Plant Evolution Chapter 26

Beginnings and Endings Impacts, Issues Video Beginnings and Endings

Setting the Stage for Plants Earth’s atmosphere was originally oxygen free Ultraviolet radiation bombarded the surface Photosynthetic cells produced oxygen and allowed formation of a protective ozone layer

Invading the Land Cyanobacteria were probably the first to spread into and up freshwater streams Later, green algae and fungi made the journey together Every plant is descended from species of green algae

Evolutionary Tree for Plants

The Plant Kingdom Nearly all are multicellular Eukaryotic Terrestrial Vast majority are photoautotrophs Energy from sun Carbon dioxide from air Minerals dissolved in water

Plant Kingdom Adaptations to land Well developed tissue Cuticle Stomata Protection of embryo Alternations of generations Sporophyte Diploid Produces spores by meiosis Reproductive structure Develops into new organism without the need to fuse with another reproductive cell

Plant Kingdom Gametophyte Haploid Produces gametes Egg and sperm Formed by mitosis Egg and sperm fuse to form zygote Undergoes mitosis Forms sporophyte

Evolutionary Trend multicelled sporophyte (2n) mitosis zygote (2n) Diploid Haploid fertilization meiosis gametes (2n) spores (2n) multicelled gametophytes (n) mitosis mitosis

Haploid to diploid dominance Evolutionary Trend Haploid to diploid dominance

zygote only, no sporophyte sporophyte’s importance gametophyte’s importance green algae bryophytes ferns gymnosperms angiosperms

4 Major Groups of Plants Nonvascular (Bryophytes) Seedless Vascular Gymnosperms Angiosperms

Nonvascular Plants 3 types of plants Hornworts Symbiotic relationship with cyanobacteria Liverworts Mosses Peat, true and rock Sphagnum Great ability to absorb water

Peat Mosses

Marchantia: A Liverwort

Marchantia: A Liverwort Female gametophyte Male gametophyte

Nonvascular Plants Lack specialized means of transporting water, nutrients Do not have true roots, stems or leaves Have root, stem and leaf like structures Rhizoids Threadlike cellular structures Absorb water and nutrients Anchor gametophytes to substrates

Nonvascular Plants Gametophyte Dominant generation Archegonia Produces and protects eggs Antheridia Produce flagellated sperm Sperm swims to egg and forms embryo - develops into sporophyte - sporophyte derives nutrition from gametophye - produces spores

Seedless Vascular Plants Like bryophytes Live in wet, humid places Require water for fertilization Unlike bryophytes Sporophyte is free-living and has vascular tissues Epiphytes Plants live on trees but are not parasitic

Seedless Vascular Plants Vascular tissue Microphylls 1 strand of vascular tissue Club mosses, horse tails, whisk ferns Macrophylls Many strands of vascular tissue Ferns

Seedless Vascular Plants Xylem Conducts water and dissolved nutrients upwards from the roots Contain lignin Stronger for support and waterproof Protects from parasites and predators Phloem Conducts sucrose and other organic compounds throughout the plant

Seedless Vascular Plants Reproduction Moist environment Homosporous Large sporophyte with vascular tissue Gametophyte small and independent

Seed-Bearing Vascular Plants Pollen grains Arise from microspores Develop into male gametophytes Can be transported without water Seeds Embryo sporophyte inside nutritive tissues and a protective coat Can withstand hostile conditions More water-conserving

Pollen pine pollen grains

Seed-Bearing Vascular Plants Female reproductive structures that become seeds Consist of: Female gametophyte with egg cell Nutrient-rich tissue Jacket of cell layers that will form seed coat Pollination Can occur by wind or by pollinators No external water is needed for fertilization

Ovules

Gymnosperms Plants with “naked seeds” Seeds don’t form inside an ovary Four groups Conifers Ginkgos Cycads Gnetophytes

Gymnosperm Characteristics Widest known, largest number of living species Woody trees or shrubs Most are evergreen Bear seeds on exposed cone scales Most produce woody cones

Gymnosperms Conifers Evergreens, pines, firs Needle like leaves Conserve water Thick cuticle Recesses stomata Monoeicious Tree produces both male and female gametophytes Pollinated by wind

Gymnosperms Ginkgo bilboa Dioecius Resistant to pollution Pollen tube bursts to release multiflagellated sperm Female trees gives off fowl odor when seeds ripen

Strobilus of a “female” cycad Gymnosperms Cycads Dioecius Pollinated by insects Palmlike appearance Strobilus of a “female” cycad

Gymnosperms Gnetophytes Don’t have archegonia Most closely related to angiosperms Produce nectar Sporophyte of Ephedra

Angiosperms Flowering plants Dominant land plants Ovules and (after fertilization) seeds are enclosed in an ovary Three main groups Magnoliids Monocots Eudicots

Angiosperms Eudicots Monocots 2 seed coats 1 seed coat Flower parts in 4’s or 5’s Woody or herbaceous Net veins Vascular bundles in ring taproot Monocots 1 seed coat Flower parts in 3’s or multiples of Herbaceous Parallel veins Scattered bundles in stem Fibrous roots

Inside seeds, two cotyledons seed leaves of embryo Inside seeds, one cotyledon seed leaf of embryo Usually four or five floral parts (or multiples of four or five) Usually three floral parts (or multiples of threes) Leaf veins usually in a netlike array Leaf veins usually running parallel with one another Three pores or furrows in the pollen grain surface One pre or furrow in the pollen grain surface Vascular bundles organized as a ring in ground tissue Vascular bundles distributed throughout ground tissue

Angiosperms 4 main parts Sepals (calyx) Protect flower bud Usually green Petals (corolla) Vary in shape, size and color Stamen 2 parts filament anther sac-like container pollen grains develop

Angiosperms Carpel 3 regions Stigma Enlarged sticky knob Style Slender stalk Ovary Enlarged base encloses 1 or more ovule Ovule becomes seed Ovary becomes fruit

petal stamen (microspores form here) sepal carpel (megaspores form here) ovule in an ovary

Angiosperms Complete flower Contains all 4 parts Incomplete flower Missing 1 of the 4 parts Perfect flower Has both stamen and carpel Imperfect flower Has either the stamen or carpel

Double Fertilization Distinctive feature of angiosperms Male gametocyte delivers two sperm to an ovule One fertilizes egg; other fertilizes a cell that gives rise to endosperm

Flowering Plant Life Cycle sporophyte Flowering Plant Life Cycle Diploid Double fertilization Meiosis Meiosis Haploid mitosis without cytoplasmic division microspores pollination two sperm enter ovule female gametophyte