Section 1

Plant Life Cycles

• Plants have a life cycle called alternation of generations, in which a multicellular haploid gametophyte stage alternates with a multicellular diploid sporophyte stage.

• In the moss life cycle, a spore develops into a leafy green gametophyte that produces eggs in archegonia and flagellated sperm in antheridia. A moss sporophyte grows from a fertilized egg.

• In the fern life cycle, a spore develops into a small, flat gametophyte that produces eggs in archegonia and flagellated sperm in antheridia. A fern sporophyte grows from a fertilized egg.

• In the gymnosperm life cycle, a large sporophyte produces two types of spores, and microscopic gametophytes produce gametes. Nonflagellated sperm reach an ovule through a pollen tube.

• Mosses and most ferns are homosporous (produce only one type of spore). All seed plants as well as a few other species are heterosporous (produce male microspores

Vocabulary antheridium (p. 609) archegonium (p. 609) homospory (p. 610) sorus (p. 611)

microspore (p. 611) megaspore (p. 611) heterospory (p. 611)

integument (p. 612) micropyle (p. 612) ovule (p. 612)

pollen grain (p. 612) pollination (p. 612) pollen tube (p. 612)

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