Study Notes
Membrane transport involves the movement of particles across cell membranes through various mechanisms, including passive and active transport.
- Simple diffusion — movement of small or lipophilic molecules from high to low concentration. Example: Oxygen (O2) and carbon dioxide (CO2) moving across cell membranes.
- Facilitated diffusion — movement of large or charged molecules via membrane proteins from high to low concentration. Example: Ions and sucrose transported through protein channels.
- Osmosis — passive movement of water molecules across a partially permeable membrane from low to high solute concentration. Example: Water moving into plant roots from the soil.
- Active transport — movement of materials against a concentration gradient using energy (ATP). Example: Sodium-potassium pump exchanging sodium and potassium ions across the cell membrane.
- Endocytosis — process of taking materials into the cell by engulfing them in a vesicle. Example: White blood cells engulfing bacteria.
- Exocytosis — process of releasing materials from the cell by vesicles fusing with the plasma membrane. Example: Secretion of hormones like insulin from pancreatic cells.
Exam Tips
Key Definitions to Remember
- Simple diffusion: Movement of molecules from high to low concentration without energy.
- Facilitated diffusion: Movement of molecules via protein channels from high to low concentration.
- Osmosis: Movement of water across a membrane from low to high solute concentration.
- Active transport: Movement of molecules against a concentration gradient using energy.
Common Confusions
- Confusing facilitated diffusion with active transport.
- Misunderstanding the role of ATP in active transport.
Typical Exam Questions
- What is the difference between simple and facilitated diffusion? Simple diffusion does not require proteins, while facilitated diffusion uses protein channels.
- How does the sodium-potassium pump function? It uses ATP to exchange three sodium ions out of the cell for two potassium ions into the cell.
- What happens to a cell in a hypertonic solution? Water moves out of the cell, causing it to shrink.
What Examiners Usually Test
- Understanding of different types of membrane transport.
- Ability to explain the sodium-potassium pump mechanism.
- Application of osmosis in real-life scenarios, such as medical procedures.