Key Terms

active transport

method of transporting material that requires energy

amphiphilic

molecule possessing a polar or charged area and a nonpolar or uncharged area capable of interacting with both hydrophilic and hydrophobic environments

antiporter

transporter that carries two ions or small molecules in different directions

aquaporin

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

caveolin

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

clathrin

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

diffusion

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

endocytosis

type of active transport that moves substances, including fluids and particles, into a cell

exocytosis

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)

glycolipid

combination of carbohydrates and lipids

glycoprotein

combination of carbohydrates and proteins

hydrophilic

molecule with the ability to bond with water; “water-loving”

hydrophobic

molecule that does not have the ability to bond with water; “water-hating”

hypertonic

situation in which extracellular fluid has a higher osmolarity than the fluid inside the cell, resulting in water moving out of the cell

hypotonic

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

isotonic

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

osmolarity

total amount of substances dissolved in a specific amount of solution

osmosis

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

pinocytosis

a variation of endocytosis that imports macromolecules that the cell needs from the extracellular fluid

plasmolysis

detaching the cell membrane from the cell wall and constricting the cell membrane when a plant cell is in a hypertonic solution

potocytosis

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

pump

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

solute

substance dissolved in a liquid to form a solution

symporter

transporter that carries two different ions or small molecules, both in the same direction

tonicity

amount of solute in a solution

transport protein

membrane protein that facilitates a substance's passage across a membrane by binding it

transporter

specific carrier proteins or pumps that facilitate movement

uniporter

transporter that carries one specific ion or molecule