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, found that they produced and secreted large amounts of proteins. Most proteins secreted by gram-negative bacteria have special signal sequences that allow them to pass through the bacterium’s double membrane. This key signal sequence was missing the proteins being secreted by Yersinia. These proteins lacked a signals... |
diseases of plants, including blights, soft rots, and wilts, also are associated with bacteria. Fire blight, which destroys pears, apple trees, and related plants, is a well-known example of bacterial disease. Most bacteria that cause plant diseases are members of the group of rod-shaped bacteria known as pseudomonads... |
—there have been alarming outbreaks of multidrug-resistant strains of tuberculosis—strains resistant to the best available anti-TB medications. Multidrug-resistant TB is particularly concerning because it requires much more time to treat, is more expensive to treat, and may prove to be fatal. The basic principles of TB... |
Botulism Clostridium botulinum Improperly prepared food Chlamydia Chlamydia trachomatis Humans, STD Cholera Vibrio cholerae Human feces, plankton Dental caries Streptococcus Humans Diphtheria Corynebacterium diphtheriae Humans Bacterial infection that can be transmitted through contact or ingested. Rare except in spor... |
without treatment An acute bacterial infection of the lungs, lymph, and meninges. Its incidence is on the rise, complicated by the development of new strains of the bacteria that are resistant to antibiotics. A systemic bacterial disease of worldwide incidence. Less than 500 cases a year are reported in the U.S. The d... |
an infected person may unwittingly transmit the disease to others. The second stage of syphilis is marked by a rash, a sore throat, and sores in the mouth. The bacteria can be transmitted at this stage through kissing or contact with an open sore. The third stage of syphilis is symptomless. This stage may last for sev... |
the bacteria in the discharge from men and women. The treatment for chlamydia is antibiotics, usually tetracycline (penicillin is not effective against chlamydia). Any woman who experiences the symptoms associated with this STD should be tested for the presence of the chlamydia bacterium; otherwise, her fertility may ... |
, and chloromycetin, are derived from bacteria. Most antibiotics seem to be substances used by bacteria to compete with one another and fungi in nature, allowing one species to exclude others from a favored habitat. Bacteria can also play a part in removing environmental pollutants (figure 34.11) Bacteria and Genetic E... |
3 Bacteria exhibit considerable diversity in both structure and metabolism. • The two bacterial kingdoms, Archaebacteria and Eubacteria, are made up of prokaryotes, with about 5000 species named so far. • The Archaebacteria differ markedly from Eubacteria and from eukaryotes in their ribosomal sequences and in other re... |
Protista contains members exhibiting a wide range of methods of locomotion, nutrition, and reproduction. 35.3 Protists can be categorized into five groups. Five Groups of Protists. The 15 major phyla of protists can be conveniently discussed in seven general groups that share certain characteristics. Heterotrophs with... |
palustris. This unique, amoebalike protist lacks mitochondria and does not undergo mitosis. Pelomyxa may represent a very early stage in the evolution of eukaryotic cells. Endosymbiosis What was the first eukaryote like? We cannot be sure, but a good model is Pelomyxa palustris, a single-celled, nonphotosynthetic orga... |
, which are able to carry out oxidative metabolism (described in chapter 9). In mitochondria, the outer membrane is smooth and is thought to be derived from the endoplasmic reticulum of the host cell, which, like Pelomyxa, may have already 694 Part IX Viruses and Simple Organisms contained a complex system of internal ... |
in most protists, or in plants or animals. We do not know if it represents an intermediate step on the evolutionary journey to the form of mitosis that is characteristic of most Internal membrane system Aerobic bacterium Endosymbiosis Mitochondrion Ancestral eukaryotic cell Eukaryotic cell with mitochondrion Chloropla... |
The theory of endosymbiosis proposes that mitochondria originated as symbiotic aerobic eubacteria. Chapter 35 Protists 695 35.2 The kingdom Protista is by far the most diverse of any kingdom. The Challenge of Classifying the Protists Protists are the most diverse of the four kingdoms in the domain Eukaryota. The kingd... |
as related (like ciliates and dinoflagellates), while the classification of others (like Giardia) is clearly in a state of flux. 696 Part IX Viruses and Simple Organisms Animals Ciliates and dinoflagellates Euglenoids, cellular slime molds, water molds, trypanosomes Rhizopods, plasmodial slime molds, fungi (basidiomyc... |
. Most are microscopic, but some are as large as trees. They represent all symmetries, and exhibit all types of nutrition. The Cell Surface Protists possess a varied array of cell surfaces. Some protists, like amoebas, are surrounded only by their plasma membranes. All other protists have a plasma membrane but some, li... |
odia can be extended or retracted. Because the tips can adhere to adjacent surfaces, the cell can move by a rolling motion, shortening the axopodia in front and extending those in the rear. Cyst Formation Many protists with delicate surfaces are successful in quite harsh habitats. How do they manage to survive so well?... |
done in the nineteenth century) into photosynthesizers (algae), heterotrophs (protozoa), and absorbers (funguslike protists). In this text, we will group the protists into five general groups according to some of the major shared characteristics (figure 35.6). These are characteristics that taxonomists are using today... |
HS WITH NO PERMANENT LOCOMOTOR APPARATUS Amoebas Rhizopoda Amoeba Move by pseudopodia Radiolarians Actinopoda Radiolarians Glassy skeletons; needlelike pseudopods Forams Foraminifera Forams PHOTOSYNTHETIC PROTISTS Dinoflagellates Pyrrhophyta Red tides Euglenoids Euglenophyta Euglena Diatoms Chrysophyta Diatoma Golden a... |
serious conditions. In some tropical areas, more than half of the population may be infected. The spread of amoebic dysentery can be limited by proper sanitation and hygiene. Actinopoda: The Radiolarians The pseudopodia of amoeboid cells give them truly amorphous bodies. One group, however, have more distinct structur... |
from place to place by means of their pseudopods, from the Greek words for “false” and “foot” (figure 35.7). Pseudopods are flowing projections of cytoplasm that extend and pull the amoeba forward or engulf food particles, a process called cytoplasmic streaming. An amoeba puts a pseudopod forward and then flows into i... |
sporic meiosis). Forams have contributed massive FIGURE 35.8 Actinosphaerium, a protist of the phylum Actinopoda (300×). This amoeba-like radiolarian has striking needlelike pseudopods. accumulations of their tests to the fossil record for more than 200 million years. Because of the excellent preservation of their test... |
ctures of these plates and the flagella are usually located within these grooves, one encircling the body like a belt, and the other perpendicular to it. By beating in their respective grooves, these flagella cause the dinoflagellate to rotate like a top as it moves. The dinoflagellates that are clad in stiff cellulose... |
frequently in coastal areas are often associated with great population explosions, or “blooms,” of dinoflagellates. The pigments in the individual, microscopic cells of the dinoflagellates are responsible for the color of the water. Red tides have a profound, detrimental effect on the fishing industry in the United St... |
small and nonfunctional. If they are put back in the light, they may become green within a few hours. Normally photosynthetic euglenoids may sometimes feed on dissolved or particulate food. Individual euglenoids range from 10 to 500 micrometers long and are highly variable in form. Interlocking proteinaceous strips ar... |
: The Diatoms and Golden Algae The Diatoms. Diatoms, members of the phylum Chrysophyta, are photosynthetic, unicellular organisms with unique double shells made of opaline silica, which are often strikingly and characteristically marked. The shells of diatoms are like small boxes with lids, one half of the shell fittin... |
. If fusion occurs, the resulting zygote regenerates a full-sized individual. In some freshwater diatoms, the gametes are amoeboid and similar in appearance. The Golden Algae. Also included within the Chrysophyta are the golden algae, named for the yellow and brown carotenoid and xanthophyll accessory pigments in their... |
. In addition to these uses, red algae such as Porphyra, called “nori,” are eaten and, in Japan, are even cultivated as a human food crop. The life cycles of red algae are complex but usually involve an alternation of generations (sporic meiosis). None of the red algae have flagella or cilia at any stage in their life ... |
haploid, swimming spores after meiosis, are formed on the sporophytes. These spores divide by mitosis, giving rise to individual gametophytes. There are two kinds of gametophytes in the kelps; one produces sperm, and the other produces eggs. If sperm and eggs fuse, the resulting zygotes grow into the mature kelp sporo... |
of mating with each other when syngamy does take place, although both may divide asexually to reproduce themselves. Among the unicellular green algae, Chlamydomonas (figure 35.15) is a well-known genus. Individuals are microscopic (usually less than 25 micrometers long), green, rounded, and have two flagella at the an... |
sphere made up of a single layer of 500 to 60,000 individual cells, each cell with two flagella. Only a small number of the cells are reproductive. The colony has definite anterior and posterior ends, and the flagella of all of the cells beat in such a way as to rotate the colony in a clockwise direction as it moves f... |
this genus, often more than 10 centimeters across, consist of undulating sheets only two cells thick. Sea lettuce attaches by protuberances of the basal cells to rocks or other substrates. The reproductive cycle of Ulva involves an alternation of generations (sporic meiosis; figure 35.16) as is typical among green alg... |
iving and parasitic organisms. Many zoomastigotes apparently reproduce only asexually, but sexual reproduction occurs in some species. The members of one order, the kinetoplastids, include the genera Trypanosoma (figure 35.17c) and Crithidia, pathogens of humans and domestic animals. The euglenoids could be viewed as a... |
elaborate genetic mechanism for repeatedly changing the antigenic nature of their protective glycoprotein coat, thus dodging the antibodies their hosts produce against them (see chapter 57). Only a single one out of some 1000 to 2000 variable antigen genes is expressed at a time. Rearrangements of these genes during t... |
sleeping sickness. (a) Trypanosoma among red blood cells. The nuclei (dark-staining bodies), anterior flagella, and undulating, changeable shape of the trypanosomes are visible in this photograph (500×). (b) The tsetse Another order of zoomastigotes, the choanoflagellates, is most likely the group from which the spong... |
humans and under what circumstances are not known with certainty. FIGURE 35.19 Giardia lamblia. Giardia are flagellated unicellular parasites that infect the human intestine. Giardia are very primitive, having only a rudimentary cytoskeleton and lacking mitochondria and chloroplasts. Sequencing of ribosomal RNA sugges... |
apparently normal diploid chromosomes, divide by meiosis and are able to undergo genetic recombination. Macronuclei are derived from certain micronuclei in a complex series of steps. Within the macronuclei are multiple copies of the genome, and the DNA is divided into small pieces—smaller than individual chromosomes. ... |
.22b,c). Only cells of two different genetically determined mating types, odd and even, are able to conjugate. Meiosis in the micronuclei of each individual produces several haploid micronuclei, and the two partners exchange a pair of these micronuclei through a cytoplasmic bridge that appears between the two partners.... |
but they involve the accumulation of a protein, which is now being studied. The zoomastigotes are a highly diverse group of flagellated unicellular heterotrophs, containing among their members the ancestors of animals as well as the very primitive Giardia. Ciliates possess characteristic cilia, and have two types of n... |
to obtain blood, it injects saliva mixed with an anticoagulant. If the mosquito is infected with Plasmodium, it will also inject the elongated sporozoites into the bloodstream of its victim. The parasite makes its way through the bloodstream to the liver, where it rapidly divides asexually. After this division phase, ... |
. The disease may be brought under control by the person’s immune system or by drugs. As discussed in chapter 21, some individuals are genetically resistant to malaria. Other persons develop immunity to it. Efforts to eradicate malaria have focused on (1) the elimination of the mosquito vectors; (2) the development of ... |
ite antigen was cloned in 1984, but it is not certain how effective a vaccine against sporozoites might be. When a mosquito inserts its proboscis into a human blood vessel, it injects about a thousand sporozoites. They travel to the liver within a few minutes, where they are no longer exposed to antibodies circulating ... |
in chapter 36. Filamentous structures of fungi and, by convention, those of oomycetes, are called hyphae. Most oomycetes live in fresh or salt water or in soil, but some are plant parasites that depend on the wind to spread their spores. A few aquatic oomycetes are animal parasitessingular, Oomycetes are distinguished... |
olds cause fish diseases, producing a kind of white fuzz on aquarium fishes. Among their terrestrial relatives are oomycetes of great importance as plant pathogens, including Plasmopara viticola, which causes downy mildew of grapes, and Phytophthora infestans, which causes the late blight of potatoes. This oomycete was... |
aggregate and form a compound, motile mass. The aggregation of the individual amoebas is induced by pulses of cyclic adenosine monophosphate (cAMP), which the cells begin to secrete when they are starving. The cells form an aggregate organism that moves to a new area where food is more plentiful. In the new area, the ... |
a microscope. They are able to pass through the mesh in cloth or simply flow around or through other obstacles. As they move, they engulf and digest bacteria, yeasts, and other small particles of organic matter. Plasmodia contain many nuclei (multinucleate), but these are not separated by cell membranes. The nuclei un... |
ia. Meiosis occurs in the spores once they have formed within the sporangium. MEIOSIS Young sporangium Initiation of sporangium formation Spores (n) Mature sporangium Mature spore Germinating spore 2n n Amoeboid gametes Flagellated gametes Diploid plasmodium (2n) Zygote SYNGAMY FIGURE 35.27 Life cycle of a plasmodial s... |
. What unique characteristic differentiates the members of Ciliophora from other protists? What is the function of two vacuoles exhibited by most members of Ciliophora? 6. Why has it been so difficult to produce a vaccine for trypanosome-caused diseases? 7. What differentiates the oomycetes from the kingdom Fungi, in w... |
. Unlike any plant, all fungi are filamentous heterotrophs with cell walls made of chitin. The Body of a Fungus. Cytoplasm flows from one cell to another within the filamentous body of a fungus. How Fungi Reproduce. Fungi reproduce sexually when filaments of different fungi encounter one another and fuse. How Fungi Obt... |
At first glance, a mushroom looks like a funny kind of plant growing up out of the soil. However, when you look more closely, fungi turn out to have nothing in common with plants except that they are multicellular and grow in the ground. As you will see, the more you examine fungi, the more unusual they are. 719 36.1 ... |
). You could build a much longer list, but already the take-home lesson is clear: fungi are not like plants at all! Their many unique features are strong evidence that fungi are not closely related to any other group of organisms. DNA studies confirm significant differences from other eukaryotes. Fungi absorb their foo... |
from the Greek word for fungus, myketos. The mycelium of a fungus (figure 36.4) constitutes a system that may, in the aggregate, be many meters long. This mycelium grows through and penetrates its substrate, resulting in a unique relationship between the fungus and its environment. All parts of such a fungus are metab... |
ae, is growing through leaves on the forest floor in Maryland. Chapter 36 Fungi 721 How Fungi Reproduce Fungi are capable of both sexual and asexual reproduction. When a fungus reproduces sexually it forms a diploid zygote, as do animals and plants. Unlike animals and plants, all fungal nuclei except for the zygote are... |
of this, fungal spores may be blown great distances from their place of origin, a factor in the extremely wide distributions of many kinds of fungi. Unfortunately, many of the fungi that cause diseases in plants and animals are spread rapidly and widely by such means. The spores of other fungi are routinely dispersed ... |
focus as a single circular clone. The large patch at the bottom of the picture is almost 8 hectares in diameter. The largest clone measured so far has been 15 hectares in diameter—pretty impressive for a single individual! Ecology of Fungi Fungi, together with bacteria, are the principal decomposers in the biosphere. ... |
algae or cyanobacteria. They are prominent nearly everywhere in the world, especially in unusually harsh habitats such as bare rock. Mycorrhizae, specialized mutualistic symbiotic associations between the roots of plants and fungi, are characteristic of about 90% of all plants. In each of them, the photosynthetic orga... |
i ) FIGURE 36.7 The four major groups of fungi. The imperfect fungi are not a true phylum, but rather a collection of fungi in which sexual structures have not been identified. Table 36.1 Fungi Phylum Typical Examples Key Characteristics Ascomycota Yeasts, truffles, morels Develop by sexual means; ascospores are formed... |
nuclei have fused, forming diploid zygote nuclei, the area where the fusion has taken place develops into an often massive and elaborate zygosporangium. A zygosporangium may contain one or more diploid nuclei and acquires a thick Spores Sporangium MEIOSIS (occurs during germination) coat. The zygosporangium helps the ... |
ota The second phylum of fungi, the ascomycetes (phylum Ascomycota), is a very large group of about 32,000 named species, with more being discovered each year. Among the ascomycetes are such familiar and economically important fungi as yeasts, common molds, morels (figure 36.9a,b), and truffles. Also included in this p... |
ae then arise from the area of the fusion. Throughout such hyphae, Ascospore Asexual reproduction by spores (conidia) – Strain Trichogyne Each haploid nucleus divides once by mitosis MEIOSIS Young ascus Zygote + Strain Monokaryotic n 2n Dikaryotic Ascogonium Antheridium Plasmogamy (cytoplasmic bridge allows strain nucl... |
reproduction is asexual and takes place by cell fission or budding, when a smaller cell forms from a larger one (figure 36.10). Sometimes two yeast cells will fuse, forming one cell containing two nuclei. This cell may then function as an ascus, with syngamy followed immediately by meiosis. The resulting ascospores fu... |
ote to be sequenced entirely, was completed. With their rapid generation time and a rapidly increasing pool of genetic and biochemical information, the yeasts in general and S. cerevisiae in particular are becoming the eukaryotic cells of choice for many types of experiments in molecular and cellular biology. Yeasts ha... |
aryotic hyphae after spore germination. These hyphae lack septa at first. Eventually, septa form between the nuclei of the monokaryotic hyphae. A basidiomycete mycelium made up of monokaryotic hyphae is called a primary mycelium. Different mating types of monokaryotic hyphae may fuse, forming a dikaryotic or secondary ... |
particular nonsexual strain has been derived usually can be determined by the features of its hyphae and asexual reproduction. It cannot, however, be classified by the standards of that group because the classification systems are based on the features related to sexual reproduction. One consequence of this system is ... |
. The great majority of the imperfect fungi are clearly ascomycetes. (b) (c) FIGURE 36.12 The imperfect fungi. (a) Verticillium alboatrum (1350×), an important pathogen of alfalfa, has whorled conidiophores. The single-celled conidia of this member of the imperfect fungi are borne at the ends of the conidiophores. (b) ... |
enabled lichens to invade the harshest habitats at the tops of mountains, in the farthest northern and southern latitudes, and on dry, bare rock faces in the desert. In harsh, exposed areas, lichens are often the first colonists, breaking down the rocks and setting the stage for the invasion of other organisms. Lichen... |
fungus” and “roots”). The fungi in mycorrhizae associations function as extensions of the root system. The fungal hyphae dramatically increase the amount of soil contact and total surface area for absorption. When mycorrhizae are present, they aid in the direct transfer of phosphorus, zinc, copper, and other nutrients ... |
willows. The fungal components in most ectomycorrhizae are basidiomycetes, but Ectomycorrhizae Endomycorrhizae (a) (b) FIGURE 36.15 Endomycorrhizae and ectomycorrhizae. (a) In endomycorrhizae, fungal hyphae penetrate and branch out in the root cells of plants. In ectomycorrhizae, fungal hyphae do not penetrate root ce... |
of the fungal cell wall? Why is this composition an advantage to the fungi? 3. Which fungal nuclei are diploid? Which are haploid? To what do the following terms refer: heterokaryotic, homokaryotic, dikaryotic, and monokaryotic? 36.2 Fungi are classified by their reproductive structures. • There are three phyla of fun... |
(almost always ascomycetes), which derive their nutrients from green algae, cyanobacteria, or both. • Mycorrhizae are mutualistic symbiotic associations between fungi and plants. Endomycorrhizae, more common, involve zygomycetes, while ectomycorrhizal fungi are mainly basidiomycetes. 9. What are lichens? Which fungal ... |
to germinate when conditions are favorable. Gymnosperms. gametophyte (ovule) is not completely enclosed by sporophyte tissue at the time of pollination by male gametophytes (pollen). Angiosperms. In angiosperms, the ovule is completely enclosed by sporophyte tissue at the time of pollination. Angiosperms, by far the m... |
but close relatives are believed to exist in freshwater lakes today. DNA sequence data is consistent with the claim that a single “Eve” gave rise to the entire kingdom Plantae 450 million years ago. At each subsequent step in evolution, the evidence suggests that only a single family of plants made the transition. The... |
provides an effective barrier to water loss. This solution creates another problem by limiting gas exchange essential for respiration and photosynthesis. Water and gas diffusion into and out of a plant occurs through tiny mouth-shaped openings called stomata (singular, stoma). The evolution of leaves resulted in incre... |
A generalized plant life cycle. Anything yellow is haploid and anything blue is diploid. Note that both haploid and diploid individuals can be multicellular. Also, spores are produced by meiosis while gametes are produced by mitosis. In turn, the haploid gametophyte produces haploid gametes by mitosis. When the gamete... |
progressive reduction of the gametophyte from group to group, a loss of multicellular gametangia (structures in which gametes are produced), and increasing specialization for life on the land, culminating with the remarkable structural adaptations of the flowering plants, the dominant plants today. Similar trends must... |
cells are haploid. Water may rise up a strand of specialized cells in the center of a moss gametophyte axis, but most water used by the plant travels up the outside of the plant. Some mosses 738 Part X Plant Form and Function also have specialized food-conducting cells surrounding those that conduct water Multicellula... |
pollution and are rarely found in abundance in or near cities or other areas with high levels of air pollution. Some mosses, such as the peat mosses (Sphagnum), can absorb up to 25 times their weight in water and are valuable commercially as a soil conditioner, or as a fuel when dry. Liverworts (Hepaticophyta) The old... |
ium n 2n Male Female Gametophytes Sporangium Bud Rhizoid Mitosis Germinating spores MEIOSIS Spores Developing sporophyte in archegonium Mature sporophyte Parent gametophyte FIGURE 37.5 Life cycle of a typical moss. The majority of the life cycle of a moss is in the haploid state. The leafy gametophyte is photosynthetic... |
vasculum, meaning a “vessel or duct.” These tissues consist of strands of specialized cylindrical or elongated cells that form a network throughout a plant, extending from near the tips of the roots, through the stems, and into true leaves. One type of vascular tissue, the xylem, conducts water and dissolved minerals ... |
specialized stems, leaves, roots, cuticles, and stomata. Many have seeds which protect embryos until conditions are suitable for further development. Table 37.1 The Nine Phyla of Extant Vascular Plants Phylum Examples Key Characteristics Anthophyta Flowering plants (angiosperms) Heterosporous seed plants. Sperm not mo... |
elike, in whorls, nonphotosynthetic at maturity. One genus. Homosporous vascular plants. Sperm motile. External water necessary for fertilization. No differentiation between root and shoot. No leaves; one of the two genera has scalelike enations and the other leaflike appendages. Heterosporous vascular seed plants. Spe... |
centimeter in diameter—as seen in small aquatic ferns such as Azolla—or more than 24 meters tall and with leaves up to 5 meters or more long in the tree ferns (figure 37.9). The sporophytes and the smaller gametophytes, which rarely reach 6 millimeters in diameter, are both photosynthetic. The fern life cycle differs ... |
are photosynthetic and can live independently. Water is necessary for fertilization. The gametes are released on the underside of the gametophyte and swim in moist soil to neighboring gametophytes. Spores are dispersed by wind. Adult sporophyte Rhizome The sperm formed in the antheridia have flagella, with which they ... |
to 18 millimeters long. They form saprobic or parasitic associations with fungi, which furnish their nutrients. Some develop elements of vascular tissue and have the distinction of being the only gametophytes known to do so. Club Mosses (Lycophyta) The club mosses are worldwide in distribution but are most abundant in... |
a much larger and more conspicuous sporophyte, with vascular tissue. Many have well-differentiated roots, stem, and leaves. The shift to a dominant sporophyte lead to the evolution of trees. 37.4 Seeds protect and aid in the dispersal of plant embryos. Seed Plants Seed plants first appeared about 425 million years ago... |
iosis. antheridium The male sperm-producing structure found in the gametophytes of seedless plants and certain fungi. archegonium The multicellular eggproducing structure in the gametophytes of seedless plants and gymnosperms. carpel A leaflike organ in angiosperms that encloses one or more ovules; a unit of a gynoeciu... |
protective layer of a seed; it develops from the integument or integuments. spore A haploid reproductive cell, produced when a diploid spore mother cell undergoes meiosis; it gives rise by mitosis to a gametophyte. sporophyte The multicellular, diploid phase of a plant life cycle; it is the generation that ultimately ... |
feet) in height. Another conifer, the bristlecone pine (Pinus longaeva) of the White Mountains of California is the oldest living tree; one is 4900 years of age. Conifers are found in the colder temperate and sometimes drier regions of the world, especially in the northern hemisphere. They are sources of timber, paper... |
, which are produced in male cones that develop in clusters of 30 to 70, typically at the tips of the lower branches; there may be hundreds of such clusters on any single tree. The male cones generally are 1 to 4 centimeters long and consist of small, papery scales arranged in a spiral or in whorls. A pair of microspor... |
cone (2nd year) Pollen tube FERTILIZATION (15 months after pollination) Embryo M E I O S I S Microspore mother cell 2n Longisection of seed, showing embryo Pine seed Pollen-bearing cone Scale Megaspore mother cell Seedling Ovulate (seed-bearing) cone Sporophyte FIGURE 37.13 Life cycle of a typical pine. The male and f... |
attain heights of 15 meters or more. Unlike palm trees—which are flowering plants—cycads produce cones and have a life cycle similar to that of pines. The female cones, which develop upright among the leaf bases, are huge in some species and can weigh up to 45 kilograms. The sperm of cycads, although conveyed to an ar... |
Java for its tender shoots, which are cooked as a vegetable. Ginkgo (Ginkgophyta) The fossil record indicates that members of the Ginkgo family were once widely distributed, particularly in the northern hemisphere; today only one living species, the maidenhair tree (Ginkgo biloba), remains. The tree, which sheds its l... |
most basal, living angiosperm— Amborella trichopoda (figure 37.15). This has ended the debate between the supporters of magnolias and those of water lilies as the closest relatives of the original angiosperm. Amborella, with small, cream-colored flowers, is even more primitive than either the magnolias or water lilies... |
considered to be modified stems bearing modified leaves. Regardless of their size and shape, they all share certain features (see figure 37.16). Each flower originates as a primordium that develops into a bud at the end of a stalk called a pedicel. The pedicel expands slightly at the tip into a base, the receptacle, t... |
.16). The ovary is the swollen base, which contains from one to hundreds of ovules; the ovary later develops into a fruit. The tip of the pistil is called a stigma. Most stigmas are sticky or feathery, causing pollen grains that land on them to adhere. Typically there is a neck or stalk called a style connecting the st... |
Stalk of ovule (funiculus) While the female gametophyte is developing, a similar but less complex process takes place in the anthers. Most anthers have patches of tissue (usually four) that eventually become chambers lined with nutritive cells. The tissue in each patch is composed of many diploid microspore mother cel... |
, the generative nucleus, lags behind. This nucleus divides, ei- Microspore mother cells (2n) MEIOSIS Anther (2n) Generative cell Tube nucleus Mitosis Sperm Tube nucleus Stigma Megaspore mother cell (2n) Microspores (n) Pollen grains (microgametophytes) (n) Megaspore (n) Pollen tube MEIOSIS Ovule 2n n Mitosis Egg Style... |
uments harden and become the seed coat of a seed. The haploid cells remaining in the embryo sac (antipodals, synergid, tube nucleus) degenerate. There is some evidence for a type of double fertilization in gymnosperms believed to be closely related to the angiosperms. Further studies of this and of fertilization in Amb... |
usually nutritionally dependent on the gametophytes, which are more conspicuous and photosynthetic. 3. Distinguish between male gametophytes and female gametophytes. Which specific haploid spores give rise to each of these? 4. What reproductive limitations would a moss tree (if one existed) face? 37.3 Seedless vascula... |
. Primary and Secondary Growth. Different meristems allow plants to grow in both height and circumference. 38.2 Plants have three basic tissues, each composed of several cell types. Dermal Tissue. This tissue forms the “skin” of the plant body, protecting it and preventing water loss. Ground Tissue. Much of a young pla... |
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