Sexual Life cycles
Plant structure and Phylogeny
The Angiosperms
Outline
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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 & Archaeaprokaryotic
• 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 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
Schematic gametic life cycle
Sporophyte
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
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 plantsavascular
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 windpollinated
• 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 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.
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
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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