Study Notes
Molecules move in and out of cells through diffusion, which is the net movement from high to low concentration areas. Brownian motion describes the random movement of particles, providing energy for diffusion. The cell membrane is partially permeable, allowing selective movement based on molecule size.
- Diffusion — the net movement of molecules from a region of higher concentration to a region of lower concentration down a concentration gradient. Example: Oxygen diffusing from alveolar air spaces into blood in capillaries.
- Brownian Motion — random movement of particles at all times. Example: Movement of pollen grains in water.
- Cell Membrane — a partially permeable membrane that allows some molecules to cross easily. Example: Allows oxygen to pass but restricts larger molecules.
Exam Tips
Key Definitions to Remember
- Diffusion: Movement from high to low concentration.
- Brownian Motion: Random movement of particles.
- Cell Membrane: Partially permeable barrier.
Common Confusions
- Confusing diffusion with osmosis, which involves water.
- Thinking all molecules can pass through cell membranes easily.
Typical Exam Questions
- What is diffusion? Movement of molecules from high to low concentration.
- How does the cell membrane affect molecule movement? It selectively allows molecules based on size.
- What role does Brownian motion play in diffusion? It provides the kinetic energy for diffusion.
What Examiners Usually Test
- Understanding of diffusion and its importance in cells.
- Examples of diffusion in living organisms.
- The role of the cell membrane in molecule movement.