sexual life cycles plant structure and phylogeny the angiosperms
TRANSCRIPT
Sexual Life cyclesPlant structure and Phylogeny
The Angiosperms
Outline
• Brief review• 9. ALTERNATION OF GENERATIONS• 8. PLANT EVOLUTION• 7. ANGIOSPERM LIFE HIST.
Define sex cell.
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
Most of the many
Eukaryotic species
reproduce sexually
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
Animal species alternate between diploid (mitotic) and haploid (meiotic)
In animals, only the diploid stage is multicellular
Sexual life cycle of Animalsgametic 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
Schematic gametic life cycle
Sporophyte
Many fungi work the opposite wayzygotic 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
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
8. PLANT EVOLUTION
Plant phylogeny
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
In mosses, the sporophyte and gametophyte are similar in size
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
The gametophyte is smaller in the fern life cycle
The gametophyte nurtures the young sporophyte
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
Gymnosperms include cycads & ginkoes
Gymnosperms have no flowers
or fruits• Mostly wind-
pollinated• The most massive
indiviual living things- Giant sequoia
The tallest and most massive- here in CA
Male & Female Gametophytes are greatly reduced in gymnosperms
Angiosperms are flowering plantsangiosperms (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.
Basic (monoecious) Flower structure
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
The female gametophyte houses the seed
• inside carpels- meiosis prod.
megaspore (1n)becomes the ovary= female gametophyte
(1n)• = ovum + central cell
(n+n)
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)
The seed is a capsule containing a plant embryo
• - 2nd sperm cell + central cell (n+n) = endosperm (3n, food in seed)
• seed - seed coat around
endosperm- zygote grows into embryo via mitosis- ovary around seed
becomes fruit
The plant embryo is already formed
• embryo - epicotyl becomes shoot• - hypocotyl becomes root• - cotyledons becomes
leaves
Plant phylogeny
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 3’s, 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 5’s, taproot• - vasc. bundles arranged in ring, • secondary growth possible
Monocots vs. Dicots