Learn: Transport Across Membranes - Diffusion to Active Transport

Welcome!You've already explored gas exchange surfaces, Fick's Law, and the fluid mosaic model of cell membranes. Now, let's learn how substances move across membranes, building on what you've studied about structure and function.

What is Transport Across Membranes?Transport across membranes refers to how molecules move in and out of cells. This is crucial for maintaining homeostasis and allowing cells to function properly. There are different mechanisms for transport, depending on the molecule and its concentration.

DiffusionDiffusion is the passive movement of molecules from an area of high concentration to low concentration. It occurs until equilibrium is reached. Small, non-polar molecules like oxygen can diffuse freely through the phospholipid bilayer.

Facilitated DiffusionFacilitated diffusion uses protein channels or carriers to help larger or polar molecules, like glucose or ions, cross the membrane. It is still passive and does not require energy.

Active TransportActive transport moves molecules from low to high concentration, against the concentration gradient. It requires energy from ATP and specific carrier proteins to work.

OsmosisOsmosis is the passive movement of water molecules across a partially permeable membrane, from an area of high water potential to low water potential. This helps regulate cell volume.

Endocytosis and ExocytosisEndocytosis allows large molecules or particles to enter the cell by engulfing them in vesicles. Exocytosis releases substances from vesicles to the outside of the cell. Both processes require energy.

Review Time!Great work! You've learned about diffusion, facilitated diffusion, osmosis, active transport, and vesicle transport. Let's test your understanding.