Sexual Reproduction in Plants

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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.

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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

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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

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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

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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

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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

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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

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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