Diffusion, Osmosis, and Types of Transport

Diffusion

• Definition: Movement of material from high concentration to low concentration.
• Example: O2 and CO2 molecules moving through a phospholipid bilayer.
• Passive Transport: Does not require energy.
  • Analogy: Rolling a ball down a hill.

Active Transport

• Definition: Movement of material from low concentration to high concentration.
• Example: Sodium ions pumped out of the cell using ATP.
• Requires Energy: Uses ATP (adenosine triphosphate).
  • Analogy: Pushing a ball up a hill.

Phospholipid Bilayer

• Structure: Composed of two layers of phospholipids.
• Components:
  • Ion Channels: Allow ions to pass through the membrane.
  • Carrier Proteins: Assist in transporting molecules like glucose.
  • Aquaporins: Allow water to flow in and out of cells.

Diffusion Types

• Simple Diffusion: Movement of nonpolar gases (e.g., CO2) through the membrane without assistance.
• Facilitated Diffusion:
  • Requires a carrier protein.
  • Example: Glucose transport.
• Facilitated Diffusion vs Simple Diffusion: Both are passive transport.
  • Facilitated uses proteins, simple does not.

Osmosis

• Definition: Diffusion of water.
• Direction: From high water concentration to low water concentration.
• Example: High concentration outside cell, low inside cell.
• Structure Involved: Aquaporins, osmosis through semi-permeable membrane.

Sodium-Potassium Pump

• Mechanism:
  • Uses ATP to pump sodium out and potassium into the cell.
  • Moves ions against their concentration gradients.

U-Tube Example

• Setup: Semi-permeable membrane; different solute concentrations on each side.
• Water Movement: From high water concentration (low solute) to low water concentration (high solute).
• Equilibrium: Forces of gravity and osmotic pressure balance out eventually.

Conclusion

• Passive Transport: High to low concentration; no energy required.
  • Includes simple diffusion, facilitated diffusion, and osmosis.
• Active Transport: Low to high concentration; energy required (ATP).

Remember:

• Diffusion: Movement from high to low concentration.
• Osmosis: Special case of diffusion for water.

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