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
molecules can pass through cell via 2 major types of transport
passive transport and active transport
the net movement of molecules from an area of high concentration to an area of low concentration until the concentration is equally distributed.
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
molecules and ions move directly through the membrane down the concentration gradient.
a transport protein aids in the transport of a molecule through the membrane. can only carry molecules from high concentration to low concentration.
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)
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.
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
impermeable junctions that act like "quilting" between cells to prevent molecules from passing through the extracellular space between adjacent cells.