14.4 The Life Cycle of Flowering Plants

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14.4 The Life Cycle of Flowering Plants

• Biology 1001
• November 25, 2005

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Alternation of GenerationsFigure 29.5!!

• Angiosperms, like all plants, have an alternation
  of generations type of life cycle
• The two generations are heteromorphic
• The gametophytes highly are reduced and dependent
  on the sporophytes
• The gametes and spores are non-motile

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Flower Structure

• The flower is an angiosperm structure specialized
  for sexual reproduction
• It is a specialized shoot with up to four rings
  of modified leaves called floral organs sepals,
  petals, stamens, and carpels
• Sepals and petals are sterile organs
• Stamens, the male reproductive organs, consist of
  an anther and a filament
• Carpels, the female reproductive organs, consist
  of the stigma, the style, and the ovary

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Flower Variety
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Figure 38.2!,!! An Overview of Angiosperm
Reproduction
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Figure 30.10!,!! - The life cycle of an angiosperm
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Development of the Gametophytes

• The flowers on the sporophyte produce microspores
  and megaspores that form male and female
  gametophytes
• The male gametophytes are the pollen grains,
  which develop within microsporangia in the anther
• The female gametophyte is the embryo sac, and it
  develops within the megasporangium within the
  ovule, which develops in the ovary
• Each pollen grain has two haploid cells, a
  generative cell that divides to produce two
  sperm, and a tube cell that produces a pollen
  tube
• The embryo sac consists of 8 haploid nuclei
  partitioned into 7 cells the egg, two synergids,
  three antipodal cells, and two polar nuclei

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Gametophyte DevelopmentFigure 38.4
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Pollination and Fertilization

• Pollination is the transfer of pollen from the
  anther to the stigma of the carpal
• After pollination, the pollen tube grows through
  the style and into the ovary and the generative
  cell divides into the two sperm cells, which are
  discharged near the embryo sac
• Pollination precedes and is necessary for
  fertilization to occur
• Fertilization is the union or syngamy of the egg
  and sperm
• In angiosperms, a process called double
  fertilization occurs
• One sperm fertilizes the egg forming the diploid
  zygote and the other combines with the two polar
  nuclei to form the triploid endosperm, which
  develops into a nutrient supply for the seed
• After fertilization, the ovule matures into the
  seed

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The Co-evolution of Flowers Pollinators

• Co-evolution refers to reciprocal evolutionary
  adaptations of two interacting species
• Animals interact with plants by helping to
  disperse their pollen and seeds, meanwhile
  receiving a benefit by eating nectar, seeds, and
  fruits of the plant
• Wind and water are also means of pollen and fruit
  dispersal

• Figure 30.13!
• Bee Pollinators
• Hummingbird Pollinators
• Bat Pollinators