AP Biology: Membrane Transport

Introduction

• Topic: Membrane transport
• Previous Topics:
  • 2.5: Membrane permeability
  • 2.4: Phospholipid bilayer structure

Key Concepts

Membrane Structure

• Composed of a phospholipid bilayer
  • Polar head
  • Two nonpolar fatty acid tails

Membrane Function

• Regulates what comes in and out of cells
• Establishes concentration gradients

Diffusion

• Definition: Movement of particles from high to low concentration
• Importance: Essential for bringing in nutrients and expelling waste
• Example: Food coloring spreading in water
• Equilibrium: Equal concentration on either side of a barrier

Concentration Gradient

• Definition: Region where the density of a substance increases or decreases
• Analogy: Like moving from high to low elevation

Types of Transport

Passive Transport

• Definition: Movement of substances across the cell membrane without energy expenditure
• Example: Oxygen (O2) and carbon dioxide (CO2) movement
• Equilibrium: No concentration gradient

Active Transport

• Definition: Movement against the concentration gradient, requiring energy (ATP)
• Mechanism: Uses membrane proteins to move substances
• Importance: Establishes concentration gradients
• Example: Sodium and potassium in neurons

Facilitated Diffusion

• Note: To be covered in future topics

Vesicular Transport

Exocytosis

• Definition: Secretion of molecules by vesicle fusion with the plasma membrane

Endocytosis

• Definition: Uptake of molecules by vesicle formation
• Types:
  • Phagocytosis: Intake of solid particles (cell eating)
  • Pinocytosis: Intake of extracellular fluids (cell drinking)

Conclusion

• Importance of transport mechanisms in cellular function
• Leads into further unit topics
• Open for questions