Plant Structure & Plant Structure & FunctionFunction

Last revised April, 2009

Before land plants…various forms of algae

Green algae thought to be predecessor to land plants

Four Main Types Four Main Types of Land Plantsof Land Plants

• Bryophytes – liverworts, mosses

• Pteridophytes – ferns, horsetails

• Gymnosperms – pines, cycads

• Angiosperms – flowering plants

Bryophytes

Liverwort

Moss

Hornwort

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; Equisetum Fern

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

• 299-360 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 Three Basic OrgansOrgans

• 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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