CHAPTER 30 PLANT DIVERSITY II: THE EVOLUTION OF SEED PLANTS

I. OVERVIEW OF REPRODUCTIVE ADAPTATIONS OF SEED PLANTS A. THE GAMETOPHYTES OF SEED PLANTS BECAME EVEN MORE REDUCED THAT GAMETOPHYTES OF SEEDLESS VASCULAR PLANTS  THE GAMETOPHYTES OF SEED PLANTS DEVELOP WITHIN THE CASES OF SPORES RETAINED WITHIN TISSUES OF THE PARENT SPOROPHYTE.

B. IN SEED PLANTS, THE SEED REPLACED THE SPORE AS THE MAIN MEANS OF DISPERSING OFFSPRING A SEED, WHICH IS A DERIVED FROM A FERTILIZED OVULE, CONSISTS OF A SPOROPHYTE EMBRYO PACKAGED ALONG WITH A FOOD SUPPLY WITHIN A SEED COAT.

C. POLLEN BECAME THE VEHICLES FOR SPERM CELLS IN SEED PLANTS A POLLEN GRAIN, WHICH IS AN IMMATURE MALE GAMETOPHYTE, CAN BE DISPERSED THROUGH THE AIR BY WIND OR TRANSPORTED BY ANIMALS.

II. GYMNOSPERMS A.THE MESOZOIC ERA WAS THE AGE OF GYMNOSPERMS GYMNOSPERMS BEAR THEIR SEEDS "NAKED" ON THE SURFACES OF SPOROPHYLLS.

B. THE FOUR DIVISIONS OF EXTANT GYMNOSPERMS ARE THE CYCADS, THE GINKGO, THE GNETOPHYTES, AND THE CONIFERS THE CONE-BEARING CONIFERS, INCLUDING PINES, FIRS, AND SPRUCES, ARE BY FAR THE MOST DIVERSE GYMNOSPERMS TODAY.

B. THE LIFE CYCLE OF A PINE DEMONSTRATES THE KEY REPRODUCTIVE ADAPTATIONS OF SEED PLANTS DOMINANCE SPOROPHYTE GENERATION, THE DEVELOPMENT OF SEEDS FROM FERTILIZED OVULES, AND THE ROLE OF POLLEN IN TRANSFERRING SPERM BETWEEN PLANTS ARE KEY FEATURES OF THE LIFE CYCLE OF A CONIFER.

III. ANGIOSPERMS (FLOWERING PLANTS) A. TERRESTRIAL ADAPTATION CONTINUED WITH THE REFINEMENT OF VASCULAR TISSUE IN ANGIOSPERMS IN ANGIOSPERMS, VESSEL ELEMENTS AND FIBERS EVOLVED FROM TRACHEIDS, A TYPE OF XYLEM.

B. THE FLOWER IS THE DEFINING REPRODUCTIVE ADAPTATION OF ANGIOSPERMS SEPALS, PETALS, STAMENS (THAT PRODUCE POLLEN), AND CARPELS (WHICH PRODUCE OVULES) ARE THE WHORLS OF MODIFIED LEAVES THAT MAKE UP FLOWERS.

C. FRUITS HELP DISPERSE THE SEEDS OF ANGIOSPERMS OVARIES RIPEN INTO FRUITS, WHICH ARE OFTEN CARRIED BY WIND OR ANIMALS TO NEW LOCATIONS.

B. THE LIFE CYCLE OF AN ANGIOSPERM IS A HIGHLY REFINED VERSION OF THE ALTER. OF GENERATIONS COMMON TO ALL PLANTS DOUBLE FERTILIZATION OCCURS WHEN A POLLEN TUBE CHARGES TWO SPERM INTO THE EMBRYO SAC, THE FEMALE GAMETOPHYTE WITHIN AN OVULE. ONE SPERM FERTILIZES THE EGG, WHILE THE OTHER COMBINES WITH TWO NUCLEI IN THE CENTER CELL OF THE EMBRYO SAC TO INITIATE DEVELOPMENT OF FOOD-STORING ENDOSPERM.

B. THE RADIATION OF ANGIOSPERMS MARKS THE TRANSITION FROM THE MESOZOIC TO THE CENOZOIC ERA THE ORIGIN OF ANGIOSPERMS IS STILL UNRESOLVED. ANGIOSPERMS AND ANIMALS HAVE SHAPED ONE ANOTHER'S EVOLUTION POLLINATION OF FLOWERS BY ANIMALS AND TRANSPORT OF SEEDS BY ANIMALS ARE TWO IMPORTANT RELATIONSHIPS IN TERRESTRIAL ECOSYSTEMS

G. AGRICULTURE IS BASED ALMOST ENTIRELY ON ANGIOSPERMS HUMAN CULTURES DEPEND ON THE CULTIVATION AND HARVEST OF ANGIOSPERMS, ESPECIALLY THE FRUITS OF GRAINS

IV. THE GLOBAL IMPACT OF PLANTS A.PLANTS TRANSFORMED THE ATMOSPHERE AND CLIMATE BY LOWERING THE CONCENTRATION OF ATMOSPHERIC CO2, PLANTS PROBABLY CONTRIBUTED TO THE COOLING EARTH DURING THE PALEOZOIC ERA B.PLANT DIVERSITY IS A NONRENEWABLE RESOURCE DESTRUCTION OF TROPICAL FORESTS IS AN ESPECIALLY URGENT PROBLEM BECAUSE THEY CONTAIN THE GREATEST DIVERSITY OF PLANTS ON EARTH.