AP Biology (Unit 6: Chapter 36)
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35 terms
Terms | Definitions |
|---|---|
 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. |
| Apoplast | In plants, the continuum of cell walls plus the extracellular spaces. |
| 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). |
| Bulk Flow | The movement of water due to a difference in pressure between two locations. |
| Casparian Strip | A water-impermeable ring of wax in the endodermal cells of plants that blocks the passive flow of water and solutes into the stele by way of cell walls. |
| Chemiosmosis | An energy-coupling mechanism that uses energy stored in the form of a hydrogen ion gradient across a membrane to drive cellular work, such as the synthesis of ATP. Most ATP synthesis in cells occurs by chemiosmosis. |
| Circadian Rhythm | A physiological cycle of about 24 hours that is present in all eukaryotic organisms and that persists even in the absence of external cues. |
| Cotransport | The coupling of the downhilldiffusion of one substance to the uphilltransport of another against its own concentration gradient. |
| Endodermis | The innermost layer of the cortex in plant roots; a cylinder one cell thick that forms the boundary between the cortex and the vascular cylinder. |
| Flaccid | Limp. A walled cell is flaccid in surroundings where there is no tendency for water to enter. |
| Guttation | The exudation of water droplets, caused by root pressure in certain plants. |
| Megapascal (MPa) | A unit of pressure equivalent to 10 atmospheres of pressure. |
| Membrane Potential | The charge difference between a cell's cytoplasm and the extracellular fluid, due to the differential distribution of ions. Affects the activity of excitable cells and the transmembrane movement of all charged substances. |
| Mycorrhizae | Mutualistic associations of plant roots and fungi. |
| Osmosis | The diffusion of water across a selectively permeable membrane. |
| Osmotic Potential | A component of water potential that is proportional to the number of dissolved solute molecules in a solution and measures the effect of solutes on the direction of water movement; also called solute potential, it can be either zero or negative. |
| Plasmolyze | To shrink and pull away from a cell wall, or when a plant cell protoplast pulls away from the cell wall as a result of water loss. |
| Pressure Potential | A component of water potential that consists of the physical pressure on a solution, which can be positive, zero, or negative. |
| 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. |
| Root Pressure | The upward push of xylem sap in the vascular tissue of roots. |
| Solute Potential | A component of water potential that is proportional to the number of dissolved solute molecules in a solution and measures the effect of solutes on the direction of water movement; also called osmotic potential, it can be either zero or negative. |
| Sugar Sink | A plant organ that is a net consumer or storer of sugar. Growing roots, shoot tips, stems, and fruits are sugar sinks supplied by phloem. |
| Sugar Source | A plant organ in which sugar is being produced by either photosynthesis or the breakdown of starch. Mature leaves are the primary sugar sources of plants. |
| Symplast | In plants, the continuum of cytoplasm connected by plasmodesmata between cells. |
| Tonoplast | A membrane that encloses the central vacuole in a plant cell, separating the cytosol from the vacuolar contents, called cell sap; also known as the vacuolar membrane. |
| Transfer Cell | A companion cell with numerous ingrowths of its wall, increasing the cell's surface area and enhancing the transfer of solutes between apoplast and symplast. |
| Translocation | The transport of organic nutrients in the phloem of vascular plants. |
| Transpiration | The evaporative loss of water from a plant. |
| 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. |
| Turgor Pressure | The force directed against a cell wall after the influx of water and the swelling of a walled cell due to osmosis. |
| Vacuolar Membrane | A membrane that encloses the central vacuole in a plant cell, separating the cytosal from the vacuolar contents, called cell sap; also known as the tonoplast. |
| Water Potential | The physical property predicting the direction in which water will flow, governed by solute concentration and applied pressure. |
| Wilting | The drooping of leaves and stems as a result of plant cells becoming flaccid. |
| Xerophyte | A plant adapted to an arid climate. |
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