THE FACTS ON FILE DICTIONARY OF BOTANY
ENTRIES A TO Z SEE ABSCISIC ACID IN STRUCTURES SUCH AS A LEAVES AND PETALS THE SIDE FACING AWAY FROM THE MAIN AXIS I E THE LOWER SURFACE IN LATERAL ORGANS SUCH AS LEAVES ABAXIAL IS SYNONY MOUS WITH THE UNDERSIDE COMPARE ADAX FACTORS OF THE ENVIRONMENT THAT INFLUENCE ECOLOGICAL SYSTEMS ABIOTIC FACTORS INCLUDE CLIMATE CHEMICAL POLLUTION GEOGRAPHICAL ABSCISIC ACID ABA A PLANT HORMONE THAT FUNCTIONS CHIEFLY AS AN INHIBITOR OF GROWTH AND CELL ELONGATION ABSCISIC ACID HAS A VARIETY OF EFFECTS RELATED TO SEED DOR MANCY AND STRESS RESPONSES IT REGULATES PROTEIN EXPRESSION IN SEED DEVELOPMENT LEADING TO DORMANCY AND IS ONE OF THE HOR MONES INVOLVED IN BUD DORMANCY IT REGU LATES STRESS RESPONSES BY FOR EXAMPLE CLOSING STOMATA IN TIMES OF WATER SHORTAGE AND INCREASING THE ABILITY OF ROOTS TO CARRY WATER IT CAN ALSO PROMOTE ROOT GROWTH AND INHIBIT SHOOT GROWTH DESPITE ITS NAME IT DOES NOT DIRECTLY PROMOTE ABSCISSION BUT ONLY INDIRECTLY THROUGH INCREASING ETHYLENE PRODUCTION FORMERLY IT WAS KNOWN AS AB SCISIN II OR DORMIN THE ORGANIZED LOSS OF PART OF A PLANT USUALLY A LEAF FRUIT OR UNFERTILIZED FLOWER AN ABSCISSION ZONE OCCURS AT THE BASE OF THE ORGAN HERE A SEPARATION LAYER ABSCISSION LAYER IS FORMED BY BREAKDOWN OR SEPARATION OF CELLS AND FINAL SEVERANCE OCCURS WHEN THE VASCULAR BUNDLES ARE BRO KEN MECHANICALLY E G BY WIND OR RAIN THE ABSCISSION LAYER IS ACTIVATED BY INCREASING LEVELS OF ETHYLENE AND A DECREASING CONCEN TRATION OF AUXIN ABSOLUTE POLLEN FREQUENCY APF 1 THE UPTAKE OF LIQUID BY CELLS AND ORGANS IN PLANTS WATER AND MIN ERAL SALTS ARE ABSORBED MAINLY BY THE ROOT HAIRS JUST BEHIND THE ROOT TIPS 2 THE CAPTURE OF RADIANT ENERGY BY PLANT PIGMENTS ABOUT 80 OF THE VISIBLE LIGHT FALLING ON A LEAF IS ABSORBED AND ABOUT 10 OF THE INFRARED RADIATION A PLOT OF THE AB SORBANCE BY A SUBSTANCE OF RADIATION AT DIF FERENT WAVELENGTHS USUALLY OF ULTRAVIOLET VISIBLE OR INFRARED RADIATION IT CAN GIVE IN FORMATION ABOUT THE IDENTITY OR QUANTITY OF A SUBSTANCE CHLOROPHYLLS FOR EXAMPLE HAVE ABSORPTION PEAKS IN THE RED AND BLUE AND THEREFORE REFLECT GREEN LIGHT COM PARE ACTION SPECTRUM SEE SUBSIDIARY CELL SEE B CHROMO DENOTING RELATIVELY LARGE TIS SUES OR ORGANISMS THAT ARE NOT COMPOSED OF DISCRETE CELLS AND ARE IN EFFECT UNICELLULAR IN FLOWERING PLANTS FOR INSTANCE THE EARLY STAGES OF ENDOSPERM DEVELOPMENT ARE OFTEN ACELLULAR OTHER EXAMPLES INCLUDE ASEPTATE FUNGAL HYPHAE AND CERTAIN GREEN ALGAE SUCH AS ACETABULARIA THE TERM IS USED IN PREFERENCE TO UNICELLULAR TO DISTINGUISH SUCH STRUCTURES WHICH ARE OFTEN MULTINU CLEATE FROM CONVENTIONAL CELLS AND SHOW THEIR EQUIVALENCE TO MULTICELLULAR STRUC TURES SEE ALSO COENOCYTE A FAMILY OF TEMPERATE AND TROPICAL TREES AND SHRUBS THAT INCLUDES THE MAPLES AND SYCAMORES CH3CHO THAT IS AN INTERMEDIATE IN THE CONVERSION OF PYRUVIC ACID TO ETHANOL DUR ING THE FINAL STAGE OF GLYCOLYSIS DURING ANAEROBIC RESPIRATION IN PLANTS IT IS IN VOLVED IN THE SYNTHESIS AND BREAKDOWN OF THE AMINO ACID THREONINE ACETIC ACID ETHANOIC ACID ACID CH3COOH OBTAINED BY THE OXIDA TION OF ETHYL ALCOHOL ACETIC ACID IS A COM PONENT OF VINEGAR WHICH IS OBTAINED BY BACTERIAL OXIDATION OF WINE WASTE IT IS USED AS AN ALTERNATIVE CARBON SOURCE BY CER TAIN GREEN ALGAE WHEN COMBINED WITH COENZYME A TO FORM ACETYL COA IT PLAYS A KEY ROLE IN AEROBIC RESPIRATION A STAIN USED TO COLOR CHROMOSOMES DEEP REDDISH BLACK FOR VIEW ING WITH A LIGHT MICROSCOPE TISSUES ARE FIXED IN ACETIC ACID BEFORE APPLYING ACETO CARMINE SEE FIXATION STAINING ACETYL COA ACETYL COENZYME A POUND MADE UP OF ACETYL AND COENZYME A LINKED BY A SULFUR BRIDGE ACETYL COA PLAYS A KEY ROLE IN METABOLISM BEING A PRECURSOR OF THE KREBS CYCLE AND GLYOXYLATE CYCLE AND THE STARTING POINT FOR SYNTHESIS OF FATTY ACIDS TERPENES AND SOME AMINO ACIDS THE SYNTHESIS OF ACETYL COA IS A HIGH ENERGY PROCESS REQUIRING ENERGY FROM ATP WHICH IS CONVERTED TO AMP A DRY INDEHISCENT FRUIT FORMED FROM AN OVARY WITH A SINGLE CARPEL CONTAIN ING A SINGLE SEED E G OAK QUERCUS DIF FERENT TYPES OF ACHENES INCLUDE THE CARYOPSIS CYPSELA NUT AND SAMARA A SUBSTANCE THAT GIVES RISE TO HY DROGEN IONS OR H3O WHEN DISSOLVED IN WATER AN ACID IN AQUEOUS SOLUTION WILL HAVE A PH BELOW 7 LOWRY BR NSTED THEORY DEFINES AN ACID AS A SUBSTANCE THAT EXHIBITS A TENDENCY TO RELEASE A PROTON AND A BASE AS A SUBSTANCE THAT TENDS TO ACCEPT A PROTON STRONG ACIDS E G HNO3 REACT COMPLETELY WITH WATER TO GIVE H3O WEAK ACIDS E G CH3COOH ARE ONLY PARTLY DIS SOCIATED BECAUSE H3O IS A STRONGER ACID THAN THE FREE ACIDS THE DEPOSITION OF ACIDS BY NAT URAL PRECIPITATION MAINLY BY RAIN BUT ALSO BY SNOW AND FOG ACIDS ARE FORMED BY RE ACTION OF GASEOUS WASTE PRODUCTS PARTICU LARLY SULFUR DIOXIDE AND ALSO NITROGEN OXIDES WITH MOISTURE IN THE AIR TO FORM SUL FURIC AND NITRIC ACIDS THE SUBSEQUENT PRE CIPITATION HAS LED TO RAISED ACIDITY IN FORESTS AND LAKES ESPECIALLY IN SCANDINAVIA AND SOME OTHER PARTS OF NORTHERN EUROPE DAM AGING THE ENVIRONMENT ACID RAIN IS OFTEN USED MORE LOOSELY FOR ANY ATMOSPHERIC POL LUTANT THAT DISSOLVES IN PRECIPITATION CAUS ING ENVIRONMENTAL DAMAGE SUCH AS CARBON MONOXIDE OR OZONE AND THESE MAY INTERACT WITH THE ACIDS THE MOST SERIOUS POLLUTANT IS SULFUR DIOXIDE WHICH COMES MAINLY FROM BURNING COAL AND IS CONSEQUENTLY LESS SERIOUS NOW THAN IN THE TWENTIETH CENTURY SULFURIC ACID IN SOILS MAY LEAD TO THE FORMATION OF AM MONIUM SULFATE WHICH CAUSES THE RELEASE OF TOXIC ALUMINUM AND HEAVY METAL IONS THAT INHIBIT METABOLIC ACTIVITY IN WATER WAYS THESE CAN DAMAGE THE GILLS OF FISH UN POLLUTED RAIN IS NORMALLY SLIGHTLY ACIDIC WITH A PH OF 5 0 5 A SOIL WITH A PH LESS THAN 6 SUCH SOILS USUALLY FORM IN AREAS OF HEAVY RAINFALL WHICH CAUSES LEACHING OF LIME FROM THE SURFACE LAYERS OR OVER ACID SUB STRATA SUCH AS GRANITE OR SAND IN THE ACIDIC CONDITIONS DECOMPOSITION OF ORGANIC MA TERIAL IN THE SOIL IS SLOW ACID SOILS OFTEN CONTAIN SUBSTANTIAL CONCENTRATIONS OF IRON AND ALUMINUM HYDROXIDES SEE BROWN ACRASIOMYCOTA CELLULAR SLIME MOLDS CLASS OF PROTOCTISTS IN THE PHYLUM RHI ZOPODA FORMERLY CONSIDERED TO BE FUNGI THEY ARE MADE UP OF INDEPENDENTLY LIVING AMEBAS THAT FEED ON BACTERIA WHICH THEY INGEST BY PHAGOCYTOSIS UNDER CONDITIONS OF FOOD SHORTAGE OR OTHER STRESSES THEY COME TOGETHER TO FORM A SLUG LIKE AGGREGA TION OF AMEBAS CALLED A PSEUDOPLASMO WHICH ACTS LIKE AN INDIVIDUAL WHICH THE REPRODUCTIVE ORGANS ARE BORNE AT THE TOP OF THE MAIN AXIS WHICH IS USUALLY ERECT SO THAT SUBSEQUENT GROWTH IS SYMPO DESCRIBING A PROCESS SUCH AS GROWTH OR DEVELOPMENT THAT PROGRESSES FROM THE BASE OR POINT OF ATTACHMENT SO THAT THE OLDEST PARTS ARE AT THE BASE AND THE YOUNGEST ARE AT THE TIP COMPARE BASIPETAL A GLOBULAR CONTRACTILE PROTEIN G ACTIN THAT MAKES UP 10 15 OF THE TOTAL CELL PROTEIN IN EUKARYOTIC CELLS IT IS A MAJOR COMPONENT OF THE CYTOSKELETON IT ALSO CONTROLS MOTILITY CELLULAR MOVEMENTS AND CYCLOSIS G ACTIN CAN POLYMERIZE INTO HELICAL STRANDS THAT COIL TOGETHER TO FORM MICROFILAMENTS CALLED FIBROUS ACTIN F ACTINOBACTERIA RAY FUNGI ACTINOMYCETES A PHYLUM OF EUBACTERIA THAT CONTAINS THE TRUE ACTINOBACTERIA AND THE CORYNEFORM BACTERIA THE TRUE ACTINOBACTERIA FORM BRANCHING FILAMENTS THAT RESEMBLE SMALL FUNGAL MYCELIA WITH HYPHAE USUALLY LESS THAN 1 5 M M IN DIAMETER THE CORYNE FORM BACTERIA ARE RODLIKE STRUCTURES THE ACTINOBACTERIA ARE DISTINGUISHED BY PRO DUCING ACTINOSPORES ENTIRE CELLS ENCYSTED IN THICK WALLS TO FORM RESISTANT SPORES ACTINODROMOUS PALMATE DIGITATE SCRIBING A FORM OF LEAF VENATION IN WHICH THREE OR MORE PRIMARY VEINS RADIATE FROM THE BASE OF THE LAMINA TOWARD THE MARGIN AS IN SYCAMORE ACER PSEUDOPLATANUS RE SULTING IN A LEAF THAT HAS SEVERAL LARGE LOBES OR SEVERAL LEAFLETS ALL ORIGINATING AT THE SEE RADIAL SYMMETRY TYPE OF PROTOSTELE IN WHICH THE XYLEM IS STAR SHAPED AND THE PHLOEM LIES BETWEEN THE POINTS OF THE STAR PROTOSTELES ARE FOUND IN THE PRIMARY ROOTS OF HIGHER PLANTS AND IN SOME SPE CIES OF LYCOPODIUM AND PSILOTUM SEE A GRAPH SHOWING THE EFFECT OF DIFFERENT WAVELENGTHS OF RADIATION USUALLY LIGHT ON A GIVEN PROCESS IT IS OFTEN SIMILAR TO THE ABSORPTION SPECTRUM OF THE SUBSTANCE THAT ABSORBS THE RADIATION AND CAN THEREFORE BE HELPFUL IN IDENTIFYING THAT SUBSTANCE FOR EXAMPLE THE ACTION SPEC TRUM OF PHOTOSYNTHESIS IS SIMILAR TO THE AB SORPTION SPECTRUM OF CHLOROPHYLL IT SHOWS THE NET ASSIMILATION PLOTTED AGAINST WAVE LENGTH SEE ABSORPTION SPECTRUM SEE ILLUS THE MINIMUM EXTRA ENERGY THAT MUST BE PUT INTO A SYSTEM TO EN ABLE A REACTION TO OCCUR IT INCREASES THE EN ERGY LEVELS OF PARTICIPATING MOLECULES AND HENCE RAISES THEIR REACTIVITY OFTEN BY RAIS ING ELECTRONS TO AN EXCITED STATE ENZYMES ENHANCE REACTION RATES BY LOWERING THE AC TIVATION ENERGY THIS IS OFTEN ACHIEVED BY THE ATTRACTION OF THE REACTANTS TO THE EN ZYME S ACTIVE SITE THUS COMING INTO CLOSER PROXIMITY OR BY THE ENZYME CAUSING CON FORMATIONAL OR ELECTROSTATIC CHANGES IN ONE OR MORE OF THE REACTANTS