Plant Structure & Function Last revised April, 2009

Before land plants…various forms of algae Green algae thought to be predecessor to land plants

Four Main Types of Land Plants Bryophytes – liverworts, mosses Pteridophytes – ferns, horsetails Gymnosperms – pines, cycads Angiosperms – flowering plants

Bryophytes Liverwort Moss Hornwort

Bryophytes Fossil evidence indicates: –EARLIEST PLANTS (475 mya) –They were the ONLY land plants for first 100 million years! Diverged BEFORE vascular plants Alternation of generations Gametophyte dominant form

Pteridophytes Club Moss Whisk Fern Horsetail; EquisetumFern

Pteridophytes Seedless Vascular Plants Pteridophyte roots derived from subterranean stems Lack seeds Alternation of generations

Pteridophytes Fern sperm cells are flagellated Must swim through film of water to reach eggs. Must have damp habitats Sporangia on fern leaf

Carboniferous Period Seedless vascular plants like club moss and whisk ferns formed forests during the Carboniferous period mya Coal forming forests

Seed Plants Evolve Reduction of the gametophyte

Seed Plants Two clades: –Gymnosperms (360 mya) –Angiosperms (140 mya) Produce flowers and fruits Most diverse 250,000 known species (vs. 720 gymnosperm)

Gymnosperms “Naked seeds” Ginkgo Cycads Gnetophytes (ephedra) Conifers

Gymnosperms cycad ginkgo Gnetophyte Norway spruce pinecone

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Angiosperms Flowering plants Flower is specialized organ for reproduction Monocots and Dicots “Double Fertilization”

Angiosperms Double fertilization –One sperm unites with egg to form diploid zygote –Other sperm unites with two nuclei at center of female gametophyte – this forms triploid nucleus –Becomes ENDOSPERM to nourish the zygote during development

Anthers with pollen Watch Campbell animation of Plant fertilization and seed development

Monocots vs. Dicots

Three Basic Organs Leaves Stems Roots

Dermal Tissue “skin” of the plant Waxy cuticle Helps plant retain water

Vascular Tissue Xylem –Conveys water and dissolved minerals upward from roots to shoots Phloem –Transports food made in the leaves to the roots and other non- photosynthetic parts

Ground Tissue Neither dermal nor vascular In dicots – pith and cortex Functions: –Photosynthesis –Storage –Support

Plant Tissues Division of labor Three basic types: –Parenchyma –Collenchyma –Sclerenchyma

Parenchyma Thin, flexible walls Large central vacuole Typical plant cells – least specialized Performs main metabolic functions

Parenchyma

Collenchyma Thicker primary walls Grouped in strands or cylinders Support structure (strings of celery) Living, flexible, no lignin, elongate with stems

Collenchyma

Sclerenchyma Support elements of plant Thick secondary walls with lignin Many are dead at functional maturity Stop growing in length

Sclerenchyma Fiber Cells

Sclerids

Meristems Cells that divide and provide plant growth Primary Growth –Root meristem For roots to ramify through soil –Apical meristem for plant to grow in length Secondary Growth –Lateral meristem

ROOTS

Stems

Stomata

Tree Trunk

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