1. Cellular Transport and Tonicity
Biology 2121

2. Selective Permeability of the Plasma Membrane
Which substances can move freely through the phospholipid bilayer?
Water, gases (oxygen, carbon dioxide); fats
Small- polar; nonpolar molecules
Which substances are blocked?
Glucose; ions
Larger substances (polar)
Processes
Passive (no ATP)
High to lower concentration gradients
Driving Force? KE of the substances
Active (requires ATP)
Low to higher concentration gradients

3. Passive Processes 1. Diffusion vs. Osmosis 2. Simple Diffusion
Gases; nonpolar; lipid soluble substances (fat-soluble vitamins)
3. Facilitated Diffusion
Sugars (glucose; amino acids; ions)
Integral or Transmembrane proteins
Channel or carrier proteins
4. Osmosis
Movement of water dependent on solute concentration (extracellular/intracellular)

4. Tonicity
Measure of the ability of a solution to cause a change in cell shape or tone caused by osmotic flow of water
Why does osmosis occur?
Water concentration differences
Solute concentration affects water concentration
Dependent on the number (concentration)
Osmolarity
Permeability of solute molecules
Permeable to all solute molecules – equilibrium
If membrane is impermeable (see U-tube)

5. Water Movement and Solute Concentration

6. Tonicity – Conditions Isotonic Hypertonic Hypotonic
Cells have same concentrations of non-penetrating solutes as found in cells
Our cellular fluids and IV’s
Hypertonic
Solutions have higher concentration of non-penetrating solutes
Salty or high saline conditions
Hypotonic
Solutions containing a lower concentration of non-penetrating solutes
“dilute”

7. Active Transport Driving Force? ATP Sodium-Potassium Pump
Solute “pumps” (ions- K+, Na+, etc.)
Sodium-Potassium Pump
“primary active transport”
Neurons, cardiac and skeletal tissue
Vesicular Transport
Fluids contain large particles and macromolecules
Vesicles

8. Vesicular Transport Exocytosis Endocytosis
“ejects” substances from cells
Hormone and mucous secretion
Endocytosis
Substance moves into cell and vesicle formed
transcytosis, vesicular trafficking
Phagocytosis
Pinocytosis