Lecture on Membrane Transport: AP Biology Section 2.6

Introduction

• Single-celled organisms use nutrient and waste methods similar to larger organisms.
• All cells require membrane transport to maintain solute concentrations, import molecules, and maintain water balance.
• Transport Methods:
  • Active Transport: Requires energy.
  • Passive Transport: Does not require energy.
• Important for AP Biology exams.

Differences Between Active and Passive Transport

Active Transport

• Requires Energy from ATP or concentration gradient.
• Moves substances against concentration gradient (low to high concentration).

Passive Transport

• Does Not Require Energy.
• Moves substances from high to low concentration.
• Includes:
  • Simple Diffusion: Small molecules pass through plasma membrane.
  • Facilitated Diffusion: Uses ion channels and carrier proteins.

Passive Transport Details

Simple Diffusion

• Small, nonpolar molecules like oxygen, water, and CO₂ pass through the membrane.
• Osmosis: Specific diffusion of water, covered in section 2.8.

Facilitated Diffusion

• For ions and large molecules, uses:
  • Channel Proteins: Ions pass through.
  • Carrier Proteins: Large molecules bind, change protein conformation, and pass through.

Active Transport Details

• Energy-Dependent: Moves substances against gradient.
• Types of Proteins:
  • Uniporters: Move one substance.
  • Symporters: Move two substances in the same direction.
  • Antiporters: Move two substances in opposite directions.

Energy Sources

• Primary Active Transport: Uses ATP.
• Secondary Active Transport: Uses potential energy from concentration gradients.

Large-Scale Transport Mechanisms

Endocytosis

• Methods for intake of large quantities/materials into cells.
• Types:
  • Phagocytosis: Engulfs large particles or cells.
  • Pinocytosis: Intakes large volumes of fluid.
  • Receptor-Mediated Endocytosis: Specific molecules (e.g., cholesterol) intake.

Exocytosis

• Expels large quantities/materials out of cells.
• Example: Neuron signal transfer via neurotransmitter release.

Conclusion

• Endocytosis and exocytosis are crucial for cell function.
• Important for AP tests.
• Additional resources and test questions available on Biology Dictionary channel.