membrane transport activity

Course Overview

  • Course Name: BIO 105 Introductory Biology I
  • Learning Activity: Membrane Transport

Supplies Bag Contents

  • 50 mini phospholipid models (negative charge)
  • 30 water molecule models
  • 5 membrane segments
  • 5 glucose models
  • 30 round sodium (Na+) models
  • 30 square potassium (K+) models
  • 1 ATP model
  • 5 grey transport protein models
  • 1 laminated beaker picture with water

Pre-Activity Review

  • Negative Charge on Phospholipid:
    • Explanation needed for the presence of a negative charge on phospholipids.
  • Structural Formula Drawing:
    • Students instructed to draw the structural formula of a phospholipid and align it with the model.
    • Questions to clarify which regions of the model correspond to which regions in the structural formula.

Activity Overview: Formation of Phospholipid Structures

Monolayer Formation

  • Phospholipid Behavior in Water:
    • Phospholipids can form a monolayer when placed in water
    • Students instructed to model a monolayer using mini phospholipid models.
  • Sketching Task:
    • Sketch appearance of the monolayer model.
  • Questions for Rationale:
    • Identify and explain the facing portions of the phospholipid model in relation to water.

Bilayer Formation

  • Submersion in Water:
    • When fully submerged, phospholipids cannot form a monolayer due to repulsion of fatty acid tails by water.
    • Instead, they can form bilayers.
  • Modeling Bilayer:
    • Utilize mini phospholipid models to demonstrate bilayer formation.
  • Stability of Arrangement:
    • Explanation required on why bilayer structure is stable when submerged in water.

Cell Membrane Modeling

Membrane Structure and Function

  • Cell Membrane Representation:
    • Use 5 membrane segments to model a cell membrane in a circular arrangement.
  • Water Molecule Distribution:
    • Place 8 water molecule models inside the membrane and 12 outside.

Questions on Molecule Movement

  • Water Molecule Movement:
    • Inquiry about whether water can move through the bilayer model.
    • Explain properties of water and phospholipid bilayers regarding permeability.

Role of Transport Proteins

Importance of Transport Proteins

  • Function of Transport Proteins:
    • Essential for assisting in the transport of nutrients and waste across the phospholipid bilayer.
    • Many substances, including water, cannot pass directly through the bilayer.

Aquaporin Model

  • Aquaporin Role:
    • Instructed to locate the aquaporin model and place it across the bilayer with correct orientation (label down against bilayer, arrows up).

Understanding Osmosis

Osmosis Process

  • Definition of Osmosis:
    • A spontaneous process requiring no input of energy, occurring as water moves down its concentration gradient (high to low concentration).
  • Observation in Model:
    • Directions in which water molecules will move based on the specific arrangement and concentration.

Equalization of Water Concentration

  • Water Molecule Movement:
    • Modeling the movement of water across the bilayer until water concentration is even on both sides.
  • Data Requirement:
    • Record how many water models need to be moved for equal concentration.

Solute Effects in Biological Systems

Solute Solutions in Model

  • Definitions of Solution Types:
    • Understand the terms: hypertonic, hypotonic, isotonic.
  • K+ Model Placement:
    • Place 2 potassium models and 8 water models inside and 6 potassium models and 4 water models outside the cell.

Identifying Solution Types

  • Determination of Solute State:
    • Identify the solution state (hypertonic, hypotonic, isotonic) created by the model.
    • Explanation required for classification based on solute distribution.

Properties of Potassium Cations (K+)

  • K+ Permeability:
    • Instructed to consider why potassium cations cannot move freely across a lipid bilayer based on their chemical properties.

Facilitated Diffusion of Potassium

K+ Leak Channel Model

  • Facilitated Diffusion Definition:
    • The process where solutes are transported down their concentration gradient with help from transport proteins.
  • Modeling K+ Movement:
    • Set up a model demonstrating the facilitated diffusion of potassium ions across the bilayer.

Directions of Movement

  • Hypertonic Movement:
    • Inquiry as to the direction of potassium movement during the demonstration of a hypertonic solution.
    • Explanation required based on concentration gradient.
Achieving Isotonic Condition
  • Reaching Equilibrium:
    • Record how many potassium models were moved to achieve isotonicity between both sides of the membrane.

Hypotonic Solutions

Modeling a Hypotonic Solution

  • Hypotonic Arrangement:
    • Students instructed to retain a total of 10 molecule models per side while adjusting the ratio of K+ and water molecules to simulate a hypotonic solution.

Resulting Potassium and Water Models

  • Count of Models:
    • Speculative counts for potassium and water models inside and outside the cell in the hypotonic simulation.

Directional Movement of Ions

K+ Directionality in Hypotonic Solution

  • K+ Movement:
    • Inquiry regarding the movement direction of potassium through the channel in the hypotonic context; reasoning needed.

Simultaneous Processes

Returning to the Original Setup

  • Reinstating Initial Conditions:
    • Revert potassium and water models to original counts for the activity, maintaining K+ leak channel and reintroducing aquaporin.

Direction of Diffusion

  • Simulated Movement of Potassium and Water:
    • Inquiry about the directionality of potassium and water movement in this setup, including reasoning based on concentration gradients.
    • Count of potassium and water models needing diffusion to achieve isotonic conditions.