The Plasma Membrane
Passive Transport across a membrane
Definitions:
Diffusion = the passive movement of particles from a region of higher concentration to a region of lower concentration.
Osmosis = the passive movement of water molecules,
across a partially permeable membrane, from a region of lower solute
concentration to a region of higher solute concentration.
Explain passive transport across membranes in terms of simple diffusion and facilitated diffusion.
Concentration gradient: Molecules can diffuse across membranes from areas of higher to lower concentration by:
Simple diffusion: traveling directly through the membrane if they
are small and uncharged avoiding repulsion by the hydrophobic,
non-polar tails of phospholipids in the middle of the membrane.
Facilitated diffusion: traveling through special transport
proteins, if they match the shape and charge requirements to fit
through the channels provided by the transport proteins.
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