Diffusion and Electrolytes Quiz

Bioelectricity and Biophotonics Engineering

• The course is titled WSC331
• Taught by Felipe Iza at Loughborough University, UK
• The course material covers bioelectricity and biophotonics engineering
• The course is on slide set Bioelec 4
• The course website is http://www.lboro.ac.uk/departments/meme/staff/felipe-iza

Recap from Previous Lecture

• This section reviews neuronal structure and function.
• The structure of neurons is depicted with a diagram, highlighting components like protein channels (transport proteins), globular proteins, cholesterol, glycolipid, peripheral proteins, extracellular fluid, glycoprotein, integral proteins, filaments, cytoskeleton, cytoplasm, and various parts of neurons including dendrites, axon hillock, axon, myelin sheath.
• The diagram also shows different types of synapses (axodendritic, axosomatic, axoaxonic)
• Action potential time course is shown graphically
• The graph indicates resting potential, threshold potential, and the excitory and inhibitory stimulus times
• The graph demonstrates the propagation of ions in the nerve fiber and the result is an action potential.

Today's Lecture

• The lecture covers transport phenomena
• Transport mechanisms, including diffusion and conduction
• The Nernst-Plank equation (drift-diffusion equation)

Transport Mechanisms

• Advection (Convection): Transport of a substance with a moving fluid (e.g., oxygen in the bloodstream).
• Diffusion: Transport from high concentration to low concentration due to random particle motion. Examples include osmosis (solvent diffusion, often water) across a semi-permeable membrane.
• Electric field mediated: Electrophoresis (for charged particles), and dielectrophoresis (for non-charged dielectric particles in an inhomogeneous field).
• Other transport mechanisms, like electrorotation, Pearl chain formation, and electro-osmosis, are also mentioned

Surface Area and Diffusion

• As organisms get larger, their surface area to volume ratio decreases.
• Smaller organisms (like bacteria) have a higher surface area to volume ratio, making diffusion efficient.
• Larger organisms (like whales) have a lower surface area to volume ratio, making diffusion less efficient.

Main Transport Mechanism

• The Peclet number (Pe) compares convection and diffusion rates
• Values of Pe and diffusion times for various molecules are displayed in a table.
• Tables show molecules like oxygen, glucose, insulin, antibodies, viruses and bacteria. And their relation to size and diffusion time.

Diffusion vs Convection

• Diffusion time scales with L².
• Convection time scales with L.
• Diffusion is critical for short distances.
• Convection is more efficient for long distances.

A Few Definitions

• Solution: A homogeneous mixture of two or more substances (Solvent + Solute).
• Solute: The substance dissolved in a solution.
• Solvent: The liquid that dissolves the solute. Water is the most common biological solvent.
• Electrolyte: An ionic solution containing ions (e.g., Na+, K+, Ca2+, Cl-) that conducts electricity.
• Anion: A negatively charged ion. Ions move towards the anode
• Cation: A positively charged ion. Ions move towards the cathode

Ionic vs Electronic Conduction

• Ionic conduction: Involves ions as charge carriers, allowing mass transfer.
• Electronic conduction: Involves electrons as charge carriers, but no mass transfer.

Electronic/Ionic Conductivity

• This section presents a table comparing the conductivity of various materials (metals, semiconductors, biological materials).

Moles/sec vs Amperes

• Chemists: Use moles to measure the amount of a substance. One mole contains Avogadro's number of entities (6.022x10^23). Unit for current = moles/sec
• Electrical Engineers: Use Coulombs to measure electric charge. One Coulombs (1C) = charge carried by an 1 amp current in 1 second. Charge of electron (unitary charge) is 1.6x10⁻¹⁹C. Unit for current = A (C/sec)

Faraday's Constant

• Faraday's constant (F) relates the unit of current measurement in chemistry (moles/sec) to electrical engineering unit (A).

Electrolyte Composition

• Important ions include sodium (Na+), potassium (K+), chloride (Cl-), and calcium (Ca2+).
• Concentrations vary between intracellular and extracellular regions

Molarity

• Molarity (or molar concentration, C): Moles of solute per unit volume of solution.
• Typically measured in mol/litre (M), although the SI unit is mol/m³.
• Millimolar (mM) equals 10⁻³ mol/L, and micromolar (µM) equals 10⁻⁶ mol/L.

Exercise (Example Calculations)

• Example problems, like calculating molarity of substance dissolved in water or molar concentration of protein.

Solution

• Exercise Problems.

Diffusion

• Diffusion is the movement of particles from an area of high concentration to an area of low concentration.

Fick's First Law

• Fick's First law describes the rate of diffusion as proportional to the concentration gradient
• The flux tends to remove spatial inhomogeneities.

Diffusion: Temperature Dependence

• The diffusion coefficient (D) increases with temperature (T) following the Arrhenius equation.

Osmosis

• Osmosis is the movement of solvent (usually water) across a selectively permeable membrane from an area of low solute concentration to an area of high solute concentration

Tonicity

• Hypotonic Solution: Lower solute concentration compared to another solution
• Hypertonic Solution: Higher solute concentration compared to another solution
• Isotonic Solution: Same solute concentration in two solutions

Question

• Why do creases appear on the fingers after prolonged exposure to water.

Mobility

• Charged particles experience forces in an electric field.
• Mobility (μ) quantifies the speed of a particle in a field.

Flux Induced by the Electric Field

• Chemists (moles/sec) and engineers (Amps/currents) approaches to the flux equation

Conductivity

• One species: The relationship between current, charge, mobility, and concentration
• Multiple species: Conductivity in a solution with multiple ions considered.

Transference Number

• The fraction of current carried by each ion in a solution.

Transference Numbers

• Values of transference numbers for various salts (e.g., KCI, HCI, LICI, NaCl) in different molar ranges.

Einstein Relation

• The relationship between diffusion coefficient (D) and mobility (μ) of an ion, derived from Brownian motion and collisions.

Diffusion + Conduction

• The Nernst-Plank Equation describing diffusion and conduction of ions simultaneously, accounting for concentration gradients and electric field influences

Nernst-Plank Equation

• Two different perspectives considering the equation from chemist's and engineer's prospective.

Today's Lecture

• Transport Phenomena, Transport mechanisms, Diffusion, Conduction, Nernst-Plank Equation

Next Lecture

• Transport across cell membranes
• Nernst Potential
• Membrane parallel conductance model

Test your knowledge on diffusion processes and electrolytes with this engaging quiz. Explore concepts such as diffusion time, solvent characteristics, and the nature of ions. It's a great way to reinforce your understanding of these fundamental topics in chemistry.