Cell Membranes and Transport
You can now identify the main components, explain the mechanism step by step, interpret an observation and distinguish related ideas.
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: 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: Oxygen crosses a cell membrane from higher to lower concentration.
3. Osmosis
Water moves across a selectively permeable membrane toward the side with lower water potential.
Observation: A cell gains or loses water when its surroundings have a different solute concentration.