35 terms

AP Biology (Unit 6: Chapter 36)

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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.