Transcript Seed Bearing Plants

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
• Flower
– 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