Term | Definition |
Active Transport | the movement of materials across a membrane through the use of cellular energy, normally against a concentration gradient. |
Aquaporins | “water pores”; specialized water channels. |
Attachment Protein | anchor the cell membrane in various ways, such as binding the plasma membrane to the network of protein filaments within the cytoplasm (cytoskeleton). |
Carrier Protein | a membrane protein that facilitates the diffusion of specific substances across the membrane. The molecule to be transported binds to the outer surface of the carrier protein; the protein then changes shape, allowing the molecule to move across the membra |
Channel Protein | a membrane protein that forms a channel or pore completely through the membrane and that is usually permeable to one or to a few water-soluble molecules, especially ions. |
Concentration | the number of particles of a dissolved substance in a given unit of volume. |
Concentration Gradient | the difference in concentration of a substance between two parts of a fluid or across a barrier such as a membrane. |
Desmosome | a strong cell-to-cell junction that attaches adjacent cells to one another. |
Diffusion | the net movement of particles from a region of high concentration of that particle to a region of low concentration, driven by the concentration gradient; may occur entirely within a fluid or across a barrier such as a membrane. |
Endocytosis | the process in which the plasma membrane engulfs extracellular material, forming membrane-bound sacs that enter the cytoplasm and thereby move material into the cell. |
Enzyme | a protein catalyst that speeds up the rate of specific biological reactions. |
Exocytosis | the process in which intracellular material is enclosed within a membrane-bound sac that moves to the plasma membrane and fuses with it, releasing the material outside the cell. |
Facilitated Diffusion | the diffusion of molecules across a membrane, assisted by protein pores or carriers embedded in the membrane. |
Fluid | a liquid or gas. |
Fluid Mosaic Model | a model of membrane structure; according to this model, membranes are composed of a double layer of phospholipids in which various proteins are embedded. The phospholipid bilayer is a somewhat fluid matrix that allows the movement of proteins within it. |
Gap Junction | a type of cell-to-cell junction in animals in which channels connect the cytoplasm of adjacent cells. |
Glycoprotein | a protein to which a carbohydrate is attached. |
Gradient | a difference in concentration, pressure, or electrical charge between two regions. |
Hypertonic | referring to a solution that has a higher concentration of dissolved particles (and therefore a lower concentration of free water) than has the cytoplasm of a cell. |
Isotonic | referring to a solution that has the same concentration of dissolved particles (and therefore the same concentration of free water) as has the cytoplasm of a cell. |
Osmosis | the diffusion of water across a differentially permeable membrane, normally down a concentration gradient of free water molecules. Water moves into the solution that has a lower concentration of free water from a solution with the higher concentration of |
Passive Transport | the movement of materials across a membrane down a gradient of concentration, pressure, or electrical charge without using cellular energy. |
Phagocytosis | a type of endocytosis in which extensions of a plasma membrane engulf extracellular particles and transport them into the interior of the cell. |
Phospholipid Bilayer | a double layer of phospholipids that forms the basis of all cellular membranes. The phospholipid heads, which are hydrophilic, face the water of extracellular fluid or the cytoplasm; the tails, which are hydrophobic, are buried in the middle of the bilaye |
Pinocytosis | the non selective movement of extracellular fluid, enclosed within a vesicle formed from the plasma membrane, into a cell. |
Plasmodesmata | a cell-to-cell junction in plants that connects the cytoplasm of adjacent cells. |
Plasmolysis | a process in which the central vacuole and cytosol of each plant cell loses water and the plasma membrane shrinks away from its cell wall as the vacuole collapses. |
Receptor-Mediated Endocytosis | the selective uptake of molecules from the extracellular fluid by binding to a receptor located at a coated pit on the plasma membrane and pinching off the coated pit into a vesicle that moves into the cytoplasm. |
Receptor Protein | a protein, located on a membrane (or in the cytoplasm), that recognizes and binds to specific molecules. Binding by receptor proteins typically triggers a response by a cell, such as endocytosis, increased metabolic rate, or cell division. |
Recognition Protein | a protein or glycoprotein protruding from the outside surface of a plasma membrane that identifies a cell as belonging to a particular species, to a specific individual of that species, and in many cases to one specific organ within the individual. |
Selectively Permeable | the quality of a membrane that allows certain molecules of ions to move through it more readily than others. |
Simple Diffusion | The diffusion of water, dissolved gases, or liquid-soluble molecules through the phospholipid bilayer of a cellular membrane. |
Solute | a substance that can be dissolved |
Solvent | a liquid capable of dissolving (uniformly dispersing) other substances in itself. |
Tight Junction | a type of cell-to-cell junction in animals that prevents the movement of materials through the spaces between cells. |
Transport Protein | a protein that regulates the movement of water-soluble molecules through the plasma membrane. |
Turgor Pressure | pressure developed within a cell (especially the central vacuole of plant cells) as a result of osmotic water entry. |