IB MYP 4-5 Biology-Mitosis- Study Notes - New Syllabus
IB MYP 4-5 Biology-Mitosis- Study Notes – New syllabus
IB MYP 4-5 Biology-Mitosis- Study Notes – IB MYP 4-5 Biology – per latest IB MYP Biology Syllabus.
Key Concepts:
- Stages of mitosis (prophase to telophase)
- Importance for growth and repair
- Cancer as uncontrolled cell division
Stages of Mitosis – How One Cell Becomes Two Identical Cells
What is Mitosis?
Mitosis is a type of cell division that produces two identical daughter cells, each with the same number of chromosomes as the parent cell.
- Growth
- Repair
- Replacement of cells
Note: Occurs in body cells (somatic cells), not in gametes.
Mitosis – The Division of the Nucleus
Mitosis has four key stages:
1. Prophase – Preparation Begins
- Chromosomes condense (become thick and visible)
- Each chromosome is made of 2 sister chromatids joined at the centromere
- The nuclear membrane breaks down
- Spindle fibers begin to form from the centrioles (in animal cells)
Tip: “Prophase = Prep stage”
2. Metaphase – Middle Line-Up
- Chromosomes are pulled to the center of the cell
- They line up along the middle (equator) of the cell
- Spindle fibers attach to the centromere of each chromosome
Tip: “Metaphase = Middle”
3. Anaphase – Apart and Away
- The centromeres split
- Sister chromatids are pulled apart by the spindle fibers
- They move to opposite poles of the cell
Tip: “Anaphase = Apart”
4. Telophase – Two Nuclei Form
- Chromatids uncoil back into thin chromatin
- Nuclear membranes reform around both sets of chromosomes
- Spindle fibers disappear
Tip: “Telophase = Two new nuclei”
After Mitosis: Cytokinesis
The cytoplasm divides. Two genetically identical daughter cells are formed. Each new cell has the same number of chromosomes as the original parent cell.
Summary Table – Stages of Mitosis
| Stage | Key Events |
|---|---|
| Prophase | Chromosomes condense, nuclear envelope breaks, spindle forms |
| Metaphase | Chromosomes line up in the center |
| Anaphase | Sister chromatids pulled to opposite sides |
| Telophase | Nuclear membranes reform, chromosomes uncoil |
| Cytokinesis | Cytoplasm divides, two identical cells form |
Mitosis = 1 cell ➝ 2 identical cells
Occurs in somatic (body) cells
Ensures same number of chromosomes in both new cells
Essential for growth, healing, and repair
Importance of Cell Division in Growth and Repair
Why Growth Matters in Living Beings?
- Growth is not just about getting taller or heavier – it’s about forming new tissues, organs, and systems.
- Every part of a growing organism must expand in size and function, and that only happens if new cells are produced.
- Growth also means development – like brain maturity, muscle formation, and immune system strengthening.
Without growth:
- Organisms would stay underdeveloped
- Organs wouldn’t reach full function
- The body wouldn’t be able to support reproduction or survival
Real-world link: Malnourished children may have stunted growth because their bodies lack resources for healthy cell division.
Why Repair Is Critical for Survival
The human body is under constant wear and tear skin rubs off, bones can crack, and internal organs get stressed.
Without continuous repair, even small damage would become dangerous over time.
Repair ensures:
- Wounds heal and skin closes
- Bones rejoin after fractures
- Organs recover from stress, infections, or minor injuries
- Tissues regenerate after surgeries or illness
Example: After intense exercise, tiny muscle tears are repaired by forming new muscle cells, making the muscle stronger.
How Growth and Repair Affect Health?
- Slower cell division = delayed healing, weakened immunity, and poor development
- Overactive cell division = can lead to tumors or cancer
The balance of cell division for growth and repair is key to:
- Healthy aging
- Strong immunity
- Tissue recovery
- Functional body systems
In Summary – Growth and Repair Matter Because:
| Growth Provides | Repair Provides |
|---|---|
| Full body development | Recovery after injury |
| Functional tissues and organs | Protection from permanent damage |
| Physical maturity | Maintains health over time |
| Support for reproduction and survival | Keeps organs working even under stress |
Cancer: Uncontrolled Cell Division
What is Cancer?
- Cancer is a disease where cells divide uncontrollably, ignoring the normal rules of the cell cycle.
- Instead of dividing only when needed (like for growth or repair), cancer cells keep multiplying – nonstop forming tumors and sometimes spreading to other parts of the body.
Healthy Cell Cycle vs Cancer
| Healthy Cells | Cancer Cells |
|---|---|
| Divide in a controlled way | Divide without stopping |
| Follow signals to grow or rest | Ignore signals and checkpoints |
| Die when damaged (apoptosis) | Avoid death and keep dividing |
| Form normal tissues | Disrupt tissues and organs |
What Causes Cancer?
Cancer usually begins when a mutation (change in DNA) affects genes that control the cell cycle. These genes include:
- Oncogenes – when overactive, push cells to divide too much
- Tumor suppressor genes – when damaged, fail to stop division
Mutations may happen due to:
- Radiation (e.g. X-rays, UV light)
- Chemicals (carcinogens like tobacco smoke)
- Certain viruses (e.g. HPV)
- Inherited faulty genes (genetic risk)
How Cancer Affects the Body
- Cancer cells don’t stop at forming tumors – some can invade nearby tissues. Others may enter the blood or lymph and spread to distant parts of the body (this is called metastasis).
- Tumors steal nutrients, press against organs, and cause pain or failure of body functions.
Types of Tumors
| Type | Description |
|---|---|
| Benign | non-cancerous, slow growing, stays in one place |
| Malignant | Cancerous, grows fast, can spread (metastasize) |
How is Cancer Treated?
Treatment aims to stop or kill the fast-dividing cells:
- Surgery: remove the tumor
- Radiation therapy: use rays to destroy cancer cells
- Chemotherapy: use drugs to stop cell division
- Targeted therapy: block specific cancer cell signals
- Immunotherapy: help the body’s immune system fight cancer
Key Points to Remember
- Cancer is caused by uncontrolled cell division
- Starts with mutations that disrupt normal cell cycle controls
- Can form tumors, damage organs, and spread across the body
- Treated by targeting rapidly dividing cells