Membranes and Membrane Transport Summary

Membranes and Membrane Transport Overview

  • Theme: Form and Function

  • Level of Organisation: Cells

IB Guiding Questions

  • How do lipids and proteins assemble into membranes?

  • What determines substance passage through membranes?

SL & HL Content

  • B2.1: Membranes and Membrane Transport

    • B2.1.1: Lipid bilayers form cell membranes.

    • B2.1.2: Lipid bilayers act as barriers.

    • B2.1.3: Simple diffusion across membranes involves uncharged particles (e.g., O₂, CO₂).

    • B2.1.4: Integral and peripheral proteins perform various functions.

    • B2.1.5: Osmosis and aquaporins regulate water movement.

    • B2.1.6: Channel proteins facilitate diffusion for specific ions.

    • B2.1.7: Pump proteins enable active transport against gradients.

    • B2.1.8: Membrane selectivity is based on size and charge.

    • B2.1.9: Glycoproteins and glycolipids function in communication and recognition.

    • B2.1.10: Fluid mosaic model describes membrane structure and function.

Key Terms

  • Phospholipid Bilayer: Forms the basis of membranes.

  • Hydrophobic/Hydrophilic: Polarity affecting membrane interaction.

  • Passive Transport: Includes simple and facilitated diffusion, no energy required.

  • Active Transport: Movement against gradient utilizing ATP.

Structures and Functions

  • Phospholipids: Comprise bilayers with hydrophilic heads and hydrophobic tails.

  • Integral Proteins: Embedded in bilayers, may transport substances.

  • Peripheral Proteins: Attached to surface, can act as receptors.

  • Aquaporins: Specialized for rapid water transport.

Transport Mechanisms

  • Simple Diffusion: Movement from high to low concentration without energy.

  • Facilitated Diffusion: Utilizes proteins for molecules unable to pass bilayers directly.

  • Active Transport: Requires ATP to move substances against their concentration gradient.

Selectivity in Membrane Permeability

  • Passive Transport: Non-selective; depends on size and charge.

  • Active Transport: Selective; proteins are specific to substances.

Membrane Components

  • Glycoproteins & Glycolipids: Involved in cell recognition and signaling.

  • Cholesterol: Stabilizes membrane fluidity.

Bulk Transport

  • Endocytosis: Process for large particles entering cells.

  • Exocytosis: Release of materials from cells.

Gated Channels and Ion Transport

  • Voltage-Gated Channels: Respond to membrane potential changes.

  • Sodium-Potassium Pumps: Maintain resting potentials; vital for neural activity.

  • Sodium-Dependent Glucose Cotransporters: Indirect active transport mechanism for glucose absorption.

Conclusion

Understanding membrane structure and transport mechanisms is key for comprehending cellular functions and interactions with the environment.