Unit III: Lively Molecules
Movement of Molecules
Chapter 3 – pp 101 - 109
Filtration
• Particles are driven through a selectively permeable membrane by
water
• Moves material between cells not thru
• Examples: coffee filter, blood capillaries
Capillary
hydrostatic
pressure
(CHP)
Small solutes
Hydrogen bond
Amino acid
Blood protein
Glucose
Water molecule
Ions
Interstitial
fluid
Endothelial
cell 1
Endothelial
cell 2
Diffusion and Osmosis
Simple Diffusion
• Passive transport
• Random motion of solutes
• Rates depend on:
– Temperature
– Size of the molecule
– Distance
– Concentration gradient
• how a cell acquires nutrients and gets rid of wastes
Diffusion
• Down gradient
• Eventually becoming uniform
• Brownian Motion – random motions of microscopic particles
caused by collisions with moving molecules
• Example: a drop of dye in water
Diffusion and Osmosis
Osmosis
• Special type of diffusion:
– the diffusion of water molecules across a semi-permeable
membrane
Diffusion and Osmosis
Osmosis
• Osmotic pressure = Hydrostatic pressure to halt osmosis
• Osmotic pressure is proportional to the solute concentration
•Example:
Diffusion and Osmosis
Osmosis
• Example: Red blood cells placed in a drop of distilled water will
swell and burst
• Explanation: The distilled water is
hypotonic to the RBC’s cytoplasm
(a) Hypotonic
Diffusion and Osmosis
Osmosis
• Example: Red blood cells placed in a drop of highly concentrated
salt solution will shrivel up
• Explanation: The salt solution is
hypertonic to the RBC’s cytoplasm
Diffusion and Osmosis
Osmosis
• Example: Red blood cells placed in a drop of blood plasma – no
change.
•Explanation: The blood plasma is
isotonic to the RBC’s cytoplasm
Diffusion and Osmosis
Osmosis
• Osmolarity – total solute concentration in an aqueous solution
• Tonicity – description of how the solution effects a cell
•Example situation: giving large volume of fluid during blood loss or
dehydration.
– Osmolarity starts the same but ECF is ______________
– Ions (thus water) moves in to ICF to equilibrate ↑ osmolarity
– Administer: ________________
Other Membrane Transports
Carrier – Mediated Transport
• Cell membrane is essential
• Employ transport proteins/carriers
• Saturation
Rate of solute transport
(molecules/sec passing
through plasma membrane)
• Specificity
Transport maximum (Tm)
Concentration of solute
Carrier – Mediated Transport
Facilitated Diffusion
• Down gradient
• No ATP used
Carrier – Mediated Transport
Active Transport
• Up gradient
• ATP energy required to change carrier
• Examples:
– sodium-potassium pump
– bring amino acids into cell
– pump Ca2+ out of cell
Carrier – Mediated Transport
Active Transport
Sodium-Potassium Pump
• Needed because Na+ and K+ constantly leak through membrane
• One ATP utilized to exchange three Na+ pushed out for two K+
brought in to cell
Carrier – Mediated Transport
Active Transport
Sodium-Potassium Pump
• Regulation of cell volume
• Heat production
• Maintenance of a membrane potential
Glucose
molecule
Sodium
ion
+
• Secondary active
transport (No ATP used)
Na+–K+
pump
CYTOPLASM
+
Vesicular Transport
• Transport large particles or fluid droplets through membrane in
vesicles
Bacterium
Pseudopodium
• Endocytosis –
– phagocytosis –
Phagocytosis
Lysosome
– pinocytosis –
– receptor mediated endocytosis –
• Exocytosis –
Golgi
apparatus
Exocytosis