BIO2 Reading 8

Selective Permeability

Allowing only substances meeting certain physical criteria to cross the membrane; controls the concentration of substances in the in the cell

Relative Permeability

Differences in membranes' mosaic compositions cause permeability rates to vary

Membrane Permeability Coefficient

Rate of movement of a substance across a biological membrane

Osmosis

Movement of water through a semipermeable membrane according to the concentration gradient of water across the membrane

Tonicity

The ability of an extracellular solution to change the volume of a cell by affecting osmosis; correlates directly with osmolarity

Osmolarity

Total solute concentration of the solution; water moves from low osmolarity to high osmolarity

Low -> Greater # of water molecules relative to # of solute particles

High -> Lower # of water molecules relative to # of solute particles

Hypotonic Solution

Extracellular fluid has lower osmolarity that intracellular fluid -> water enters the cell

Hypertonic Solution

Extracellular fluid has higher osmolarity than intracellular fluid -> water exits the cell

Isotonic Solution

Osmolarity of extracellular fluid equals that of intracellular fluid; no net movement of water

Osmoregulation

Method to control the effects of osmosis, such as plasmolysis in plant cells (cell does not shrink in hypertonic solution due to the cell wall) and contractile vacuoles in protists (collect excess water and pump it out)

Passive Transport

Exergonic movement of substances across the membrane from a high concentration to a low concentration; energetically favorable

Types of Passive Transport (2)

Simple diffusion and facilitated transport/diffusion

Simple Diffusion

Substance moves across a concentration gradient until the concentration with the cell equals that outside the cell

What factors can impact simple diffusion? (6)

Extent of the concentration difference inside and outside the cell

Shape/size/mass of substance

Temperature

Solvent density

Surface area/thickness of the membrane

Distance travelled by the substance

Facilitate Transport/Diffusion

Substances diffuse across the membrane with the help of transmembrane proteins

Channel Protein

Provide a "passageway"/"tunnel" for either a specific substance or multiple substances sharing characteristic(s); can be open at all times or gated (controlled by binding of small molecules/ions or by environmental conditions)

Aquaporins

Protein channels that facilitate the movement of water into and out of a cell

Carrier Proteins

Bind to a substance, triggering a change in its shape that moves the substance to the other side of the membrane depending on the concentration gradient; usually serve a particular substance

Active Transport

Endergonic movement of substances across the membrane from a low concentration to a high concentration coupled with an exergonic reaction; energetically unfavorable

Pump

Active transport mechanism

Electrogenic Pump

Pump creating a charge imbalance across a membrane

Primary Active Transport

Moves ions across a membrane, creating a difference in charge on either side (uses ATP/energy)

Secondary Active Transport

Moves substances using the electrochemical gradient established by primary active transport (indirectly uses ATP/energy)

Uniporter

Carrier protein that moves one ion/molecule across the membrane

Symporter

Carrier protein that moves two ions/molecules across the membrane in the same direction

Antiporter

Carrier protein that moves two ions/molecules across the membrane in the opposite direction