Life Cycles of nonflowering plants

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Life Cycles of nonflowering plants
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• Like the algae they evolved from, nonflowering
  plants have a life cycle made up of two different
  stages.

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• plants alternate between a sexual stage and a
  nonsexual stage.

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• In the sexual stage, a plant called the
  gametophyte (guh MEET uh FYT) produces egg and
  sperm cells.

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• The sperm and egg combine to form a fertilized
  egg cell, which grows into an embryo.

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• The embryo grows into a sporophyte (SPOR roh
  FYT), the plant that makes up the nonsexual stage.

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• The sporophyte produces spores. A spore is a
  nonsexual reproductive cell with a protective
  coat.

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• A spore develops into a gametophyte. The
  gametophyte reproduces sexually, and the cycle
  continues.

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• Some plants have separate male and female
  gametophytes.

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• In other plants, one gametophyte produces both
  eggs and sperm.

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• This two-stage life cycle evolved in a water
  environment, where water was a means of transport
  for the sperm.

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• The gametophyte could live independent of the
  sporophyte.

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• A few land plants have this arrangement. They
  must rely on rainwater for transporting sperm,
  limiting where they can live.

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• Other plants adapted more completely to land by
  modifying their sexual stage.

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• It became shorter, and the gametophytes became
  smaller. These two changes allowed the sporophyte
  to evolve ways of protecting the gametophyte and
  helping the eggs and sperm to come together
  without water.

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• In the most complex nonflowering plants, the
  gymnosperms, the sexual stage takes place almost
  completely within the sporophyte.

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• This adaptation was made possible in part by the
  evolution of the seed. A seed is made up of an
  embryo, a stored energy supply, and a protective
  seed coat .

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• End