Cells and Cellular Transport: every key term you need (+ practice quiz)
25 flashcard terms for Anatomy & Physiology I Topic 2, written to match the course framework. Study them here, then drill them as interactive flashcards, or test yourself with the 15-question quiz — free, no account needed.
The description of the plasma membrane as a two-dimensional fluid of phospholipids in which proteins, cholesterol and glycolipids drift laterally. Fluidity permits vesicle budding, membrane fusion and protein clustering.
Phospholipid bilayer
Two opposed sheets of amphipathic lipids with polar heads facing the aqueous compartments and fatty acid tails facing inward. The hydrophobic core is the barrier that blocks ions and polar molecules from crossing freely.
Membrane cholesterol
A steroid wedged among phospholipid tails that buffers membrane fluidity. It restrains movement at warm temperatures and prevents tight packing at cool ones, keeping the bilayer workable across a physiological range.
Integral membrane protein
A protein embedded within the lipid core, often spanning it completely as a transmembrane protein. This class supplies channels, carriers, pumps, receptors and cell adhesion molecules.
Peripheral membrane protein
A protein bound loosely to one membrane face or to an integral protein rather than inserted into the lipid core. Many act as enzymes or as links to the underlying cytoskeleton.
Glycocalyx
The sugary coat of carbohydrate chains attached to membrane lipids and proteins on the outer surface. It contributes to cell recognition, immune identity, blood typing and protection from mechanical and enzymatic damage.
Selective permeability
The property by which a membrane admits some substances and excludes others. Small nonpolar molecules cross the lipid core readily, while ions and large polar solutes require a dedicated protein pathway.
Simple diffusion
Net movement of a solute down its concentration gradient directly through the lipid bilayer, requiring no protein and no cellular energy. Oxygen, carbon dioxide and steroid hormones move this way.
Facilitated diffusion
Passive movement of a solute down its gradient through a channel or carrier protein. It requires no energy input but is saturable and specific because a finite number of transport proteins is available.
Osmosis
Diffusion of water across a selectively permeable membrane from the region of lower solute concentration toward the region of higher solute concentration, often accelerated by aquaporin water channels.
Tonicity
The effect a solution has on cell volume, determined by the concentration of solutes that cannot cross the membrane. Hypotonic solutions swell cells, hypertonic solutions shrink them, isotonic solutions leave volume unchanged.
Osmolarity
The total concentration of all solute particles in a solution, expressed per liter. It is a chemical measurement and, unlike tonicity, does not by itself predict whether a cell will swell or shrink.
Primary active transport
Movement of a solute against its electrochemical gradient using energy released directly by hydrolysis of adenosine triphosphate at the transport protein itself. Ion pumps of the P-type family work this way.
Sodium potassium pump
A primary active transporter that exports three sodium ions and imports two potassium ions per molecule of adenosine triphosphate consumed. It maintains the ionic gradients and contributes a small direct electrical current.
Secondary active transport
Uphill movement of one solute powered indirectly by the downhill flow of another, usually sodium, whose gradient was established by a pump. Glucose absorption in the intestine uses this arrangement.
Symport and antiport
Two patterns of coupled transport. A symporter carries both solutes in the same direction across the membrane, while an antiporter exchanges them in opposite directions.
Electrochemical gradient
The combined driving force on an ion arising from its concentration difference and from the voltage across the membrane. Net ion movement follows this sum, not the concentration difference alone.
Endocytosis
Bulk uptake in which the membrane invaginates and pinches off an internal vesicle. Phagocytosis engulfs particles, pinocytosis samples fluid, and receptor-mediated endocytosis concentrates specific ligands in coated pits.
Exocytosis
Bulk export in which a secretory vesicle docks at the plasma membrane and fuses with it, releasing contents outside and adding vesicle membrane to the cell surface. Neurotransmitter and hormone release depend on it.
Mitochondrion
The organelle bounded by a smooth outer and folded inner membrane where the citric acid cycle and oxidative phosphorylation generate most cellular adenosine triphosphate. Cells with high energy demand carry the largest populations.
Rough endoplasmic reticulum
Ribosome-studded membrane cisternae where proteins destined for secretion, lysosomes or the plasma membrane are synthesized, folded and given initial sugar groups before transfer to the Golgi apparatus.
Smooth endoplasmic reticulum
Ribosome-free tubular membrane that synthesizes lipids and steroids, detoxifies drugs in liver cells, and in muscle serves as the calcium store known as sarcoplasmic reticulum.
Golgi apparatus
A stack of flattened cisternae that receives vesicles from the endoplasmic reticulum, modifies and sorts their protein cargo, and dispatches finished products to lysosomes, the membrane or secretory vesicles.
Lysosome
A membrane-bound vesicle containing acid hydrolases that digest ingested material, worn organelles and bacteria. Its interior is kept acidic by a proton pump, which also limits damage if the enzymes leak.
Cytoskeleton
The internal protein scaffolding of microfilaments, intermediate filaments and microtubules. It maintains shape, anchors organelles, provides tracks for motor proteins and generates movement during division and crawling.