Lab 5 Difusion and Osmosis

Diffusion and Osmosis

• Diffusion is the passive movement of molecules from high concentration to low concentration until equilibrium is reached.

• Osmosis is a special case of diffusion - specifically, the movement of water across a selectively permeable membrane from an area of low solute concentration (high water concentration) to an area of high solute concentration (low water concentration).

Tonicity vs. Osmolarity

Osmolarity refers to the total concentration of all solute particles in a solution, measured in osmoles per liter (Osm/L). Human blood plasma has an osmolarity of approximately 300 mOsm/L (or about 0.9% NaCl).

Tonicity describes how a solution affects cell volume - it depends on the concentration of non penetrating solute

Isotonic vs hypotonic vs hypertonic

Isotonic: Same effective osmotic pressure as the cell; no net water movement; cell volume unchanged:

• no net water movement

• cell volume unchanged

Hypotonic: Lower effective osmotic pressure than the cell:

• water enters the cell

• cell swells

Hypertonic: Higher effective osmotic pressure than the cell:

• water exist the cell

• cell shrink

Why osmosis is critical in healthcare

• IV fluids must be isotonic (0.9% NaCl or "normal saline") to prevent cell damage

• Blood transfusions require isotonic solutions

• Dehydration creates hypertonic conditions in the body

• Over hydration (hyponatremia) creates hypotonic conditions

• Edema (swelling) results from osmotic imbalances

• Kidney disease affects the body's ability to regulate osmolarity

The rate of diffusion is affected by several factors

• Temperature:

  • Higher temperatures increase molecular kinetic energy, causing faster diffusion.

Questions - Part A

Which beaker showed faster diffusion? By approximately how much (calculate the ratio)?