Chapter 29&30: Plants and Conquest of the Land, Gymnosperms and Angiosperms

Progymnosperms

(Extinct) -First wood - Vascular tissue in a ring (eustele) -Produces vascular cambium and wood -Reproduced by means of spores, not seeds -Wood came before seeds

Flowers

- Complex reproductive structures -Specialized for efficient production of pollen and seeds -4 types of organs 1. Sepals 2. Petals 3. Stamens-produce pollen 4. Carpels- produce ovules

What adaptations foster stable internal water content

-->Waxy cuticle present on most surfaces of vascular plant sporophytes -->Cutin found in cuticle that helps prevent pathogen attack -->Wax prevents dessication -->Stomata are pores that open and close to allow gas exchange while minimizing water loss

Phylum Cycadophyta

-300 cycad species today - primarily tropical and suptropical - many species are rare -habitats threatened by human activities -nonwoody stems may emerge like tree trunks or be underground -leaves palm-like -Produce corraloid roots (roots are above ground and resemble corals, harborcyanobacteria for nitrogen fixation) -Produce toxins to deter herbivorous animals -Distinctive reproduction (Conelike structures bearing ovules and seeds or pollen, cones emit odors that attract beetles, beetles carry pollen to ovules)

Modern Angiosperms

-Defining features are flowers and fruits -"Enclosed seeds" -Presence of seeds within fruits -Seed endosperm another defining feature

Overview of Seed Plants

-First seed plants or spermatophytes evolved from earlier seedless vascular plants similar to modern lycophytes and pteridophytes -following the early diversification of gymnosperms, one ancestral gymnosperm lineage gave rise to the angiosperms, the flowering plants

More facts about Flowers

-Flower organs supported by receptacle -Pedicel-tip of the flower stalk -Perinath- petals and sepals -complete flowers-all 4 flower organs -incomplete flowers-lack one or more organs -perfect flowers- contain both stamens and carpels -imperfect flowers- lack either stamens or carpels - Single and compound carpels called pistil

Phylum Ginkgophyta

-Ginkgo biloba single remaining species -Nearly extinct in the wild -Widely planted along city streets (only males) -Individual trees produce either ovules and seed or pollen -Flagellate sperm -Ginkgos are long-lived individuals can live for more than a thousand years and grow to 30 m in height

bryophytes

-Include liverworts, hornworts, and mosses -Each forms a monophyletic phyla -Share common structural, reproductive and ecological features -models of earliest terrestrial plants -display apical meristems that produce specialized tissues and other features that evolved early in the history of land plants, such as the sporic life cycle.

Phylum Coniferophyta

-Named for seed cones -500 species in 50 genera -Particularly common in mountain and high latitude forests -Simple pollen cones (leaflike structures bearing microsporangia producing pollen) -More complex ovule- bearing cones (composed of short branch system that bears ovules) -Mature pollen released to the wind -Seed coats may develop wings for wind dispersal -others produce seeds or cones with bright-colored, have fleshy coatings to attract birds for dispersal -Wood contains tracheids for water transport (Pits on side and end walls through which water moves, valve-like torus to prevent spread of air bubbles) -Resin ducts- resin helps prevent attack by pathogens and herbivores -cold climate adaptations- conical shape and flexible branches, scale-like or needle-shaped leaves, thick waxy cuticle -Most conifers are evergreens

Life Cycle of Lycophyte and Pteridophyte

-Reproduction of Lycophyte and pteridophyte is limited by dry conditions, as is the case for bryophytes -However, if fertilization occurs, lycophytes and pteridophytes can produce many more spores due to their larger sporophyte generation (Vascular plant sporophytes are dependent upon maternal gametophytes for only a short time during early embryo development, Stems of vascular plant sporophytes are able to produce branches, forming relatively large adult plants having many leaves)

Pistil anatomy

-Stigma: receives and recognizes pollen->only appropriate pollen will be allowed to germinate -Style Ovary: encloses and protects the ovules, pollen tube delivers sperm to ovule, ovaries develop into fruits

Pteridophytes

-about 12,000 species of horsetails, while ferns and other ferns

Whole Genome Duplication Influenced Flowering Plant diversification

-an estimated 40-70% of all plants are polyploid -2 major types of polyploidy -plants are known to obtain mitochondrial genes from other plant species by horizontal gene transfer

Fruits

-develop from ovary walls -aid the dispersal of enclosed seeds -dispersal prevents competition and aids in colonization -fruits may be adapted to attract animals to eat them, wind dispersal, attach to animal fur or float in water

Characteristics of Bryophytes

-display features absent from charophycean algae but present in plants -likely early adaptations to land -Charophycean algae display a zygotic life cycle with a one cell diploid zygote -Bryophytes and other plants exhibit a sporic life cycle with alternation of generations (diploid- spore producing sporophyte generation, haploid- gamete producing gametophyte generation)

Early Flowers

-first appeared in 140 mya -flowers were a critical innovation that led to extensive angiosperm diversification -Stamen development (early flowers had broad leaf-shaped stamens, narrowed to form filaments and anthers (clusters or microsporangia producing pollen)) -Carpels also developed from leaf-like structures (folded to protect ovules)

Monocots and eudicots

-named for differences in the number of embryonic leaves called cotyledons -monocots differ from eudicots in several additional ways

Lycophytes and Pteridophytes

-vascular plants that do not produce seeds - Lycophytes- more numerous and larger in the past but now about 1000 relatively small species -Pteridophytes-about 12,000 species of horsetails, while ferns and other ferns -Diverged prior to origin of seeds (seedless vascular plants) -Lycophytes, pteridophytes and sees-producing plants are vascular plants or tracheophytes (-> possess tracheids for water and mineral conduction and structural support, ->Vascular tissues occur in the major plant organs: stems, roots, and leaves)

2 major types of polyploidy

1. Autoploidy- nondisjunction results in extra chromosomes in gametes 2. Alloploidy - hybridization between 2 species with different chromosome counts followed by whole genome duplication

What are some features that distinguish bryophytes?

1. Gametophytes dominant generation--> as opposed to dominant sporophyte generation in other plants 2. Sporophytes are dependent on gametophyte- small and short lived--> as opposed to independent, large and long-lived in other plants 3. Nonvascular or lacking tissues for structural support and conduction found in other plants (vascular plants)

Sporophytes

1. Matrotrophy- zygotes remain sheltered and fed within gametophyte tissue 2. Embryophytes- all land plants have matrotrophic embryos 3. When mature, spores are produced in protective enclosures known as sporangia 4. Plant spore cell walls contain sporopollenin to help prevent cellular damage 5. During evolution, plant sporophytes become larger and more complex

What derived traits do complex charophyceans share with land plants?

1. Plasmodesmata 2. Sexual reproduction using egg and smaller sperm

Gymnosperms

1. Produce seeds that are exposed rather than enclosed in fruits 2. "Naked Seeds" 3. Most modern forms are woody shrubs or trees 4. Seeds and wood are adaptations that allow gymnosperms to cope with global climate changes and to live in relatively cold and dry habitats

What are the distinctive features of land plants?

1. Represent early adaptations to land 2. Bodies composed of 3D tissues (increased ability to avoid water loss) 3. Tissues arise from apical meristems at growing tips 4. Able to produce thick, robust bodies 5. Tissues and organs with specialized functions 6. Distinctive reproductive features (alteration of generations, dry air resistant reproductive cell, specialized structures to generate, protect, and disperse reproductive cells)

Gametophytes

1. Role to produce haploid gametes 2. Produced by mitosis 3. Gametangia protects developing gametes from drying out and microbial attack (Antheridia- round or elongate gametangia producing sperm, Archegonia- flask shaped gamertangia enclosing an egg) 4. Sperm swim to egg and fuse to form diploid zygote 5. Zygotes grow into sporophytes

Gymnosperms

Among the vascular plants, the seed plant phyla dominate most modern landscapes. The modern seed plant phyla commonly known as cycads, ginkgos, conifers, and gnetophytes are col-lectively known as gymnosperms ( Figure 29.14 shows an exam-ple). Gymnosperms reproduce using both spores and seeds, as do the flowering plants, the angiosperms ( Figure 29.15). For this reason, gymnosperms and angiosperms are known informally as the seed plants. Seeds are complex structures having special-ized tissues that protectively enclose embryos and contain stores of carbohydrate, lipid, and protein. Embryos use such food stores to grow and develop. As explained in Section 29.4, the ability to produce seeds helps to free seed plants from the repro-ductive limitations experienced by the seedless plants, revealing why seed plants are the dominant plants on Earth today.

Stems

Contain vascular tissue and produce leaves and sporangia, Contain phloem and xylem (contains tracheids and lignin) -> conducting tissues enable vascular plants to con-duct organic compounds, water, and minerals throughout the plant body. The xylem also provides structural support for vascular plants to grow taller than nonvascular plants

Gametophytes

From an evolutionary and reproductive view-point, the role of plant gametophytes is to produce haploid gametes. Because the gametophyte cells are already haploid, meiosis is not involved in producing plant gametes. Instead, plant gametes are produced by mitosis; therefore, all gametes produced from a single gametophyte are genetically identical. The gametophytes of bryophytes and many other land plants produce gametes in specialized structures known as gametangia ( from the Greek, meaning gamete containers). Cer-tain cells of gametangia develop into gametes, and other cells form an outer jacket of tissue. The gametangial jacket protects delicate gametes from drying out and from microbial attack while they develop. Flask- shaped gametangia that each enclose a single egg cell are known as archegonia; spherical or elongate gametangia that each produce many sperm are known as anthe-ridia ( Figure 29.7). When the plant sperm are mature, if moist conditions exist, they are released from antheridia into films of water. Under the influence of sex- attractant molecules secreted from archegonia, the sperm swim toward the eggs, twisting their way down the tubular archegonial necks. The sperm then fuse with egg cells in the process of fertilization to form diploid zygotes, which grow into embryos. New sporophytes develop from embryos. Fertilization cannot occur in bryophytes unless water is present because the sperm are flagellate and need water to reach eggs. Conditions of uncertain moisture, common in the land habitat, can thus limit plant reproductive success. As we explain next, plant embryos and sporophytes are adaptive responses to this environmental challenge.

Apical meristems

Land plant tissues arise from one or more actively dividing cells that occur at growing tips. Such localized regions of cell division are known as apical meristems. The tissue-producing apical meristems of land plants are able to produce relatively thick, robust bodies able to withstand drought and mechanical stress and to produce tissues and organs having specialized functions.

More Critical Innovations

Lycophytes (Supportive vascular tissue; dominant branched sporophyte generation) -> Pteridophytes (Euphylls having broad leaves with branched veins) -> Cycads, Ginkgo, Conifers, Gnetophytes (Wood, ovules, seeds, pollen) -> Angiosperms (flowers; fruits; endosperms; vessel common)

Adaptations to land

Multicellular diploid sporophyte generation advantageous because it allows a single plant to disperse widely by using meiosis to produce numerous, genetically variable haploid spores. Each spore has the potential to grow into a gametophyte.

Kingdom Plantae (Plants or Land Plants)

Multicellular eukaryotic organisms composed of cells having plastids, primarily live on land, evolved from green 'algal' ancestors that lived in aquatic habitats, distinguished from modern algal relatives by adaptations to terrestrial life

Leaves

Photosynthetic function

How are plants different from their algae ancestors?

Plants are dis-tinguished from their modern algal relatives by the presence of traits that foster survival in terrestrial conditions, which are drier, sunnier, hotter, colder, and less physically supportive than aquatic habitats.

Ancestry of Land Plants

Probably originated from a photsynthetic protist ancestor having a relatively complex body (Filament of cells with side branches), Either Chara or Coleochaete are modern protists most closely related to ancestry of land plants

Critical Innovations of Seed Plants

Shared by all Seed Plants: 1. Pollen allows seed plants to disperse male gametophytes 2. Ovules allow seed plants to disperse female gametophytes 3. Seeds allow plants to reproduce in diverse habitats 4. Wood strengthens plants, allowing them to grow tall and produce many branches, leaves, and seeds

Roots

Specialized for uptake of water and minerals form soil

Sporophytes of Hornworts

Sporophytes One reproductive advantage of the plant life cycle is that zygotes remain enclosed within gametophyte tis-sues, where they are sheltered and fed ( a process described in more detail in Section 29.3). This critical innovation, known as matrotrophy ( from the Latin, meaning mother, and the Greek, meaning food) gives zygotes a good start while they grow into embryos. Because all groups of land plants possess matrotrophic embryos, they are known as embryophytes. Sheltering and feeding embryos is particularly important when embryo pro-duction is limited by water availability, as is often the case for bryophytes. Another reproductive advantage to plants of the sporic life cycle is that, when mature, specialized cells within multicel-lular sporophytes undergo meiosis to produce many geneti-cally diverse spores.

Sporic life cycle of bryophytes

The charophycean algae display a zygotic life cycle in which the diploid generation consists of only one cell, the zygote ( Figure 29.6a). Zygotic life cycles take their name from the observation that the zygote is the only cell that undergoes meiosis ( see Figure 28.25). By contrast, sexual reproduction in bryophytes and all other plants follows what is called a sporic life cycle, in which there is an alternation of generations ( see Figures 15.15c and 28.26). In the sporic life cycle, meiosis results in the formation of spores, which are reproductive cells that allow organisms to disperse in the environment ( Figure 29.6b). Alternation of generations means that land plants pro-duce two types of multicellular bodies that alternate in time. These two types of bodies are known as the diploid, spore-producing sporophyte generation and the haploid, gamete-producing gametophyte generation.

Wood

Tissue composed of numerous empty water-conducting cells strengthened by lignin (allows woody tissue to transport water upward for great distances, and also provides structural support) Vascular cambium (Produces thick layer of wood and thin layer of inner bark, and inner bark used for transporting watery solutions of organic compounds)