IB MYP 4-5 Biology-Cell Division- Study Notes - New Syllabus
IB MYP 4-5 Biology-Cell Division- Study Notes – New syllabus
IB MYP 4-5 Biology-Cell Division- Study Notes – IB MYP 4-5 Biology – per latest IB MYP Biology Syllabus.
Key Concepts:
- Purpose of cell division
- Cell cycle stages
Purpose of Cell Division
What is Cell Division?
Cell division is the process by which a cell splits into two or more new cells. It’s how living things:
- Grow
- Repair damage
- Reproduce
- Maintain healthy body functions
There are two main types of cell division:
- Mitosis – for growth and repair
- Meiosis – for reproduction (formation of gametes like sperm and egg)
Why is Cell Division Important? – The 4 Main Purposes
1. Growth of an Organism
- All living things start life as a single cell (zygote)
- As cells divide, the organism gets bigger and more complex
- Cell division increases the number of cells in the body
Example: A baby grows into an adult because its cells keep dividing and multiplying.
2. Repair and Replacement
- Body cells are constantly damaged or worn out
- Cell division makes new cells to replace dead or damaged ones
Example: When you cut your skin, cell division helps heal the wound by making new skin cells.
3. Maintenance of Body Functions
- Even when we’re not growing or injured, our cells renew themselves regularly
- Old blood, skin, and digestive cells are replaced to keep the body working smoothly
Example: Red blood cells live for only about 120 days and are constantly replaced by new ones.
4. Reproduction (in some organisms)
- In unicellular organisms (like bacteria), cell division is how they reproduce
- In multicellular organisms, special division (meiosis) forms gametes for sexual reproduction
Example: Bacteria divide by binary fission (a type of cell division) to make identical offspring.
Quick Look at the Two Types of Cell Division:
| Type | Purpose | Where it Happens |
|---|---|---|
| Mitosis | Growth, repair, maintenance | Body (somatic) cells |
| Meiosis | Reproduction | Reproductive organs (testes, ovaries) |
Why Cells Can’t Just Grow Bigger Instead of Dividing?
- Larger cells can’t work efficiently
- Harder to move nutrients, oxygen, and waste in and out
- Division keeps cells small and efficient
Analogy: Think of it like cutting a large cake into slices so everyone gets an equal piece.
Summary – Purpose of Cell Division
| Purpose | Explanation |
|---|---|
| Growth | More cells = bigger organism |
| Repair | New cells fix injuries |
| Replacement | Old/worn-out cells are renewed |
| Reproduction | Makes new organisms (asexual) or gametes (sexual) |
Final Recap
- Cell division is essential for life
- It helps us grow, heal, maintain our bodies, and reproduce
- Without cell division, life could not continue
Cell Cycle Stages
What is the Cell Cycle?
The cell cycle is the series of stages a cell goes through to grow, prepare for division, and finally divide into two new cells. It’s like the life story of a cell from birth to reproduction!
Main Purpose of the Cell Cycle:
- To help the organism grow, repair, and replace damaged cells
- To make sure the genetic material (DNA) is copied accurately and passed on
The 2 Major Phases of the Cell Cycle:
- Interphase – cell prepares for division
- Mitotic Phase – cell actually divides
1. Interphase – The Preparation Stage
(Takes up 90% of the cycle)
This is when the cell is not dividing, but doing important work like growing, copying DNA, and getting ready to split.
Interphase has 3 sub-stages:
| Stage | What Happens Here? |
|---|---|
| G₁ phase (Gap 1) | Cell grows in size, makes proteins and organelles |
| S phase (Synthesis) | DNA is copied (replicated), so each new cell gets a full set |
| G₂ phase (Gap 2) | Final checks and preparations before division |
Tip: If DNA isn’t copied in S phase, new cells won’t have correct genetic info.
2. Mitotic (M) Phase – The Division Stage
This is when the cell splits into two. It includes:
- Mitosis – division of the nucleus
- Cytokinesis – division of the cytoplasm
Mitosis itself has 4 stages:
| Stage | What Happens? |
|---|---|
| Prophase | Chromosomes condense, nucleus breaks down, spindle forms |
| Metaphase | Chromosomes line up in the middle of the cell |
| Anaphase | Chromosomes are pulled apart to opposite sides |
| Telophase | Two new nuclei form, chromosomes uncoil |
Cytokinesis comes after mitosis:
The cell membrane pinches and splits, forming 2 identical daughter cells.
Summary Table – Full Cell Cycle
| Phase | Function |
|---|---|
| G₁ | Growth and normal function |
| S | DNA replication |
| G₂ | Final preparation for division |
| Mitosis | Division of nucleus (PMAT) |
| Cytokinesis | Division of cytoplasm; two new cells form |
Why Understanding the Cell Cycle Matters?
- It helps us learn how cells grow and heal the body
- Mistakes in the cycle can lead to diseases like cancer
- Understanding it is important for medicine, biology, and genetics
Final Recap – The Cell Cycle in One Line:
The cell cycle is how cells grow, copy DNA, and divide to keep the body alive and healthy.