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# Cell Membrane Transport Mechanisms The document describes different mechanisms of transport across cell membranes. ## Passive Transport * **Filtration:** Particles are driven through a membrane by physical pressure (e.g., water and small solutes moving through capillary walls). * **Simple Diff...

# Cell Membrane Transport Mechanisms The document describes different mechanisms of transport across cell membranes. ## Passive Transport * **Filtration:** Particles are driven through a membrane by physical pressure (e.g., water and small solutes moving through capillary walls). * **Simple Diffusion:** Movement of solute particles from high to low concentration, without requiring membrane proteins. * Examples of substances that can move through using simple diffusion are: gases (CO2, N2, O2), and small hydrophobic molecules (steroids). * **Facilitated Diffusion:** Movement of specific large uncharged polar molecules (glucose), charged polar molecules (amino acids, ATP) and along a concentration gradient with the help of transport proteins. No ATP is required, but a carrier is necessary. * **Osmosis:** Net flow of water across a selectively permeable membrane from high to low water concentration. The movement depends on solute concentrations across the membrane. ## Active Transport * **Primary Active Transport:** Uses ATP directly to move substances against their concentration gradient, often through pumps. * **Secondary Active Transport:** Does not use ATP directly; instead, it depends on the concentration gradient. One substance naturally diffuses, while another substance "hitches a ride" through symporters or antiporters—a type of co-transport. ## Tonicity * **Tonicity:** The comparison of solute concentrations inside and outside a cell, determining the movement of water. * **Hypotonic:** Lower solute concentration outside the cell causing water to move into the cell (round, one color). * **Isotonic:** Equivalent solute concentration inside and outside the cell. Water movement is balanced (round, light inside color; normal). * **Hypertonic:** Higher solute concentration outside the cell causing water to move out of the cell (shriveled, spiky shape). The document also mentions that the type of transport may or may not be facilitated, and that this is crucial to consider when preparing intravenous (I.V.) fluids.