Biodiversity Exam 3

*Algal lineages and land plants: Monophyletic lineage.

*Land plants: Sister group in charales; Appear in Ordovician (fossil spores); Fossils from Silurian

*Coleochaete: Plasmodesmata: Intercellular connections in plants; Tendency to protect sporophyte/egg.

*Chara: Molecular data (DNA, rRNA); Chloroplast structure; Cell division; Sister group to land plants.

*Ancestral habitat for plants was margins of ponds/marshes.

*Multicellar photoautotrophs.

*Chlorophyll a and b: Chlorophyll b absorbs more blue light.

*Chloroplasts via primary endosymbiosis.

*Starch for sugar storage.

*Cell walls of cellulose.

*Heteromorphic alternation of generations: Sporophyte (2n) and gametophyte (n); Prominent generation differs.

*Embryonic sporophyte protected by parent (gametophyte) tissue.

Challenges
*Water conservation.
*Extreme environments.
*Skeletal support.
*Protection of gametes/fertilization.

Opportunities
*Uninhabited space.
*Access to sunlight.
*Access to CO2 and O2.
*Avoid herbivores.

*Cuticle: Waxy layer for waterproofing.

*Pigments: Protect from UV radiation.

*Gametangia (Archegonia and Antheridia): Enclose and protect gametes.

*Embryos: Sporophyte generation protected by parent plant.

*Resistant spores: Resist decay, desiccation.

*Vascular tissue: Transport of material throughout plant body, skeletal support; Xylem = Water and minerals from roots and skeletal support (non-living tissue). Phloem = Products of photosynthesis from site of production (living tissue). Specialized organs (roots, stems, etc.)

*Mutualistic associations with fungi (mycorrhizae)

*250,000 species of plant.

*10 living (extant) phyla.

*Liverworts, Mosses, Hornworts, Lycophytes, Horsetails, Whisk ferns, Leptosporangiate ferns; Gymnosperms; Flowering plants.

*Dominant gametophyte generation.

*Lack true vascular tissue (tracheid cells) for support and transport: Small plants (less than 1 meter).

*Occur in moist habitats: Entire plant with access to water; Water required for fertilization; Limited water conservation, but some with cuticle.

*Lack differentiated organs: Anchored to substrate by rhizoids.

*Hepatophyta (liverworts): Most ancestral plant group; Asexual reproduction (fragmentation, gemmae).

*Bryophyta (mosses): Most successful nontracheophyte; Apical sporophyte growth (capsule added at end); Hydroid cells for transport; Sphagnum bogs.

*Anthocerophyta (hornworts): Exhibit stomata on leafy gametophyte; Sporophyte grows from base; Reaches ca. 20 cm; Symbiosis with cyanobacteria.

See notes!

*Vascular tissue derived from Tracheids:
----Xylem tissue conducts water: Pitted cells undergo programmed cell death (die and leave cell wall])
----Xylem tissue provides support: Cell wall reinforced with lignin (abundant organic molecule, provides strength).
----Phloem conducts sugars and other organic nutrients: Tissue is living; Evolutionary history less clear.

*Complex leaves, stems, roots: Plant organs; Comprised of specialized tissues.

*Sporophyte dominant generation.

*Silurian Period: First fossil tracheophytes.

*Devonian: Tracheophytes well established; Forests by end of Devonian.

*Rhyniophyta--Extinct lineage: Silurian and Devonian; Rhynie chert deposits in Scotland; Support common ancestry of tracheophytes.

*Xylem and phloem present.

*Height ca. 20 cm.

*Sporophyte dominant: Fossilized spores; Tetrads (products of meiosis).

*Rhizome (underground stem).

*Mycorrhizal fungi: Mutualistic symbiosis.

*Stomata: Pores/openings on leaves; Gas exchange.

*Cuticle

*Roots: Anchor plant; Absorb water and minerals; Associated with symbiotic organisms; Derived from underground stems (homologous structures); Different selective pressures above and underground.

Multiple origin of leaves
Microphyll: Small; Single strand of vascular tissue; Derived from sporangia. Ex) Lycophyta.

Megaphyll: Larger, complex; Branched stems; Overtopping; Photosynthetic tissue; Highly modified in some plants. Ex) Pterophyta

Pollination is the process of transporting pollen from anther to stigma in flowering plants, Fertilization refers to the fusing of egg and sperm to form a zygote. This occurs after pollination has taken place.

Examples: Grasses, Hazels, Willows, Cottonwoods, Catkins.

Characteristics: These plants tend to have small, drab, unscented, and inconspicuous flowers because they don't have to attract pollinators. Anthers and stigmas often project from the flower in order to be exposed to the wind.