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Plant Diversity II
The Evolution of Seed Plants
SEEDS!• Seeds are plant embryos packaged with a food supply in a protective coat
Evolution of Plants
Five Reproductive Adaptations
1. Reduction of the gametophyte: shift from haploid to diploid condition female gametophyte and embryo depend
on sporophyte protection against drought Protects the delicate antheridia and
archegonia Increasing reproductive success
2. Heterospory Production of two types of spores
Megaspores – female gametophyte – eggs
Microspores – male gametophyte - sperm
Five Reproductive Adaptations
3. Ovules: production of eggs• Megasporangium, megaspore plus
protective tissue = ovule• Increases protection of the egg and
developing zygote• Increases reproductive fitness
4. Evolution of pollen• Male gametophyte = pollen grain• Contain two sperm nuclei• Waterproof coat for transfer by
wind• Remember before – water was
required for fertilization• THIS IS A KEY ADAPTATION
Five Reproductive Adaptations
5. Seeds• Advantages over spores
• Multicellular• Layers of protective
material• Supply of stored energy
means seed can WAIT for good germination conditions
• Stored energy supplements early growth of the embryo
Gymnosperms (bare naked)
Cone-bearing plants Lack enclosed chambers
(ovaries) for seeds Ovules and seeds develop
on specialized leaves called sporophylls
Ginkgo, cycads, and conifers All are “evergreens” Needle-shaped leaves Vascular tissue refinement:
tracheids~ water conducting and supportive element of xylem
Reproduction in Gymnosperms
Reproductive Cycle
Gymnosperm Life Cycle
• Sporophyte– produce gametophytes
inside of cones– Pollen cone (male)
• produces microspore via meiosis
– Ovulate cone (female)• produces megaspores
via meiosis• Fertilization
– pollen grains discharge sperm into egg
Angiosperms – Flowers and Fruits
Seed plants that produce the reproductive structures called flowers and fruits.
90% of all plant species
“Flowering plants” Anthophyta
The Flowerdefining structure of angiosperms
Reproductive structure: pollen transfer; specialized shoot with modified leaves
Sepals: enclose flower before it opens - protection
Petals: attract pollinatorsStamens: male, produce
microspores in the anther that develops the pollen grain
Carpels: female, produce megaspores - stigma, style, ovary, ovules
FruitsFruits are the
mature ovaries of the plant
The wall of the ovary thickens to become the fruit.
The purpose of fruit is to disperse the seeds
Monocots and Eudicots
Angiosperms are divided into two groups Monocots
~70,000 species One cotyledon in the seed Parallel leaf veins Flowering parts in multiples of
three
Monocots and Eudicots
Angiosperms are divided into two groups Eudicots
~170,000 species Two cotyledon in the
seed Net leaf veins Flowing parts in
multiples of fours or fives
Angiosperm life cycle