Physics Exam III

What causes diffusion & what happens at equilibrium?

RANDOM THERMAL MOTION causes net movement from high → low concentration

@ equilibrium, molecules still move randomly, but theres no net motion.

What factors increase Diffusion RATE?

• Fick’s law?

• Greater Diffusion constant (D)

• Surface Area (A)

• Concentration Difference (dC)

• Temperature

• Shorter Distance

Flux: J = D dC / dx

Flux is inversly proportional to distanec

How does molecule size, emphysema, and membrane thickness affect diffusion?

• Smaller molecules = faster diffusion

because they move more easily through the spaces between particles in a medium, experiencing less resistance.

• Emphysema = slower diffusion

because reduced alveolar SA

• Bigger Membrane thickness = reduced flux

increases distance dx

x = sqrt (2Dt)

Compare:

• simple diffusion

• facilitated diffusion

• osmosis

• active transport

simple: down gradient, no atp

facilitated: down gradient through proteins, no atp

osmosis: water diffusing across selectively permeable membrane

active: uses energu to move against gradient

What determines ion movement

• how can ion flux increase?

Ions follow electrochemical gradients (concentration + electrical fx)

• opening more channels increases available pathways and total flux without changing the gradient.