1.4  Membrane Transport

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Essential Idea:

Membranes control the composition of cells

by active and passive transport


  • Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport
  • The fluidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis
  • Vesicles move materials within cells


  • Structure and function of sodium-potassium pumps for active transport and potassium channels for facilitated diffusion in axons
  • Tissues or organs to be used in medical procedures must be bathed in a solution with the same osmolarity as the cytoplasm to prevent osmosis


  • Estimation of osmolarity in tissues by bathing samples in hypotonic and hypertonic solutions