General Biology/Classification of Living Things/Eukaryotes/Plants

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General Biology | Getting Started | Cells | Genetics | Classification | Evolution | Tissues & Systems | Additional Material

Multicellular Photosynthetic Autotrophs[edit]


  • Multicellular
  • Cellulose cell walls
  • Chlorophylls a and b
  • Develop from embryophyte
  • Alternation of generations
  • Major food source for terrestrial life
  • Atmospheric O2 and CO2 balance
  • Coal deposits
  • Intimate association with mycorrhizal fungi
  • >250,000 species (~500,000?)
  • Taxonomy
    • State of flux
  • DNA sequencing
  • Developmental studies
    • Division (old literature) = phylum (new literature)
    • ~12 phyla, 9 of which are vascular plants

Plant phyla[edit]

Phyla are 12 groupings

Plant evolution[edit]

  • Evolved from green algae, likely related to charophytes
  • Evidence
    • DNA sequences
    • homologous chloroplasts: chlorophyll b and beta-carotene; thylakoids in grana;
    • Cellulose in both groups; also peroxisomes
    • Mitosis and cytokinesis similar
    • Sperm ultrastructure

Terrestrial adaptations[edit]

  • Stomata: pores in leaves for exchange of gases; prevent desiccation
  • Secondary metabolites:
    • cuticle: waxy coating to prevent H2O loss
    • lignin: hardens wood
    • sporopollenin: resistant polymer; coats pollen
    • predator defenses
  • Embryonic development
    • gametangia in early plants
    • spores; seeds
  • Mycorrhizae
  • Water/food conducting systems

Plant phylogeny[edit]

Plant life cycles[edit]

  • Alternation of generations
  • Sporophyte
    • diploid
    • produces spores in sporangia
  • Gametophyte
    • develops from spore
    • haploid
    • produces gametes in gametangia
  • Haplodiplontic life cycle

Moss life cycle[edit]

Vascular plants[edit]

  • Most have roots
  • Aerial shoot systems
  • Vascular tissue
    • xylem: water, mineral transport
    • phloem: food transport
  • Lignin
  • Branched sporophyte is dominant stage
    • amplified production of spores
    • evolution of complex plant bodies
  • Dominated Carboniferous (360 my)

Vascular plant life cycles[edit]

  • Homosporous (single type of spore)
  • Heterosporous (two types of spore)

Pterophyta (ferns)[edit]

  • Non-seed plant
  • Sporophyte conspicuous (vascular tissue)
  • Rhizome: ground stem, roots
  • Fronds: leaves
  • Sori: clusters of sporangia
  • Motile sperm require external water for fertilization
  • Originated in Devonian, 350 my

Tree fern Fern life cycle

Non-seed plants, continued[edit]

  • Lycophyta: club mosses
    • E.g., Lycopodium (“ground pine”)
    • Many species became extinct 270 my, once dominant (coal formations)
    • Gametophyte non-photosynthetic, nourished by fungi
  • Arthrophyta: horsetails
    • Equisitum
    • Some fossil forms (300 my) were tree-size (coal)
    • Photosynthetic stems, no leaves
    • Silica deposits in epidermal cells

Seed plants[edit]

  • 1st appeared in Devonian, 360 my
  • Seed develops from ovule, protects embryo
    • withstands drought
    • dispersal is enhanced
    • no immediate need for water for germination
  • Heterosporous
    • male gametophyte: arise from microspores
    • female gametophyte: arise from megaspores in ovule in ovary
  • Two groups
    • gymnosperms
    • angiosperms


Megasporangium (nucellus)[edit]

  • Key to seed development
  • Nucellus: solid, fleshy, surrounded by integuments derived from sporophyte (seed coat)
  • Entire structure called ovule
  • Flower may have many ovules


  • Develop from microspores, become male gametophyte
  • Protected by sporopellenin
  • In most plants, sperm lack flagella (loss)
  • Many mechanisms to transport pollen
    • wind
    • insects, birds,


  • “naked seed”
    • ovule not fully enclosed by sporophyte at time of pollination
  • Conifers, cycads, gnetophytes, Ginkgo
  • Small, inconspicuous plants to giants like sequoia
  • Conifers: to carry cones fv
    • male cones, Female conesvv
    • evergreen

Pine life cycle[edit]

Other Coniferophyta[edit]

  • Cycadophyta: cycads
    • tropical, subtropical
    • flagellated sperm
  • Gnetophyta
    • e.g., Ephedra, Mormon Tea
  • Ginkgophyta: Ginkgo
    • only one surviving species
    • diocious (separate % and &trees)

Other gymnosperms[edit]


  • Flowering plants, Anthophyta
    • monocots- single seed leaf (grasses, lilies, etc.)
    • dicots- two seed leaves (roses, pulses, maples)
  • More specialized xylem (water transport)
    • vessel elements
    • fiber cells
  • Fossils date to 130 my
  • Animal (e.g., insect) coevolution

Monocots vs dicots[edit]

Earliest angiosperm[edit]

  • What is earliest angiosperm?
  • Recent analysis of nucleotide and amino acid sequences suggests that Amborella, a tropical plant found only on the island of New Caledonia, is closest relative to flowering plants

Angiosperm flower[edit]

Angiosperm life cycle[edit]

This text is based on notes very generously donated by Paul Doerder, Ph.D., of the Cleveland State University.