Plant Evolution Chapter 23

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 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

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

Haploid to diploid dominance Evolutionary Trend

sporophyte’s importance gametophyte’s importance green algaebryophytesfernsgymnospermsangiosperms zygote only, no sporophyte

4 Major Groups of Plants  Nonvascular  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

Female gametophyte Male gametophyte Marchantia: A Liverwort

Moss life cycle Moss Life Cycle

Zygote grows, develops into a sporophyte while still attached to gametophyte. Fertilization zygote sperm- producing structure egg- producing structure Diploid Stage Haploid Stage mature sporophyte Meiosis Spores germinate. male gametophyte female 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

Ferns  Most common sporophyte structure Perennial underground stem  rhizome Roots and fronds arise from rhizome Young fronds are coiled “fiddleheads” Mature fronds divided into leaflets Spores form on lower surface of some fronds

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Fern life cycle Fern Life Cycle

Spores are released Sporophyte still attached to gametophyte zygote fertilization Diploid Stage Haploid Stage egg sperm mature gametophyte Spores develop meiosis Spore germinates rhizome sorus

Seed-Bearing Vascular Plants  Gymnosperms arose first Cycads Ginkgos Gnetophytes Conifers  Angiosperms arose later Monocots Dicots

Adaptations to Land  Root systems  Shoot systems  Vascular tissues  Waxy cuticle

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

pine pollen grains Pollen

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

Gymnosperm Characteristics  Reproduction Time between pollination and fertilization could take a year or more Male strobili  Sporophyte  Microspores Walled structure protects male gametophyte Become pollen grains Female strobili  Sporophyte  Megaspore Develops within ovule Stays attached to parent plant

Pine cones Pine Life Cycle

Pine life cycle Pine Life Cycle

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

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

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

Flower parts Flowering Plant Life Cycle

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

stamen (microspores form here) carpel (megaspores form here) petal sepal 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

Monocot life cycle Monocot Life Cycle

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 Double fertilizationMeiosis microspores female gametophyte pollination mitosis without cytoplasmic division two sperm enter ovule Diploid Haploid sporophyte