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Passive vs. Active Transport definitions

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  • Passive Transport
    Movement of molecules across membranes without energy input, following concentration gradients from high to low.
  • Active Transport
    Movement of molecules across membranes requiring energy, typically from ATP, against concentration gradients.
  • ATP
    Primary energy source used to drive processes that move molecules against their natural concentration gradients.
  • Concentration Gradient
    Difference in molecule concentration across a membrane, dictating the direction of spontaneous molecular movement.
  • Exergonic Process
    Thermodynamically favorable event with negative Gibbs free energy, occurring spontaneously without energy input.
  • Endergonic Process
    Thermodynamically unfavorable event with positive Gibbs free energy, requiring energy input to proceed.
  • Protein Facilitation
    Assistance by membrane proteins in transporting molecules, sometimes needed for passive, always for active transport.
  • Uniporter
    Membrane protein that transports a single molecule in one direction across the membrane.
  • Symporter
    Membrane protein that co-transports two molecules simultaneously in the same direction across the membrane.
  • Antiporter
    Membrane protein that co-transports two molecules in opposite directions across the membrane.
  • Biological Membrane
    Barrier composed of lipid bilayers and proteins, regulating molecular movement into and out of cells.
  • Thermodynamic Favorability
    Characteristic of a process that occurs spontaneously, often associated with passive transport and negative delta G.
  • Spontaneity
    Quality of a process to occur without external energy input, typical of passive transport across membranes.
  • Molecular Transport
    Movement of small molecules across biological membranes, categorized as passive or active based on energy requirements.