PLANT EVOLUTION Evolutionary Trends Bryophytes The rise of the vascular plants The rise of the seed plants

K INGDOM P LANTAE 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

T HE P HYLA 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

F ERNS

C ONE B EARING P LANT

F LOWERING PLANT

S ETTING THE S TAGE Earth’s atmosphere was originally oxygen free Ultraviolet radiation bombarded the surface Photosynthetic cells produced oxygen and allowed formation of protective ozone layer

P IONEERS IN A N EW W ORLD Cyanobacteria were probably first to produce oxygen Later, green algae evolved and gave rise to plants

A DVANTAGES AND D ISADVANTAGES 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:

E VOLUTIONARY 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 ligin 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

E VOLUTIONARY T RENDS 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)

E VOLUTIONARY T RENDS IN P LANT 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

H APLOID TO D IPLOID  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.

E VOLUTIONARY T REND zygote SPOROPHYTE (2n) GAMETOPHYTE (n) GREEN ALGAEBRYOPHYTEFERNGYMNOSPERMANGIOSPERM Relative size Life span

G ENERAL T REND = 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?

S POROPHYTE 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 29-9 D Polytrichum commune, hairy cap moss Sporophyte Gametophyte