Biology 122 terms for weeks 12 to 14

Term	Definition

vicariance	the splitting of the range of a taxon (family, genus, species, etc.) into two or more widely separated areas due to plate tectonics or some other process that produces a physical barrier to dispersal (mountains, deserts, canyons, etc.); for example, some plant families occur in tropical South America, and also in tropical Africa, apparently due to the splitting apart of the two continents (rather than due to transoceanic dispersal of the plants after the continental split occurred)
vagility	the dispersability of a plant species; some plant species or families are highly vagile (disperse over large distances easily), while others are not
pantropical distribution	occurring in all tropical areas of the world
paleotropical distribution	occurring in all of the old world tropics (African tropics plus all Asian tropical areas)
neotropical distribution	occurring in the new world tropics (tropical areas of South America)
temperate regions	areas of the earth located between the tropical and the polar regions (technically, the north temperate region lies between the Tropic of Cancer and the Arctic Circle, and the south temperate region lies between the tropic of Capricorn and the Antarctic Circle)
north temperate distribution	occurring in temperate areas of the northern hemisphere
south temperate distribution	occurring in temperate areas of the southern hemisphere
circumpolar distribution	occurring in all polar regions of the northern hemisphere (far northern parts of North America, Europe and Asia)
biome	a large geographical region within which the climate is the same from place to place, and the growth forms of the dominant plants are the same from place to place; for example, the grassland biome has a characteristic climate (cold winters with warm summers and occasional drought years) and characteristic plant growth forms (mainly grasses, with forbs and some shrubs); the genera and species of the plants can vary from one grassland to another in the world, but the climates and growth forms remain the same
dispersal	spread of a family, genus, species, etc. from one region into another
disjunct	describes the range of a family, genus, species, etc. that consists of two or more widely separated areas; for example, the genus Cedrus occurs only in three small patches: the Atlas Mountains of northern Africa, the middle east, and the Himalayas
chloroplast	the organelle of eukaryotic cells that performs photosynthesis
chemiosmosis	the process by which a flow of protons (H⁺) through an ATPase complex in the thylakoid membrane powers the synthesis of ATP from ADP and P_i
ATPase	a molecular complex in the thylakoid membrane; it has within it a passageway through which protons (H⁺) will flow by diffusion from an area of high proton concentration (inside the thylakoid) to an area of low concentration (stroma); the proton-motive force inherent in this flow is used by the ATPase to synthesize ATP from ADP and P_i
thylakoid	a small closed membranous sac within a chloroplast; thylakoids are often stacked into piles called grana; the molecules that perform the light reactions of photosynthesis are all embedded within the membranes of the thylakoids
stroma	the watery cytoplasm-like filler of a chloroplast, in which the thylakoids float; the enzymes of the carbon cycle of photosynthesis are located in the stroma
hormone	an organic substance produced within the body of a plant, and usually transported to another area within the plant body, where it has some specific physiological effect; hormones are active at very low concentrations
xylem	one of the two vascular tissues of a vascular plant; xylem consists mostly of cells that are dead at maturity, and that transport water up from the roots to the leaves of the plant
phloem	one of the two vascular tissues of a vascular plant; phloem consists mostly of cells that are living at maturity, and that transport sugars and other organic materials around the plant body
water potential	a measure of the ability of any object or substance to draw water into itself; an object (such as a cell wall) that has a negative water potential will draw water into itself from any other object that has a less negative water potential
matric forces	one of the components of water potential; originates in the tendency of some materials to adsorb water; for example, cell walls (such as those of xylem) have a strong tendency to attract and hold water
osmotic potential	a measure of the ability of a cell to attract water into itself through the mechanism of osmosis; in plants, this is one of the components of water potential
turgor pressure	the outward pressure exerted against the inside surface of a plant cell wall as water tries to flow into the cell by osmosis, and the inelastic cell wall resists any expansion; turgor pressure in a plant cell is analogous to air pressure in a car tire; turgor pressure is one component of water potential, and it has a positive value (that is, it will cancel out some or all of the osmotic potential of a cell); turgor pressure and osmotic potential can exist only in cells that have an intact cell membrane
source	in the context of phloem function, any plant part that produces more sugar that it requires for its own use and which, therefore, has sugar available to export to other plant parts via the phloem; the sugar produced by a source could be new sugar made by photosynthesis, as happens in a leaf, or it could be sugar produced by the breakdown of stored starch, as happens in the roots of many plants in the spring
sink	in the context of phloem function, any plant part that produces less sugar that it requires for its own use and which, therefore, must import sugar from other plant parts via the phloem; roots are always net sinks, since they never produce any new sugar (they may be temporary sources when they release stored sugar that they have received from the shoot); other common sinks in plants are flowers, fruits, seeds, stems, developing leaves and meristems