The Angiosperms

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The Angiosperms

• Division Magnoliophyta

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• General information about the Angiosperms. . .
• They are the most successful of all plants
• They possess specialized water-conducting cells
  called vessel elements in the xylem tissue
• They possess efficient sugar-conducting cells
  called sieve tube members in their phloem
• They reproduce sexually - producing flowers,
  fruits, and seeds
• The double fertilization that occurs during
  sexual reproduction is unique
• They are used by humans extensively as a source
  for food, grains, vegetables, fruit, hardwoods,
  fibers, medicines, etc.

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Monocots (Class Liliopsida) Dicots (Class
Magnoliopsida) are the two classes of Angiosperms

• Monocots include palms, grasses, orchids, and
  lilies

• Dicots include oaks, roses, cacti, sunflowers,
  and strawberries

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Tap roots
Fibrous roots
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• The floral parts consist of. . .
• The petals - commonly colorful extensions
• The sepals - Insert below the petals and are
  usually green
• The pistil (containing the carpels) - the female
  part of the flower - eggs are produced here
• The stamens - the male part of the flower - the
  pollen grains (male gametophyte) are produced
  here
• Floral parts insert into an expanded receptacle

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• Some terminology. . .
• Complete flowers have all four floral parts
  (sepals, petals, stamens, and pistil
• Incomplete flowers are missing at least one
  floral part
• Perfect flowers have both stamens and pistil
• Imperfect flowers are missing either the stamens
  or the pistil
• So which of these statements are true and which
  are false?
• All perfect flowers are complete.
• All complete flowers are perfect
• All imperfect flowers are incomplete
• All incomplete flowers are imperfect

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• Flowering plants have a life cycle that involves
  an alternation of generations. . .
• The sporophyte generation is clearly dominant
• The gametophyte generation is reduced to only a
  few cells
• Double fertilization is an important feature
• Flowering plants are heterosporus - they produce
  both microspores and megaspores
• Each ovule within an ovary contains a megaspore
  mother cell that undergoes meiosis, producing 4
  haploid megaspores
• Three of these megaspores degenerate leaving one
  haploid megaspore
• This megaspore divides mitotically and develops
  into a female gametophyte (the embryo sac)
• The embryo sac contains eight haploid nuclei
  three of which will participate in fertilization

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The embryo sac (female gametophyte)

• The nuclei which will participate in
  fertilization are the two polar nuclei and the egg

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• The anther contains microspore mother cells that
  each undergo meiosis to form four haploid
  microspores. .
• Each microspore develops into a male gametophyte
  (a pollen grain)
• Pollen grains are transferred to the stigma of
  the pistil by wind or animals
• If the pollen grain is compatible with the pistil
  of the flower it landed on, then it will
  germinate and grow a pollen tube down the style
  and into the ovary
• A cell within the pollen grain divides to form
  two nonflagellated sperm
• Both sperm are involved in the fertilization
  process
• One sperm fertilizes the egg forming a diploid
  zygote and the other sperm fuses with the two
  polar nuclei to form a triploid (3n) cell that
  develops into the endosperm in the seed

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double
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n
2n
X 3
Embryo sac
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• The flowering plants are the most successful
  plants for several reasons. .
• The flower attracts insects and other types of
  pollinators insuring cross-pollination
• Closed carpels which produce fruits around the
  seeds increase dispersal
• Double fertilization resulting in a nutritive
  endosperm to nourish the developing embryo
• Vessel elements in the xylem and sieve tube
  members in the phloem provide extremely efficient
  conduction systems for these plants
• The leaf shape is conducive to photosynthesis
• abscission (shedding) of the leaves in harsh
  conditions allows the flowering plants to live in
  a variety of habitats
• Extremely adaptable sporophyte plants have
  developed a degree of diversity unknown in other
  plant types

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