46 Key Terms

active transport
method of transporting material that requires energy
molecule possessing a polar or charged area and a nonpolar or uncharged area capable of interacting with both hydrophilic and hydrophobic environments
transporter that carries two ions or small molecules in different directions
channel protein that allows water through the membrane at a very high rate
carrier protein
membrane protein that moves a substance across the plasma membrane by changing its own shape
protein that coats the plasma membrane’s cytoplasmic side and participates in the liquid uptake process by potocytosis
channel protein
membrane protein that allows a substance to pass through its hollow core across the plasma membrane
protein that coats the plasma membrane’s inward-facing surface and assists in forming specialized structures, like coated pits, for phagocytosis
concentration gradient
area of high concentration adjacent to an area of low concentration
passive transport process of low-molecular weight material according to its concentration gradient
electrochemical gradient
a combined electrical and chemical force that produces a gradient
electrogenic pump
pump that creates a charge imbalance
type of active transport that moves substances, including fluids and particles, into a cell
process of passing bulk material out of a cell
facilitated transport
process by which material moves down a concentration gradient (from high to low concentration) using integral membrane proteins
fluid mosaic model
describes the plasma membrane’s structure as a mosaic of components including phospholipids, cholesterol, proteins, glycoproteins, and glycolipids (sugar chains attached to proteins or lipids, respectively), resulting in a fluid character (fluidity)
combination of carbohydrates and lipids
combination of carbohydrates and proteins
molecule with the ability to bond with water; “water-loving”
molecule that does not have the ability to bond with water; “water-hating”
situation in which extracellular fluid has a higher osmolarity than the fluid inside the cell, resulting in water moving out of the cell
situation in which extracellular fluid has a lower osmolarity than the fluid inside the cell, resulting in water moving into the cell
integral protein
protein integrated into the membrane structure that interacts extensively with the membrane lipids’ hydrocarbon chains and often spans the membrane
situation in which the extracellular fluid has the same osmolarity as the fluid inside the cell, resulting in no net water movement into or out of the cell
total amount of solutes dissolved in a specific amount of solution
transport of water through a semipermeable membrane according to the water’s concentration gradient across the membrane that results from the presence of solute that cannot pass through the membrane
passive transport
method of transporting material through a membrane that does not require energy
peripheral protein
protein at the plasma membrane’s surface either on its exterior or interior side
a variation of endocytosis that imports macromolecules that the cell needs from the extracellular fluid
detaching the cell membrane from the cell wall and constricting the cell membrane when a plant cell is in a hypertonic solution
variation of pinocytosis that uses a different coating protein (caveolin) on the plasma membrane’s cytoplasmic side
primary active transport
active transport that moves ions or small molecules across a membrane and may create a difference in charge across that membrane
active transport mechanism that works against electrochemical gradients
receptor-mediated endocytosis
variation of endocytosis that involves using specific binding proteins in the plasma membrane for specific molecules or particles, and clathrin-coated pits that become clathrin-coated vesicles
secondary active transport
movement of material that results from primary active transport to the electrochemical gradient
selectively permeable
membrane characteristic that allows some substances through (also known as semipermeable)
substance dissolved in a liquid to form a solution
transporter that carries two different ions or small molecules, both in the same direction
amount of solute in a solution
transport protein
membrane protein that facilitates a substance’s passage across a membrane by binding it
specific carrier proteins or pumps that facilitate movement
transporter that carries one specific ion or molecule


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