(5) Other examples of mitosis:

Plant cell reproduction and growth and growth of cancer cells

(A) Plant growth and development by mitosis cell division

In vegetative growth plants cells reproduce by mitosis in roots, stem and leaves.

With plants, most growth in height is due to cell elongation.

Most plant cell division by mitosis occurs in the tips of the roots and shoots in parts called meristems.

Most plants grow continuously producing new branches i.e. plants continue to differentiate producing new leaves, flowers or roots through most of their life.

For more details see hormone control of plant growth

 

(B) Cancer growth and factors affecting cell division by mitosis

You can quite easily estimate the number of cells produced by mitosis from the simple formula 2ⁿ, where n = the number of cell divisions by mitosis, so the number of cancer cells can rapidly increase with each phase of cell division.

Cells normally grow and divide by mitosis when the body needs new cells to replace old or damaged cells.

A random change in a gene can produce a mutation - though it takes an accumulation of several mutations to create a rogue cancer cell.

The rate at which cells divide by mitosis is controlled by the cell's genes - source of DNA instructions.

Therefore, if mutations in one or more of the genes that controls cell division occurs, a cell may start to divide in an uncontrolled manner - these are known as cancerous cells and the body does NOT need them!

This uncontrolled cell division producing potentially cancerous cells can result in a mass of abnormal cells to form a tumour.

If the tumour invades and kills surrounding tissue it is called a cancer.

The cancer can only affect the individual, so it is a non-communicable disease - cannot spread to someone else.

For more details on cancer see notes on non-communicable diseases - cancer

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Key points - Summary of ideas

Based on the syllabus-specifications for students taking the AQA, Edexcel and OCR GCSE level biology examinations (~US grades 9-10).

(A) Cell Division by Mitosis in Plant Cells – Reproduction and Growth of Leaves, Roots & Stems

Mitosis is the process by which a cell divides to produce two genetically identical daughter cells.

It is essential for growth, repair, and asexual reproduction in plants.

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(A) The Role of Mitosis in Plants

Plants rely on mitosis for three key functions:

1. Growth – Increasing the number of cells in tissues such as roots, stems, and leaves.

2. Repair and Maintenance – Replacing damaged cells in plant structures.

3. Asexual Reproduction – Producing genetically identical offspring through processes like vegetative propagation.

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The Cell Cycle

The cell cycle consists of Interphase, Mitosis, and Cytokinesis.

1. Interphase

   • The cell grows and carries out normal functions.

   • DNA replication occurs, ensuring each new cell receives an identical set of genetic material.

   • Organelles and proteins needed for cell division are produced.

2. Mitosis (Nuclear Division)

   • Divided into four stages:

     • Prophase – Chromosomes condense and become visible; nuclear membrane begins to break down.

     • Metaphase – Chromosomes align at the center of the cell (equator) and spindle fibers attach to centromeres.

     • Anaphase – Spindle fibers pull sister chromatids apart to opposite sides of the cell.

     • Telophase – Chromosomes decondense; two new nuclear membranes form around each set of chromosomes.

3. Cytokinesis (Cell Splitting)

   • The cytoplasm splits, forming two identical daughter cells.

   • In plant cells, a cell plate forms between the two nuclei, which later develops into a new cell wall.

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Mitosis and Plant Growth

Growth in Leaves

• Mitosis enables the expansion of leaves, increasing photosynthetic surface area.

• New cells differentiate into various leaf tissues, including epidermis, mesophyll, and vascular tissue.

Growth in Roots

• Root tips contain meristematic tissue, where rapid mitosis occurs.

• New cells elongate, pushing the root further into the soil, allowing efficient water and nutrient absorption.

Growth in Stems

• Stems grow via mitotic divisions in the apical meristem, leading to lengthening of the plant.

• Lateral meristems contribute to stem thickening (secondary growth), producing wood and bark in some species.

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Importance of Mitosis in Plants

• Ensures genetic stability by producing identical cells.

• Facilitates continuous growth throughout the plant's life.

• Enables asexual reproduction, vital for propagation and cloning in agriculture and horticulture.

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(B) Growth of Cancer Cells by Mitosis into a Tumor

Introduction to Cancer and Mitosis

• Mitosis is a type of cell division that produces two identical diploid daughter cells.

• Normally, cells divide by mitosis for growth, repair, and replacement of old or damaged cells.

• Cancer occurs when normal cells mutate and begin to divide uncontrollably, forming a tumor.

Formation of Tumors

1. Uncontrolled Cell Division:

   • Cancerous cells ignore signals that regulate the cell cycle.

   • They continue dividing even when new cells are not needed.

2. Tumor Development:

   • A mass of abnormal cells forms, known as a tumor.

   • Tumors can be benign or malignant.

Types of Tumors

• Benign Tumors:

  • Grow slowly.

  • Usually contained within a membrane, making them easier to remove.

  • Do not invade other tissues.

• Malignant Tumors:

  • Grow rapidly.

  • Invade neighboring tissues and spread via the bloodstream.

  • Can form secondary tumors in other parts of the body (metastasis).

Metastasis – Spread of Cancer

• Malignant tumors release cancer cells into the bloodstream.

• These cells travel to other organs, forming secondary tumors.

• This process is called metastasis.

Causes of Cancer

• Genetic mutations can lead to uncontrolled cell division.

• Carcinogens (cancer-causing substances) damage DNA, increasing the risk of mutations.

• Lifestyle factors such as smoking, UV radiation, and diet can contribute to cancer development.

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Summary of learning objectives and key words or phrases

Be able to describe the growth of plant cells by mitosis.

Appreciate plant cell reproduction and growth of leaves and roots stem by mitosis.

Be able to describe the growth of cancer cells by mitosis into a tumor - formation of cancerous tissue.

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