# General Biology/Classification of Living Things/Eukaryotes/Plants

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

# Multicellular Photosynthetic Autotrophs
## Plants

* 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

Phyla are 12 groupings

## Plant evolution

* 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

* 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 life cycles

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

## Moss life cycle

Moss has no vascular tissues or flowers. It is a thallus plant (it does not have true roots,stem and leaves). It does not produce seeds like the angiosperm.

## Vascular plants

* 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

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

## Pterophyta (ferns)

* 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

* 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

* 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)

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

## Pollen

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

## Gymnosperms

* “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

## Other Coniferophyta

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

## Angiosperms

* 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
## Earliest angiosperm

* 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 life cycle

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