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| 3014681113 | fluid mosaic model | The currently accepted model of cell membrane structure, depicting the membrane as a mosaic of diverse protein molecules embedded in a fluid bilayer of phospholipid molecules. | 0 | |
| 3014697254 | selective permeability | A property of biological membranes that allows some substances to cross more easily than others and blocks the passage of other substances altogether. | 1 | |
| 3014708240 | diffusion | The random movement of particles that results in the net movement of a substance down its concentration gradient from a region where it is more concentrated to a region where it is less concentrated. | 2 | |
| 3014708241 | concentration gradient | A region along which the density of a chemical substance increases or decreases. Substances tend to move from where they are more concentrated to where they are less concentrated. | 3 | |
| 3014711534 | passive transport | The diffusion of a substance across a biological membrane, with no expenditure of energy. | 4 | |
| 3014713897 | osmosis | The diffusion of free water across a selectively permeable membrane. | 5 | |
| 3014713898 | tonicity | The ability of a solution surrounding a cell to cause that cell to gain or lose water. | 6 | |
| 3014716345 | isotonic | Referring to a solution that, when surrounding a cell, causes no net movement of water into or out of the cell. | 7 | |
| 3014716346 | hypotonic | Referring to a solution that, when surrounding a cell, will cause the cell to take up water. | 8 | |
| 3014718957 | hypertonic | Referring to a solution that, when surrounding a cell, will cause the cell to lose water. | 9 | |
| 3014718958 | osmoregulation | The homeostatic maintenance of solute concentrations and water balance by a cell or organism. | 10 | |
| 3014770168 | facilitated diffusion | The passage of a substance through a specific transport protein across a biological membrane down its concentration gradient. | 11 | |
| 3014774521 | aquaporin | A transport protein in the plasma membrane of an animal, plant, or microorganism cell that facilitates the diffusion of water across the membrane (osmosis). | 12 | |
| 3014776057 | active transport | The movement of a substance across a biological membrane against its concentration gradient, aided by specific transport proteins and requiring an input of energy (often as ATP). | 13 | |
| 3014776058 | exocytosis | The movement of materials out of a cell by the fusion of vesicles with the plasma membrane. | 14 | |
| 3014778736 | endocytosis | Cellular uptake of molecules or particles via formation of new vesicles from the plasma membrane. | 15 | |
| 3014780407 | phagocytosis | Cellular "eating"; a type of endocytosis in which a cell engulfs macromolecules, other cells, or particles into its cytoplasm. | 16 | |
| 3014783158 | receptor-mediated endocytosis | The movement of specific molecules into a cell by the infolding of vesicles containing proteins with receptor sites specific to the molecules being taken in. | 17 | |
| 3015056464 | energy | The capacity to cause change, especially to perform work. | 18 | |
| 3015056516 | kinetic energy | The energy associated with the motion of objects. Moving matter does work by imparting motion to other matter. | 19 | |
| 3015061936 | thermal energy | Kinetic energy due to the random motion of atoms and molecules; energy in its most random form. | 20 | |
| 3015064122 | heat | Thermal energy in transfer from one body of matter to another. | 21 | |
| 3015066804 | potential energy | The energy that matter possesses because of its location or spatial arrangement. Water behind a dam possesses it and so does chemical bonds. | 22 | |
| 3015072505 | chemical energy | Energy available in molecules for release in a chemical reaction; a form of potential energy. | 23 | |
| 3015074195 | thermodynamics | The study of energy transformation that occurs in a collection of matter. | 24 | |
| 3015080687 | first law of thermodynamics | The principle of conservation of energy. Energy can be transferred and transformed, but it cannot be created or destroyed. | 25 | |
| 3015087451 | entropy | A measure of disorder, or randomness. | 26 | |
| 3015090935 | second law of thermodynamics | The principle stating that every energy conversion reduces the order of the universe, increasing its entropy. Ordered forms of energy are at least partly converted to heat. | 27 | |
| 3015121093 | cellular respiration | The aerobic harvesting of energy from food molecules, the energy-releasing chemical breakdown of food molecules, such as glucose, and the storage of potential energy in a form that cells can use to perform work. | 28 | |
| 3015406485 | exergonic reaction | An energy-releasing chemical reaction in which the reactants contain more potential energy than the products. | 29 | |
| 3015419982 | endergonic reaction | An energy-requiring chemical reaction, which yields products with more potential energy than the reactants. | 30 | |
| 3015428703 | metabolism | The totality of an organism's chemical reactions. | 31 | |
| 3015446129 | metabolic pathway | A series of chemical reactions that either builds a complex molecule or breaks down a complex molecule into simpler compounds. | 32 | |
| 3015454853 | energy coupling | In cellular metabolism, the use of energy released from an exergonic reaction to drive an endergonic reaction. | 33 | |
| 3015859869 | ATP | Adenosine triphosphate, the main energy source for cells. Releases energy when its phosphate bounds are hydrolyzed. | 34 | |
| 3015871937 | phosphorylation | The transfer of a phosphate group, usually from ATP, to a molecule. Nearly all cellular work depends on ATP energizing other molecules by this transfer. | 35 |
