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biology in english 4a Kingdom Fungi and Plants..

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Kingdom Fungi Objectives After studying this chapter, the reader should be able to: Describe the major features of the kingdom Fungi and its three subkingdoms. List distinguishing characteristics for each major group of fungi. Trace the life cycles of representative fungi. Describe the ecologic and economic importance of fungi. Discuss the mutualistic relationships formed by lichens and mycorrhizae. I. Fungal Structure, Nutrition, and Ecology A. General information 1. Fungi historically have been classified with plants, but major differences between these organisms necessitated the formation of a separate kingdom Fungi are eukaryotic, usually multicellular, multinucleate organisms They obtain nutrients by secreting enzymes into their substrate and absorbing the digested materials Most fungal cell walls contain the polysaccharide chitin The fungal structure is characterized by long slender filaments called hyphae (see Types of Fungal Hyphae for an illustration) a. Coenocytic hyphae consist of long cellular strands with many nuclei, which are not contained within individual cells b. Hyphae with complete septa (barriers) are separated into individual cells; septate hyphae may contain a single nucleus in each cell or two nuclei in each cell (called dikaryotic hyphae) c. Hyphae with incomplete septa allow cytoplasm to flow freely from cell to cell d. Some parasitic fungi have haustoria, which are specialized hyphae that ex- tend into individual host cells 6. The mycelium is the mass of hyphae that constitutes the body of a fungus; it is the most recognizable structure of a mushroom (toadstool) B. Modes of nutrition and metabolism Fungi (along with bacteria) are the principal decomposers in every ecosystem They can break down lignin, a major component of wood Some fungi also attack living organic matter, causing agricultural damage and de- stroying food stores; food contaminated by fungi may be unpalatable or poisonous to humans  4. Warm, moist, dark conditions are most favorable for fungal growth; however, fungi can grow in various other habitats 5. If conditions become too stressful, fungi survive by producing spores, which are resistant to temperature and moisture extremes 6. Parasitic fungi use haustoria to penetrate individual host cells and absorb nutri- ents directly from the cytoplasm C. Ecology Fungi typically form symbiotic relationships with plants or algae Two types of fungal symbionts are lichens and mycorrhizae Lichens are a combination of fungi (Ascomycetes or Basidiomycetes) and green algae (phylum Chlorophyta) or cyanobacteria (kingdom Monera) a. The algae portion of the lichen provides food through photosynthesis; the fungal portion acts as a living sponge to improve water retention (1) Some evidence suggests that the fungal partner parasitizes the algae in a controlled fashion and sometimes may even destroy algal cells (2) The fungal component of lichens rarely grows independently, although the algal component may do so b. Lichens inhabit cold, dry, and generally harsh environments, where they help break rock surfaces and prepare the habitat for other organisms c. They survive harsh or adverse conditions by becoming dehydrated, which subsequently slows their metabolism (1) When the lichen's water content drops dramatically, the upper portion of the thallus becomes opaque enough to exclude light from the photo-synthetic algae (2) Dehydrated lichen are unaffected by most environmental extremes be- cause they are temporarily dormant and do not engage in photosynthesis d. Lichens absorb nutrients from rain and air; for this reason, they are very sen- sitive to air quality and are among the first organisms to perish in a polluted environment e. Lichens are grouped into three major growth forms (1) Crustose lichens attach to or embed in their substrate and often form brightly colored, crusty patches on bare rocks and tree bark (2) Foliose lichens have leaflike thalli, are weakly attached to their sub- strate, and have edges that are crinkly or divided into lobes (3) Fruticose lichens resemble miniature upright shrubs or may hang from tree branches; their thalli are usually branched and cylindrical 4. Mycorrhlzae are a combination of fungi and plant roots a. Mycorrhizae enhance the absorption of essential nutrients by plant roots (1) They also may provide protection against the effects of acidic soil and may make a plant more resistant to drought, cold, and harsh conditions They can prevent the accumulation of toxic metals in plants They can help plants to grow better in poor soils They can speed the seed germination of orchids b. About 90% of all plants have a symbiotic relationship with mycorrhizae c. Plants with mycorrhizae develop fewer root hairs than those without mycorrhi- zae; the mycorrhizae perform the same functions as root hairs, making them less necessary d. Mycorrhizae are highly susceptible to acid rain, which may negatively affect the growth of some plants e. The two forms of mycorrhizae are endomycorrhizae and ectomycorrhizae (1) Endomycorrhizae, the more common variety, are characteristic of many crop species and develop when the fungal hyphae penetrate the outer root cells (2) Ectomycorrhizae, the less common variety, are characteristic of shrubs and trees and develop when the hyphae surround, rather than penetrate, the root cells II. Reproduction A. General information Fungi reproduce both asexually and sexually by means of spores Fungi also can reproduce asexually by means of binary fission, budding, or frag- mentation B. Spore production 1. Spores are unicellular reproductive cells capable of developing into adult organ- isms without fusing with another cell Spores enable fungi to colonize in new areas Because they typically are resistant to temperature and moisture extremes, spores can survive harsh environmental conditions 4. Spores are produced by cell division during asexual or sexual reproduction a. Asexual spores are produced directly from the cells of the hyphae b. Sexual spores are produced in a saclike structure called the ascus c. Sporangiospores are produced in specialized hyphae called sporangio- phores (spore-bearing hyphae), which contain specialized structures for spore formation (sporangia) 5. Some fungal species (Ascomycetes and Basidiomycetes) produce spores in a specialized reproductive structure called a fruiting body C. Asexual reproduction Fungi reproduce asexually by binary fission, budding, or fragmentation In binary fission, individual fungal cells divide to form two identical daughter cells, which in turn grow into new individual organisms 3. In budding, which is usually restricted to single-cell fungi (such as yeast), a new organism is formed from a small, pinched-off portion of a mature cell 4. In fragmentation, strands of hyphae that are mechanically separated from the original mycelium grow and develop independently into new organisms D. Sexual reproduction Not all fungi reproduce sexually Fungi do not have distinguishable male and female sexes; they have mating types, usually designated as "plus" and "minus" strains Gametes are produced by specialized hyphae called gametangia During fertilization, the two haploid gametes fuse to form a diploid zygote After the zygote forms, the nucleus undergoes meiosis to produce new (now hap- loid) spores, which disperse, settle into favorable habitats, and grow to produce new organisms 6. The largest portion of the fungal life cycle is haploid; only the zygote is diploid III. Taxonomic Classification A. General information 1. Fungi are generally classified according to the characteristics of their spores and fruiting body 2. The kingdom Fungi is divided into three subkingdoms: Mastigomycotineae, Eumy- cotineae, and Myxomycotineae 3. Authorities do not agree on fungal classification; Myxomycotineae are sometimes considered part of the kingdom Protista B. Subkingdom Mastigomycotineae (water molds) 1. Water molds share several features with brown algae, from which they are thought to have evolved a. Their cell walls are composed of cellulose b. Their bodies vary from unicellular to highly branched coenocytic and filamen- tous forms c. Their spores are flagellated and require free-standing water for swimming 2. Many water molds are aquatic, commonly growing on dead insects and plant de- bris in water 3. Mastigomycotineae reproduce sexually, which results in the formation of spores that are dispersed to form new mycelia 4. Examples include Saprolegnia, a parasite of fish that grows on cuts and bruises and is a common aquarium pest, and Phytophthora infestans, the species responsible for the potato blight that devastated Ireland in the mid-1800s C. Subkingdom Eumycotineae (true fungi) 1. True fungi are filamentous organisms that have a cell wall containing chitin but do not possess motile cells 2. The four major phyla in this subkingdom are Zygomyocota, Ascomycota, Basidiomycota, and Deuteromycota 3. Zygomyocota (black bread molds) is a common fungi that grows on bread and other baked goods and is thus responsible for their spoilage a. When spores land on a suitable substrate, they germinate and produce ex- tensive coenocytic mycelia b. Once the mycelia is established, asexual reproduction begins in the spo- rangiophores, which produce black spores c. As the walls of the sporangia break down, the spores are released and car- ried away by air currents to germinate and establish the cycle again d. Sexual reproduction occurs when the gametangia of two different mating strains fuse to form a zygospore e. The zygospores may remain dormant for months, but eventually undergo meiosis and germination to produce spore-bearing hyphae f. The spores produced in these hyphae are released to start the cycle again 4. Ascomycota (sac fungi) are the largest class of sexually reproducing fungi and in- clude yeast, powdery mildews, molds, morels, and truffles a. This class is named for the ascus, a reproductive structure in which spores are produced b. The hyphae of sac fungi have incomplete septa dividing adjacent cells c. Some ascomycetes cause plant diseases, including Dutch elm disease, chestnut blight, and ergot d. Asexual reproduction is accomplished by means of spore production, bud- ding, or binary fission (1) Some ascomycetes produce long chains of asexual spores (conidia) in specialized hyphae called conidiophores (2) Other ascomycetes (such as yeasts) reproduce asexually by binary fis- sion and budding e. Sexual reproduction occurs when the haploid hyphae of two different mating strains grow together (1) The fusion of cells at the tip of mating haploid hyphae produces new, di-karyotic hyphae whose cells each contain two nuclei (one nucleus from each mating strain); the fusion of the cytoplasm of the hyphal cells is called plasmogamy (2) When dikaryotic hyphae mature, the nuclei in some of the cells fuse to form an ascus; the fusion of the nuclei within the dikaryotic hyphae is called karyogamy Numerous asci form a layer of cells, or ascocarp, within a fruiting body Within individual asci, the diploid nuclei undergo meiosis and sub- sequent mitosis to form a total of eight haploid ascospores (spores developed from an ascus) (5) The ascus ruptures to release the ascospores, which are dispersed to germinate and establish new hyphae 5. Basidiomycota (club fungi) include mushrooms, puffballs, bracket fungi, rusts, and smuts a. Asexual reproduction is not common among basidiomycetes; when it occurs, it is usually by means of spore production b. Sexual reproduction begins with the formation of spore-producing structures, called basidia, within the fruiting body (1) The spores (basidiospores) germinate to produce the primary myce- lium, a haploid structure that contains mononucleate cells (those having only one nucleus) (2) Two compatible mating strains of primary mycelia grow together and fuse to form a secondary mycelium, which contains dikaryotic cells (those possessing two haploid nucleione from each mating strain) (3) The secondary mycelium grows to form a dense, solid mass called a button or young basidiocarp (4) The burton expands to form the mature basidiocarp, which is the read- ily recognizable structure of a mushroom (5) The umbrella-like basidiocarp consists of thin gill-like structures that house the basidia (6) As each basidium matures, karyogamy (nuclear fusion) takes place and is immediately followed by meiosis, a process that produces the haploid basidiospores (7) The basidiospores are dispersed to germinate, form a primary myce- lium, and complete the cycle 6. Deuteromycota (imperfect fungi) are so named because their life cycle is imper- fect, that is, asexual a. As far as scientists know, imperfect fungi reproduce only asexually, usually by means of spore production (conidia) b. Deuteromycetes include Penicillium notatum (from which the antibiotic peni- cillin is extracted), Penicillium roquefortii (which gives flavor to Roquefort cheese), and Aspergillus tamarrii (which is used to produce soy sauce); other members of this phyla cause athlete's foot and ringworm D. Subkingdom Myxomycotineae (slime molds) Slime molds bear little resemblance to other members of the kingdom Fungi During part of their life cycle, slime molds lack cell walls and consist of a multinu- cleate mass of cytoplasm called a plasmodium a. Plasmodia often appear white, but can be blue, orange, yellow, or black b. They flow or creep along substrates much like the protozoan amoeba c. Plasmodia contain many (sometimes several thousand) diploid nuclei 3. Under stressful environmental conditions (drought or starvation), plasmodia are converted into a stationary structure from which sporangia begin to form 4. Sporangia, tiny spheres held above the substrate on small stalks, produce spores 5. Meiosis occurs in the individual spores, forming four nuclei, three of which disinte- grate; the remaining haploid spore is released and later germinates 6. The germination of the haploid spore produces an amoeba-like cell known as a myxamoeba or a flagellated cell called a swarm cell 7. After feeding on bacteria and other small organisms, the myxamoebae or swarm cells fuse to form a diploid zygote, from which a new plasmodium develops, thereby completing the cycle IV. Importance A. General information 1. Naturally occurring fungi are important in the decomposition of dead organisms and also can cause disease 2. Cultivated fungi are used as food and as sources of antibiotics and other valuable substances B. Edible varieties 1. Edible fungi include truffles and morels (sac fungi), Agaricus bisporus or culti- vated mushrooms (club fungi), and shiitake mushrooms from China and Japan (also club fungi) 2. The sac fungus yeast (Saccharomyces cerevisiae) is used in baking and fermen- tation processes C. Decomposer varieties 1. In nature, fungi serve as decomposers, breaking down dead plant and animal matter into their component organic materials 2. As decomposers, fungi play an important role in sustaining ecosystems a. They permit recycling of nutrients bound up in the tissues of organisms b. These nutrients would otherwise be unavailable to sustain new growth D. Intoxicating, poisonous, and hallucinogenic varieties 1. The Conocybe and Psilocybe mushrooms have intoxicating and hallucinogenic properties; they were used by the ancient Mayans for religious ceremonies and are still used by the native peoples of Mexico and Central America 2. Amanita phalloides and Amanita verna (collectively known as the destroying an- gel, death angel, or death cup) are extremely poisonous; both species appear similar to edible varieties, but can be lethal even if ingested in small quantities Kingdom Plantae: Nonvascular Plants Objectives After studying this chapter, the reader should be able to: Describe the most important characteristics of members of the Plant kingdom. Explain the concept of alternation of generations. Describe the ecologic importance of bryophytes. Describe the life cycles of liverworts, hornworts, and mosses. I. Introduction to the Plant Kingdom A. General information 1. All member of the plant kingdom are multicellular organisms composed of eu- karyotic cells All plants contain chlorophylls a and b, and many possess carotenoid as well Plant cells use starch as the storage carbohydrate and cellulose as the structural polysaccharide in cell walls Plant reproduction is primarily sexual, although asexual reproduction occurs Evolutionary trends in the Plant kingdom are related to the modifications or adap- tations necessary for living in terrestrial environments; for example, because dehydration is a possibility in such environments, plants have developed methods of controlling water loss B. Alternation of generations 1. Alternation of generations is the typical sexual life cycle of a plant in which a sporophyte generation alternates with a gametophyte generation 2. The sporophyte generation is the spore-producing diploid generation of the life cycle a. Spores are produced by meiosis within the sporophyte b. These spores undergo cell division to form a multicellular gametophyte 3. The gametophyte generation is the gamete-forming haploid generation of the life cycle a. The gametes (egg and sperm) are produced by mitosis and contained within a sterile jacket of cells to prevent desiccation (drying out) b. The haploid gametes unite through fertilization to produce a diploid zygote, or sporophyte 4. Plant divisions vary as to which generation (sporophyte or gametophyte) predomi- nates (I. Nonvascular Plants (Bryophytes) A. General information 1. Nonvascular plants lack the vascular and transport tissue (xylem and phloem) found in other plants 2. These plants are members of the division Bryophyta and are found in cool, shaded, extremely moist areas; however, many bryophytes can withstand long periods of desiccation 3. Bryophytes are ecologically important in forming bogs (peat moss) and in devel- oping ecologic communities, a process known as succession Many bryophytes have associated mycorrhizal fungi They have flagellated, swimming sperm and require water for successful fertiliza- tion 6. They spend most of the life cycle as gametophytes; the sporophyte remains at- tached to and lives off the gametophyte 7. The three classes of bryophytes are liverworts, hornworts, and mosses B. Class Hepaticae (liverworts) 1. Liverworts consist of a thin, flattened structure called a thallus a. The thallus develops directly from a spore b. Its smooth upper surface has various markings and pores; the underside bears many tiny, single-cell, roothke structures known as rhizoids, which anchor the thallus to the substrate 2. Representative liverworts are Marchantia (common liverwort) and Porella (leafy liverwort) 3. The life cycle of the liverwort is typified by Marchantia a. Asexual reproduction occurs by fragmentation and the production of gem- mae, clusters of lens-shaped cells that detach from the parent (1) Gemmae are produced in specialized cuplike structures formed on the upper surface of the thallus (2) The gemmae are dispersed by rainfall, and each gemma is capable of growing into a new thallus b. Sexual reproduction begins with the gametophyte generation (1) The male and female thalli of the gametophyte generation produce male and female gametangia (2) The gametangia are upright, umbrella-like structures that extend above the thallus and produce gametes within specialized structures known as antheridia and archegonia (a) The numerous antheridia within the upper surface of the male gametangium produce many sperm (b) The archegonia on the under surface of the female gametangium contains a single egg (3) When the flagellated sperm are released during a rainstorm, they swim to the archegonia to fertilize the egg (4) Fertilization produces a zygote that develops into an embryo (imma- ture sporophyte) (5) The embryo remains attached to the archegonium as it grows into a mature sporophyte, which consists of three parts: foot (point of attachment to archegonium); seta (short thick stalk); and capsule or sporangium (structure in which meiosis occurs to form haploid spores)  (6) At maturity, the spores are released from the capsule and form a new thallus when they reach a suitable habitat C. Class Anthocerotae (hornworts) 1. Hornworts resemble liverworts, but during the sporophyte generation, they form hornlike structures that give the class its name 2. The hornwort thalli often produce a mucilage secretion in which nitrogen-fixing cyanobacteria grow a. This relationship provides the hornwort with a source of nitrogen b. The presence of cyanobacteria may also provide some coloration D. Class Musci (mosses) 1. Mosses consist of leaflike structures that contain photosynthetic material but lack a midrib with vascular tissue and therefore are not considered true leaves These low-growing green plants typically are found in moist, shady habitats Asexual reproduction occurs by fragmentation Sexual reproduction begins with the germination of a haploid spore (see Life Cy- cle of Moss, page 89) a. The spore forms an algae-like, green filamentous structure called a pro- tonema b. The protonema eventually grows to become a leafy gametophyte, which pro- duces male and female gametangia in its sperm-producing antheridia and egg-producing archegonia c. The zygote that results from fertilization develops into an embryo while still within the archegonium d. The embryo grows to form a sporophyte e. Haploid spores produced by meiosis within the sporophyte capsule are re- leased when the operculum (cap) falls off f. They are dispersed by wind and eventually germinate to complete the life cycle E. Importance Bryophytes may have been the first plants to grow on barren or bare surfaces They are a chief source of food in the arctic circle, where they are eaten by rein- deer, caribou, and other animals 3. Mosses retain moisture and can potentially reduce flooding and erosion in natu- ral ecosystems 4. They also contribute to the humus content of soil; for example, peat moss is used as a soil conditioner to promote moisture retention and increase the nutrient status of soils Nonseed Vascular Plants: Ferns and Their Relatives Objectives After studying this chapter, the reader should be able to: Explain the difference between nonseed and seed vascular plants. Name the major divisions of nonseed vascular plants. Describe the life cycles of whisk ferns, club mosses, horsetails, and ferns. List the uses of nonseed vascular plants. I. Vascular Plants A. General information 1. Vascular plants contain conducting tissue consisting of xylem and phloem a. Vascular tissue allows plants to inhabit drier habitats b. The ability to conduct water through the plant body permits some vascular plants to grow extremely large (such as giant redwood trees) Unlike the bryophytes, vascular plants possess true roots, stems, or leaves Many vascular plants can simultaneously control water loss and permit gas ex- change because of a waxy outer covering (cuticle) and small porelike openings on the leaf (stomata) 4. The diploid sporophyte generation is the predominant generation in vascular plants; the gametophyte is small, short-lived, and often inconspicuous B. Taxonomic classification Vascular plants are classified according to the type of propagule produced Nonseed vascular plants reproduce using spores; this group includes ferns and their relatives 3. Seed vascular plants reproduce using seeds; this group includes gymnosperms and angiosperms II. Nonseed Vascular Plants A. General information 1. Nonseed vascular plants are categorized according to the type of spores that they produce 2. Homosporous plants produce only one kind of spore in a single sporangium a. The spore undergoes cell division to produce bisexual gametophytes that have both antheridia and archegonia b. The gametophytes develop outside the spore wall c. Homospory is characteristic of whisk ferns, horsetails, some club mosses, and most ferns 3. Heterosporous plants produce two types of spores in two different sporangia a. Heterospory is characteristic of some club mosses, a few ferns, and all seed plants b. The two types of spores, called microspores and megaspores, are much larger than those produced by homosporous vascular plants (1) Microspores, which may or may not be smaller than megaspores, give rise to male gametophytes (2) Megaspores give rise to female gametophytes c. The free-living, nutritionally independent gametophytes develop within the spore wall d. The gametophytes require water for fertilization so that the flagellated sperm can reach the egg B. Taxonomic groups 1. The four divisions of nonseed vascular plants are Psilophyta, Lycophyta, Spheno- phyta, and Pterophyta 2. With the exception of Pterophyta (ferns), most of these plants are uncommon, un- familiar species III. Division Psilophyta (Whisk Ferns) A. General information 1. Psilophyta are tropical and subtropical plants that consist of only one existent family, Psilotaceae, with just two genera: Psilotum and Tmesipteris 2. In the United States, whisk ferns grow naturally in Florida, Louisiana, Texas, Ari- zona, and Hawaii 3. They have no economic importance, although florists occasionally use them in ar- rangements B. Structure 1. Whisk ferns do not have true leaves or roots; photosynthesis occurs in the outer epidermal cells of the stem 2. The dichotomously forking stems develop from rhizomes that grow horizontally just under the soil surface 3. The stem and branches contain a central core of vascular tissue, with phloem sur- rounding a star-shaped core of xylem 4. Surrounding the stele is an area of cortex comprised of parenchyma and scler- enchyma tissue 5. These homosporous plants produce spores within sporangia, which are clustered on the stem and branches C. Reproduction 1. The life cycle of the whisk fern reflects the alternation of generations found in all plants 2. Spores released from the sporangia of the sporophyte germinate and grow to form a gametophyte within the soil, on the bark of trees, or on other surfaces a. The colorless, saprophytic gametophyte lacks chlorophyll and obtains nutri- ents by association with fungi b. The gametophyte is approximately 2 mm in diameter and 6 mm long 3. Archegonia and antheridia are produced randomly on the surface of the gameto- phyte 4. Fertilization requires water so that the flagellated sperm can swim to the archego- nia 5. The fertilized egg, now a diploid zygote, develops into an embryo within the arche- gonium 6. As the embryo continues to grow, it forms a foot and a shoot apex a. The foot permits the growing sporophyte to obtain nourishment from the gametophyte b. The shoot apex undergoes repeated cell division to form the mature sporo- phyte 7. The sporophyte ultimately detaches from its foot and lives independently of the gametophyte a. The sporophyte consists of an underground rhizome, which performs the same functions as a root, and a series of upright aerial branches that arise from the rhizome b. As the rhizome grows, it becomes infected with mycorrhizae, which help the rhizome anchor the plant and absorb water and nutrients from the soil 8. Sporangia develop in clusters on the upright, dichotomously forked branches of the sporophyte 9. Spores are released from the sporangia, and the cycle is repeated IV. Division Lycophyta (Club Mosses) A. General information 1. The principal club mosses are Lycopodium, Selaginella, and Isoetes a. Lycopodium (ground pine) commonly grow on forest floors in temperate cli- mates b. Selaginella (spike mosses) grow in wet areas throughout the world, but are common in the tropics and are occasionally a weed in greenhouses c. Isoetes (quillworts) grow partially submerged in marshy areas 2. Treelike ancestral varieties of lycophytes were dominant plants in the forests of the Carboniferous period some 286 to 360 million years ago; their fossilized remains helped produce fossil fuels (coal and petroleum) used today 3. Historically, club moss spores were used to produce flash powders and explo- sives; various parts of the plant were also used in folk medicine and remedies 4. Club mosses are currently used to create Christmas decorations and wreaths; they are so popular with crafts people that several species are now endangered from over-collection 5. Many species are an important food source for wildlife  B. Structure 1. The upright or occasionally prostrate stems develop from branched rhizomes; the stems are covered with small leaves called microphylls 2. Adventitious roots develop along the rhizome, allowing segments of the rhizome to become independent plants 3. Sporangia typically are located in terminal clusters called strobilior on special- ized leaves called sporophylls a. Ground pine sporophytes are generally less than 30 cm tall b. Quillwort sporophytes are generally less than 10 cm tall C. Reproduction 1. The life cycle of the club moss begins with the production of spores within the sporangia of the sporophyte 2. The spores are dispersed and germinate to form independent gametophytes, which typically grow on the soil surface 3. When mature, the gametophytes spawn both antheridia and archegonia, which produce sperm and eggs 4. Water is required for the flagellated sperm to swim from the antheridia to the archegonia so that fertilization can occur 5. Fertilization results in a zygote with foot, stem, and leaves V. Division Sphenophyta (Horsetails and Scouring Rushes) A. General information 1. Historically, horsetails were used by native Americans for medicinal purposes, food, and scouring pads (for cleaning cooking utensils) 2. Equisetum, which is typically found along streams, water bodies, and wetlands, is the most common genus B. Structure Equisetum are tall, reedlike plants that resemble a horse's tail Stems develop from horizontal rhizomes, which can be quite extensive and form large horsetail colonies a. The distinctly ribbed, jointed stems are the site of photosynthesis b. The stems have scalelike leaves that occur in whorls at regular intervals c. The stems of the sporophyte contain silica deposits on the inner walls of the epidermal cells C. Reproduction 1. Asexual reproduction occurs by fragmentation of the stem or rhizome; if these structures are broken up by a disturbance, such as a storm or foraging animals, the fragments can grow into new sporophytes 2. Sexual reproduction begins with the formation of strobili at the stem tips a. The small, conelike strobili bear the sporangia in which spores are produced b. After dispersal, the spores produce small green gametophytes that generate archegonia and antheridia c. Because the sperm are flagellated, they need water to swim to the archego- nia d. When the egg is fertilized, a zygote forms and develops into the new sporo- phyte generation VI. Division Pterophyta (Ferns) A. General information 1. Historically, ferns have been used as food and medicine and were often an ingre- dient in folk remedies Today ferns are commonly used as houseplants and ornamental plants In natural ecosystems, they are an important food source for wildlife B. Structure 1. Ferns vary in size from small floating forms less than 1 cm in diameter to large, tropical, treelike ferns up to 25 meters tall 2. These plants possess large, highly divided, feathery leaves called fronds a. Fronds first appear as small, tightly coiled structures called fiddleheads, which uncurl to form mature fronds b. There are two types of fronds Vegetative fronds are involved only in photosynthesis Reproductive fronds have sporangia for the production of spores C. Reproduction 1. Spore production begins in the sporangia, which are often found in clusters (called sori) on the underside of fronds (see Life Cycle of the Fern, page 94) a. In many ferns, the sori are protected by flaps of covering tissue called an in- dusium; as the sporangia mature, the indusium shrivels to expose the sporangia beneath it b. Each sporangium has a conspicuous row of thick-walled cells along one edge, which are known as the annulus c. The annulus catapults spores out of the sporangium using a snapping action that is influenced by moisture changes within the cells d. The individual sporangia contain diploid cells (parental cells) that undergo meiosis to produce haploid spores Released spores germinate and form a heart-shaped prothallus The prothallus is a multicellular, independent, photosynthetic gametophyte Archegonia develop on the under surface of the prothallus near a notch in the heart shape; antheridia develop near the apex 5. After fertilization, the zygote formed in the archegonium continues to grow into an independent sporophyte, which is the recognizable fern Seed Vascular Plants: Gymnosperms Objectives After studying this chapter, the reader should be able to: Define gymnosperm. Differentiate between gymnosperms and angiosperms. List and describe the major divisions of gymnosperms. Describe the life cycle of a pine tree. Discuss the human and ecologic importance of gymnosperms. I. Seed Vascular Plants A. General information 1. Seed plants are so named because the seed is the chief reproductive propagule a. A seed consists of an embryo that is packaged with stored food and sur- rounded by a protective seed coat; the stored food is used for energy during germination and early seedling development b. The seed permits the plant to survive harsh environmental conditions (cold or lack of moisture) during a period of seed dormancy All seed vascular plants have conducting tissue consisting of xylem and phloem All seed-bearing plants exhibit alternation of generations a. The gametophyte generation in these plants is extremely small and develops within the tissues of the sporophyte The male gametophyte is the pollen grain The female gametophyte is the embryo sac b. All seed plants are heterosporous (produce two kinds of spores); the mega- spore gives rise to the female gametophyte and the microspore gives rise to the male gametophyte c. Seed plants generally do not require water for fertilization because, in most varieties, the sperm are not flagellated and do not swim to the archegonia B.Taxonomic classification 1. Seed plants are classified as gymnosperms or angiosperms a. Gymnosperms produce seeds in structures open to the environment b. Angiosperms (flowering plants) produce seeds in specialized reproductive structures called flowers c. Gymnosperms are primarily trees and shrubs; angiosperms encompass a di- verse variety of life forms 2. The four divisions of gymnosperms are Coniferophyta, Cycadophyta, Ginkgo-phyta, and Gnetophyta II. Division Coniferophyta (Conifers) A. General information Conifers are the largest group of gymnosperms The more than 575 species of conifers include pines (Pinus), firs (Abies), spruces (Picea), hemlocks (Tsuga), cypresses (Cupressus), Douglas firs (Pseudot-suga), and junipers (Juniperus) B. Pines 1. Most pines are found in the northern hemisphere, although they have been exten- sively planted in the southern hemisphere 2. Needles are a distinctive characteristic of the pines a. They usually appear in clusters known as fascicles b. They have adapted to winter conditions, when the ground water is frozen and the needles are exposed to drying winds The needles have a thick epidermis with a heavy cuticle Several layers of thickened cells just below the epidermis (called the hypodermis) further reduce the potential for water loss Stomata are located in pits to shield them from the wind's drying action Veins are surrounded by endodermis, which is another layer of large cells that prevents excessive water loss (5) Mesophyll cells are packed tightly together; they do not have the obvi- ous air spaces seen in the spongy mesophyll cells of deciduous leaves (6) The presence of resin canals, which are produced in response to in- jury, may prevent insect and fungal damage c. The fascicles drop off two to five years after maturation; they are lost a few at a time rather than all at once as with the leaves of deciduous trees 3. The xylem tissue of conifers contains tracheids as the conducting cells instead of the vessels found in angiosperms a. Because the secondary xylem of conifers lacks thick-walled vessels and fi- bers, conifer woods are labeled soft woods b. The resin canals in the secondary xylem serve to inhibit fungal infections and prevent damage by plant-eating animals (herbivores) 4. The thick bark of conifers contains large amounts of secondary phloem; the phloem contains albuminous cells that perform the same function as the companion cells of angiosperms Pines almost always have mycorrhizae attached to their roots As a heterosporous plant, the pine begins its reproductive life cycle with the pro- duction of two types of sporesmale microspores and female megaspores (see Life Cycle of the Pine) a. Microspores are produced in a process called microsporogenesis (1) Male cones, which are typically 1 to 4 cm long, usually are found in clusters of 50 or more on tips of the lower branches (2) Male cones last for only a few weeks, during which time each diploid microspore parent cell, or microsporocyte, undergoes meiosis to form four haploid microspores  (3) Each haploid microspore undergoes mitosis and matures into a pollen grain, which consists of four to five cells and a pair of external air sacs or wings (4) The pollen grain contains a tube cell (which forms the pollen tube); a generative cell (which, after dividing, produces sperm nuclei); and two to three prothallial cells (which are the remnant vegetative cells of the gametophyte generation) (5) Vast numbers of pollen grains are shed from the cones and dispersed by the wind to pollinate the female cones (6) To aid wind pollination, pollen grains have two wings that develop from the microspore cell wall (7) Once the pollen grains are released, the male cones dry up and drop from the tree b. Megaspores are produced in a process called megasporogenesis (1) Female cones are larger than male cones and develop in the spring These woody cones persist for long periods of time They are generally located on the upper branches (2) The female cone consists of a number of modified leaflike organs called sporophylls that bear sporangia and serve as shelves on which the seeds develop (3) Two ovules are located on each sporophyll (a) Each ovule has an opening, called a micropyle, through which the pollen tube enters, and a megasporangium (also called the nucellus) surrounded by two integuments (outer tissue layers) (b) Each megasporangium contains a megasporocyte, or mega- spore parent cell (4) The megasporocyte produced within the ovule undergoes meiosis to form four haploid megaspores; three disintegrate and one develops into the female gametophyte (5) The female gametophyte grows slowly, taking approximately 13 months to reach maturity (6) Once mature, the female gametophyte consists of several thousand cells and two to six archegonia, each containing a single egg (7) Typically all eggs in the archegonia are fertilized and begin to develop into embryos (a phenomenon called polyembryony, or multiple embryo production); only one embryo develops fully and the others spontaneously abort 7. Fertilization and seed development occur within the female pine cone a. In the first spring of the reproductive cycle, the immature cone scales spread apart; pollen grains (carried by air currents) sift down between the sporophylls and are caught in sticky secretions near the micropyle b. The pollen grain germinates within the micropyle to produce a pollen tube c. As the pollen tube grows toward the archegonium, the generative cell of the pollen grain divides, producing a sterile cell and a spermatogenous cell (1) The spermatogenous cell further divides to form two sperm; the sterile cell, whose function is unknown, disintegrates (2) The mature male gametophyte consists of the pollen grain and the two sperm d. About 15 months after pollination, the pollen tube reaches the archegonium and releases its contents e. One sperm unites with the egg and the other disintegrates f. The zygote formed from the union develops into an embryo g. The developing embryo is surrounded by integument, which consists of rem- nant sporophyte tissue and forms a seed coat h. The mature embryo consists of an epicotyl, hypocotyl, radicle, and multiple cotyledons 8. In pines, the seed matures approximately 12 months after fertilization, and the complete life cycle takes about two years a. Male and female cones are formed during the summer of the first year b. In the spring of the following year, microspores and megaspores are pro- duced by meiosis c. Pollination occurs during the early summer, and fertilization takes place in the late spring of the second year d. By the summer of the second year, the embryo develops e. Seeds are produced and dispersed in the fall of the second year 9. Seeds can remain dormant for many years, and some may be embedded in the mature cones for six years or more 10. Pine seeds are shed from the cones during the autumn of the second year a. When mature, the cone scales of most pine species separate, and the winged seeds are carried through the air by wind currents b. In species whose seeds do not have wings, the seeds may be dropped by birds during flight or when attempting to eat c. In some species, such as the lodgepole, jack, and knobcone pines, the cones open only when exposed to heat (a fire, for example), which melts the resin that holds the cone scale closed 11. Other conifers lack the needle clusters of pines and may have slightly different re- productive cycles a. The yews (family Taxaceae) do not produce woody female cones; instead, the ovule is at least partially surrounded by a fleshy, cuplike covering b. The Norfolk Island pine (Araucaria excelsa) lacks the needle clusters of other pines and bears its needles singly along stems and branches; it is native to the southern hemisphere and is a common houseplant III. Other Gymnosperms A. General information 1. In addition to the conifers, a number of tropical and subtropical plant species are classified as gymnosperms 2. Other gymnosperms that have economic value or unique characteristics include the Cycadophyta, Ginkgophyta, and Gnetophyta B. Division Cycadophyta (cycads) 1. Cycads are slow-growing tropical and subtropical plants that consist of un- branched trunks with a crown of pinnately divided (palmlike) leaves Cycads are dioecious (pollen and seeds are produced on different plants) Their sperm are atypical because they have numerous flagella C. Division Ginkgophyta (ginkgoes) The only living species in this division is Ginkgo biloba, or the maidenhair tree This dioecious tree has broad, notched, fan-shaped leaves with no prominent midrib; it is commonly planted along sidewalks in the United States 3. Its seeds resemble small apricots or plums, but produce a rank odor because of the butyric acid in the seeds' fleshy coat 4. The sperm are delivered to the egg through a pollen tube D. Division Gnetophyta 1. This unique group of heterogeneous gymnosperms shares some characteristics with angiosperms, the most important of which are the presence of vessels (in addition to tracheids) in xylem tissue and the similarity of their strobili to angio-sperm inflorescences 2. The three living genera of Gnetophyta are Gnetum, Ephedra, and Welwitschia a. Gnetum is a woody vine with broad leaves; it is native to the tropics b. Ephedra is a shrublike plant with jointed stems and small leaves; it is usually found in desert or semidesert habitats c. Welwitschia is a rare and exotic plant found only in the coastal regions of An- gola and southwest Africa IV. Human and Ecologic Importance A. General information 1. The most exploited group of gymnosperms are the conifers, which have been used for food, paper, lumber, and ornamental purposes 2. Ecologically, spruces and firs are the predominant species of the northern conifer- ous forests (called taiga) B. Conifers 1. Historically, conifers were used by native Americans, who ate the bark raw or dried and ground it into a flour, and by early New England settlers, who made a tea high in vitamin C from the needles 2. Resins extracted from conifers are used to produce turpentine, menthol, floor waxes, printing ink, paper coatings, varnishes, and perfumes 3. About 40 species of firs (particularly the Douglas fir) are widely used in the con- struction, plastic, and paper industries 4. Spruces, firs, eastern white cedars (arborvitae), and pines are used as Christ- mas trees and ornamentals Spruces are an important source of pulpwood for newsprint Cedars are harvested to make pencils C. Other gymnosperms Ginkgo seeds are commonly eaten in the Orient Many other gymnosperms, such as yews, are used as ornamental plants Flowering Plants: Angiosperms Objectives After studying this chapter, the reader should be able to: Describe the characteristics of angiosperms. Describe the life cycle of angiosperms. List the various methods of pollination. Explain double fertilization. Explain apomixis and the formation of parthenocarpic fruits. Distinguish between monocots and dicots. Discuss the major evolutionary trends involving angiosperms. I. Flowering Plants A. General information 1. The flowering plants, or angiosperms, belong to the division Anthophytait is the largest division of the plant kingdom, containing more than 240,000 species a. The flower is a distinguishing characteristic of this group b. Angiosperm seeds are contained within a vessel-like, female structure called the carpel (Note that some texts use the term carpel in place of pistil) c. The angiosperm ovary develops into a fruit 2. Angiosperms have small, brief gametophyte generations B. Female gametophyte 1. In megasporogenesis, megaspores are formed within the megasporangium (nucellus) and ultimately develop into the female gametophyte (see Life Cycle of an Angiosperm, page 104) 2. The ovule is composed entirely of nucellus at the beginning of the reproductive cycle, but it soon begins to differentiate a. During ovule development, one or two enveloping layers called integuments are formed b. Each integument has a small opening (micropyle) at one end through which the pollen tube enters 3. While the flower is still in bud, a diploid megaspore parent cell forms in the ovule and subsequently undergoes meiosis to produce four haploid megaspores, of which three disintegrate 4. The remaining megaspore undergoes a series of nuclear divisions without sub- sequent cytoplasmic division, resulting in a cell with eight haploid nuclei  5. This eight-nuclei stage comprises the female gametophyte, or embryo sac a. It consists of two polar nuclei located in the middle of the cell and a single egg cell with two "helper cells" (called synergids) at the micropyle end b. Three antipodal cells of unknown function are located at the end opposite the egg C. Male gametophyte The male gametophyte is the germinated pollen grain Its formation begins within the anther, where the microspore parent cells undergo meiosis to form haploid microspores 3. The microspore nucleus divides to produce two nucleithe tube nucleus and the generative nucleus a. The tube nucleus is contained within a pollen tube cell, which is responsible for germination of the pollen grain and growth of the pollen tube toward the micropyle b. The generative nucleus is contained within a generative cell, which is re- sponsible for the formation of sperm when the pollen grain germinates 4. The thick cell wall that develops around the mature pollen grain is resistant to moisture loss; it protects and preserves the tube and generative nuclei during pollination (^Pollination 1. Pollination is the transfer of pollen from the stamen to the stigma of a flower, and often occurs from plant to plant 2. Plants use a variety of mechanisms to transfer pollen, including physical forces, such as wind or water currents, and reliance on specific organisms, such as insects, birds, and mammals 3. Wind-pollinated flowers are typically small and inconspicuous and have well- exposed anthers and stigmas a. They tend to produce large amounts of pollen because much of it is lost dur- ing transfer owing to the unpredictability of wind direction and air currents b. They generally do not produce odors for attraction or provide rewards for pol- linators c. Examples include walnut, grasses, and corn 4. Insect-pollinated flowers must have a mechanism to attract and reward the polli- nators a. Bee-pollinated flowers produce a sweet nectar and pleasant fragrances and are usually brightly colored (predominately blue or yellow, rarely red) (1) These flowers often have lines or other distinctive markings visible in the ultraviolet range that may lure the bees to the nectar Bees often consume nectar and pollen as rewards for pollination Examples include larkspur, snapdragon, violet, rosemary, foxglove, and clover b. Beetle-pollinated flowers have strong, yeasty, spicy, or fruity odors; such odors are important because beetles have poor eyesight but a keen sense of smell These flowers are white or dull-colored and usually produce no nectar They often provide pollen as a food source for the beetle or possess special food glands; occasionally the beetles chew flower parts (3) Examples include magnolia and dogwood c. Fly-pollinated flowers have foul odors to attract the insects (1) These flowers are usually dull red or brown and provide nectar as a re- ward for pollination They tend to remain wide open to allow easy access by flies Examples include carrion flower, certain cacti, skunk cabbage, and some lilies d. Moth-pollinated flowers have strong, sweet fragrances that are released at night when moths are most active These flowers are pale white or yellow and provide nectar as a reward Examples include tobacco, Easter lily, some cacti, evening primrose, and amaryllis e. Butterfly-pollinated flowers have sweet fragrances and are often bright red, orange, or yellow (1) These flowers produce fragrances during the day, when butterflies are active, and provide nectar as a reward (2) Examples include the butterfly weed and daisy 5. Animal-pollinated flowers must provide larger rewards because of the greater en- ergy needs of the pollinators a. Bat-pollinated flowers are dull colored and produce strong, perfume-like odors (1) These flowers open at night when bats are active and are large enough for the bat to insert its head in the flower (2) They produce large amounts of nectar; bats also eat pollen and other flower parts (3) Examples include organ pipe cactus and numerous tropical species b. Bird-pollinated flowers are usually bright red or yellow and produce little or no odor (1) The large or numerous, usually tubular-shaped flowers attract hum- mingbirds or sunbirds by providing nectar as a reward (2) Examples include red columbine, fuchsia, hibiscus, passion flower, eucalyptus, and poinsettia 6. Pollen can be transferred within individual flowers of the same plant or between flowers of plants separated by great distances a. Self-pollination is the transfer of pollen from stamen to stigma within the same flower or between the flowers of the same plant; it reduces the chances of genetic variation b. Cross-pollination is the transfer of pollen from stamen to stigma of different, genetically distinct flowers; it promotes genetic variation within the population, which helps plants adapt to changes in the environment and ensures the survival of the species E. Fertilization and seed development 1. Pollen grains transferred during pollination adhere to the stigma of the pistil, where they germinate 2. Germination produces a generative cell that divides to form two sperm cells and the tube nucleus 3. The pollen tube grows toward the ovary by digesting its way through the style of the pistil 4. When the pollen tube reaches the embryo sac, it triggers a unique set of events called double fertilizationthe simultaneous fusion of the two sperm cells in the pollen tube with the cells of the embryo sac a. In double fertilization, the tube nucleus disappears and the two sperm move into the embryo sac b. One sperm fuses with the egg and forms a zygote c. The other sperm fuses with the two polar nuclei of the embryo sac to form a triploid endosperm nucleus, which eventually divides to form the endosperm d. In some angiosperms, the endosperm becomes an extensive part of the seed; in others, the endosperm is consumed in the formation of cotyledons and thus disappears by the time the seed is mature e. The seed is a mature ovule that contains an embryo surrounded by a protec- tive seed coat The embryo is an immature sporophyte The cotyledon, which stores food, is part of the embryo The seed coat, which develops from the integuments, is the outer boundary of the seed f. In some plants, double fertilization stimulates the ovary wall to thicken and form a fruit, or pericarp F. Apomixis 1. Apomixis is a form of atypical reproduction in angiosperms in which seeds de- velop without fertilization; the development of other plant parts, such as flowers and fruits, is normal 2. The embryo in unfertilized angiosperms may develop from a nutritive cell of the ovary 3. Fruits that develop from unfertilized ovaries are called parthenocarpic a. These fruits are usually seedless b. Examples include bananas, navel oranges, some figs, and seedless grapes II. Monocotyledons and Dicotyledons A. General information 1. The two classes of the division Anthophyta are monocotyledons and dicotyle- dons, commonly referred to as monocots and dicots 2. Although the terms monocot and dicot refer specifically to the number of cotyle- dons, or food storage organs, within the seeds of angiosperms, several other characteristics separate the two classes (see Comparison of Monocots and Dicots, page 108) B. Monocots 1. Monocots have only one cotyledon in each seed a. The single cotyledon enzymatically absorbs food from the endosperm and transports it to the growing embryo b. The large cotyledon in the mature seeds of grass species is called the scutel- lum (1) The scutellum is attached to one side of the embryo, midway between the plumule at the upper end of the embryo and the radicle at the lower end (2.) The radicle, or embryonic root, is enclosed in a protective sheath known as a coleorhiza (3) The plumule (epicotyl and young leaves) is enclosed within a protective sheath called the coleoptile c. The endosperm persists in the seed and is the primary source of stored food for the embryo and young seedling during the early stages of germination 2. The flower parts (sepals, petals, stamen) usually occur in groups of three or multi- ples of three The leaves have parallel veins Monocots tend to have fibrous root systems The primary vascular bundles in stems are scattered throughout the cross section Comparison of Monocots and Dicots CHARACTERISTIC MONOCOTS DICOTS Embryo One cotyledon Two cotyledons Flower parts Occur in groups of three Occur in groups of four or five Leaves Parallel veined Net veined Roots Many main roots (fibrous root system) One mam root (taproot system) Stem anatomy Scattered vascular bundles Vascular bundles arranged in rings Root anatomy Pith Xylem in center Secondary growth No Yes 6. The roots contain a central core of pith (parenchyma tissue derived from the pro- cambium) 7. True secondary growth is rare or nonexistent because most monocots lack vascu- lar cambium and cork cambium 8. Examples of monocots include cereal grains (such as corn, wheat, and oats), sugarcane, lilies, daffodils, orchids, bananas, palms, and grasses C. Dicots 1. Dicots have two cotyledons in each seed a. The cotyledons are the food storage organs of the embryo b. The endosperm does not remain unchanged in dicots; it is converted to a cotyledon during seed development The flower parts occur in multiples of four or five The leaves have netlike veins Dicots lend to have root systems consisting of a single main root (taproot) with small branches The primary vascular bundles in stems form a ring pattern Most dicot roots, with the exception of those of a few herbaceous dicots, do not have a central core of pith 7. True and often abundant secondary growth occurs in many species because of the presence of vascular and cork cambium 8. Examples of dicots include many annual plants (such as tomatoes, peppers, beans, sunflowers, mustards, and common weeds), flowering herbaceous species, and most flowering trees and shrubs III. Evolutionary Trends A. General information 1. Angiosperms are the most modern plants, having evolved from gymnosperm an- cestors more than 125 million years ago 2. This diverse group is the dominant plant type on earth B. Angiosperm evolution 1. As plants evolved, the gametophyte generation became progressively smaller and less conspicuous; it is very prominent in primitive plants, such as bryo-phytes, less so in ferns, and even less so in angiosperms 2. Carpels (ovule-bearing units within the pistils) allow angiosperms to shelter seeds from dehydration and pests and develop a fruit, which aids in seed dispersal 3. Double fertilization allows angiosperms to use energy reserves efficiently be- cause fruit development (and subsequent energy investment) is triggered only after fertilization occurs 4. Most angiosperms rely on animal pollination, which is considered more reliable than wind pollination 5. The specialization of angiosperm flowers, manifested as a reduction and fusion of parts, is considered by some scientists to be a method of saving energy PAGE  PAGE 10