Terms
- Active Transport
- The movement of a substance across a biological membrane against its concentration or electrochemical gradient with the help of energy input and specific transport proteins.
- Amphipathic Molecule
- A molecule that has both a hydrophilic region and a hydrophobic region.
- Aquaporin
- A transport protein in the plasma membrane of a plant or animal cell that specifically facilitates the diffusion of water across the membrane (osmosis).
- Concentration Gradient
- An increase or decrease in the density of a chemical substance in an area. Cells often maintain concentration gradients of ions across their membranes. When a gradient exists, the ions or other chemical substances involved tend to move from where they are more concentrated to where they are less concentrated.
- Cotransport
- The coupling of the downhill diffusion of one substance to the uphill transport of another against its own concentration gradient.
- Diffusion
- The spontaneous tendency of a substance to move down its concentration gradient from a more concentrated to a less concentrated area.
- Electrochemical Gradient
- The diffusion gradient of an ion, representing a type of potential energy that accounts for both the concentration difference of the ion across a membrane and its tendency to move relative to the membrane potential.
- Electrogenic Pump
- An ion transport protein that generates voltage across a membrane.
- Endocytosis
- The cellular uptake of macromolecules and particulate substances by localized regions of the plasma membrane that surround the substance and pinch off to form an intracellular vesicle.
- Exocytosis
- The cellular secretion of macromolecules by the fusion of vesicles with the plasma membrane.
- Facilitated Diffusion
- The spontaneous passage of molecules and ions, bound to specific carrier proteins, across a biological membrane down their concentration gradients.
- Flaccid
- Limp. A walled cell is flaccid in surroundings where there is no tendency for water to enter.
- Fluid Mosaic Model
- The currently accepted model of cell membrane structure, which envisions the membrane as a mosaic of individually inserted protein molecules drifting laterally in a fluid bilayer of phospholipids.
- Gated Channel
- A protein channel in a cell membrane that opens or closes in response to a particular stimulus.
- Glycolipid
- A lipid covalently attached to a carbohydrate.
- Glycoprotein
- A protein covalently attached to a carbohydrate.
- Hypertonic
- In comparing two solutions, referring to the one with a greater solute concentration.
- Hypotonic
- In comparing two solutions, referring to the one with a lower solute concentration.
- Integral Protein
- Typically a transmembrane protein with hydrophobic regions that completely spans the hydrophobic interior of the membrane.
- Ion Channel
- Protein channel in a cell membrane that allows passage of a specific ion down its concentration gradient.
- Isotonic
- Having the same solute concentration as another solution.
- Ligand
- A molecule that binds specifically to a receptor site of another molecule.
- Membrane Potential
- The charge difference between a cell’s cytoplasm and the extracellular fluid, due to the differential distribution of ions. Membrane potential affects the activity of excitable cells and the transmembrane movement of all charged substances.
- Osmoregulation
- The regulation of solute and water concentrations in body fluids by organisms living in hyperosmotic, hypoosmotic, and terrestrial environments.
- Osmosis
- The diffusion of water across a selectively permeable membrane.
- Passive Transport
- The diffusion of a substance across a biological membrane.
- Peripheral Protein
- A protein appendage loosely bound to the surface of a membrane and not embedded in the lipid bilayer.
- Phagocytosis
- A type of endocytosis involving large, particulate substances, accomplished mainly by macrophages, neutrophils, and dendritic cells.
- Pinocytosis
- A type of endocytosis in which the cell ingests extracellular fluid and its dissolved solutes.
- Plasmolysis
- A phenomenon in walled cells in which the cytoplasm shrivels and the plasma membrane pulls away from the cell wall when the cell loses water to a hypertonic environment.
- Proton Pump
- An active transport mechanism in cell membranes that uses ATP to force hydrogen ions out of a cell, generating a membrane potential in the process.
- Receptor-Mediated Endocytosis
- The movement of specific molecules into a cell by the inward budding of membranous vesicles containing proteins with receptor sites specific to the molecules being taken in; enables a cell to acquire bulk quantities of specific substances.
- Selective Permeability
- A property of biological membranes that allows some substances to cross more easily than others.
- Sodium-Potassium Pump
- A special transport protein in the plasma membrane of animal cells that transports sodium out of the cell and potassium into the cell against their concentration gradients.
- Tonicity
- The ability of a solution to cause a cell within it to gain or lose water.
- Transport Protein
- A transmembrane protein that helps a certain substance or class of closely related substances to cross the membrane.
- Turgid
- Very firm. A walled cell become turgid if it has a greater solute concentration than its surroundings, resulting in entry of water.
