Chapter 3 – pp 101 - 109

Unit III: Lively MoleculesMovement of Molecules

Interstitial fluid

Ions

GlucoseBlood proteinAmino acid

Capillaryhydrostatic

pressure(CHP)

Filtration

• Particles are driven through a selectively permeable membrane by water

• Moves material between cells not thru

• Examples: coffee filter, blood capillaries

Endothelialcell 1

Endothelialcell 2

Water molecule

Hydrogen bond

Small solutes

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 and Osmosis

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: ________________

Carrier – Mediated Transport

• Cell membrane is essential

• Employ transport proteins/carriers

• Specificity

• Saturation

Other Membrane Transports

Concentration of solute

Rat

e o

f so

lute

tra

nsp

ort

(mo

lecu

les/

sec

pas

sin

gth

rou

gh

pla

sma

mem

bra

ne)

Transport maximum (Tm)

Facilitated Diffusion

• Down gradient• No ATP used

Carrier – Mediated Transport

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

CYTOPLASM

Glucosemolecule

Sodiumion

Na+–K+

pump

+

+

• Regulation of cell volume

• Heat production

• Maintenance of a membrane potential

• Secondary active transport (No ATP used)

Vesicular Transport

• Transport large particles or fluid droplets through membrane in vesicles

• Endocytosis –

– phagocytosis –

– pinocytosis –

– receptor mediated endocytosis –

• Exocytosis –

Bacterium

Pseudopodium

Phagocytosis

Lysosome

Golgiapparatus

Exocytosis