sexual life cycles plant structure and phylogeny the angiosperms

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