History of Life on Earth
The age of fossils can sometimes be determined by radiometric dating, which is based on the constant rate of decay of radioactive isotopes. The time required for half of a radioactive isotope to decay is called the half-life of that isotope. For example, the isotope carbon-14 has a half-life of 5,730 years. If a fossilized leaf contains 12.5% of the carbon-14 that was present when the fossil formed, how old is the fossil?
1.72×104 years Radiometric dating is a technique for determining the age of fossils that is based on the fact that specific radioactive isotopes decay at a constant rate. Each isotope has a characteristic half-life, which is the time required for half of that isotope to decay. After one half-life has elapsed, 50% of the isotope has decayed and 50% remains. After two half-lives, 75% has decayed and 25% remains. After three half-lives, 87.5% has decayed and 12.5% remains. For carbon-14, which has a half-life of 5,730 years, three half-lives corresponds to 17,190 years.
The oxygenic Revolution
21 percent of the atmosphere is O2. Researchers who study the composition of the atmosphere are virtually certain that no free molecular (o2) existed for the first 2.3 billion years of Earth's existence. This conclusion is based on two observations: - There was no plausible source of oxygen at the time the planet formed - Chemical analysis of the oldest Earth rocks suggest that they formed in the absence of atmospheric oxygen Cyanobacteria is a lineage of photosynthetic battery. According to the fossil record, species of cyanobacteria first because numerous in the oceans about 2.7-2.5 billion years ago. They were the first to perform oxygenic-photosynthesis. Aerobic respiration was now a possibility. The evolution of aerobic respiration was a crucial event in the history of life. Because oxygen is extremely electronegative, it is an efficient electron acceptor. Much more energy is released as electrons move through electron transport chains when oxygen as the ultimate acceptor than is released with other substances as the electron acceptor. CYANOBACTERIA WERE RESPONSIBLE FOR A FUNDAMENTAL CHANGE IN EARTH'S ATMOSPHERE-A HIGH CONCENTRATION OF OXYGEN.
The cambrian explosion
635 million years ago animals - early sponges - appeared. In a relatively short time, creatures with shells, exoskeletons, internal skeletons, legs, heads, tails, eyes, antennae, jaw-like mandibles, segmented bodies, muscles, and brains had evolved. It was arguably the most spectacular period of evolutionary change in the history of life. All organisms were small for 3 billion years; then life got big, in just 50 million years - 1/60th of the total time life had existed. The Cambrian explosion was documented by 3 major fossils: Doushantuo, Ediacaran, and Early Cambrian Fossils
What is a fossil?
A fossil is physical evidence of an organism that lived in the past.
_____ is rapid speciation under conditions in which there is little competition.
Adaptive radiation Adaptive radiation is rapid speciation under conditions in which there is little competition.
What triggered the cambrian explosion?
Array of hypotheses: - Higher levels of oxygen - rocks from the period had gradually increased in oxygen levels. the atmosphere and oceans increased in oxygen levels too. increased oxygen levels make aerobic respiration more efficient and supports larger, active bodies. - the evolution of predation - when predators evolved, they exerted selection pressure for shells, hard exoskeletons, rapid movement, and other adaptions for prey to defend themselves. - new niches beget more new niches - once animals could move off the benthic habitat that Doushantuo and Edicaran animals lived in, they could exploit algae and other resources that were available above the ocean floor. The presence of animals at an array of depths created selection pressure for the evolution of species that could eat them. In this way, the ability to exploit new niches created new niches, driving speciation and ecological diversification. - new genes, new bodies - Hox genes play a key role in organizing the development of the body in diverse animals by signaling where cells are in embryo. gene duplication and diversification increased the number of Hox genes in animals and made it possible for larger, more complex bodies to evolve. it is important to recognize that most or all hypotheses could be correct. They are not mutually exclusive
Life's Time Line
Best estimate is that the earth formed 4.6 billion years ago, and life began 3.5 billion years ago. Originally, geologists used distinctive rock formations or fossilized organisms to identify the boundaries between named time intervals. Later researchers were able to use radiometric dating to assign absolute dates - expressed as years before the present - to events in the fossil record. Precambrian -> Phanerozoic Eon -> Present (1. Paleozoic Era 2. Mesozoic Era 3. Cenozoic Era)
True or false? The evolution of different ecomorphs on the Caribbean islands is an example of stabilizing selection.
False The evolution of different ecomorphs is an example of disruptive selection. Each new ecomorph had characteristics that were ideal for a particular habitat, but as these characteristics developed, the lizards lost the ability to survive effectively in the other habitats on the island.
How do the three levels of homology interact?
Genetic homologyies cause the developmental homologies observed in embryos, which then lead to the structural homologies recognized in adults. the most fundamental of all homologies is the genetic code. With a few minor exceptioons - all organisms use the same rules for transferring the information coded in DNA into proteins The theory of evolution by natural selection predicts that homologies will occur. if species were created independently of one another, as special creation claims, these types of similarities would not occur
Limitations of the Fossil Record
Habitat Bias: Organisms that live in areas where sediments are actively being deposited - including beach, mudflats, and swamp - are much more likely to form fossils than are organisms that live in other habitats. Organisms that live aboveground in dry forests, grasslands, and deserts are much less likely to fossilize. Taxonomic and Tissue Bias: Slow decay is almost always essential to fossilization, so organisms with hard parts such as bones or shells are most likely to leave fossil evidence. Claims, snails, and other organisms with hard parts have a much higher tendency to be preserved than do worms.. Pollen grains are incased in a tough outer coat (tissue of flowers) that resists decay, so they fossilize much more readily than do flowers, Shark teeth are abundant in the fossil record, but shark skill elements, which are made of cartilage, are almost nonexistent Temporal Bias: Recent fossils are much more common than ancient fossils. This causes temporal bias in the fossil record. The older a fossil is, the longer it has been exposed to potentially destructive forces. Older fossils usually occur in sedimentary rock layers deep below newer layers. The fossils are more vulnerable to crushing, heating, melting, and distortion by various chemical and physical processes. Older fossils are also more likely to be subjected further into Earths's interior by the sliding and collision of Earth's tectonic plates. Abundance Bias: Organisms that are abundant, widespread, and/or present on Earth for long periods of time leave evidence much more often than do species that are rare, local, r ephemeral.
Which sequence of eons, from oldest to youngest, is correct?
Hadean, Archaean, Proterozoic, Phanerozoic
The sixth mass extinction
Many scientists now proposed that life on Earth is on the verge of the sixth mass extinction, precipitated by human impacts such as habitat loss, pollution, overfishing, invasive species, and climate change,
How do mass extinctions differ from background extinctions?
Mass extinctions cause a larger proportion of organisms to go extinct than background extinctions
Why are morphological innovations often associated with adaptive radiations?
Morphological innovations can open up new adaptive options that allow a species to exploit an underused resource. Normally, competition for limited resources limits the success of variants; a key innovation provides the ability to exploit a new resource and allows variants able to exploit that resource time to diverge from other lineages before competition becomes too intense.
How do fossils form?
Most of the processes that form fossils begin when a part or all of an organism is buried in ash, sand, mud, or some other type of sediment. Once burial occurs, several things can happen: - If decomposition does not occur, the organic remains can be preserved intact. - If sediments accumulate on top of the material and become cemented into the rocks such as mudstone or shale, the sediments' weight can compress the organic material below into a thin, carbonaceous film. - If the remains decompose after they are buried, the whole that remains can fill with dissolved minerals and create an accurate case of the remains - If the remains rot extremely slowly, dissolved minerals can gradually infiltrate the interior of the cells and harden into stone, performing a permineralized fossil, such as petrified wood. After many centuries have passed, fossils can be exposed at the surface by erosion, a road cut, quarrying, or other processes. If researchers find a fossil, they can prepare it for study by painstakingly clearing away the surrounding rock. If the species is new, researchers describe its morphology in a scientific publication, name the species, estimate the fossils age based on dates assigned t nearby rock layer, and add the specimen to a collection so that it is available for study by other researchers. It is now apart of the fossil record.
The End-Permian Extinction
Mother of Mass Extincitons. - Flood basalts are outpourings of molten rock that flow across Earth's surface. The largest flood basalts on Earth, called the Siberian traps, occurred during the end-Permian. They added enormous quantities of heat, CO2, and sulfur dioxide to the atmosphere - High levels of atmospheric CO2 trapped heat, causing intense global warming, the stratification of the oceans, and reaction of deep-dulfur dioxide with water to form sulfuric acid which is toxic to most organisms - Rocks that formed during the interval indicated that the oceans became completely or largely anoxic (lacked oxygen). - Sea level dropped dramatically during the extinction event, reducing the amount of habitat available for marine organisms. -Terrestrial animals may have been restricted to small patches of low-elevation habitats, due to low oxygen concentrations and high CO2 levels in the atmosphere.
Multicellularity and large body size of eukaryotic organisms requires high metabolic rates and efficient ATP production by aerobic respiration. How did bacteria change Earth's atmosphere to enable aerobic respiration?
Oxygenic photosynthesis by cyanobacteria significantly increased the amount of oxygen in the atmosphere.
The largest extinction, measured as a percentage of species that disappeared, occurred at the end of which geological period?
Permian
Which are specific to just prokaryotes, or just plants, or just animals? chloroplasts lysosomes nucleiod magnetite-containing structures lysosomes photosynthetic membranes vacuoles flagella and fimbriae
Plant Cell - chloroplasts, vacuoles Animal Cell - lysosomes, lysosomes Prokaryotic Cell - flagella and fimbriae, photosynthetic membranes, magnetite-containing structures, nucleiod
Which statement about fossilization is correct?
Rare, local, or ephemeral species leave a poor fossil record. Fossils are more likely to be found from species that have more abundant individuals, whether due to commonness, longevity of the species, or geographic range.
What is one genetic hypothesis proposed for the rapid diversification of body plans during the Cambrian period?
Several duplications of the homeotic genes that control major characteristics in body plans apparently arose about 540 million years ago, creating new body plans and appendage configurations. The homeotic genes are major regulators of development and so are likely to be implicated in the evolution of new body plans. Gene duplications would provide a second "copy" of information that natural selection could act on to generate new body plans.
What is exceptional about the Burgess Shale, Doushantuo, and Ediacaran faunas?
Soft-bodied animals are well represented in these faunas. Soft-bodied fossils are usually uncommon
What was the main selective pressure behind the evolution of different Anolis lizard species in the Caribbean?
Specific ecological niches Different species evolved in response to the selective pressures created by specific ecological niches on the islands.
Phanerozoic Eon
The interval between 542 mya and the present. Divided into three eras - Paleozoic, Mesozoic, and Cenozoic.
Precambrian
The interval between the formation of Earth about 4.6 billion years ago and the appearance of most animal groups about 542 million years ago (mya). Divided into the Hadean, Archaean, and Proterozoic eons. Need to Know about Precambrian: -Life was exclusively unicellular for the most of Earth's history -Oxygen was virtually absent from the oceans and atmosphere for almost 2 billion years after the origin of life. Photosynthetic bacteria were responsible for the creation of the oxygen atmosphere.
What evidence supports the hypothesis that the nuclear envelope of eukaryotes arose from infolding of the plasma membrane?
The nuclear membrane and endoplasmic reticulum (ER) of modern eukaryotes are continuous. A stepwise process would have given rise to small infoldings of the plasma membrane that eventually detached to produce the nuclear envelope and the ER
Which statement is one of the two observations supporting the hypothesis that no free molecular oxygen existed for the first 2.3 billion years after the planet formed?
There was no plausible source of oxygen at the time the planet cooled to solid state. The other observation is that the oldest Earth rocks indicate that, for many years after the planet cooled, any oxygen that formed reacted immediately with iron atoms to produce iron oxides.
Why do mass extinctions wipe out species more or less randomly?
They are caused by exceptionally harsh, short-term conditions. Because they are caused by extraordinary, sudden, and temporary changes in the environment, mass extinctions are largely random with respect to the fitness of individuals under normal conditions.
True or false? Convergent evolution is said to have occurred if the mouse species on two islands with similar habitats are found to have similar characteristics even though they originated from different species that did not have these characteristics.
True Convergent evolution occurs when selective pressures produced by similar conditions (such as habitat) favor the evolution of similar solutions.
Why do adaptive radiations occur?
Two general mechanisms can trigger adaptive radiations: new resources, and new ways to exploit resources
adaptive radiation
When a single lineage rapidly produces many descendant species with a wide range of adaptive forms. Rapid evolutionary diversification within one lineage, producing many descendant species with a wide range of adaptive forms Adaptive radiations cause dramatic changes to the tree of life. They can be observed as a sudden appearance of related diverse species in the fossil record and also by phylogenic analysis. Example - The Hawaiian silverwords. The 30 species in the lineage evolved from a species of tarred, native to California, that colonized from the islands about 5 million years ago. This is an example of allopatric speciation by dispersal. Compared to the speciation rates in other groups, this rate is extremely raps. Today's silverswords vary from moss-like mats to vines and rosettes. The Hawaiian silverswords fulfill the three hallmarks of an adaptive radiation 1. They are monophyletic group 2. They speciated rapidly 3. They diversify ecologically ( in terms of the recourses they use and the habitats they occupy)
Hox genes
a class of genes found in several animal phyla, including vertebrates, that are expressed in a distinctive patter along the anterior-posterior axis in early embryos and control formation of specific structures. Hox genes code for transcription factors with a DNA-binding sequence called a homeobox insects and vertabrates have hox genes thats are derived from the same acestral sequences - that is, they are homologous.
paraphyletic group
a group that includes an ancestral population and some but not all of its decendants.
fossil
a piece of physical evidence from an organism that lived in the past
Which of the following events best illustrates an adaptive radiation? a. A fishless lake is colonized by a single fish species, which over a few thousand years gives rise to several species, each with a series of unique feeding adaptations. b. A small group of tree-dwelling lizards of a single species migrates to an uninhabited, treeless island and adapts to use the open grassland habitat. c. A population of a cricket species takes up residence in a cave. Over many generations, the cave crickets eventually lose their eyes, like many other cave-dwelling animals. d. A colonizing species of fruit fly takes up residence on a new continent and displaces two closely related native species.
a. A fishless lake is colonized by a single fish species, which over a few thousand years gives rise to several species, each with a series of unique feeding adaptations.
Which bacterial phylum is least likely to contain human pathogens? a. Cyanobacteria b. Spirochetes c. Firmicutes d. Actinobacteria
a. Cyanobacteria Cyanobacteria are photoautotrophs. They could not perform photosynthesis inside a human host. No cyanobacteria have been found to be human pathogens.
Which of the following statements about the evolution of Anolis lizards in the Caribbean islands is true? a. The phylogeny of ecomorphs on a given island reveals that adaptive radiation has taken place. b. The genetic relatedness of ecomorphs was determined by comparing their nuclear DNA sequences. c. Twig ecomorphs can jump very well. d. A crown ecomorph living on one island is always the same species as a crown ecomorph living on a neighboring island.
a. The phylogeny of ecomorphs on a given island reveals that adaptive radiation has taken place. the historical evidence of adaptive radiation on an island is recorded in the evolutionary history of the ecomorphs currently living on the island.
Whatever its ultimate cause(s), the Cambrian explosion is a prime example of _____.
adaptive radiation
Mass extinctions create conditions that promote _____.
adaptive radiation Mass extinctions reduce competition and allow for periods of rapid speciation.
The appearance of an evolutionary novelty promotes _____.
adaptive radiation The appearance of an evolutionary novelty may allow for the exploitation of previously unexploited niches.
The different finch species found on the Galápagos Islands probably arose as a result of _____.
adaptive radiation The finches that initially immigrated to the Galápagos Islands experienced little competition, the result of which was the promotion of speciation.
Researchers have identified closely related plant species native to Hawaii that have very diverse adaptations to their particular environments. Significant diversity among closely related species is a characteristic of
adaptive radiation.
lineage/clade/monophyletic group
an evolutionary unit that includes an ancestral population and all of its descendants but no others.
polyphyletic group
an unnatural group based on convergent (homoplastic) characteristic that are not present in the common ancestor
photoautotrophs
are capable of synthesizing their own food from inorganic substances using light as an energy source.
Which of the following BEST characterizes gas exchange in animal versus plant metabolism: a. Animals take in O2 and release CO2. Plants take in CO2 and release O2. b. Animals take in O2 and release CO2. Plants take in and release both O2 and CO2. c. Animals take in and release both O2 and CO2. Plants take in CO2 and release O2. d. Both animals and plants take in and release O2 and CO2.
b. Animals take in O2 and release CO2. Plants take in and release both O2 and CO2.
In the study of Anolis lizards that colonized various Caribbean islands, similar habitats and ecological types were found on Hispaniola and Jamaica. What observations suggest that adaptive radiations occur in response to habitat availability and the absence of competitors? a. Each island was initially colonized by a different species that occupied its preferred habitat. Subsequent colonizing species were successful only if they could use an unoccupied habitat type. The phylogeny for each island was the same throughout the region because no evolution occurred, only colonization. b. Different islands were initially colonized by different species that differed in habitat preference, but in both cases subsequent speciation produced a range of ecological specialists occupying similar habitat niches. The phylogeny for each island was unique, but species evolved having similar sets of adaptations for each habitat. c. Each island was colonized by a different species initially, and that species underwent a radiation, giving rise to new species that occupied different habitat types. There was no similarity, however, in the adaptations from one island to another. The phylogeny for each island was completely unique and totally unlike that of any other island. d. The first colonists on every island were always the same species, a twig-dwelling specialist. However, in every case, that species gave rise to the same set of other species that specialized in different habitats. The phylogeny for each island had the same root and the same pattern of speciation.
b. Different islands were initially colonized by different species that differed in habitat preference, but in both cases subsequent speciation produced a range of ecological specialists occupying similar habitat niches. The phylogeny for each island was unique, but species evolved having similar sets of adaptations for each habitat. The pattern is that each island ended up with a unique set of species, but those species had convergent adaptations for life in a particular habitat.
Which evidence is consistent with the endosymbiotic hypothesis for the origin of the mitochondrion? a. All genes vital for the functioning of mitochondria are found in the nucleus. b. Mitochondria have their own ribosomes and manufacture their own proteins. c. Streptomycin inhibits eukaryotic and mitochondrial ribosomes. d. Mitochondria are much smaller than an average bacterium.
b. Mitochondria have their own ribosomes and manufacture their own proteins. Mitochondrial ribosomes closely resemble bacterial ribosomes in size and composition.
All of the following events can trigger an adaptive radiation EXCEPT _____. a. Hox gene duplication events b. an unusual event splitting a habitat, such as a severe hurricane c. the colonization of a new habitat d. the extinction of competitors e. the evolution of a new morphological feature
b. an unusual event splitting a habitat, such as a severe hurricane
Phanerozoic Eon: Paleozoic
begins with the appearance of most major animal lineages and ends with the obliteration of almost all multicellular life-forms at the end of the Permian period (last period of the Paleozoic era). The Paleozoic era includes the origin and initial diversification of the animals, land plants and fungi, as well as the appearance of land animals.
Phanerozoic Eon: Mesozoic
begins with the end-Permian extinction events and ends with the extinction of the dinosaurs (except birds) and other groups at the boundary between the Cretaceous period (last period of mesozoic) and the Paleogene period (first period of cenozoic). In terrestrial environments of the Mesozoic, gymnosperms were the most dominant plants and dinosaurs were the most dominant vertebrates.
For many years scientists believed that almost all animal lineages burst into being during the Cambrian era (just after the end of the Precambrian super eon). However, there have been many recent findings of animal-like fossils and "trace fossils" (fossils of an animal-like organisms movement) from the late Precambrian. Which of the following best explains why it took so long to realize there was animal-like life in the Precambrian? a. There were many hard-shelled animals in the Cambrian. b. The global climate was such that there was poor fossilization in the Precambrian. c. Animals from the late Precambrian had soft bodies. d. There were no animals in the Precambrian. e. There were very few animals during this period.
c. Animals from the late Precambrian had soft bodies.
Which organisms are not examples of an adaptive radiation? a. Anolis lizards of the Caribbean b. Honeycreeper songbirds of the Hawaiian islands c. Mammals and reptiles in the post-dinosaur age d. Horses and deer in the post-dinosaur age
c. Mammals and reptiles in the post-dinosaur age Mammals and reptiles are not descended from a single lineage.
Which of the following statements about speciation is true? a. Speciation requires natural selection. b. Speciation will occur more slowly if gene flow is low. c. Speciation will occur more slowly if gene flow is high. d. Speciation requires genetic drift.
c. Speciation will occur more slowly if gene flow is high.
Which statement accurately describes the roles of the light-dependent reactions (LDRs), the Calvin cycle, and cellular respiration? a. The LDRs convert small high-energy molecules into sugars, the Calvin cycle converts light energy into chemical energy, and cellular respiration breaks down sugars to produce ATP. b. The LDRs convert light energy into chemical energy, the Calvin cycle breaks down sugars to produce ATP, and cellular respiration converts small high-energy molecules into sugars. c. The LDRs convert light energy into chemical energy, the Calvin cycle converts small high-energy molecules into sugars, and cellular respiration breaks down sugars to produce ATP. d. The LDRs convert small high-energy molecules into sugars, the Calvin cycle breaks down sugars to produce ATP, and cellular respiration converts light energy into chemical energy.
c. The LDRs convert light energy into chemical energy, the Calvin cycle converts small high-energy molecules into sugars, and cellular respiration breaks down sugars to produce ATP.
Which statement is most consistent with the hypothesis that the Cambrian explosion was caused by the rise of predator-prey relationships? The fossil record reveals an increased incidence of _____. a. worm burrows b. larger animals c. hard parts d.organic material e. fern galls
c. hard parts
What feature was not present in the first eukaryotes?
cell wall Because early-branching eukaryote lineages lack cell walls, biologists suggest that their common ancestor also lacked this feature.
Which features are common to all cells?
cytoskeleton, cytoplasm, ribosomes, plasma membrane, genetic information in chromosomes
Which of the following best characterizes an adaptive radiation? a. Natural selection is particularly intense, because disruptive selection occurs. b. Speciation occurs extremely rapidly, and descendant populations occupy a large geographic area. c. Species recover after a mass extinction. d. A single lineage diversifies rapidly, and descendant populations occupy many habitats and ecological roles.
d. A single lineage diversifies rapidly, and descendant populations occupy many habitats and ecological roles.
Which of the following statements about adaptive radiation is correct? a. Adaptive radiation occurs in species that live in one habitat. b. Adaptive radiation occurs in the presence of competitors. c. Adaptive radiation occurs very slowly over time. d. Adaptive radiation occurs within a single lineage.
d. Adaptive radiation occurs within a single lineage. Adaptive radiation occurs when a single lineage produces many descendant species.
Which of the following accurately describes a difference between prokaryotic and eukaryotic cells? a. Prokaryotic cells have nuclei and eukaryotic cells have nucleoids. b. Prokaryotic cells have fimbriae that allow the cell to swim whereas eukaryotic cells have flagella. c. Eukaryotic cells have organelles. d. Eukaryotic cells are generally larger than prokaryotic cells.
d. Eukaryotic cells are generally larger than prokaryotic cells.
Consistently overwatering a potted tomato plant will eventually kill it. Why waterlogged soil results in plant death? a. Light energy cannot reach the chloroplasts, preventing ATP and NADPH production by the light-dependent reactions. The plant cannot make food and starves. b. CO2 cannot reach the chloroplasts, preventing production of glucose by the Calvin cycle. The plant cannot make food and starves. c. CO2 cannot reach photosynthesizing root cells, preventing production of glucose by the Calvin cycle. The plant cannot make food and starves. d. O2 cannot reach respiring root cells. The plant cannot oxidize food and starves.
d. O2 cannot reach respiring root cells. The plant cannot oxidize food and starves.
Which processes establish a gradient of protons to drive ATP synthesis? a. Mitochondrial electron transport chain and photosystem I reactions b. Photosystem II and Calvin cycle reactions c. Glycolysis and photosystem I reactions d. Photosystem II and mitochondrial electron transport chain reactions
d. Photosystem II and mitochondrial electron transport chain reactions
What is true of the Cambrian explosion? a. The Cambrian explosion marks the appearance of filter-feeding animals in the fossil record. b. The Cambrian explosion is evidence for the instantaneous creation of life on Earth. c. Only the fossils of microorganisms are found in geological strata older than the Cambrian explosion. d. There are fossils of animals in geological strata that are older than the Cambrian explosion.
d. There are fossils of animals in geological strata that are older than the Cambrian explosion. the Cambrian explosion - the rapid diversification of animal body type and lineages that occurred between the species in the Doushanto faunas (570 mya), Ediacaran faunas (550 mya), and the Early Cambrian fauna (520 mya). creatures with shells, exoskeletoss, legs, heads, tails, eyes, muscles, segmented-bodies, brains etc. had evolved.
Which of the following observations is NOT consistent with the hypothesis that increasing metazoan complexity is associated with an increase in the number of Hox loci? a. Hox loci are similar in structure and DNA sequence and are grouped in clusters. Hence, they are assumed to have arisen through duplication. When a new Hox gene appears within a lineage, most of the descendant taxa have a homologous Hox locus. b. Phyla that branch off early, such as sponges and cnidarians, have simple body plans with relatively few Hox loci. c. In vertebrates, the Hox clusters themselves appear to be duplicated several times. d. Within phyla, there is no correspondence between the number of Hox genes and complexity.
d. Within phyla, there is no correspondence between the number of Hox genes and complexity.
structural homologies are directly influenced by
development homology
mesozoic era
dinosaurs evolve and radiate origin of mammals
Phylogenetic analyses are powerful ways to infer the order in which events occurred during evolution and to understand how particular groups of species are related, but only fossil record provides...
direct evidence about what organisms that lived in the past looked, like. where they lived, and when they existed
You are the lucky student of a wacky professor who develops a time machine. He asks if you will test it with him. You get in and there is an immediate glitch-the date readout fails so that when you land you are not sure what era you are in. Your professor begins to panic, but you see something that tells you are in the Cenozoic era. Which of the following could it be? a. many birds flying and roosting near giant turtles b. a water lily floating in a pond c. masses of green ferns with dragonflies hovering above them d. a bee pollinating a flower e. a rabbit eating a daisy
e. a rabbit eating a daisy
Feathers either play a role, or may have played a role, in ____
extended hops flight courtship gliding All of these are, or may have been, functions of feathers.
Impact hypothesis
for the extinction of the dinosaurs, first put forth in the early 1970s by Luis and Walter Alvarez, proposed that an asteroid struck the Earth and snuffed out an estimated 60-80 percent of the multicellular species alive. K-P asterioud strike.
development homology is directly influenced by-
genetic homology
cenozoic era
humans appear major radiation of pollinating insects
What do some photosynthetic bacteria use as a source of electrons instead of water?
hydrogen sulfide (H2S)
Doushantuo microfossils
include tiny sponges and corals, less than 1 mm across. These creatures - the first animals on Earth - probably made their living by filtering organic debris from the water
Ediacaran faunas
including sponges, jellyfish, and comb jellies as well as fossilized burrows, track, and other traces from unidentified animals. None of these organisms have shells, limbs, heads, or feeding appendages. Ediacaran animals likely filtered or absorbed organic material as they burrowed in sediments, sat immobile on the seafloor, or floated in water
The leading hypothesis to explain the origin of the nuclear envelope is based on...
infolding of the plasma membrane
Phanerozoic Eon: Cenozoic
is divided into the Paleocene, Neogene, and Quaternary periods. On land, angiosperms were the most dominant plants and mammals were the largest vertebrates. Homo sapiens appeared int he Quaternary period
Which evolutionary mechanism creates new alleles?
mutation
Archaean eon
oldest fossils of cells (prokaryotes) appear origin of Earth
Proterozoic
oldest fossils of eukaryotic cells appear
chemoorganoheterotrophs
organism that requires organic substrates to get its carbon for growth and development, and that produces its energy from oxido-reduction of an organic compound.
photoheterotrophs
organisms that use light for energy, but cannot use carbon dioxide as their sole carbon source.
chemoorganoautotrophs
organisms which oxidize the chemical bonds in organic compounds as their energy source. Chemoorganotrophs also attain the carbon molecules that they need for cellular function from these organic compounds.
Cyanobacteria are thought to be the first organisms to evolve ____.
oxygenic photosynthesis Cyanobacteria use light energy to split or oxidize water, with oxygen gas as a by-product. The electrons are passed through an electron transport chain and used to make NADPH and ATP.
Heliobacteria are classified as _____.
photoheterotrophs
endosymbiosis theory
proposes that mitochondria originated when a bacterial cell took up residence inside another cell about 2 billion years ago. symbiosis- two individuals from different species live in physical contact. The relationship between the archaea host and the engulfed bacterial cell was presumed the be stable because a mutual advantage existed between them: the host supplied the bacterium with protection and carbon compounds from its prey, while the bacterium produced much more ATP than the host cell could synthesize on it own. Mitochondrial gene sequences are much more closely related to the sequences from the alpha-proteobacteria than to sequences from the nuclear DNA of eukaryotes
fossilization is an extremely ___ event
rare
Paleontologists
scientists who study fossils.
Biologist hypothesized that the earliest eukaryotes were probably...
single celled organisms with mitochondria, a nucleus and endomembrane system, and a cytoskeleton, but no cell wall. based on the knowledge that all eukaryotes today have either mitochondria or genes that are normally found in mitochondria, a nucleus and endomembrane system, and cytoskeleton.
ecomorphs
species with the same structural habitat/niche, similar in morphology and behavior, but not necessarily close phyletically
Cambrian faunas
sponges, jellyfish, and comb jellies are abundant in these rocks too, but so are several worm-like creatures and arthropods, in addition to mollusks echinoderms, and virtually all the other major animal lineages. This list includes our own lineage - chordates - represented by early vertebrate fossils with streamlined, fishlike bodies and a skull made of cartilage. A tremendous increase in the size and morphological complexity of animals occurred accompanied by diversification in how they made a living. Species in these faunas swam, burrowed, walked, ran, slithered, clung, or floated; there were predators, scavengers, filter feeders, and grazers.
Ecological Opportunity
the ability of new or novel types of resources Has driven a wide array of adaptive radiations. ex. biologists explain the diversification of silverswords by hypothesizing that few other flowering plants species were present on the Hawaiian Islands 5 million years ago. With few competitors, the descendants of the colonizing tarred were able to grow in a wide range of habitats. Over time - by the process of mutation, genetic drift, and natural selection - some became specialized for growth in different niches. ex. The same ecological opportunity was hypothesized to explain the adaptive radiation of Anolis lizards on the islands of the Caribbean. The lineage includes 150 species. They thrive in a wide array of habitats and have diverse body sizes and shapes. and in most cases, a lizard's size and shape are correlated with the habitat it occupies. for example: - Species that live on tree twigs have short legs and tails that allow them to move efficiently on narrow surfaces - species that spend most of their time clinging t broad tree trunks or running along the ground have long legs and tails, making them fast and agile on broad surfaces. Researchers estimated the phylogeny of Anolis from DNA sequence data. Proved that the lizards were monophyletic
Paleozoic era
the cambrian explosion first tetrapods and insects appear
morphological innovation
the evolution of a key morphological trait - one that allowed the descendants to live in new area, exploit new sources of food, or move in new ways - triggered many of the important diversifications in the history of life. ex. Flowers are a unique reproductive structure that helped trigger the diversification of angiosperms (flowering plants). Because flowers are particularly efficient at attracting pollinators, the evolution of the flower made angiosperms more efficient in reproduction. Today, angiosperms are the most species-rich lineage of land plants - 250,000 species. ex. Feathers and wings gave some dinosaurs the ability to fly. Feathers originally evolved for display or insulation; later they were used in gliding and powered flight. Today the lineage called birds contains about 10,000 species, whose representatives live in virtually every habitat on the planet.
Background extinction
the lower, average rate of extinction observed when a mass extinction is not occurring. Although there is no hard-and-fast rule for distinguishing between background and mass extinction rates, paleontologists traditionally recognize and study five historic mass extinction events (The Big Five End-Ordovician extinction, Late-Devonian extinction, End-Permian extinction, Late-Triassic extinction, End-Cretaceous extinction). Background extinctions are thought to occur when normal environmental change, emerging disease, predation pressure, or competition with another species reduces certain populations to zero
anoxygenic photosynthesis
the phototrophic process where light energy is captured and converted to ATP, without the production of oxygen. Water is therefore not used as an electron donor.
Mass extincton
the rapid extinction of a large number of lineages scattered throughout the tree of life. occurs when at least 60% of the species present are wiped out with in 1 million years results from extraordinary, sudden, and temporary changes in the environment. During mass extinction, species do not die out because individuals are poorly adapted to normal or gradually changing environment conditions. Rather, species die out from exposure to exponentially harsh, short-term conditions - such as huge volcanic eruptions or catastrophic sea-level changes.
fossil record
the total collection of fossils that have been found throughout the world.
A key factor that allows some bacteria and archaea to be used for bioremediation is ____.
their metabolic diversity Nearly any organic compound can be used as a food source by some species of prokaryote. During the metabolism of the toxin, it can be converted to a less toxic form.
