Ch 7: Membrane Structure and Function Flashcards
What is passive transport?
Passive transport is diffusion of a substance across a membrane with no energy investment
What is diffusion?
diffusion is the movement of particles of any substnace so that they spread out evenly into the available space
What is a concentration gradient?
the region along which the density of a chemical substance increases or decreases
What does concentration gradient represent?
it represents potential energy that drives diffusion
What does rate of diffusion depend on?
it depends on membrane permeability to the specific substance
What is osmosis?
it is the diffusion of free water (water molecules not clustered around another substance) across a selectively permeable membrane, free water molecules diffuse across a membrane from the region of lower solute concentration to the region of higher solute concentration
What is tonicity?
the ability of a surroudning solution to cause a cell to gain or lose water
What does tonicity depend on?
tonicity depends on the concentration of these solutes in the solution that cannot cross the membran, relative to that inside the cell, if the solution has a higher concentration of these solutes than the inside of the cell, water will tend to leave the cell, and vice versa.
What does it mean for a solution to be isotonic?
the solute concentration is the same as that inside the cell, meaning water diffuses across the membrane at the same rate in both directions
How is the cell wall in an isotonic solution?
the volume of a cell without a cell wall is stable in an isotonic solution
What does hypertonic mean?
a solution is hypertonic is the solute concentration is greater than that inside the cell
What is plasmolysis?
a phenomenon where the cell shrivels and the membrane pulls away from the cell wall in multiple locations
What is hypotonic?
when the solute concentration is less than that inside the cell
What does a plant cell do in a hypotonic solution?
a plant cell will take up water and swell until the inelastic wall exerts back a pressure on the cell, called turgor pressure
What is osmoregulation?
when cells without walls cant tolerate excessive water loss or uptake so they have to have a control of solute concentration and water balance
What is facilitated diffusion?
when transport proteins speed the passive movement of molecules across the plasma membrane, ex. aquaporins facilitate the diffusion of water
What is the function of a channel protein?
a channel protein provides corridors that allow a specific molecule or ion to cross the membrane
Ion Channels
facilitate the transport of ions
What is a gated channel?
some ion channels open or close in response to a stimulus (chemical or electrical)
Why is facilitated diffusion passive?
the solute moves down its concentration gradient and the transport requires no energy
What is active transport?
requires energy, usually in the form of ATP hydrolysis, to move substances against their concentration gradients, all proteins involved in active transport are carrier proteins
Active transport enables
cells to maintain solute concentrations that differ from the environment, ex. sodium-potassium pump
What is membrane potential?
the voltage (electrical potential energy) across a membrane
How is voltage created?
by differences in the distribution of positive and negative ions across a membrane
What is a electrochemical gradient?
Two combined forces, a chemical and electrical force, drive the diffusions of ions across a membrane
What is an electrogenic pump?
a transport protein that generates voltage across a membrane, storing energy that can be used for cellular work
Main electrogenic pump for plants
in plants, fungi, and bacteria is the proton pump, which actively transports hydrogen ions out of the cell
Main electrogenic pump for animals
in animals it is the sodium-potassium pump
What is cotransport?
when active transport of a solute indirectly drives transport of other substances, the “downhill” diffusion of solute is coupled to the “uphill” transport of a second substance against its own concentration gradient
What is exocytosis?
transport vesicles migrate to the membrane, fuse with it, and release their contents outside the cell
What is endocytosis?
macromolecules are taken into the cell in vesicles, the membrane forms a pocket that deepens and pinches off forming a vesicle around the material for transport
What are the three types of endocytosis?
phagocytosis, pinocytosis, and receptor-mediated endocytosis
What is phagocytosis?
a cell engulfs a particle by extending pseudopodia around it and packing it in a membranous sac called a food vacuole
What is pinocytosis?
molecules are taken up when extracellular fluid is “gulped” into tiny vesicles, any and all solutes are taken into the cell
What is receptor-mediated endocytosis?
vesicle formation is triggered by solute binding to receptors
