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Phospholipid Bilayer

phospholipids are amphipathic(phobic and philic end) which causes layers to naturally form their bilayer structure. the philic heads are attracted to the extracellular water, the phobic tails are attracted to the intermembraneous grease

Fluid Mosaic

fluid phospholipid bilayer embedded with proteins

2 types of embedded proteins

carrier proteins and channel proteins

carrier proteins

"draw bridge" has an opening for one specific molecule

channel proteins

"regular bridge" allows molecules to freely pass through

molecules can pass through cell via 2 major types of transport

passive transport and active transport

passive transport

no energy is required for transport

active transport

energy is required for transport


the net movement of molecules from an area of high concentration to an area of low concentration until the concentration is equally distributed.

concentration gradient

uneven distribution of particles, potential energy exists on the side with the higher concentration. spreads from an area of high concentration to an area of low concentration: moving down the concentration gradient. Once evenly distributed: particles move in a dynamic equilibrium

dynamic equilibrium

when particles are evenly distributed: movement, but no net change

2 types of diffusion

1) simple diffusion and facilitated diffusion

simple diffusion

molecules and ions move directly through the membrane down the concentration gradient.

facilitated diffusion

a transport protein aids in the transport of a molecule through the membrane. can only carry molecules from high concentration to low concentration.


the diffusion of water across a selectively permeable membrane, water does the moving.




particles disolved in water



hypertonic solution

a solution with the higher solute concentration

hypotonic solution

a solution with the lower solute concentration

isotonic solution

equal concentrations of solute

osmotic pressure

the pressure that must be exerted on the hypertonic side of a selectively permeable membrane to prevent the diffusion of water from the hypotonic side of the membrane

human blood cell tonicity

when placed in a hypotonic solution the cell swells. when placed in a hypertonic solution the cell shrinks

turgor pressure (plant cells)

pushes the plasma membrane against the cell wall of plants. water enters the cell-> cell fills up-> cell swells putting pressure against the cell wall providing stability


the separation of the cell membrane from the cell wall, the cell membrane pulls away from the cell wall as the cell shrinks. lack of water->less turgor pressure-> wilting(plasmolysis)

active transport

requires energy input, cell uses energy from metabolic activities to pump substances

direct active transport (Na+K+ pump)

uses energy from ATP to pump 3 Na+ ions out and 2 K+ ions in. extracellular environment has more Na+ions and less K+ ions. Na+ and K+ are both pumped against their concentration gradient

indirect active transport(co-transport, sodium glucose pump)

a transport protein co-transports 2 solutes: 1 solute down its concentration gradient and 1 solute against its concentration gradient.


the active transport of a substance against its concentration gradient (low to high) by coupling its transport with the facilitated diffusion of another substance down its concentration gradient. Both Na+ and K+ travel through the same protein, but Na+ travels down the concentration gradient and glucose travels against its concentration gradient. It is active transport because energy was used earlier by the Na+ K+ pump to maintain a hight Na+ concentration in the extracellular environment. It is indirect active transport because a different protein had already used energy(ATP) to establish the right conditions for transport.

Cell Junctions (3 types)

Anchoring Junction( a and b), Tight junctions, Gap junctions

Anchoring Junctions

1)Adhering Junctions: cement cells together, cadherins: proteins that lock together and connect to the microfillaments in the cytoskeleton 2) desmosomes: protein plaque "rivets", scattered along the sides of cells, abundant in cells under large amounts of mechanical stress

tight junctions

impermeable junctions that act like "quilting" between cells to prevent molecules from passing through the extracellular space between adjacent cells.

Gap Junctions

animal cells/ plasmodesmata in plant cells: donut shaped channels made of connexin proteins that allow cells to share small molecules and fluids; can twist to open and close channels "communication junctions" found in cells requiring synchronization such as heart muscle cells.

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