Chapter 23 Dallas

Plants

Multicellular, photosynthetic eukaryotes whose evolution is marked by adaptations to life on land

Charophytes

Freshwater green algae (Chara, Coleochaete) most closely related to land plants

Chara

Charophyte with a body of single-file long cells, branches in whorls at multicellular nodes, reproductive structures at the nodes, and a protected zygote

Coleochaete

Disklike charophyte whose body is actually made of long, branched filaments of cells

Whorls

Rings of branches arranged around a node (seen in Chara and horsetails)

Nodes

Multicellular points on a stem where branches and reproductive structures grow

Plasmodesmata

Channels between neighboring cells that allow communication; may have aided the evolution of specialized tissues

Placenta (plants)

Tissue that transfers nutrients from haploid cells of the previous generation to the diploid zygote

Desiccation

Drying out; the main threat to plants living on land

Cuticle

Waxy, water-impervious covering on the land plant body that conserves water

Stomata

Pores that allow gas exchange but can also let water vapor escape

Tracheids

Specialized cells with proteins that resist gravity and carry water and minerals upward

Alternation of generations

Two-generation life cycle of land plants with a diploid sporophyte and a haploid gametophyte

Sporophyte

Diploid (2n), spore-producing generation

Gametophyte

Haploid (n), gamete-producing generation

Sporangium

Structure on the sporophyte where meiosis produces haploid spores

Spore

Haploid reproductive cell that develops into a new organism without fusing with another cell

Gametangia

Gamete-producing regions of the gametophyte

Antheridia

Male gametangia that produce sperm

Archegonia

Female gametangia that produce eggs

Zygote

Diploid cell formed when sperm and egg fuse; becomes the sporophyte embryo

Dominant generation in nonvascular plants

Gametophyte

Dominant generation in vascular plants

Sporophyte; its dominance is an adaptation to life on land

Bryophytes

Nonvascular plants (liverworts, hornworts, mosses); the first plants to colonize land, evolved during the Ordovician

Nonvascular plants

Plants lacking true roots, stems, and leaves (though they have rootlike, stemlike, or leaflike structures)

Vascular tissue

Tissue specialized for transport of water and organic nutrients throughout a plant

Traits shared by bryophytes and vascular plants

Alternation of generations, apical tissue producing complex tissues, a cuticle-covered body; hornworts and mosses also have stomata

Why bryophytes live in moist places

They lack vascular tissue and have flagellated sperm that must swim to the egg in a film of water

Liverworts

Bryophytes in two groups: thallose (flattened thallus) and leafy (resemble mosses)

Thallus

Flattened body of a thallose liverwort

Marchantia

Liverwort with a flat, lobed thallus; reproduces both asexually and sexually

Rhizoids

Hairlike extensions that anchor a plant and absorb water and minerals

Gemmae

Structures in gemmae cups on a liverwort thallus that can start a new plant asexually

Hornworts

Photosynthetic bryophytes with tiny broom-handle-like sporophytes and a symbiosis with nitrogen-fixing cyanobacteria; can reproduce by fragmentation

Mosses

Largest group of nonvascular plants (over 15,000 species): peat mosses, granite mosses, and true mosses

Protonema

Algalike branching filament that begins the moss gametophyte and produces upright leafy shoots

Moss sporophyte

Dependent sporophyte made of a foot, stalk, and capsule; always attached to the gametophyte; green at first, brown and nonphotosynthetic at maturity

Totipotency

Ability of a plant cell to become an entire plant; shown in bryophytes revived after about 400 years frozen in glacier ice

Xylem

Vascular tissue that conducts water and minerals upward from the roots

Phloem

Vascular tissue that transports sucrose and hormones throughout the plant

Lignin

Compound that strengthens the walls of xylem conducting cells

Cooksonia

Early extinct vascular plant (rhyniophyte) of the Silurian; had photosynthetic stems and branches ending in sporangia, no true leaves or roots

Seedless vascular plants

Vascular plants that reproduce by windblown spores (lycophytes and pteridophytes)

Lycophytes

Seedless vascular plants (club mosses) with stems, roots, and microphylls; about 1,200 species

Club mosses

Common name for living lycophytes: ground pines (Lycopodium), spike mosses (Selaginella), and quillworts (Isoetes)

Microphylls

Leaves with only one strand of vascular tissue

Rhizome

Branching underground stem from which roots arise

Sporophylls

Microphylls that bear sporangia

Strobili

Club-shaped groupings of sporophylls (cones)

Homosporous

Producing one type of spore that grows into one type of gametophyte

Heterosporous

Producing two types of spores: microspores and megaspores

Microspores

Spores that grow into male gametophytes

Megaspores

Spores that grow into female gametophytes

Pteridophytes

Seedless vascular plants with megaphylls: ferns, horsetails, and whisk ferns

Megaphylls

Broad leaves with several strands of vascular tissue; evolved about 370 MYA

Horsetails

Pteridophytes of one genus (Equisetum, about 25 species) with whorled branches and silica in stem cell walls

Whisk ferns

Pteridophytes (Psilotum, Tmesipteris) with no leaves or roots; use a rhizome with rhizoids and a mycorrhizal fungus to gather nutrients

Epiphytes

Plants that grow on other plants without harming them

Ferns

Pteridophytes with about 11,000 species, most abundant in warm, moist tropics

Fronds

Fern leaves; megaphylls that vary in size and shape

Sori

Clusters of sporangia on the underside of fern leaflets

Fossil fuel

Remains of organic material from ancient times, such as coal

Carboniferous forests

Swamp forests of giant lycophytes, horsetails, and ferns whose buried remains became coal

Seed plants

Vascular plants that use seeds as the dispersal stage of their life cycle

Seed

Mature ovule containing an embryonic sporophyte and stored food in a protective seed coat

Pollen grains

Male gametophytes of seed plants (develop from microspores)

Pollination

Transfer of pollen to the vicinity of the female gametophyte

Pollen tube

Tube that delivers sperm to the egg, so no external water is needed for fertilization

Ovule

Structure containing the female gametophyte; becomes a seed after fertilization

Gymnosperms

Seed plants whose ovules are not completely enclosed by sporophyte tissue at pollination

Conifers

Cone-bearing gymnosperms with needlelike evergreen leaves (pines, hemlocks, spruces); about 630 species

Monoecious

A single plant has both male and female reproductive structures (conifers)

Dioecious

A single plant has only male or only female reproductive structures (ginkgoes)

Cycads

Palm-like gymnosperms with pollen and seed cones on separate plants; pollinated by insects; about 320 species

Ginkgo biloba

Only living ginkgo species; the dioecious maidenhair tree

Gnetophytes

Gymnosperms (Gnetum, Ephedra, Welwitschia) that lack archegonia and are most closely related to angiosperms

Ephedra

Desert shrub gnetophyte that is the source of ephedrine

Welwitschia

Gnetophyte of southwest African deserts, mostly underground with two enormous leaves

Angiosperms

Flowering plants whose ovules are enclosed in diploid tissue; about 270,000 species

Monocots

Angiosperms with one cotyledon (about 65,000 species)

Eudicots

Angiosperms with two cotyledons (about 175,000 species); preferred term over dicots

Cotyledons

Seed leaves that contain nutrients for the plant embryo

Sepals (calyx)

Outer ring of modified leaves, usually green, that protect the flower before it opens

Petals (corolla)

Ring of large, colorful modified leaves inside the sepals that attract pollinators

Stamen

Male flower part made of a filament topped by an anther

Anther

Tip of the stamen that produces pollen

Carpel

Female flower part made of a stigma, style, and ovary

Ovary

Base of the carpel enclosing the ovules; becomes the fruit

Complete flower

Flower with all four parts: sepals, petals, stamens, and carpels

Incomplete flower

Flower missing one or more of the four parts

Embryo sac

Female gametophyte of flowering plants, usually seven cells including an egg and two polar nuclei

Double fertilization

One sperm fertilizes the egg; the other unites with polar nuclei to form triploid endosperm

Endosperm

Triploid (3n) nutritive tissue formed during double fertilization

Fruit

Mature ovary (plus possible accessory parts); may be fleshy or dry and aids seed dispersal

Amborella trichopoda

Shrub from New Caledonia that may be the most primitive surviving angiosperm

Teosinte

Wild Mexican grass from which all corn varieties descend

Shattering

Breaking apart of wild corn ears to disperse grains; lost early in corn domestication

Land plants evolved from

Freshwater green algae about 590 MYA

Traits shared by green algae and plants

Chlorophylls a and b, starch as food reserve, and cellulose cell walls

Key difference between algae and land plants

Land plants protect and nourish the embryo