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Sexual Reproduction in Plants

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... in Angiosperms ... Seed Dispersal in Angiosperms. Dispersal is the transport of seeds away from ... Like an angiosperm, the seed of a gymnosperm contains an ... – PowerPoint PPT presentation

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Title: Sexual Reproduction in Plants


1
Sexual Reproduction in Plants
  • Continued

2
Pollination in Angiosperms
  • Before seeds can develop inside a flower, pollen
    grain from the anthers must reach the stigma of
    the pistil this is called pollination
  • There are two types of pollination,
    self-pollination and cross-pollination.

3
Self-Pollination
  • Both male and female gametes come from the same
    plant

Cross-Pollination
  • The pollen from one flower is transferred to a
    flower on a different plant
  • The two most common agents of cross-pollination
    are wind and insects

4
How does pollination occur??
  • First a grain of pollen lands on the stigma
  • Second, a pollen tube grows down the style into
    the ovary and enters the ovule
  • Third, a sperm is formed through meiosis and
    travels down the tube to fertilize one egg
  • Forth, one sperm fertilizes one egg

5
Seed Development in Angiosperms
  • While the pollen tube is growing, cells inside
    the ovule prepare for its arrival
  • When the sperm reaches an egg, a zygote is formed
  • Other cells in the ovule develop into a cotyledon
    which contains stored food
  • The zygote itself goes through mitotic division
    to form a many-celled embryo with a miniature
    leaf, root, and stem
  • This cotyledon surronds the embryo and the sac
    around the ovule develops into a seed coat

6
Seed Dispersal in Angiosperms
  • Dispersal is the transport of seeds away from the
    parent plant
  • Some fruits can launch their own seeds while
    others need help from outside agents

7
Sexual Reproduction in Gymnosperms
  • Remember that gymnosperms do not bear flowers
  • Most gymnosperms produce their seeds inside cones
    they are often called conifers
  • In most familiar species the same tree produces
    both types of cone
  • Like an angiosperm, the seed of a gymnosperm
    contains an embryo, a food supply, and a coat
    that protects it from drying out

8
Seed Development in Gymnosperms
  • The mature plant produces cones for sexual
    reproduction
  • Female cones produce ovules an egg is produced
    inside the ovule through meiosis
  • Male cones produce pollen by meiosis
  • A pollen grain carried by the wind lands directly
    on an ovule and forms a pollen tube

9
Seed Development in Gymnosperms Cont..
  • A sperm travels down the pollen tube and
    fertilizes an egg to form a zygote
  • The zygote develops into an embryo and a food
    supply is built up
  • The female cone sheds a winged seed that may
    germinate and grow into a seedling, if conditions
    are favorable
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