Moving_Across_Membranes_Methods

Movement Across the Cell Membrane

Overview

• Essential topic covering the mechanisms by which substances cross cell membranes.

Review from Yesterday

• Quick quiz to assess understanding of previous content.

• Reminder for absent students to email for catching up on missed work.

Key Factors Influencing Membrane Transport

• Size, Charge, Polarity:

  • Small, non-polar, or lipid-soluble substances pass through membranes more easily.

Size and Charge Affecting Diffusion

• Hydrophobic Molecules:

  • Example: Oxygen (O₂), Carbon Dioxide (CO₂), Nitrogen (N₂).

• Small Polar Molecules:

  • Example: Water (H₂O), Indole, Glycerol.

• Large Uncharged Polar Molecules:

  • Example: Glucose, Sucrose.

• Ions:

  • Example: Chloride (Cl-), Potassium (K+), Sodium (Na+).

Methods to Move Substances Across Membranes

Group Activity

• Research and discuss different methods for substances to move across membranes.

• Fill out a summary table on the findings.

• Model processes using plasticine and pipe cleaners.

• Optional: Look at future practical exercises.

Summary Table Topics

• Occurs across lipid bilayer?

• Requires protein carrier or channel?

• Movement down vs. against the concentration gradient?

• Requires a source of ATP?

Key Transport Processes

• Diffusion:

  • Movement from high to low concentration passively across a semi-permeable membrane.

• Osmosis:

  • Specific for water movement through a partially-permeable membrane.

Understanding Osmosis

• Direction of Water Movement:

  • Determined by total solute concentrations:

    • Hypertonic: More solute, less water.

    • Hypotonic: Less solute, more water.

    • Isotonic: Equal solute and water.

Managing Water Balance for Cells

• Animal Cells:

  • Hypotonic: Lysed, Normal.

  • Hypertonic: Shriveled.

• Plant Cells:

  • Hypotonic: Turgid.

  • Isotonic: Flaccid.

  • Hypertonic: Plasmolyzed.

Aquaporins

• Water proteins facilitate rapid movement of water across cell membranes.

• Key researchers include Peter Agre and John Hopkins.

Diffusion & Osmosis Summary

• Essential processes for substance movement across membranes.

Channels through Cell Membrane

• Membrane semi-permeability enhanced by protein channels.

• Specific channels allow selective material to cross.

Facilitated Diffusion

• Passive transport through protein channels without energy.

• Effectively moves polar molecules and ions across membranes.

Active Transport

• Required when moving substances against the concentration gradient (low to high).

• ATP is utilized to provide necessary energy.

Getting Through the Cell Membrane

• Transport Types:

  • Passive Transport: Simple diffusion (high to low) through lipid barrier.

  • Facilitated Transport: Needs protein channels for polar molecules.

  • Active Transport: Requires ATP for movement against concentration gradient.

Transport Summary

• Simple diffusion and facilitated diffusion require no ATP.

• Active transport requires ATP.

Moving Large Molecules

• Molecules move in and out via vesicles and vacuoles using:

  • Endocytosis:

    • Phagocytosis: Cellular eating.

    • Pinocytosis: Cellular drinking.

  • Exocytosis: releases substances from the cell.