Plant Reproduction

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Plant Reproduction
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Rafflesia arnoldii, monster flower, Indonesia,
nearly 1m diameter, up to 11 kg
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Plant ReproductionFigure 34.2

• Angiosperms and other vascular plants undergo
  alternation of generations, in which the diploid
  plant, or sporophyte, is the dominant generation
  and produces haploid spores by meiosis
• The spores develop into male and female
  gametophytes.
• The gametophytes develop and produce gametes by
  mitosis, which may undergo fertilization and form
  new sporophytes

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Plant ReproductionFigure 34.3 34.4

• Flowers contain the gametophyte(s) and are the
  reproductive organs of angiosperms.
• Sepals protect the floral bud before it opens
• Petals attract insects and other pollinators to
  the plant with their color and fragrance
• Stamens male reproductive organs, consist of
  anthers and filaments
• Carpels (aka pistils) female reproductive
  organs, consist of ovary, stigma and style

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Plant Reproduction

• Complete flowers have all four of these basic
  structures (sepals, petals, carpels, stamens).
• Incomplete flowers lack one or more of the basic
  structures.
• Staminate (male) and carpellate (female) flowers
  are incomplete because they contain either only
  functional stamens or functional carpels.

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Plant Reproduction

• Dioecious species have staminate flowers and
  carpellate flowers on different plants (dioecious
  two houses).
• Buffalo grass and cottonwood are examples.
• Monoecious species have staminate and carpellate
  flowers located on the same plant (monoecious
  one house).
• An example of a monoecious plant is corn.
• The male and female structures are located in
  separate flowers but both are located on the same
  plant.
• The stamens, or the male floral structures, are
  the tassels located at the top of the plant.
• The carpel or female reproductive structure, is
  the ear, which is located about midway up the
  stalk of each plant.

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Corn

• The monoecious corn plant has female flowers that
  develop on the side of the plant and emerge from
  the leaf node.
• As these flowers emerge they develop into the
  familiar ear of corn.
• These flowers only have carpels. The styles of
  corn are long and grow up from the ovary and out
  of the sepals (husks). The styles are called
  silks because of their length and delicate
  nature.
• When pollen from the tassel flower lands on the
  stigma at the end of the silk, the pollen tube
  can grow through the silk to the ovary.

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Plant ReproductionFigure 34.5

• In the sporangia of an anther, there are many
  diploid cells called microsporocytes.
• Each microsporocyte undergoes meiosis to form 4
  haploid microspores, each of which eventually
  become the mature male gametophytes (pollen
  grains).
• Each pollen grain contains a generative cell,
  which will form two sperm, and the tube cell
  nucleus, which forms the pollen tube.
• In the ovary, ovules form - each of them
  containing a single sporangium. Within the
  sporangium, a single cell called the
  megasporocyte grows and undergoes meiosis to form
  four haploid megaspores.
• In many angiosperms, only one megaspore survives,
  and a series of steps produces the mature female
  gametophyte (embryo sac). The embryo sac consists
  of one egg and two polar nuclei.

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Double FertilizationFigure 34.6

• When a pollen grain lands on a stigma, it
  germinates.
• The generative cell forms two sperm and the tube
  cell nucleus produces a pollen tube that extends
  towards the ovary.
• One sperm fertilizes the egg to form the 2n
  embryo.
• The other sperm combines with the two polar
  nuclei to form the triploid (3n) endosperm. The
  endosperm is the food source for the embryo.
• This process of forming an embryo and endosperm
  is called double fertilization

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The SeedFigure 34.8

• After double fertilization, the ovule develops
  into a seed, which consists of the developing
  embryo and its food supply.
• The seed coat protects the embryo and its food
  supply.
• A radicle is the embryonic root.
• Cotyledons are the embryonic leaves. They are
  attached at the epicotyl.
• As the seed matures, it enters dormancy, in which
  it has a low metabolic rate and its growth and
  development are suspended.
• The seed resumes growth when there are suitable
  environmental conditions.

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The FruitFigure 34.9 34.10

• After double fertilization, the ovary develops
  into a fruit, which encloses the seed (a seed is
  the developing embryo and its food supply).
• Simple fruit. A simple fruit develops from a
  single carpel (or several fused carpels) of one
  flower (pea, lemon, peanut).
• Aggregate fruit. An aggregate fruit develops from
  many separate carpels of one flower (raspberry,
  blackberry, strawberry).
• Multiple fruit. A multiple fruit develops from
  many carpels of many flowers (pineapple, fig).

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Developmental origin of fruits
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Other Reproduction

• Asexual reproduction, or vegetative reproduction,
  produces clones. In this process, fragmentation
  occurs, in which pieces of the parent plant break
  off to form new individuals that are exact
  genetic replicas of the parent.
• Agriculture uses several techniques of artificial
  reproduction such as grafting, growing clones
  from cuttings, and test-tube cloning.
• Humans have manipulated plants for thousands of
  years by artificial selection
• Genetic modification allows plants to express
  genes from other organisms.