Movement through the Plasma Membrane

plasma membrane selectively permeable

only allows certain substances to pass through it, must maintain homeostasis though composition inside and out of cell are different, cell volume must stay the same even with movement of material in and out of cell, lipid soluble molecules and steroids readily dissolve in the lipid bilayer to pass through the membrane, large nonlipid soluble molecules and ions need transport proteins or vesicles to pass through membrane

passive membrane transport

the cell does not expend ATP; movement from higher concentration to lower concentration; diffusion, osmosis, and facilitated diffusion

active membrane transport

ATP is used to move from lower concentration to higher concentration; active transport, secondary active transport

vesicular membrane transport

uses a membrane-bound sac; endocytosis, exocytosis

diffusion

net movement of solutes from an area of higher concentration to lower concentration in solution

concentration gradient

concentration difference between two points, solutes move down this until an equilibrium is established

rate of diffusion factors

magnitude of concentration gradient (the more steep the faster), temp of solution (the higher the temp the faster), size of molecules (the larger the slower), and viscosity of solvent (the more viscous the more slow)

osmosis

diffusion of water (solvent) across a selectively permeable membrane; water moves from an area of low concentration of solute (high amount of water) to an area of high concentration (low amount)

aquaporins

water channel proteins

osmotic pressure

force required to prevent water from moving across a membrane by osmosis

isosmotic

solutions with the same concentrations of solute particles; equal osmotic pressures

hyper-osmotic

solution with a greater concentration of solute; greater osmotic pressures

hypoosmotic

solution with lesser concentration of solute; lesser osmotic pressures

osmosis and cells

important because large volume changes caused by water movement disrupt normal cell function

isotonic

cell neither shrinks or swells when placed in a solution

hypertonic

cell shrinks (crenation) when placed in a solution; water moves out of cell

hypotonic

cell swells and may rupture (lysis) when placed in solution; water moves into cell

facilitated diffusion

mediated transport process carried out by carrier/channel proteins; no ATP required, move large, water soluble molecules or electrically charged molecules across the plasma membrane, amino acids and glucose in, manufactured proteins out

active transport

required ATP, substances can be moved against their concentration gradient (low to high), allowing the substance to accumulate on one side of plasma membrane, rate of transport depends on substrate concentration, number of ATP pumps, and amount of ATP

secondary active transport

use of potential energy in concentration gradient of one substance (established by primary active transport) to help move another substance

vesicular transport

movement of larger substances by formation or release of a vesicle, requires ATP

endocytosis

movement into cell; vesicular transport type

phagocytosis

solid particle in ingested and large vesicle is formed; vesicular transport type

pinocytosis

dissolved molecules ingested and small vesicles are formed; vesicular transport type

exocytosis

movement out of cell; vesicular transport type

transcytosis

movement through a cell by a combination of endocytosis on one surface and exocytosis on the opposite surface; vesicular transport type