The membrane is a picky gate. Some things drift across for free, going with the crowd. Some need a protein doorway. Some must be pumped uphill using energy. Pick a method and watch molecules cross.
Simple diffusion
Simple diffusionfree, downhill
Pick a method
📷 Reference image
A real labeled figure to compare with the interactive above.
Membrane Transport — OpenStax, CC BY 4.0 (via Wikimedia Commons)
