Passive Transport

• Passive Transport


  • It is the movement of materials across a semi-permeable membrane from an area of high concentration (a lot of particles) to an area of low concentration (fewer particles)
  • This does NOT require energy
• There are 3 types of Passive Transport

  1. Diffusion
  2. Facilitated Diffusion
  3. Osmosis
• Diffusion


  • it is the net movement of particles from an area of high concentration to low concentration - down a concentration gradient.
  • Smaller particles such as oxygen and carbon dioxide can diffuse easily and directly across the membrane.
• Factors that determine the rate of diffusion are:

  1. Membrane thickness
  2. Concentration gradient
  3. Pressure
  4. Temperature
  5. Surface area
• Facilitated Diffusion


  • It is the transport of materials across a membrane from an area of high concentration to low concentration with the help of a carrier protein.
  • Larger and charged molecules struggle to get through the hydrophobic (lipid tails) layer of the plasma membrane.
  • Therefore, cells use specialised proteins called ion channels as a tunnel, allowing the specific ions to diffuse through them.
  • It is driven solely by the concentration gradient and does not require energy (ATP).
• Osmosis 


  • it is diffusion of water/solvent across a selectively permeable membrane from an area of high concentration of water to low concentration of water.

  
• Osmosis and Water Potential

  • Water potential is the relative concentration of solutes on either side of the cell membrane. It determines the direction and extent of which water moves by osmosis.
  • Water moves from an area with high water potential to an area with low water potential.
  • We can have hypertonic solutions, isotonic solutions or hypotonic solutions.

  
• Hypertonic Solution


  • High concentration of solutes (low concentration of water) outside of the cell
  • It causes a net movement of water out of the cell
  • Cells shrivel due to the loss of water
• In Hypertonic Solution


  When cells shrivel due to the loss of water:

  • Animal cells like red blood cells become star-shaped
  • In plant cells the membrane tears away from the cell wall (called plasmolysis) and causes the plants to die

  
• Hypotonic Solution


  • Lower concentration of solutes (higher concentration of water) outside of the cell than inside the cell.
  • This causes a net movement of water into the cell
  • Cells swell due to the water entering
• In Hypotonic Solution


  When cells swell due to water entering:

  • Animal cells like red blood cells swell and burst (lysis)
  • Plant cells swell and the membrane starts to push on the cell wall. The tough cell wall limits the volume and pressure builds. This water pressure keeps the plant cells turgid (swollen and firm).

  
• Isotonic solutions


  • Same concentration of solutes (same concentration of water) inside and outside of the cell
  • There is no net movement of water across the cell membrane
• In Isotonic solution

  Due to no movement of water:

  • Animal cells are unaffected
  • Plant cells may become flaccid (soft/drooping)

  
• Water Potential

  A) Hypotonic

  B) Hypertonic

  C) Isotonic

  D) Lysed

  E) Shriveled

  F) Normal

  G) Turgid

  H) Plasmolyzed

  I) Flaccid