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ALTERNATION OF GENERATIONS

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  • ALTERNATION OF GENERATIONSTHE ANGIOSPERM LIFE CYCLE INCLUDES ALTERNATION OF GENERATIONS DURING WHICH MULTICELLULAR HAPLOID GAMETOPHYTE GENERATIONS ALTERNATE WITH DIPOLOID SPOROPHYTE GENERATIONSTHE SPOROPHYTE IS THE RECOGNIZABLE PLANT MOST FAMILIAR TO USSPORES WILL UNDERGO MITOTIC DIVISION TO FORM A MALE OR FEMALE GAMETOPHYTE

  • ALTERNATION OF GENERATIONS

  • ANTHERS AND OVARIESANTHERS: MALEOVARIES: FEMALEFLOWERS ARE THE REPRODUCTIVE STRUCTURE OF ANGIOSPERM SPOROPHYTESFOUR SETS OF MODIFIED LEAVES ARE:SEPALS, PETALS, STAMENS, CARPELS

    STAMENS/CARPELS: CONTAIN THE SPORANGIA AND ARE THE REPRODUCTIVE PARTS OF THE FLOWER

  • FEMALE GAMETOPHYTE-DEVELOP IN CARPEL SPORANGIA AS EMBRYO SACS, WHICH CONTAIN THE EGGS. THIS OCCURS INSIDE THE OVULES, WHICH ARE AT THE BASE OF THE CARPEL AND SURROUNDED BY OVARIESMALE GAMETOPHYTES-DEVELOP IN THE STAMEN SPORANGIA AS POLLEN GRAINS. THESE FORM AT THE STAMEN TIPS WITHIN CHAMBERS OF THE ANTHERS

  • FLOWER STRUCTURE

  • POLLINATIONPOLLINATION OCCURS WHEN WIND OR ANIMAL BORN POLLEN RELEASED FROM ANTHERS LANDS ON THE STIGMA AT TIP OF A CARPELA POLLEN TUBE GROWS FROM THE POLLEN GRAIN, DOWN THE CARPEL, INTO THE EMBRYO SACSPERM ARE DISCHARGED RESULTING IN FERTILIZATION OF THE EGGSTHE ZYGOTES WILL DEVELOP INTO AN EMBRYO; AS THE EMBRYO GROWS, THE OVULE SURROUNDING IT DEVELOPS INTO A SEEDWHILE SEED FORMATION IS TAKING PLACE, THE ENTIRE OVARY IS DEVELOPING INTO A FRUIT, WHICH WILL CONTAIN ONE OR MORE SEED

  • SEEDSSEEDS ARE DISPERSED FROM THE SOURCE PLANT WHEN FRUITS ARE MOVED ABOUT BY WIND OR ANIMALSSEEDS DEPOSITED IN SOIL OF THE PROPER CONDITION (MOISTURE,NUTRIENTS) WILL GERMINATETHE EMBRYO STARTS GROWING AND DEVELOPS INTO A NEW SPOROPHYTEAFTER FLOWERS ARE PRODUCED BY THE SPOROPHYTE, A NEW GENERATION OF GAMETOPHYTES DEVELOP AND THE LIFE CYCLE CONTINUES

  • FLOWER TYPESCOMPLETE FLOWER= A FLOWER WITH SEPALS, PETALS, STAMENS, CARPELSINCOMPLETE FLOWER= MISSING ONE OR MORE PARTS ABOVEPERFECT FLOWER= HAS BOTH STAMENS AND CARPELSIMPERFECT = IS EITHER STAMINATE (HAVING STAMENS BUT NO CARPELS) OR CARPELLATE; A UNISEX FLOWERMONECIOUS = HAVE BOTH STAMINATE FLOWERS AND CARPELLATE FLOWERS ON THE SAME PLANTDIOECIOUS = HAS STAMINATE AND CARPELLATE FLOWERS ON SEPARATE INDIVIDUAL PLANTS OF THE SPECIES

  • POLLEN DEVELOPMENTPOLLEN GRAIN = THE IMMATURE MALE GAMETOPHTE THAT DEVELOPS WITHIN THE ANTHERS OF STAMENS IN AN ANGIOSPERMEXTREMELY DURABLE; RESISTANT TO BIODEGRADATIONFOSSILIZED POLLEN HAS PROVIDED MANY IMPORTANT EVOLUTIONARY CLUESFORMATION OF POLLEN GRAIN IS AS FOLLOWS:

  • WITHIN THE SPORANGIAL CHAMBER OF AN ANTHER, DIPLOID MICROSPOROCYTES UNDERGO MEIOSIS TO FORM 4 HAPLOID MICROSPORES

    THE HAPLOID MICROSPORE NUCLEUS UNDERGOES MITOTIC DIVISION TO GIVE RISE TO A GENERATIVE CELL AND A TUBE CELL

    THE WALL OF THE MICROSPORE THEN THICKENS AND BECOMES SCULPTURED INTO A SPECIES-SPECIFIC PATTERN

    THESE 2 CELLS AND THE THICKENED WALL ARE THE POLLEN GRAIN, AN IMMATURE MALE GAMETOPHYTE

  • OVULE FORMATIONA MEGASPOROCYTE IN THE SPORANGIUM OF EACH OVULE GROWS AND GOES THROUGH MEIOSIS TO FORM FOUR HAPLOID MEGASPORES (ONLY ONE SURVIVES)

    THE REMAINING MEGASPORE GROWS AND ITS NUCLEUS UNDERGOES 3 MITOTIC DIVISIONS, FORMING ONE LARGE CELL WITH 8 HAPLOID NUCLEI

    MEMBRANES PARTITION THIS INTO A MULTICELLULAR EMBRYO SAC

  • ACTIVE POLLINATIONPOLLINATION = THE PLACEMENT OF POLLEN ONTO THE STIGMA OF A CARPELSOME PLANTS USE WIND TO DISPERSE POLLENOTHER PLANTS INTERACT WITH ANIMALS THAT TRANSFER POLLENSOME PLANTS SELF-POLLINATE, BUT MOST CROSS-POLLINATEMOST MONOECIOUS ANGIOSPERMS HAVE MECHANISMS TO PREVENT SELF-POLLINATIONMATURATION TIMES, STRUCTURAL DIFFERENCES AND SELF-INCOMPATIBILITY ARE ALL REASONS THAT THEY CANNOT SELF-POLLINATE

  • SELF-INCOMPATIBILITYSELF-INCOMPATIBILITY - THE REJECTION OF POLLEN FROM THE SAME, OR CLOSELY RELATED PLANT BY THE STIGMATHE RECOGNITION OF SELF POLLEN IS BASED ON S-GENES (NAMED FOR SELF-INCOMPATIBILITY)MANY ALLELES FOR THE S-LOCUS ARE FOUND IN A PLANT POPULATIONS GENE POOLA POLLEN GRAIN THAT LANDS ON A STIGMA WITH MATCHING ALLELES AT THE S-LOCU IS SELF-INCOMPATIBILETHE POLLEN GRAIN WILL EITHER NOT INITIATE OR COMPLETE FORMATION OF THE POLLEN TUBETHIS PREVENTS SELF-FERTILIZATION AND FERTILIZATION BETWEEN PLANTS WITH A COMMON S-LOCUS

  • GENETIC BASIS OF SELF-INCOMPATIBILITY

  • A POSSIBLE MECHANISM OF SPOROPHYTIC SELF-INCOMPA- TABILITY

  • DOUBLE FERTILIZATIONWHEN A COMPATIBLE POLLEN GRAIN (DIFFERENT S-LOCUS ALLELES) LANDS ON A STIGMA OF AN ANGIOSPERM, DOUBLE FERTILIZATION OCCURSDOUBLE FERTILIZATION = THE UNION OF TWO SPERM CELLS WITH TWO CELLS OF THE EMBRYO SACAFTER ADHERING TO A STIGMA, THE POLLEN GRAIN GERMINATES AND EXTENDS A POLLEN TUBE BETWEEN THE CELLS OF THE STYLE TOWARD THE OVARYTHE GENERATIVE CELL DIVIDES TO FORM 2 SPERMDIRECTED BY A CHEMICAL ATTRACTANT (USUALLY Ca+), THE TIP OF THE POLLEN TUBE ENTERS THROUGH THE MICROPYLE AND DISCHARGES ITS 2 SPERM NUCLEI INTO THE EMBRYO SAC ONE SPERM UNITES WITH THE EGG TO FORM THE ZYGOTETHE OTHER SPERM COMBINES WITH THE 2 POLAR NUCLEI TO FORM A 3n NUCLEUS IN THE LARGE CENTRAL CELL OF THE EMBRYO SAC

  • POLLEN TUBE AND DOUBLE FERTILIZATION

  • SEED DEVELOPMENTENDOSPERM DEVELOPMENTBEGINS BEFORE EMBRYO DEVELOPMENTTHE TRIPLOID NUCLEUS DIVIDES TO FORM A MILKY, MULTINUCLEATE SUPERCELL AFTER DOUBLE FERTILIZATIONTHIS ENDOSPERM UNDERGOES CYTOKINESIS TO FORM MEMBRANES AND CELL WALLS BETWEEN THE NUCLEI, THUS BECOMING MULTICELLULARENDOSPERM IS RICH IN NUTRIENTS, WHICH IT PROVIDES TO THE DEVELOPING EMBRYOIN MOST MONOCOTS, THE ENDOSPERM STOCKS NUTRIENTS THAT CAN BE USED BY THE SEEDLING AFTER GERMINATIONIN MANY DICOTS, FOOD RESERVES OF THE ENDOSPERM ARE EXPORTED TO THE COTYLEDONS, THUS MATURE SEEDS HAVE NO ENDOSPERM

  • VIDEO: ENDOSPERM DEVELOPMENT

  • EMBRYO DEVELOPMENTTHE ZYGOTES FIRST MITOTIC DIVISION IS TRANSVERSE, CREATING A LARGER BASAL CELL AND A SMALLER TERMINAL CELLTHE BASAL CELL DIVIDES TRANSVERSELY TO FORM THE SUSPENSOR, WH ICH ANCHORS THE EMBRYO AND TRANSFERS NUTRIENTS TO IT FROM THE PARENT PLANTTHE TERMINAL CELL DIVIDES SEVERAL TIMES TO FORM A SHPERICAL PROEMBRYO ATTACHED TO THE SUSPENSOR

  • COTYLEDONS APPEAR AS BUMPS ON THE PROEMBRYO AND THE EMBRYO ELONGATESTHE APICAL MERISTEM OF THE EMBRYONIC SHOOT IS LOCATED BETWEEN THE COTYLEDONSTHE SUSPENSOR ATTACHES AT THE APEX OF THE EMBRYONIC ROOT WITH ITS MERISTEMTHE BASAL CELL GIVES RISE TO PART OF THE ROOT MERISTEM IN SOME SPECIESAFTER GERMINATION, THE APICAL MERISTEMS AT THE ROOT AND SHOOT TIPS WILL SUSTAIN PRIMARY GROWTHTHE EMBRYO ALSO CONTAINS PROTODERM, GROUND MERISTEM, AND PROCAMBIUMAS THE EMBRYO DEVELOPS, PROTEINS, OIL, AND STARCH ACCUMULATE AND ARE STORED UNTIL THE SEED GERMINATES

  • DEVELOPMENT OF DICOT PLANT EMBRYO

  • IN MATURE SEEDS, THE EMBRYO IS DORMANT UNTIL GERMINATIONTHE SEED DEHYDRATES UNTIL ITS WATER CONTENT IS ONLY 5 -15% BY WEIGHTTHE EMBRYO IS SURROUNDED BY ENDOSPERM, ENLARGED COTYLEDONS, OR BOTHTHE SEED COAT IS FORMED FROM THE INTEGUMENTS OF THE OVULETHE ARRANGEMENT WITHIN THE SEED OF A DICOTBELOW THE COTYLEDON ATTACHMENT POINT, THE EMBRYONIC AXIS IS CALLED THE HYPOCOTYL, WHICH TERMINATES IN THE RADICLE, OR EMBRYONIC ROOTABOVE THE COTYLEDONS, THE EMBRYONIC AXIS IS CALLED THE EPICOTYL, WHICH TERMINATES IN THE PLUMULE (SHOOT TIP WITH A PAIR OF TINY LEAVES)A MONOCOT SEED HAS A SINGLE COTYLEDON. MEMBERS OF THE GRASS FAMILY, INCLUDING WHEAT AND CORN, HAVE A SPECIALIZED COTYLEDON CALLED THE SCUTELLUM

    STRUCTURE OF MATURE SEED

  • SEED STRUCTURETHE SCUTELLUM HAS A LARGESURFACE AREA AND ABSORBSNUTRIENTS FROM THE ENDOSPERMDURING GERMINATION

  • OVARY DEVELOPS INTO A FRUITA FRUIT DEVELOPS FROM THE OVARY OF THE FLOWER WHILE SEEDS ARE DEVELOPING FROM THE OVULESA FRUIT PROTECTS THE SEEDS AND AIDS IN THEIR DISPERSAL BY WIND OR ANIMALSTHE CORE OF AN APPLE IS THE TRUE FRUITTHE FLESHY PART OF THE APPLE IS MAINLY DERIVED FROM THE FUSION OF FLOWER PARTS LOCATED AT THE BASE OF THE FLOWERA TRUE FRUIT IS A RIPENED OVARYPOLLINATION TRIGGERS HORMONAL CHANGES THAT CAUSE THE OVARY TO GROWTHE WALL OF THE OVARY THICKENS TO BECOME THE PERICARPTRANSFORMATION OF A FLOWER INTO A FRUIT PARALLELS SEED DEVELOPMENT

  • RELATIONSHIP BETWEEN A PEA FLOWER AND A FRUIT (PEA POD)

  • FRUIT CLASSIFICATIONSIMPLE FRUITS = FRUIT DERIVED FROM A SINGLE OVARY; FOR EXAMPLE CHERRIES (FLESHY) OR SOYBEANS (DRY)AGGREGATE FRUITS = FRUITS FROM A SINGLE FLOWER WITH SEVERAL SEPARATE CARPELS; FOR EXAMPLE, STRAWBERRIESMULTIPLE FRUITS = FRUITS FROM AN INFLORESCENCE OR SEPARATE TIGHTLY CLUSTERED FLOWERS, EX: PINEAPPLE

    SEE TABLE 38.1

  • FRUIT RIPENINGFRUITS RIPEN ABOUT THE TIME SEEDS ARE BECOMING FULLY DEVELOPEDIN DRY FRUITS (SOY), THE FRUIT TISSUES AGE AND THE FRUIT (POD) OPENS AND RELEASES THE SEEDSFLESHY FRUITS RIPEN THROUGH A SERIES OF STEPS GUIDED BY HORMONAL INTERATIONSTHE FRUIT BECOMES SOFTER AS A RESULT OF ENZYMES DIGESTING THE CELL WALL COMPONENTSCOLORS USUALLY CHANGE AND THE FRUIT BECOMES SWEETER AS ORGANIC ACIDS OR STARCH ARE CONVERTED TO SUGARTHESE CHANGES PRODUCE AN EDIBLE FRUIT WHICH ENTICES ANIMALS TO FEED, THUS DISPERSING THE SEEDS

  • VIDEO: FRUIT DEVELOPMENT

  • SEED DORMANCYTHE EVOLUTION OF THE SEED WAS AN IMPORTANT ADAPTATION BY PLANTS TO LIVING IN TERRESTRIAL HABITATSSEED DORMANCY PREVENTS GERMINATION WHEN CONDITIONS FOR SEEDLING GROWTH ARE UNFAVORABLE (DAYS TO YEARS)IT INCREASES SURVIVAL RATECONDITIONS FOR BREAKING DORMANCY VARY DEPENDING ON THE TYPE OF ENVIRONMENT THE PLANT INHABITSEXAMPLES: DESERT PLANTS MAY NEED HEAVY RAIN, CHAPARRAL PLANTS NEED EXPOSURE TO INTENSE HEAT (BRUSHFIRES), OTHER SEEDS MAY NEED EXPOSURE TO COLD, SUNLIGHT, OR PASSAGE THROUGH AN ANIMALS DIGESTIVE SYSTEM

  • VIDEO: SEED DEVELOPMENT

  • FRO

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