Seed Bearing Plants

Alternation of Generations All plant life cycles involve alternation of generations between the sporophyte and the gametophyte In different types of plants the relationship changes Mosses: the gametophye is the longest phase Flowering plants: the sporophyte is the longest phase

Seeds Recall the definition of the seed Tougher and more resistant to drying than spores Most spores: single cell Seeds: fully formed plant embryo and stored food; specialized for distribution Evolution of the seed uncoupled reproduction from water

Cones and Flowers Contrast with the life cycle of the fern Tiny gametophytes of the seed bearing plants do not have independent life of their own Gametophytes life inside the sporophyte (in pine cones and flowers) Two kinds of spores: pollen and eggs (these are not gametes in plants)

Reproduction in Conifers (gymnosperms) Study the picture on page 582: the life cycle of a gymnosperm Alternation of generations: gametophyte develops within the sporophyte Two kinds of cones: male cones (produce pollen), female cones (produce eggs) Typically fertilization and seed formation takes a year Seed release is the next year

Reproduction in Angiosperms (flowering plants) 1 Angiosperms produce seeds encased in a protective tissue of the sporophyte called an ovary The combination of seed and ovary is called a fruit Specialized reproductive structure called the flower

Reproduction in Angiosperms (flowering plants) 2 Typical flowers produce both male and female gametophytes Some have separate male and female flowers on the same plant (corn) Some have separate male and female plants (willow) Formed from 4 types of leaves (sepals, petals, stamens and carpels) See diagram of flower on page 586

Reproduction in Angiosperms (flowering plants) 3 Flower parts Sepals Leaflike, green, protect the bud Petals Colorful, advertise the flower to pollinators Stamens Male leaves produce pollen (anther and filament make up the filament) Carpels Female leaves each has an ovary (stigma and style make up the pistil)

Reproduction in Angiosperms (flowering plants) Follows the pattern of alternation of generations Production of gametophyte, fertilization of eggs, development of seed takes place within the flower See life cycle of an angiosperm on page 587

Reproduction in Angiosperms (flowering plants) 4 Key difference between gymnosperm life cycle and angiosperm is double fertilization A sperm nucleus fuses with one of the 2n embryos to make a 3n cell; which divides to produce the endosperm (food for the embryo) In angiosperms, endosperm is produced after the fertilization In gymnosperms endosperm is produced before fertilization

Reproduction in Angiosperms (flowering plants) 5 Fertilization sets into action a number of events Sepals and petals and stamens fall away, Carpel thickens, nutrients directed to endosperm and walls of the ovary This produces a fruit (an ovary containing seeds) Review difference between monocots and dicots