell goes through from formation to division.

Cell continuity means all cells come from pre-existing cells. Every cell in your body traces back to the original fertilised egg (zygote).

The Cell Cycle

The cell cycle has these stages:

Interphase - the cell grows, carries out its normal functions, replicates its DNA, and copies organelles. This is the longest phase.
Mitosis - division of the nucleus into two identical nuclei
Cytokinesis - division of the cytoplasm to form two daughter cells

Mitosis - PMAT

Phase	What Happens
Prophase	Chromatin condenses into visible chromosomes. Nuclear membrane breaks down.
Metaphase	Chromosomes line up along the equator (middle) of the cell.
Anaphase	Sister chromatids are pulled apart to opposite poles of the cell.
Telophase	Nuclear membranes reform around each set of chromosomes. Chromosomes uncoil.

Cytokinesis then splits the cell into two genetically identical daughter cells.

Role of Mitosis

Growth of multicellular organisms
Repair and replacement of damaged/dead cells
Asexual reproduction in some organisms

Meiosis — Overview of meiosis producing four haploid cells
Wikimedia Commons (CC)

Semi-conservative DNA replication
Wikimedia Commons (CC)

Key Points

1Cell continuity: all cells come from pre-existing cells
2Interphase: cell grows, DNA replicates, organelles copy - longest phase
3Mitosis has 4 stages: Prophase, Metaphase, Anaphase, Telophase (PMAT)
4Mitosis produces two genetically identical daughter cells
5~50 billion new cells are produced in your body every day

Learning Outcomes

Outline the cell cycle
Explain the role of DNA replication and mitosis in the cell cycle

2. Meiosis, Binary Fission & Cancer

In brief:Meiosis produces sex cells with half the chromosome number. Uncontrolled cell division leads to cancer.

Meiosis

Meiosis is the type of cell division that produces gametes (sex cells: sperm and egg). It involves two divisions, resulting in four non-identical daughter cells, each with half the chromosome number (haploid).

Feature	Mitosis	Meiosis
Daughter cells	2 identical	4 non-identical
Chromosome number	Same (diploid)	Half (haploid)
Purpose	Growth, repair	Gamete production
Divisions	1	2
Genetic variation	No	Yes (crossing over)

Binary Fission

How bacteria reproduce (asexual). Steps: DNA replicates → cell elongates → cross wall forms → two identical cells. Can take less than 20 minutes.

Cancer

Cancer occurs when cells divide uncontrollably due to mutations in genes that regulate the cell cycle. A mass of abnormal cells forms a tumour.

Benign: non-spreading, localised
Malignant: invades surrounding tissue and can spread (metastasis)

Causes of cancer mutations: UV radiation, cigarette smoke, certain viruses (e.g. HPV), chemical carcinogens.

Key Points

1Meiosis produces 4 haploid, non-identical gametes via 2 divisions
2Binary fission is asexual reproduction in bacteria - produces identical cells
3Cancer results from uncontrolled cell division due to mutations
4Benign tumours are localised; malignant tumours spread (metastasis)
5Mutagens include UV light, cigarette smoke, and certain viruses

Learning Outcomes

Compare the roles of mitosis and meiosis in transmitting genetic information in unicellular and multicellular organisms
Outline how uncontrolled cell proliferation can lead to development of cancers
Examine the role of infectious agents, environmental factors and/or genetic susceptibility in the development of different cancers in an organism; evaluate factors that impact the development of cancers