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improving the productivity of existing crops, although the search for new crops continues. 3. What three species supply more than half of the human energy requirements on earth? How many plants supply over 90%? 30.3 Human activity is placing the environment under increasing stress. • Human activities present many chal... |
Hot Spots. Some geographic areas are particularly rich in species that occur nowhere else. What’s So Bad about Losing Biodiversity? Biodiversity is of considerable direct economic value, and provides key support to the biosphere. 31.2 Vulnerable species are more likely to become extinct. Predicting Which Species Are V... |
We finish with a review of recovery efforts at the species and community level. 625 31.1 The new science of conservation biology is focused on conserving biodiversity. Overview of the Biodiversity Crisis Extinction is a fact of life, as normal and necessary as species formation is to a stable world ecosystem. Most spe... |
climate change, but that hypothesis doesn’t explain why the end of earlier ice ages was not associated with mass extinctions, nor does it explain why extinctions occurred primarily among larger animals, with smaller species relatively unaffected). 626 Part VIII The Global Environment FIGURE 31.2 North America before h... |
0.05 0.1 0.01 0.2 Source: Reid and Miller, 1989; data from various sources. *There has been an alarming decline in amphibian populations recently, and many species may be on the verge of extinction. in table 31.1, based on the best available evidence, shows recorded extinctions from 1600 to the present. These estimate... |
majority of extinctions have occurred on islands, with birds and mammals particularly affected (although this may reflect to some degree our more limited knowledge of other groups). species. Moreover, although species diversity usually recovers after a few million years, this is a long time to deny our descendants the... |
destruction with consequent species extinctions. In Madagascar, it is estimated that 90% of the Table 31.2 Numbers of Endemic Vertebrate Species in Some “Hot Spot” Areas Region Mammals Reptiles Amphibians Atlantic coastal Brazil Colombian Chocó Philippines Northern Borneo Southwestern Australia Madagascar Cae region (... |
prescription and nonprescription drugs used today have active ingredients extracted from plants or animals. Aspirin, the world’s most widely used drug, was first extracted from the leaves of the tropical willow, Salix alba. The rosy periwinkle, Catharanthus roseus, from Madagascar has yielded potent drugs for combatin... |
and Aesthetic Value Many people believe that preserving biodiversity is an ethical issue, feeling that every species is of value in its own right, even if humans are not able to exploit or benefit from it. It is clear that humans have the power to exploit and destroy other species, but it is not as ethically clear tha... |
affect a population. The smaller the population, the more likely it is that a random event, such as a disease epidemic or an environmental disturbance (such as a flood or a fire) could decimate a population and lead to extinction. Similarly, small populations are most likely to lose genetic variation due to genetic dr... |
history later in this chapter). Without whales to keep their numbers in check, ocean zooplankton thrived, leading in turn to proliferation of a species of fish called pollock that feed on the now-abundant zooplankton. Given this ample food supply, the pollock proved to be very successful competitors of other northern ... |
Kelp forests Severely thinned by the sea urchins, the kelp beds no longer support a diversity of fish species, which may lead to a decline in populations of eagles that feed on the fish. Sea urchins Usually the preferred food of sea otters, sea urchin populations now exploded and fed on kelp. Sea otters Sea otter popu... |
in the individual is the forerunner of death—to feel no surprise at sickness, but when the sick man dies, to wonder and to suspect that he dies of some deed of violence.” Although long-term trends toward smaller population numbers suggest that a species may be at risk in future years, abrupt recent declines in populat... |
example of overharvesting of a socalled commercial species is the commercial harvesting of fish in the North Atlantic. Fishing fleets continued to harvest large amounts of cod off Newfoundland during the 1980s, even as the population numbers declined precipitously. By 1992 the cod population had dropped to less than 1... |
35 68 58 53 77 78 23 11 32 4 54 30 63 29 12 20 22 42 30 6 28 17 14 28 12 1 6 3 2 36 37 21 48 — — — — — *Some species may be influenced by more than one factor; thus, some rows may exceed 100%. Source: Reid and Miller, 1989. Chapter 31 Conservation Biology 633 Habitat Loss As figure 31.8 and table 31.3 indicate, habita... |
and North America, for example, have been essentially sterilized by acid rain. Human Disruption Africa Before human colonization 1950 1985 FIGURE 31.9 Extinction and habitat destruction. The rain forest covering the eastern coast of Madagascar, an island off the coast of East Africa, has been progressively destroyed a... |
on the edge are exposed to direct sunlight and, consequently, hotter and drier conditions than they are accustomed to in the cool, moist forest interior. As a result, within 100 meters of the forest edge, tree biomass decreased by 36% in the first 17 years after fragment isolation in one study. Also, increasing habita... |
but sometimes called “whalebone” even though it is actually made of keratin, like fingernails) was used in undergarments. Because a whale is such a large animal, each individual captured is of significant commercial value. Right whales were the first to bear the brunt of commercial whaling. They were called right whal... |
, out of a world population estimated to have been 100,000. 30 25 20 15 10 1910 Fin Sperm Blue Minke Sei Humpback 1920 1930 1940 1950 1960 1970 1980 1990 Year FIGURE 31.14 A history of commercial whaling. These data show the world catch of whales in the twentieth century. Each species in turn is hunted until its number... |
runoff and sewage from towns and villages had led to algal blooms that severely depleted oxygen levels in deeper parts of the lake. Cichlids feed on algae, and initially their population numbers are thought to have risen in response to this increase in their food supply, but unlike similar algal blooms of the past, th... |
but are now confined to under 700,000 acres (table 31.4). Their ecological niche devastated, populations of the black-footed ferret collapsed. Increasingly rare in the second half of the century, the black-footed ferret was thought to have gone extinct in the late 1970s, when the only known wild population—a small col... |
Kansas Montana Nebraska New Mexico North Dakota Oklahoma South Dakota Texas Wyoming 1899-1990 unknown 7,000,000 2,500,000 6,000,000 6,000,000 12,000,000 2,000,000 950,000 1,757,000 56,833,000 16,000,000 1998 extinct 44,000 36,000 65,000 60,000 15,000 20,400 9,500* 244,500 22,650 70,000–180,000 Loss of its natural prey... |
population sizes and a mating ritual where one male may dominate a flock, the Illinois prairie chickens had lost so much genetic variability as to create serious inbreeding problems. To test this idea, biologists at the University of Illinois compared DNA from frozen tissue samples of birds that died in Illinois betwe... |
more variable birds appears to have reversed the decline. Chapter 31 Conservation Biology 639 Case Study: Habitat Loss and Fragmentation—Songbirds Every year since 1966, the U.S. Fish and Wildlife Service has organized thousands of amateur ornithologists and bird watchers in an annual bird count called the Breeding Bi... |
ope 13C. Plants growing in the best overwintering habitats in Jamaica and Honduras (mangroves and wetland forests) have low levels of 13C, and so do the redstarts that feed on them. Sixty-five percent of the wet forest birds maintained or gained weight over the winter. Plants growing in substandard dry scrub, by contra... |
and protect the threatened species. If the cause is habitat loss, plans can be instituted to restore lost habitat. Loss of genetic variability in isolated subpopulations can be countered by transplanting individuals from genetically different populations. Populations in immediate danger of extinction can be captured, ... |
the introduced species. Restoration of the oncediverse cichlid fishes to Lake Victoria will require more than breeding and restocking the endangered species. Eutrophication will have to be reversed, and the introduced water hyacinth and Nile perch populations brought under control or removed. It is important to act qu... |
of 1986, over 850 birds had been released in 13 eastern states, producing an astonishingly strong recovery (figure 31.22). Case History: The California Condor. Numbers of the California condor (Gymnogyps californianus), a large vulturelike bird with a wingspan of nearly 3 meters, have been declining gradually for the ... |
. The wolves adapted well, breeding so successfully that by 1998 the park contained nine free-ranging packs, a total of 90 wolves. While ranchers near the park have been unhappy about the return of the wolves, little damage to livestock has been noted, and the ecological equilibrium of Yellowstone Park seems well on th... |
is not a practical possibility. A more feasible solution would be to move individuals between populations. Managing the black rhino populations for genetic diversity could fully restore the species to its original numbers and much of its range. Placing black rhinos from a number of different locations together in a sa... |
on these bats for pollination. Some have evolved features like night-blooming flowers that prevent any other potential pollinators from taking over the role of the fruit bats. In Guam, where the two local species of flying fox have recently been driven extinct or nearly so, the impact on the ecosystem appears to be su... |
habitat of such a size are doomed to failure. As it has become clear that isolated patches of habitat lose species far more rapidly than large preserves do, conservation biologists have promoted the creation, particularly in the tropics, of so-called megareserves, large areas of land containing a core of one or more u... |
Costa Rica. Costa Rica has placed about 12% of its land into national parks and eight megareserves. Santa Rosa-Guanacaste N.P. Rincón de la NICARAGUA Caño Negro N.W.R. Vieja N.P. Lomas Barbudal Biological Reserve Lake Arenal La Selva Biological Station Barra del Colorado N.W.R. Caribbean Sea Palo Verde N.P. Barra Hond... |
by the species-area relationship, a reduced habitat will support fewer numbers of species. • This reduction in habitat can occur in four different ways: a habitat can be completely removed or destroyed, a habitat can become fragmented and disjunct, a habitat can be degraded or altered, or a habitat can become too freq... |
, medicine, fuel, and aesthetics) to our quality of life and financial well being, as well as contribute to ecosystem stability. 31.2 Vulnerable species are more likely to become extinct. • Species are more in danger of going extinct if they have a limited geographic distribution, a small and/or declining population si... |
stochasticity genetic stochasticity metapopulations 31.3 edge effects 31.4 community importance megareserves LEARNING BY EXPERIENCE 1. Consider the following scenario: you are the leader of a tropical country that is very poor, has a rapidly growing human population, and is rapidly losing its forests for three main re... |
of endemic species? a. Florida b. Texas c. Alaska d. New York e. California 6. What terms apply to solutions to the biodiversity crisis? 14. When talking about biodiversity, the term “hot 7. Why are megareserves effective? 8. Using the plight of the black rhinoceros as an example, explain how recovery plans for endang... |
overexploitation of it by humans? a. black-footed ferret b. peregrine falcon c. Lake Victoria cichlids d. right whales e. all of the above 24. Eutrophication is linked to the death and song birds extinction of a. b. passenger pigeons c. humpback whales d. prairie chickens e. Lake Victoria cichlids 25. In what year did... |
support to help. 2. can never get back to the exact same environmental conditions and the exact same species assemblages; ecosystems are too complex; the restoration will have a different starting point and there will be different influences and interactions over time than would have occurred in the original ecosystem... |
the biodiversity crisis are complex, expensive and must be multidimensional *7. megareserves are effective because they recognize human and economic needs and provide limited-use buffer zones around the protected core areas *8. black rhinos illustrate that in trying to increase genetic diversity, unique adaptations of... |
. It infects only humans and our close relatives—chimpanzees and tamarins. Because it is very expensive to maintain these animals in research laboratories, only small numbers of animals can be employed in any one study. Thus, the virus could not be isolated by the traditional means of purification from extracts of infe... |
infected animals contains antibodies directed against a broad range of HCV proteins encountered while combating the animal's HCV infection. The serum can thus be used as a probe for the presence of HCV proteins in other cells. Out of a million bacterial clones tested, just one was found that reacted with the chimp HCV ... |
. Sexual transmission does not seem likely, although the possibility is still being investigated. Married partners of infected individuals rarely get the virus, and its incidence among promiscuous gay men is no higher than among the population at large. 648 Part IX Viruses and Simple Organisms Why not move vigorously t... |
system. Species Names. Every kind of organism is assigned a unique name. The Taxonomic Hierarchy. The higher groups into which an organism is placed reveal a great deal about the organism. What Is a Species? Species are groups of similar organisms that tend not to interbreed with individuals of other groups. 32.2 Scie... |
animals. He classified animals as either land, water, or air dwellers, and he divided plants into three kinds based on stem differences. This simple classification system was expanded by the Greeks and Romans, who grouped animals and plants into basic units such as cats, horses, and oaks. Eventually, these units began... |
oak, Quercus rubra. Although they are both oaks (Quercus), these two species differ sharply in leaf shape and size and in many other features, including geographical range. books, employed the polynomial system. But as a kind of shorthand, Linnaeus also included in these books a twopart name for each species. For exam... |
a standard and precise way of communicating, whether the language of a particular biologist is Chinese, Arabic, Spanish, or English. This is a great improvement over the use of common names, which often vary from one place to the next. As you can see in figure 32.3, corn in Europe refers to the plant Americans call wh... |
recognize six kingdoms: two kinds of bacteria (Archaebacteria and Eubacteria), a largely unicellular group of eukaryotes (Protista), and three multicellular groups (Fungi, Plantae, and Animalia). In order to remember the seven categories of the taxonomic hierarchy in their proper order, it may prove useful to memorize... |
first recognized as a eukaryote (domain: Eukarya). Second, within this domain, it is an animal (kingdom: Animalia). Among the different phyla of animals, it is a vertebrate (phylum: Chordata, subphylum: Vertebrata). The organism’s fur characterizes it as a mammal (class: Mammalia). Within this class, it is distinguish... |
among alternative species concepts relates to solving this problem. When do we assign fossil specimens a unique species name, and when do we assign them to species living today? If we trace the lineage of two sister species backwards through time, how far must we go before the two species converge on their common ance... |
. Species are groups of organisms that differ from one another in recognizable ways and generally do not interbreed with one another in nature. Chapter 32 How We Classify Organisms 653 32.2 Scientists construct phylogenies to understand the evolutionary relationships among organisms. Evolutionary Classifications After ... |
omorphy. The key to the approach is being able to identify morphological, physiological, or behavioral traits that differ among the organisms being studied and can be attributed to a common ancestor. By examining the distribution of these traits among the organisms, it is possible to construct a clado- 654 Part IX Viru... |
derived character, and a “0” indicates the absence of the trait. A tree, or cladogram, diagrams the proposed evolutionary relationships among the organisms based on the presence of derived characters. The derived characters between the cladogram branch points are shared by all organisms above the branch point and are ... |
Reflecting the importance of evolutionary processes to all fields of biology, most taxonomy today includes at least some element of cladistic analysis. Chapter 32 How We Classify Organisms 655 Class Mammalia Class Reptilia Class Aves Mammalia Reptilia Archosaurs Mammals Turtles Crocodilians Birds Lizards and snakes Ma... |
to guide character weighting, while cladistics is a good approach when little information is available about how the character affects the life of the organism. DNA sequence comparisons, for example, lend themselves well to cladistics—you have a great many derived characters (DNA sequence differences) but little or no... |
When the full genomic DNA sequences of an archaebacterium and a eubacterium were first compared in 1996, the differences proved striking. Archaebacteria are as different from eubacteria as eubacteria are from eukaryotes. Recognizing this, biologists are increasingly adopting a classification of living organisms that r... |
of which contradict each other. It appears that during their early evolution microorganisms have swapped genetic information, making constructing phylogenetic trees very difficult. As an example of the problem, we can look at Thermotoga, a thermophile found on Volcano Island off Italy. The sequence of one of its RNAs ... |
diverged early from the evolutionary line that gave rise to the archaebacteria and eukaryotes. thermophilic archaebacteria form the basis of food webs around deep-sea thermal vents where they must withstand extreme temperatures and pressures. Other types, like Sulfolobus, inhabit the hot sulfur springs of Yellowstone ... |
The base of the tree was determined by examining genes that are duplicated in all three domains, the duplication presumably having occurred in the common ancestor. When one of the duplicates is used to construct the tree, the other can be used to root it. This approach clearly indicates that the root of the tree is wi... |
anebounded organelles Membrane lipid structure Nuclear envelope Number of different RNA polymerases Peptidoglycan in cell wall Response to the antibiotics streptomycin and chloramphenicol Chapter 32 How We Classify Organisms 659 Domain Eukarya (Eukaryotes) For at least 2 billion years, bacteria ruled the earth. No othe... |
ing organelles. Mitochondria and chloroplasts are both believed to have entered early eukaryotic cells by a process called endosymbiosis (endo, inside). We discussed the theory of the endosymbiotic origin of mitochondria and chloroplasts in chapter 5; also see figure 32.12. Both organelles contain their own ribosomes, ... |
tissues, and organs can be differentiated within the complex bodies of multicellular organisms. With such a functional division within its body, a multicellular organism can do many things, like protect itself, resist drought efficiently, regulate its internal conditions, move about, seek mates and prey, and carry out... |
. Except for gametes, the cells of most animals and plants are diploid, containing two sets of chromosomes, during some part of their life cycle. A few eukaryotes complete their life cycle in the haploid condition, with only one set of chromosomes in each cell. As we have seen, in diploid cells, one set of chromosomes ... |
is the only diploid cell. Such a life cycle is said to be characterized by zygotic meiosis, because the zygote immediately undergoes meiosis. 2. In most animals, the gametes are the only haploid cells. Animals exhibit gametic meiosis, meiosis producing gametes which fuse, giving rise to a zygote. 3. Plants show a regu... |
life that they do display is reproduction, which they do by hijacking the metabolism of living cells. Viruses thus present a special classification problem. Because they are not organisms, we cannot logically place them in any of the kingdoms. Viruses are really just complicated associations of molecules, bits of nucl... |
a into kingdoms. • There are perhaps 10 million species of plants, animals, fungi, and eukaryotic microorganisms, but only about 1.5 million of them have been assigned names. About 15% of the total number of species are marine; the remainder are mostly terrestrial. 1. What was the polynomial system? Why didn’t this sys... |
prokaryotes and eukaryotes? Explain. 6. From which of the four eukaryotic kingdoms have the other three evolved? 7. What is the apparent origin of the organelles found in almost all eukaryotes? 8. What defines if a collection of cells is truly multicellular? Did multicellularity arise once or many times in the evoluti... |
a virus have such a profound effect on living organisms? (30,000) We start our exploration of the diversity of life with viruses. Viruses are genetic elements enclosed in protein and are not considered to be organisms, as they cannot reproduce independently. Because of their diseaseproducing potential, viruses are imp... |
ometers in its greatest dimension. Biologists first began to suspect the existence of viruses near the end of the nineteenth century. European scientists attempting to isolate the infectious agent responsible for hoof-and-mouth disease in cattle concluded that it was smaller than a bacterium. Investigating the agent fu... |
. Individual viruses contain only a single type of nucleic acid, either DNA or RNA. The DNA or RNA genome may be linear or circular, and single-stranded or double-stranded. Viruses are frequently classified by the nature of their genomes. RNA-based viruses are known as retroviruses. Nearly all viruses form a protein sh... |
.3 The structure of a bacterial, plant, and animal virus. (a) Bacterial viruses, called bacteriophages, often have a complex structure. (b) TMV infects plants and consists of 2130 identical protein molecules (purple) that form a cylindrical coat around the single strand of RNA (green). The RNA backbone determines the s... |
” series (T1, T2, and so forth); others have been given different kinds of names. To illustrate the diversity of these viruses, T3 and T7 phages are icosahedral and have short tails. In contrast, the so-called T-even phages (T2, T4, and T6) have an icosahedral head, a capsid that consists primarily of three proteins, a... |
, is called a lysogenic cycle. Viruses that become stably integrated within the genome of their host cells are called lysogenic viruses or temperate viruses. Bacteriophages are a diverse group of viruses that attack bacteria. Some kill their host in a lytic cycle; others integrate into the host’s genome, initiating a l... |
by viral genes is provided by the bacterium responsible for an often-fatal human disease. The disease-causing bacteria Vibrio cholerae usually exists in a harmless form, but a second disease-causing, virulent form also occurs. In this latter form, the bacterium causes the deadly disease cholera, but how the bacteria c... |
is growing very rapidly in the United States. It is estimated that over 33 million people worldwide are infected with HIV. Many—perhaps all of them—will eventually come down with AIDS. Over 16 million people have died already since the outbreak of the epidemic. AIDS incidence is already very high in many African count... |
liver, and rabies to the brain. How does a virus such as HIV recognize a specific kind of target cell? Recall from chapter 7 that every kind of cell in the human body has a specific array of cell-surface glycoprotein markers that serve to identify them to other, similar cells. Each HIV particle possesses a glycoprotei... |
a virus enzyme that was also within the virus shell. This enzyme, called reverse transcriptase, synthesizes a double strand of DNA complementary to the virus RNA, often making mistakes and so introducing new mutations. This double-stranded DNA directs the host cell machinery to produce many copies of the virus. HIV do... |
segments). When combinations of these drugs were administered to people with HIV in controlled studies, their condition improved. A combination of a protease inhibitor and two AZT analog drugs entirely eliminated the HIV virus from many of the patients’ bloodstreams. Importantly, all of these patients began to receive... |
nef do not reproduce, as seen in the cases of the six Australians. Research is currently underway to develop a drug that targets the nef protein. Chemokines and CAF In the laboratory, chemicals called chemokines appear to inhibit HIV infection by binding to and blocking the CCR5 and CXCR4 coreceptors. As you might exp... |
CR5 or CXCR4 Chemokine blocking receptor CD4+ cell Mutated coreceptor CD4 CCR5 or CXCR4 Replication CAF FIGURE 33.8 Research is currently underway to develop new treatments for HIV. Among them are these five: (1) Combination therapy involves using two drugs, AZT to block replication of the virus and protease inhibitors... |
is easy to see why the late Sir Peter Medawar, Nobel laureate in Physiology or Medicine, wrote, “A virus is a piece of bad news wrapped in protein.” Viruses not only cause many human diseases, but also cause major losses in agriculture, forestry, and in the productivity of natural ecosystems. Influenza Perhaps the mos... |
URE 33.9 The influenza virus. (a) TEM of the so-called “bird flu” influenza virus, A(H5N1), which first infected humans in Hong Kong in 1997. (b) Diagram of an influenza virus. The coiled RNA has been revealed by cutting through the outer lipid-rich envelope, with its two kinds of projecting spikes, and the inner prote... |
Rarely fatal. Spread through contact with infected saliva. Vaccine available; rarely fatal. No cure. Acute infection of the lungs, often fatal without treatment. Acute viral infection of the CNS that can lead to paralysis and is often fatal. Prior to the development of Salk’s vaccine in 1954, 60,000 people a year cont... |
H3N2), then passed back to humans, creating an epidemic because the human population has never experienced that H N combination before. A potentially deadly new strain of flu virus emerged in Hong Kong in 1997, A(H5N1). Unlike all previous instances of new flu strains, A(H5N1) passed to humans directly from birds, in t... |
of Ebola virus in the summer of 1995 in Zaire killed 245 people out of 316 infected—a mortality rate of 78%. The latest outbreak occurred in Gabon, West Africa, in February 1996. The natural host of Ebola is unknown. Another type of emerging virus caused a sudden outbreak of a hemorrhagic-type infection in the southwe... |
brains of infected individuals. Mad cow disease spread widely among the cattle herds of England in the 1990s because cows were fed bone meal prepared from cattle carcasses to increase the protein content of their diet. Like the Fore, the British cattle were literally eating the tissue of cattle that had died of the di... |
that mice genetically engineered to lack Prusiner’s prion protein are immune to TSE infection. However, if brain tissue with the prion protein is grafted into the mice, the grafted tissue—but not the rest of the brain—can then be infected with TSE. In 1997, Prusiner was awarded the Nobel Prize in Physiology or Medicin... |
perate bacteriophages, upon entering a bacterial cell, insert their DNA into the cell genome, where they may remain integrated into the bacterial genome as a prophage for many generations. 33.3 HIV is a complex animal virus. • AIDS, a viral infection that destroys the immune system, is caused by HIV (human immunodefici... |
they may have complex internal membranes. 34.3 Bacteria exhibit considerable diversity in both structure and metabolism. Bacterial Diversity. There are at least 16 phyla of bacteria, although many more remain to be discovered. Bacterial Variation. Mutation and recombination generate enormous variation within bacterial... |
with the production of oxygen which lead to extreme bacterial and eukaryotic diversity. Bacteria play a vital role both in productivity and in cycling the substances essential to all other life-forms. Bacteria are the only organisms capable of fixing atmospheric nitrogen. About 5000 different kinds of bac- (a) (b) (c)... |
basic structures: bacillus (plural, bacilli) straight and rodshaped, coccus (plural, cocci) spherical-shaped, and spirillus (plural, spirilla) long and helical-shaped, also called spirochetes. Spirilla bacteria generally do not form associations with other cells and swim singly through their environments. They have a ... |
or less in diameter. Most eukaryotic cells are well over 10 times that size. 3. Chromosomes. Eukaryotic cells have a membranebound nucleus containing chromosomes made up of both nucleic acids and proteins. Bacteria do not have membrane-bound nuclei, nor do they have chromosomes of the kind present in eukaryotes, in wh... |
the formation of end products such as sulfur, sulfate, and oxygen (see chapter 10). Prokaryotic cells can also be chemoautotrophic, using the energy stored in chemical bonds of inorganic molecules to synthesize carbohydrates; eukaryotes are not capable of this metabolic process. Bacteria are the oldest and most abunda... |
rometers long, and about 7.5 to 10 nanometers thick. Pili help the bacterial cells attach to appropriate substrates and exchange genetic information. Some bacteria form thick-walled endospores around their chromosome and a small portion of the surrounding cytoplasm when they are exposed to nutrient-poor conditions. The... |
.7). Nucleoid region. Bacteria lack nuclei and do not possess the complex chromosomes characteristic of eukaryotes. Instead, their genes are encoded within a single double-stranded ring of DNA that is crammed into one region of the cell known as the nucleoid region. Many bacterial cells also possess small, independentl... |
ic acid sequencing especially looking at ribosomal RNA. Lynn Margulis and Karlene Schwartz proposed a useful classification system that divides bacteria into 16 phyla, according to their most significant features. Table 34.1 outlines some of the major features of the phyla we describe. Kinds of Bacteria Although they l... |
the cell. The cell walls of eubacteria are constructed of carbohydrate-protein complexes called peptidoglycan, which link together to create a strong mesh that gives the eubacterial cell wall great strength. The cell walls of archaebacteria lack peptidoglycan. 2. Plasma membranes. All bacteria have plasma membranes wi... |
bubonic plague and cholera. Gliding and budding bacteria Myxobacteria, Chondromyces Gram-negative bacteria. Exhibit gliding motility by secreting slimy polysaccharides over which masses of cells glide; some groups form upright multicelluar structures carrying spores called fruiting bodies. Pseudomonads Pseudomonas Gra... |
has a medium that includes special growth factors, while B has a medium that lacks some of these growth factors. Bacteria that are not mutated can produce their own growth factors and do not require them to be added to the medium. The colonies absent in B were unable to grow on the deficient medium and were thus mutan... |
species is exchanged with or transferred to E. coli by plasmids. Because of its abundance in the human digestive tract, E. coli poses a special threat if it acquires harmful traits. Because of the short generation time of bacteria, mutation and recombination play an important role in generating genetic diversity. Bact... |
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