IB MYP 4-5 Biology-Cells- Study Notes - New Syllabus
IB MYP 4-5 Biology-Cells- Study Notes – New syllabus
IB MYP 4-5 Biology-Cells- Study Notes – IB MYP 4-5 Biology – per latest IB MYP Biology Syllabus.
Key Concepts:
- Cell theory (prokaryotic vs. eukaryotic cells).
- Organelles and their functions (mitochondria, chloroplasts, nucleus)
- Stem cells (embryonic vs. adult, therapeutic uses).
- Microscopy (calculating magnification, drawing lab diagrams).
- Osmosis, diffusion, and active transport (experiments with potato/salt water).
Cell Theory & Prokaryotic vs. Eukaryotic Cells
🔬 What is Cell Theory?
Cell theory is the foundation of all biology. It explains what cells are and how life works at the smallest level.
🧾 The 3 Main Parts of Cell Theory:
- All living organisms are made of one or more cells.
- The cell is the basic unit of structure and function in living things.
- All cells come from pre-existing cells.
👉 This means every living thing – from bacteria to humans – started with cells!
🧪 Types of Cells
Cells can be grouped based on whether they have a nucleus and membrane-bound organelles.
| Feature | Prokaryotic Cells 🦠 | Eukaryotic Cells 🧫 |
|---|---|---|
| Nucleus | ❌ No true nucleus | ✅ True nucleus |
| DNA | Circular DNA in cytoplasm | Linear DNA in the nucleus |
| Size | Very small (0.1–5 µm) | Larger (10–100 µm) |
| Organelles | No membrane-bound organelles | Many complex organelles |
| Example | Bacteria, Archaea | Plants, Animals, Fungi, Protists |
| Cell Wall | ✅ Present | ✅ Plants & fungi, ❌ Animals |
| Ribosomes | Small (70S) | Larger (80S) |
🏗️ How to Remember the Difference
🧠 “Pro = No” → Prokaryotes have no nucleus and no complex organelles
🧠 “Eu = True” → Eukaryotes have a true nucleus and membrane-bound organelles
Animal Cell Plant Cell
🏭 Cell = Mini Factory Analogy
| Cell Part | Factory Role | Description |
|---|---|---|
| Nucleus | Head Office | Controls everything (contains DNA) |
| Ribosomes | Workers | Build proteins (products) |
| ER (Rough/Smooth) | Machinery | Makes proteins (RER) and lipids (SER) |
| Golgi Body | Packaging Dept. | Modifies, sorts, and ships proteins |
| Mitochondria | Powerhouse | Makes energy (ATP) by respiration |
| Cell Membrane | Security | Controls what goes in and out |
| Cytoplasm | Workspace | Where all activities happen |
| Vacuole | Storage | Stores water, ions, and waste |
| Lysosome | Clean-up Crew | Breaks down old parts/waste |
| Chloroplast (plants) | Solar Panel | Makes food via photosynthesis |
| Cell Wall (plants) | Support Beam | Gives shape & strength |
🧬 Examples to Visualize
- Bacteria → Tiny, simple, no nucleus → prokaryote
- Human skin cell → Large, has organelles → eukaryote
- Plant cell → Has a nucleus, chloroplasts, vacuole → eukaryote
🔍 Quick Recap Box
✅ Prokaryotes = Simple, no nucleus (ex: bacteria)
✅ Eukaryotes = Complex, nucleus + organelles (ex: humans, plants)
✅ Cells are like mini factories – each part has a job!
Organelles and Their Functions
🔋 Mitochondria – The Powerhouse of the Cell
What is it?
Mitochondria are double-membraned organelles found in almost all eukaryotic cells. They break down glucose and use oxygen to release energy.
- Function:
- Site of aerobic respiration
- Produces ATP (adenosine triphosphate) – the energy currency of the cell
- Contains its own DNA (yes, it’s semi-independent!)
- Structure Highlights:
- Inner membrane is folded into cristae to increase surface area
- Fluid-filled center called the matrix
Mitochondria can reproduce on their own like mini power factories with independence!
🌱 Chloroplasts – The Solar Panel of Plant Cells
What is it?
Chloroplasts are found only in plant cells and algae. They carry out photosynthesis – converting sunlight into glucose.
- Function:
- Photosynthesis: Light energy → chemical energy (glucose)
- Contains the pigment chlorophyll (makes leaves green!)
- Makes oxygen as a by-product 🌬️
- Structure Highlights:
- Double membrane
- Contains thylakoid membranes stacked into grana
- Fluid around thylakoids is the stroma
Chloroplasts have stacks inside called grana just like stacks of solar panels!
🧠 Nucleus – The Control Center of the Cell
What is it?
The nucleus is a large, central organelle that stores DNA and controls all cell activities.
- Function:
- Stores the genetic blueprint (DNA)
- Directs protein synthesis by sending out mRNA
- Controls cell growth, division, and repair
- Structure Highlights:
- Surrounded by nuclear envelope (double membrane with pores)
- Contains nucleoplasm, chromatin, and nucleolus
- Nucleolus makes ribosomes
Red blood cells don’t have a nucleus more space for oxygen!
🔄 Quick Recap Table:
| Organelle | Function | Special Feature |
|---|---|---|
| Mitochondria | Produces ATP (energy) via respiration | Has own DNA, folded inner membrane (cristae) |
| Chloroplast | Does photosynthesis | Contains chlorophyll, stacks called grana |
| Nucleus | Stores DNA, controls cell activities | Has nuclear pores, nucleolus makes ribosomes |
Stem Cells: Embryonic vs. Adult + Therapeutic Uses
🧠 What Are Stem Cells?
Stem cells are raw, unspecialized cells that can:
- Divide (by mitosis)
- Differentiate into other specialized cells (like muscle, blood, or nerve cells)
🧬 One embryonic stem cell can become 200+ types of cells!
🌱 Types of Stem Cells
| Type | What they are | Power | Uses | Limitations |
|---|---|---|---|---|
| Embryonic Stem Cells | From early-stage embryos (zygote → blastocyst) | 💥 Pluripotent – can become ANY cell type | Create neurons, insulin cells, heart muscle, etc. | Ethical concerns, rejection risk |
| Adult Stem Cells | Found in bone marrow, skin, brain | 🔁 Multipotent – only certain related cells | Bone marrow transplants | Limited types, harder to grow |
| Plant Meristem Cells | In shoot/root tips | Totipotent for plants | Clone rare plants or preserve traits | Only for plants |
🧪 Therapeutic Uses of Stem Cells
- Diabetes: Replace insulin-producing cells
- Neurodegenerative diseases: Replace damaged nerve cells (e.g., Alzheimer’s, Parkinson’s)
- Spinal cord injuries: Regrow neurons
- Leukemia: Bone marrow stem cell transplant
🌿 Meristem cells in plants help clone rare species with sweet fruit or disease resistance!
🧠 Adult stem cells are already used in real treatments like bone marrow transplants!
😬 Challenges & Risks
| ⚠️ Problem | 💬 Why It Matters |
|---|---|
| ❌ Ethical Issues | Using embryos raises moral concerns |
| 🧬 Rejection Risk | Body might reject stem cells as foreign |
| 🧫 Tumor Formation | Embryonic stem cells divide quickly and might form tumors |
| 🦠 Virus Contamination | Stem cells grown in labs may carry infections |
🧠 Quick Recap: Embryonic vs. Adult Stem Cells
| Feature | Embryonic | Adult |
|---|---|---|
| Source | Embryo (zygote stage) | Adult tissues (bone marrow) |
| Cell Potential | Pluripotent (any type) | Multipotent (few related types) |
| Ethics | Controversial | Less concern |
| Usage | Broad medical use | More limited |
| Risk | Higher risk of rejection/tumors | Lower risk |
Microscopy
🔠 What Is Microscopy?
Microscopy is the science of using microscopes to view objects too small for the naked eye – like cells, organelles, or bacteria.
🔍 Types of Microscopes
| 🔍 Microscope Type | 📌 Description | 🧪 Resolution | 💡 Magnification |
|---|---|---|---|
| Light Microscope | Uses visible light and lenses to magnify images. Common in school labs. | Low (can’t see organelles clearly) | Up to ~1500× |
| Electron Microscope | Uses beams of electrons. Shows fine detail like ribosomes. | Very high | Up to 2,000,000×! |
📏 How to Calculate Magnification
You can use this formula:
You see a drawing of a cell that’s 5 mm long. The actual size is 0.05 mm.
Magnification = 5 mm ÷ 0.05 mm = 100×
📀 Units You Must Know
| Unit | Symbol | In meters |
|---|---|---|
| Millimeter | mm | 1 mm = 10⁻³ m |
| Micrometer | µm | 1 µm = 10⁻⁶ m |
| Nanometer | nm | 1 nm = 10⁻⁹ m |
1 mm = 1000 µm
1 µm = 1000 nm
🌟 Did You Know?
Osmosis, Diffusion & Active Transport
🔁 What Is Transport?
Transport is how substances move in and out of cells across the cell membrane.
There are 2 main types of transport:
| 🚫 Needs No Energy (Passive) | ⚡ Needs Energy (Active) |
|---|---|
| 🔹 Diffusion 🔹 Osmosis | 🔸 Active Transport |
💨 Diffusion
Movement of particles from an area of high concentration to low concentration. Happens until equilibrium is reached.
🧪 Example: Oxygen diffusing from lungs into red blood cells.
💧 Osmosis
Diffusion of water molecules across a partially permeable membrane, from high water potential to low water potential.
🔬 Osmosis in Potatoes – Classic Experiment
| Type | Description | What Happens to Potato? |
|---|---|---|
| 🧂 Hypertonic | More solute outside (e.g., salt water) | Potato loses water → shrinks |
| 💧 Hypotonic | More water outside | Potato gains water → swells |
| ⚖️ Isotonic | Equal solute & water | No net change |
⚡ Active Transport
Movement of substances against the concentration gradient (from low to high concentration). Uses ATP and carrier proteins.
🧪 Example: Root hair cells absorb minerals even when more are inside the root than outside in the soil.
🧠 Quick Comparison
| Diffusion | Osmosis | Active Transport |
|---|---|---|
| High → Low | Water: High → Low | Low → High |
| No energy | No energy | Needs energy (ATP) |
| Random motion | Through membrane | Uses carrier proteins |
🧪 Brownian Motion
All particles move randomly due to kinetic energy. This motion drives diffusion and osmosis.
🎯 Fun Fact: Smaller particles in warmer environments move faster!
🌱 Osmosis in Cells
| Cell Type | In Hypotonic Solution | In Hypertonic Solution |
|---|---|---|
| 🐶 Animal Cell | Swells and may burst (lysis) | Shrinks (crenation) |
| 🌿 Plant Cell | Swells → turgid (good!) | Shrinks → plasmolysis |
🔒 Why plants don’t burst: The cell wall resists pressure. Swelling builds turgor pressure – supports the plant!
💡 Did You Know?