PLANT EVOLUTIONEvolutionary Trends

Bryophytes

The rise of the vascular plants

The rise of the seed plants

KINGDOM PLANTAE

General features:

Eukaryotic, multicellular, photosynthetic autotrophic

organisms

P.S.= H2O + CO2+ sunlight oxygen + sugar

C.R. = sugar + O2 CO2 and H2O + NRG

Origins = blue-green bacteria ancestral green

algae algae bryophytes tracheophytes

THE PHYLA

Phyla grouped into:

- Nonvascular

plants (lack true

(lignified) vascular

tissue)

- Seedless vascular

plants (true vascular

tissue (phloem and

xylem), but reproduce

only by spores (no

seeds made)

- Seed bearing

vascular plants

FERNS

CONE BEARING PLANT

FLOWERING PLANT

SETTING THE STAGE

Earth’s atmosphere was originally

oxygen free

Ultraviolet radiation bombarded

the surface

Photosynthetic cells produced oxygen and allowed

formation of protective

ozone layer

PIONEERS IN A NEW WORLD

Cyanobacteria were probably first to produce oxygen

Later, green algae evolved and gave rise to plants

ADVANTAGES AND DISADVANTAGES

OF LIFE ON LAND

Sunlight unfiltered by water and plankton

Atmosphere had more CO2 than water

Soil was rich in mineral nutrients

Originally relatively few herbivores and pathogens

Relative scarcity of

water

Lack of structural

support against

gravity

Advantages: Disadvantages:

EVOLUTIONARY TRENDS IN PLANTS

STRUCTURE:

Plants came from the sea which support, keep

temp constant, bath whole plant with nutrients

Adaptations to terrestrial Life =

Roots to anchor and absorb

Conducting vessels xylem & phloem to carry

nutrients up and glucose around VASCULAR

TISSUE

Stiffening lignin to support the plant

Waxy cuticle on leaves and stem to prevent

evaporation

Stomata pores in leaves to allow gas exchange, but

close to prevent water loss

EVOLUTIONARY TRENDS IN REPRODUCTION:

Algae reproduce in water so gametes are carries

by water, form zygotes in water and disperse in

water. Ie No protection from dehydration

required

Land plants needed:

Transport gametes (pollen, flowers)

Protection from drying out (seeds)

Dispersal (seed coats & fruits)

EVOLUTIONARY TRENDS IN PLANT LIFE CYCLES:

Alternation of Generations = haploid

gametophytes produces sex cells by mitosis. Gametes

unite to from a diploid zygote, which develops into

diploid sporophyte that develops haploid spores by

meiosis

HAPLOID TO DIPLOID

Gametophyte

▪ Haploid gamete producing body

Sporophyte

▪ Diploid product of fused gametes

Spore

▪ Resting structure

The most recently evolved groups produce seeds and

pollen grains which were the key innovations that

allowed the seed plants to spread widely into diverse

habitats.

EVOLUTIONARY TRENDzygote

GREEN ALGAE BRYOPHYTE FERN GYMNOSPERM ANGIOSPERM

Relative size

Life span

GENERAL TREND = DECREASED SIZE, DURATION, AND

PROMINENCE OF GAMETOPHYTE GENERATION RELATIVE

TO SPOROPHYTE

Algae = some have no sporophyte or only the zygote

Mosses = gametophyte is green leafy and sporophyte is small and short lived

Ferns = sporophyte is the fronds of the ferns, gametophyte is smaller yet independent

Seeded plants = male and female gametophytes are microscopic and produce gametes to form sporophyte embryo

Recall: evolution occurs because of advantageous traits being selected therefore what is the

advantage of diploid sporophyte dominance?

SPOROPHYTE

The generation in the life cycle of a plant that

produces spores.

Is diploid but its spores are haploid.

Either completely or partially dependent on

the gametophyte generation in mosses and

liverworts, but is the dominant plant in the

life cycle of clubmosses, horsetails, ferns

and seed plants.

LE 29-9D

Polytrichum

commune,

hairy cap

moss

Sporophyte

Gametophyte