Cell Division » Mitosis in Growth and Repair

What you'll learn this session

Study time: 30 minutes

The process of mitosis and its stages
The role of mitosis in growth and repair of organisms
How cells divide to produce identical daughter cells
The importance of DNA replication before cell division
How mitosis differs from other types of cell division
Examples of mitosis in human body systems

Introduction to Cell Division and Mitosis

Cell division is one of the most amazing processes in living organisms. Imagine cutting a cake and getting two identical pieces - that's a bit like what happens during mitosis! Your body is constantly making new cells through mitosis to help you grow and repair damaged tissues.

Key Definitions:

Cell division: The process by which a parent cell divides into two or more daughter cells.
Mitosis: A type of cell division that results in two identical daughter cells, each with the same number of chromosomes as the parent cell.
Chromosomes: Thread-like structures made of DNA that carry genetic information.
DNA: The molecule that contains the genetic instructions for development and functioning of all living organisms.

📈 Why Cells Divide

Cells divide for several important reasons:

Growth: As organisms grow, they need more cells.
Repair: To replace damaged or dead cells.
Reproduction: Single-celled organisms reproduce by dividing.

🌱 Cell Cycle

The cell cycle is the series of events that takes place in a cell leading to its division. It includes:

Interphase: Cell grows and copies its DNA.
Mitosis: The nucleus divides.
Cytokinesis: The cytoplasm divides, creating two cells.

The Stages of Mitosis

Mitosis is like a carefully choreographed dance that ensures each new cell gets exactly the right genetic information. It happens in four main stages, plus a preparation stage called interphase.

Interphase: Getting Ready to Divide

Before mitosis begins, the cell enters interphase. This isn't technically part of mitosis, but it's crucial preparation. During interphase:

The cell grows larger
It makes a copy of all its DNA (this is called DNA replication)
Each chromosome now consists of two identical copies (called chromatids) joined at a point called the centromere
The cell makes more organelles and proteins needed for division

Think of interphase as packing your bag the night before a trip - everything needs to be ready before the journey begins!

🟢 Prophase

The first stage of mitosis:

Chromosomes condense and become visible
Nuclear membrane starts to break down
Spindle fibres begin to form

🟡 Metaphase

The second stage of mitosis:

Chromosomes line up along the middle (equator) of the cell
Spindle fibres attach to the centromeres
This precise alignment ensures equal division of genetic material

🟠 Anaphase

The third stage of mitosis:

Chromatids separate and are pulled to opposite poles of the cell
The cell begins to elongate
Each pole now has a complete set of chromosomes

🔵 Telophase

The final stage of mitosis:

Nuclear membranes reform around each set of chromosomes
Chromosomes begin to uncoil
Spindle fibres disappear
Cytokinesis usually begins during this stage

✂ Cytokinesis

The division of the cytoplasm:

In animal cells, a "pinching" process divides the cell in two
In plant cells, a cell plate forms between the two new nuclei
Results in two separate daughter cells
Each daughter cell is genetically identical to the parent cell

Mitosis in Growth and Repair

Mitosis is essential for multicellular organisms to grow from a single cell into a complex organism with billions or trillions of cells. It's also vital for repairing damaged tissues throughout life.

🚀 Mitosis in Growth

From the moment you were a single fertilised egg cell, mitosis has been crucial for your development:

Enables a single-celled zygote to develop into an embryo
Allows children to grow taller and develop new tissues
Creates new cells for expanding organs and tissues
Continues throughout childhood and adolescence

🩹 Mitosis in Repair

Throughout your life, your body uses mitosis to repair and replace damaged cells:

Healing cuts and wounds in the skin
Replacing cells in the lining of the gut every few days
Repairing damaged muscle tissue
Replacing red blood cells (which live for about 120 days)

Case Study Focus: Skin Healing

When you cut your skin, a complex healing process begins that relies heavily on mitosis:

Inflammation: Blood clotting and immune cells arrive at the wound.
Proliferation: Skin cells at the edges of the wound undergo rapid mitosis to create new cells.
Migration: These new cells move across the wound to close the gap.
Maturation: The new tissue strengthens over time.

Without mitosis, even a small cut could be dangerous because your body wouldn't be able to replace the damaged cells!

Amazing Examples of Mitosis in Your Body

Cells That Divide Rapidly

Some cells in your body divide much more frequently than others:

Skin cells: Your skin completely replaces itself every 27-30 days through mitosis.
Intestinal lining cells: These cells are replaced every 2-3 days, making the lining of your gut one of the most actively dividing tissues in your body.
Bone marrow cells: These produce about 2 million red blood cells every second through mitosis!

⚠ When Mitosis Goes Wrong

Sometimes the process of mitosis can malfunction:

If cells divide too slowly, wounds may not heal properly
If cells divide too quickly and uncontrollably, cancer can develop
Errors during DNA replication can lead to mutations
Problems during chromosome separation can result in cells with the wrong number of chromosomes

🔬 Observing Mitosis

Scientists can observe mitosis under a microscope:

Plant root tips are often used as they contain many dividing cells
Special stains can make chromosomes more visible
Time-lapse photography can show the entire process
The onion root tip is a classic example used in school labs

Mitosis vs. Other Types of Cell Division

Mitosis isn't the only way cells divide. Another important type of cell division is meiosis, which is used to produce gametes (egg and sperm cells).

📊 Mitosis

Creates two identical daughter cells
Daughter cells have the same number of chromosomes as the parent cell (diploid)
Used for growth and repair
Occurs in somatic (body) cells
Involves one division

🎨 Meiosis

Creates four genetically different daughter cells
Daughter cells have half the number of chromosomes as the parent cell (haploid)
Used for sexual reproduction
Occurs in reproductive cells
Involves two divisions

Fun Fact: Mitosis in Numbers

Your body contains about 37.2 trillion cells and around 50-70 billion cells die and are replaced each day through mitosis. That's about 1-3 million cells dying and being replaced every second! The cells that line your stomach are replaced every 2-9 days, while some cells in your brain may never be replaced during your entire lifetime.

Summary: Why Mitosis Matters

Mitosis is a remarkable process that allows multicellular organisms like humans to grow from a single cell into complex beings with trillions of cells. It ensures that each new cell contains exactly the same genetic information as the original cell. Without mitosis, you wouldn't be able to grow and your body couldn't repair itself when damaged.

The next time you notice a healing cut or realise you've grown taller, remember that mitosis is the cellular process making it all possible!

🧠 Test Your Knowledge!