Question

cells need to exchange materials with the extracellular environment in order to survive. this exchange may involve passive transport processes, which do not require the expenditure of energy by the cell, or active transport processes, which require atp. the driving force behind the directional movement of all passive transport processes is the presence of a concentration gradient between the intracellular and extracellular fluids, which are separated by a semipermeable plasma membrane. simple and facilitated diffusion are both passive transport processes. solutes that can cross the membrane unassisted, such as small, lipid - soluble molecules, do so by simple diffusion. substances that are incapable of crossing the phospholipid bilayer unassisted, such as ions and polar molecules, depend upon the presence of specific membrane - bound protein channels or protein carriers in order to pass through the membrane. this type of transport is referred to as facilitated diffusion. facilitated diffusion can involve non - gated leakage channels, which are always open, or channels that are gated open by specific stimuli. such channels include ligand - gated, voltage - gated, or mechanically gated protein channels.

1. the directional movement of ions by facilitated diffusion through protein channels is determined by ___.

○ the formation of a secretory vesicle
○ the availability of atp
○ the concentration gradient of the ion being transported

1. simple and facilitated diffusion differ because ___.

○ simple diffusion requires the presence of a transport protein within the plasma membrane, while facilitated diffusion does not
○ ions being transported by simple diffusion move against their electrochemical gradients, while ions being transported by facilitated diffusion move along their electrochemical gradients
○ ions being transported by simple diffusion move along their electrochemical gradients, while ions being transported by facilitated diffusion move against their electrochemical gradients
○ facilitated diffusion requires the presence of a transport protein within the plasma membrane, while simple diffusion does not

1. electrical changes across the membrane trigger the opening or closing of ___.

○ ligand - gated channels
○ voltage - gated channels
○ mechanically gated channels

Explanation:

1. Passive transport like facilitated diffusion of ions is driven by concentration gradients. Secretory vesicles are for exocytosis and ATP is for active transport.
2. Simple diffusion is for small, lipid - soluble molecules crossing the membrane unassisted. Facilitated diffusion needs transport proteins for substances like ions and polar molecules.
3. Voltage - gated channels open or close in response to electrical changes (voltage changes) across the membrane. Ligand - gated channels respond to ligands and mechanically gated channels to mechanical stimuli.

Answer:

1. the concentration gradient of the ion being transported
2. facilitated diffusion requires the presence of a transport protein within the plasma membrane, while simple diffusion does not
3. voltage - gated channels