Cell Membranes and Transport
This lesson connects molecular mechanisms, cell behavior and biological evidence. Instead of memorizing isolated terms, follow what changes, what is measured, where the process occurs and why the outcome matters to a living system.
Big idea
A dynamic phospholipid bilayer contains proteins, cholesterol and carbohydrates with different roles. Small nonpolar molecules move down their concentration gradient without transport proteins or ATP.
Learning goals
- Fluid mosaic membrane: A dynamic phospholipid bilayer contains proteins, cholesterol and carbohydrates with different roles.
- Simple diffusion: Small nonpolar molecules move down their concentration gradient without transport proteins or ATP.
- Osmosis: Water moves across a selectively permeable membrane toward the side with lower water potential.
- Facilitated diffusion: Channels and carriers move specific polar or charged substances down a gradient without ATP.
- Active transport: Carrier proteins use energy to move substances against an electrochemical gradient.
Core concepts
1. Fluid mosaic membrane
A dynamic phospholipid bilayer contains proteins, cholesterol and carbohydrates with different roles.
Observation or application: Membrane components move laterally while the bilayer remains an effective boundary.
2. Simple diffusion
Small nonpolar molecules move down their concentration gradient without transport proteins or ATP.
Observation or application: Oxygen crosses a cell membrane from higher to lower concentration.