Transport Across the Cell

• Cell membranes are differentially permeable meaning they only allow certain ions and molecules to pass through but restrict the movement of others
• Materials pass through a membrane either through an active process or a passive process
• Active transport is the movement of molecules from an area of low concentration to an area of high concentration against a concentration gradient
• Active transport requires energy which is supplied by ATP
• Passive transport is the movement of substances from an area of high concentration to an area of low concentration
• Passive transport does not require energy
• Concentration is the amount of given substance contained within a solution or in a particular volume of space
• Concentrated gradient is is the difference in concentration of a solution, often between the inside and outside of a cell
• Diffusion rate is the steeper the concentration gradient, the faster the rate of diffusion
• Diffusion is the spreading out of particles so that they are evenly distributed over the space available
• Osmosis: a process by which molecules of a solvent tend to pass through a semipermeable membrane in order to balance the concentration of another substance
• Osmosis is the spontaneous net movement of water
• Osmosis is a passive process
• Tonicity refers to the concentration of solutes within a solvent
• Three terms to describe tonicity:

  • Hypertonic: greater solute to solvent ratio (high osmotic pressure)
  • Hypotonic: lower solute to solvent ratio (lower osmotic pressure)
  • Isotonic: same solute to solvent ratio
• Carrier-mediated transport is the movement of molecules across a membrane by a carrier protein
• Rules for Carrier-Mediated Transport:

  1. Carrier proteins are specific
  2. Carriers can become saturated
  3. Carrier activity is regulated by hormones and other substances
• Facilitated diffusion is a passive process
• Facilitated diffusion is the movement of molecules across a cell membrane using a carrier protein

  
• Vesicular transport is the movement of substances across the cell membrane in membranous bags called vesicles
• Vesicular transport is an active process because energy is needed to form vesicles
• Phagocytosis is the process of taking solids into the cell
• Pinocytosis is the process of taking liquid into the cell
• Pinocytosis and phagocytosis are both examples of endocytosis

  
• Exocytosis is when the contents of a vesicle inside the cell are passed to the outside of the cell

  
• Endocytosis is the taking in of solids or liquids into the cell via vesicular transport