Solute: substances that are dissolved in fluid (eg. salt)

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Solvent: the liquid the solute is dissolved in (eg. water)

Passive Transport

movement of materials across a cell membrane without energy; Movement along a concentration gradient

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  • movement of particles from an area of high concentration to an area of low concentration
  • movement will continue until equilibrium is achieved

Example: – Perfume

– CO2 and O2 exchange in lungs


  • diffusion of water through a selectively permeable membrane (eg. cell membrane)
  • Water moves from higher concentration to lower concentration.

Hypertonic – the concentration of solutes outside the cell is higher than inside the cell.

  • water moves out.

Isotonic – the concentration of solutes outside the cell is the same as inside the cell.

  • equilibrium

Hypotonic – the concentration of solutes inside the cell is higher than outside the cell.

  • water moves in.
  • this is important to aquatic organisms
  • Your kidney uses osmosis to regulate water balance in the blood. This determines the amount of water in urine.

Facilitated Diffusion

  • Molecules too large for simple diffusion use protein carriers in the cell membrane to assist them. They pass through a protein, that acts like a channel in the membrane.
  • Substances still move across a concentration gradient. No energy is used!!!!
Diffusion, Osmosis, and Movement Across a Membrane


  • Glucose is too large to diffuse through the membrane
  • It uses the protein carriers to enter the cell – glucose is constantly being used up in a cell so there is a lower concentration inside the cell.

Active Transport – Using energy to move materials across the cell membrane; materials usually move against the concentration gradient

Sodium/Potassium Pump
  • Located in nerve cells and critical to their function
  • Nerve cells must maintain a higher concentration of Na+ outside the cell and K+ inside the cell.
  • Special transport proteins in the membrane pump Na+ out of the cell and K+ into the cell. This takes energy


  • moving materials into the cell by pinching the cell membrane
  • this forms a vesicle inside the cell
  • molecules too large to pass through the cell membrane

Phagocytosis “cell eating”movement of large molecules

Example: how white blood cells “eat” bacteria

Pinocytosis “cell drinking” – transport of liquids into the cell

  • Exporting large molecules outside the cell
  • A vesicle inside the cell fuses with the cell membrane and then releases it’s contents outside the cell.

Example: – how insulin is moved out of the pancreas into the blood

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