BIO 112 chapter 25: seedless plants

chlorophytes, charophytes, and plantae share

-multicellularity

-cell walls with cellulose

-chloroplasts with same pigments (chlorophyll a/b)

-storage molecule is starch

charophytes also share with plantae

- similar flagellated sperm (liverworts)

- cellulose synthesis proteins (rings)

- cytokinesis process (cell plate formation)

- sporopollenin

sporopollenin

durable polymer that protects:

zygotes in charophytes

spores in seedless plants

pollen grains in seed plants

selection for land life

by 470 mya, multicellular green algae expanded from shallow seas into rivers & lakes

first plants were similar to today's liverworts

green algae along lake shores

- more resources; less competition

- subjected to periodic dehydration

- populations with land adaptations thrive

derived characteristics of plants

-alternation of generations

-walled haploid spores

-multicellular gametangia

-sporophyte embryos grow protected within female gametophyte

-apical meristems

-waxy cuticle

-secondary compounds

-mycorrhizae

alternation of generations

plant sporophyte (2n) makes huge # unique diverse offspring per fertilization

compare to charophyte life cycle: only multicellular is haploid, zygote does meiosis to produce only 4 diverse offspring

walled haploid spores

-dispersal thru air: sporopollenin protects

-made within multicellular sporangium

multicellular gametangia

- protecting sperm within the antheridium

- egg protected within archegonium (fertilization here, forming zygote)

sporophyte embryos grow protected within female gametophyte

nourished via placental transfer cells

apical meristems

-continuously dividing cells

-roots and shoots grow toward resources

waxy cuticle

-waxy coat stops desiccation

-pores needed to allow CO2/O2 exchange (controllable stomata in most plants)

secondary compounds

chemicals that deter, repel, or poison competitors, herbivores, and parasites

mycorrhizae

mutualism with fungi; helps water and mineral absorption

dates back to first land plants (before true roots)!

diversification of plants

- One bryophyte-like ancestor of all plants

• about 470 mya

- Key adaptations: major plant "grades"

What are bryophytes?

mosses, liverworts, hornworts

bryophyte characteristics

-haploid gametophyte is dominant form

-diploid sporophyte depends on gametophyte for food and water

haploid gametophyte is dominant form

dominant=longest lasting or largest

makes eggs and flagellated sperm

most are small, low growing, moist areas

lacks vascular/supportive tissue

very thin body: depends on diffusion

with rhizoids for attachment (not true roots)

diploid sporophyte depends on gametophyte for food and water

grows within archegonium of gametophyte

sporangium makes many haploid spores

moss life cycle

A sporophyte has a specialized capsule that holds the spores which grow into separate male and female gametophytes. Antheridia produce sperm on the male gametophytes and the archegonia produce eggs on the female gametophyte. Antheridium fertilizes the egg of the archegonia which grows into a new sporophyte.

bryophytes ecological importance

pioneer species in poor soils

moss are major 1 degree producers in cold or high regions (sphagnum "peat moss" bogs: important wetlands, also harvested for fuel and gardening)

from unbranched to branching sporophytes

-from 1 to many sporangia

-more spores = more offspring

supportive vascular tissue

allowed larger, taller sporophytes

phloem moves sugars and organic products

xylem carries water and minerals (most vascular plants have tracheas with walls strengthened by tough polymer: lignin)

arranged in continuous branching bundles of tubular cells connected end to end

provides bulk flow over longer distances

adds support

sporophyte photosynthesis increases

-improved access to light; many stems

-does not need food from gametophyte

-becomes dominant part of life cycle

roots evolve from underground stems

-anchor larger plant

-absorb water and minerals

-mycorrhizae helped

leaves evolve from branched stems

• microphylls first: single vein

- today still (and only) present in Lycophytes

• later megaphylls: branched veins

- today in Monilophytes & seed plants

sporangia shift to leaves=sporophylls

sori=clusters of sporangia on sporophylls

strobilus=cone-like group of sporophylls

success of seedless vascular plants changed the Paleozoic world

covered the earth, increasing organic C on land (for food, conditioned the soil too)

further increases in O2 levels

reduced CO2 levels

all favoring success of land animals

tree-size seedless forests in carboniferous swamps formed today's coal deposits

phylum lycophyta: lycophytes

-Relict group

• closest group to ancestral vascular plants

• all now very small

• with microphylls & strobili

• include club moss & spike moss

• little economic/ecological importance today

phylum monilophyta: monilophytes

- whisk ferns (psilotum)

- horsetails (equisetum)

- ferns

Whisk Ferns (Psilotum)

-dichotomous branching

-no true leaves or roots (lost secondarily)

Horsetails (Equisetum)

- jointed hollow stems with tiny leaves

- strobili

ferns

• most widespread & diverse Monilophytes

• large megaphylls

• sori on underside of sporophylls

• mostly in understory or as epiphytes

some tree-size ferns today

fern life cycle

1). Zygote develops into leafy fern plant.

2) the sporophyte.

3) Spores are released from spore cases and grow into tiny, heart-shaped gametophytes. Each gametophyte has both male and female structures.

4) Sperm swim to another gametophyte to fertilize eggs.