Sexual Life cycles Plant structure and Phylogeny

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Sexual Life cyclesPlant structure and Phylogeny

• The Angiosperms

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Outline

• Brief review
• 9. ALTERNATION OF GENERATIONS
• 8. PLANT EVOLUTION
• 7. ANGIOSPERM LIFE HIST.

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Define sex cell.
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All life is organized into 3 domains

• 2 Domains of prokaryotes, 1 of all eukaryotes
• Bacteria Archaea- prokaryotic
• Eukaryota- Includes all 4 eukaryotic kingdoms
  protista, animalia, plantae, fungi

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Most of the many Eukaryotic species reproduce
sexually
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Despite an inherent twofold cost, higher species
reproduce sexually

• Sexually reproducing species must have 2
  offspring to break even
• 2 offspring from an asexually reproducing species
  doubles the population

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Animal species alternate between diploid
(mitotic) and haploid (meiotic)
In animals, only the diploid stage is
multicellular
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Sexual life cycle of Animals

• gametic or diplontic
• - meiosis forms gametes, no spores
• - mainly like a sporophyte (2n)
• - produce gametes (1n) via meiosis
• - fertilization results in zygote (2n)
• - sporophyte grows via mitosis 

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Schematic gametic life cycle
Sporophyte?
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Many fungi work the opposite way

• zygotic or haplontic
• - zygote undergoes meiosis
• - mainly like a gametophyte (1n)
• - produce gametes (1n) via mitosis
• - fertiliz. results in zygote (2n)
• - produce spores (1n) via meiosis
• - gametophyte grows via mitosis 

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Most plants have two multicellular life cycle
stages- gametophyte and sporophyte

• plants - sporic or diplohaplontic
• - alternate sporo- gametophyte
• - meiosis forms spores
• - sporophytes (2n) dominate
• - produce spores (1n) via meiosis
• - gametophyte (1n) develops inside cone/flower
  via mitosis
• - prod. gametes (1n) via mitosis
• - fertiliz. results in zygote (2n)
• - sporophyte grows via mitosis

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8. PLANT EVOLUTION
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Plant phylogeny
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The Phylum Bryophyta includes liverworts and
mosses

• Simplest terrestrial plants- avascular
• evolve multicell. terrestrial
• - adapt to gravity, so small/low
• - no roots, rhizoids only anchor
• sperm needs H2O to fertilize ova

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In mosses, the sporophyte and gametophyte are
similar in size
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Ferns are vascular plants

• ferns (Phylum Pterophyta)
• evolve vasculature (vessels),
• allows fronds to grow large
• - true roots absorb H2O, minerals
• - no seeds, sperm still needs H2O

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The gametophyte is smaller in the fern life cycle
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The gametophyte nurtures the young sporophyte
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Conifers are the prototypical gymnosperm

• gymnosperms (Phy. Coniferophyta)
• - evergreen needles reduce evap.
• ova in larger female cones
• sperm in pollen grains from male cones,
  dispersed by wind
• no fruit, naked seeds protect provide
  nutrients to embryo 

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Gymnosperms include cycads ginkoes
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Gymnosperms have no flowers or fruits

• Mostly wind-pollinated
• The most massive indiviual living things- Giant
  sequoia

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The tallest and most massive- here in CA
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Male Female Gametophytes are greatly reduced in
gymnosperms
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Angiosperms are flowering plants

• angiosperms (Phylum Anthophyta)
• - deciduous leaves drop off in winter, surv. low
  temp/H2O
• flowers attract animal pollinators with
  color-smell-nectar,
• more efficient for fertilization
• endosperm in seeds stores nutrients, esp. in
  grains/nuts
• fruit attracts animals to disperse fertilize
  seeds, reduces comp.

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Basic (monoecious) Flower structure
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The male angiosperm gametophyte is even smaller

• inside anthers
• - meiosis prod. microspore (1n)
• - becomes the pollen grain
• male gametophyte (1n)
• - with 2 sperm cells tube cell

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The female gametophyte houses the seed

• inside carpels
• - meiosis prod. megaspore (1n)
• becomes the ovary
• female gametophyte (1n)
• ovum central cell (nn)

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Pollination

• pollination - pollen grain to stigma
• - tube cell grows pollen tube to reach ovary
• double fertilization
• - 1st sperm cell (1n) ovum (1n)
• zygote (2n sporophyte)

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The seed is a capsule containing a plant embryo

• - 2nd sperm cell central cell (nn)
  endosperm (3n, food in seed)
• seed
• - seed coat around endosperm
• - zygote grows into embryo
• via mitosis
• - ovary around seed becomes fruit

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The plant embryo is already formed

• embryo
• - epicotyl becomes shoot
• - hypocotyl becomes root
• - cotyledons becomes leaves

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Plant phylogeny
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6. MONOCOTS VS. DICOTS

• angiosperms - flowering plants
• - divided into 2 major groups
• monocots - corn, grasses
• - 1 cotyledon (embryonic leaf)
• - narrow leaves with parallel veins
• - flower parts in 3s, fibrous roots
• - vascular bundles scattered,
• primary growth only
• dicots - most other angiosperms
• - 2 cotyledons absorb endosperm
• - broad leaves with network veins
• - flower parts in 4 or 5s, taproot
• - vasc. bundles arranged in ring,
• secondary growth possible

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Monocots vs. Dicots