Study Notes
Membrane transport involves the movement of particles across cell membranes through processes like simple diffusion, facilitated diffusion, osmosis, and active transport. These processes can be either passive, requiring no energy, or active, requiring energy input.
- Simple diffusion — movement of small or lipophilic molecules from high to low concentration. Example: Oxygen and carbon dioxide moving across cell membranes.
- Facilitated diffusion — movement of large or charged molecules via membrane proteins from high to low concentration. Example: Ions moving through ion channels.
- Osmosis — passive movement of water molecules across a partially permeable membrane from low to high solute concentration. Example: Water absorption in plant roots.
- Active transport — movement of molecules against a concentration gradient using energy. Example: Sodium-potassium pump exchanging sodium and potassium ions across the cell membrane.
Exam Tips
Key Definitions to Remember
- Simple diffusion: Movement of molecules from high to low concentration without energy.
- Facilitated diffusion: Movement of molecules via proteins from high to low concentration without energy.
- Osmosis: Movement of water across a membrane from low to high solute concentration.
- Active transport: Movement of molecules against a gradient using energy.
Common Confusions
- Confusing osmosis with diffusion, as osmosis specifically involves water.
- Thinking facilitated diffusion requires energy; it does not.
Typical Exam Questions
- What is the difference between simple and facilitated diffusion? Simple diffusion does not involve proteins, while facilitated diffusion does.
- How does the sodium-potassium pump work? It uses ATP to exchange three sodium ions out of the cell and two potassium ions into the cell.
- What happens to a cell in a hypertonic solution? Water moves out, causing the cell to shrink.
What Examiners Usually Test
- Understanding of passive vs. active transport.
- Ability to explain the role of membrane proteins in transport.
- Knowledge of the effects of different solutions on cells.