AP Biology 2.8 Mechanisms of Transport Study Notes - New Syllabus Effective 2025
AP Biology 2.8 Mechanisms of Transport Study Notes- New syllabus
AP Biology 2.8 Mechanisms of Transport Study Notes – AP Biology – per latest AP Biology Syllabus.
LEARNING OBJECTIVE
Describe the processes that allow ions and other molecules to move across membranes.
Key Concepts:
- Mechanisms of Transport
2.8.A – Mechanisms of Transport Across Membranes
Cells use various processes to move ions and molecules across membranes, based on size, charge, and energy use.
⚙️ Main Transport Processes
| Transport Type | Energy? | What It Moves | Direction | Example 🧪 |
|---|---|---|---|---|
| Simple Diffusion | ❌ No | Small, nonpolar molecules | High → Low | O₂, CO₂ across membrane |
| Facilitated Diffusion | ❌ No | Large or charged molecules | High → Low via protein | Glucose, Na⁺, K⁺ via channels |
| Osmosis | ❌ No | Water only | High → Low (water potential) | H₂O via aquaporins |
| Active Transport | ✅ Yes | Ions, solutes (any size) | Low → High (against gradient) | Na⁺/K⁺ pump |
| Endocytosis | ✅ Yes | Large particles/substances | Into the cell via vesicles | White blood cells ingesting bacteria |
| Exocytosis | ✅ Yes | Large waste/secretion | Out of the cell via vesicles | Insulin secretion from pancreas |
🧠 How It Works:
Passive transport (diffusion, osmosis) = no energy, relies on gradients
Active transport & vesicle transport = uses ATP to move substances when needed
✅ Summary
Cells move substances using diffusion, protein channels, pumps, and vesicles – based on the molecule’s size, charge, and the concentration gradient. This keeps the cell balanced and functional.
2.8.A.1 – Active Transport & Electrochemical Gradients
ATP is used to actively move molecules and maintain membrane potential using protein pumps.
🔋 Active Transport Needs Energy
ATP provides the energy to:
- Move molecules against their concentration gradient (low → high)
- Maintain ion balances essential for cell function
🧱 Key Players
| Component | Role 🧪 |
|---|---|
| Membrane proteins | Do the actual pumping (transport proteins) |
| Na⁺/K⁺ pump (ATPase) | Uses ATP to pump 3 Na⁺ out and 2 K⁺ in → sets up electrochemical gradient |
⚡ Electrochemical Gradient = Charge + Concentration
Creates membrane potential (inside of cell is slightly negative)
Used for:
- Nerve impulses
- Muscle contractions
- Secondary active transport (like glucose uptake)
✅ Summary
Active transport uses ATP and membrane proteins (like the Na⁺/K⁺ pump) to move ions against gradients and maintain a charged membrane key for nerve function and overall cell health.