PLANT DIVERSITY II:

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CHAPTER 30

• PLANT DIVERSITY II
• THE EVOLUTION OF SEED PLANTS

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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.

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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.

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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.

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II. GYMNOSPERMS

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

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 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.

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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.

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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.

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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.

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C. FRUITS HELP DISPERSE THE SEEDS OF ANGIOSPERMS

• OVARIES RIPEN INTO FRUITS, WHICH ARE OFTEN
  CARRIED BY WIND OR ANIMALS TO NEW LOCATIONS.

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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.

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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

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G. AGRICULTURE IS BASED ALMOST ENTIRELY ON
ANGIOSPERMS

• HUMAN CULTURES DEPEND ON THE CULTIVATION AND
  HARVEST OF ANGIOSPERMS, ESPECIALLY THE FRUITS OF
  GRAINS

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IV. THE GLOBAL IMPACT OF PLANTS

• PLANTS TRANSFORMED THE ATMOSPHERE AND CLIMATE
• BY LOWERING THE CONCENTRATION OF ATMOSPHERIC CO2,
  PLANTS PROBABLY CONTRIBUTED TO THE COOLING EARTH
  DURING THE PALEOZOIC ERA
• 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.