Study 3 Cellular Transport with 12 free online flashcards. Review key terms, definitions, and concepts with this interactive flashcard deck.
What does it mean that a membrane is selectively permeable?
Cellular membranes allow some substances to cross more readily than others: small nonpolar molecules can often cross the lipid bilayer, while ions and many polar molecules need proteins or vesicles.
How do oxygen and carbon dioxide cross the lipid bilayer?
Small nonpolar molecules, such as oxygen and carbon dioxide, move through the lipid bilayer from higher to lower concentration without direct energy input.
How does facilitated diffusion move substances across a membrane?
Channels or carrier proteins help specific ions or polar molecules move down their gradient. The movement does not itself require ATP.
In which direction does water move during osmosis?
Water moves across a selectively permeable membrane toward the side with the higher effective concentration of solutes that cannot cross.
How does a carrier protein differ from a channel?
A channel permits rapid passage of particular ions; a carrier binds its substrate and changes shape to move it across the membrane.
What defines active transport?
Active transport moves substances against an electrochemical gradient by coupling their movement to an energy source.
What does the sodium–potassium pump move per ATP?
Using energy from one ATP, the sodium–potassium pump moves three Na⁺ ions out of the cell and two K⁺ ions in.
What powers secondary active transport?
Secondary active transport uses energy stored in an ion gradient, often established by primary active transport, to move another substance against its gradient.
How do symport and antiport differ?
In symport, two substances move in the same direction; in antiport, they move in opposite directions.
What is the membrane potential?
The membrane potential is the voltage difference across a membrane, usually described as the cell interior’s electrical potential relative to the exterior.
What determines the passive movement direction of an ion?
An ion’s electrochemical gradient combines its concentration gradient with the electrical attraction or repulsion across the membrane; the combined force determines passive movement.
How does vesicular transport move large cargo across the plasma membrane?
Vesicular transport moves large particles and many macromolecules by membrane budding or fusion, rather than by passage directly through the lipid bilayer; it requires cellular energy.