Chapter 25

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1) Which of the following is the correct sequence of events in the origin of life?

I. formation of protobionts

II. synthesis of organic monomers

III. synthesis of organic polymers

IV. formation of DNA-based genetic systems

A) I, II, III, IV

B) I, III, II, IV

C) II, III, I, IV

D) II, III, IV, I

C

2

2) Which of the following is a defining characteristic that all protocells had in common?

A) the ability to synthesize enzymes

B) a surrounding membrane or membrane-like structure

C) RNA genes

D) the ability to replicate RNA

B

3

3) The first genetic material on Earth was probably _____.

A) DNA produced by reverse transcriptase from abiotically produced RNA

B) DNA molecules whose information was transcribed to RNA and later translated in polypeptides

C) self-replicating RNA molecules

D) oligopeptides located within protobionts

C

4

4) Several scientific laboratories across the globe are involved in research concerning the origin of life on Earth. Which of these questions is currently the most problematic and would have the greatest impact on our understanding if we were able to answer it?

A) How can amino acids, simple sugars, and nucleotides be synthesized abiotically?

B) How did RNA sequences come to carry the code for amino acid sequences?

C) How could polymers involving lipids and/or proteins form membranes in aqueous environments?

D) How can RNA molecules act as templates for the synthesis of complementary RNA molecules?

B

5

5) Which of the following steps has yet to be accomplished by scientists studying the origin of life?

A) synthesis of small RNA polymers by ribozymes

B) abiotic synthesis of polypeptides

C) formation of molecular aggregates with selectively permeable membranes

D) formation of protocells that use DNA to direct the polymerization of amino acids

D

6

6) How were conditions on the early Earth of more than three billion years ago different from those on today's Earth? Unlike Earth today, early Earth _____.

A) had an atmosphere rich in gases released from volcanic eruptions

B) had an oxidizing atmosphere

C) experienced little high energy radiation from the sun

D) had an atmosphere with significant quantities of ozone

A

7
card image

The figure below represents a cross section of the sea floor through a mid-ocean rift valley, with alternating patches of black and white indicating sea floor with reversed magnetic polarities. At the arrow labeled "I" (the rift valley), the igneous rock of the sea floor is so young that it can be accurately dated using carbon-14 dating. At the arrow labeled "III," however, the igneous rock is about one million years old, and potassium-40 dating is typically used to date such rocks. Note: The horizontal arrows indicate the direction of sea-floor spreading, away from the rift valley.

8) Which section of sea-floor crust should have the thickest layer of overlying sediment, assuming a continuous rate of sediment deposition?

A) A

B) B

C) D

D) E

D

8
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9) If a particular marine organism is fossilized in the sediments immediately overlying the igneous rock at the arrow labeled "II," at which other location, labeled A-E, would a search be most likely to find more fossils of this organism?

A) B

B) C

C) D

D) E

B

9

10) Which of the following organisms would be most likely to fossilize?

A) a rare worm

B) a common worm

C) a rare squirrel

D) a common squirrel

D

10

11) Which of the following would be LEAST likely in the fossil record?

A) burrowing species

B) marine-dwelling species

C) marsh-dwelling species

D) desert-dwelling species

D

11

12) If the half-life of carbon-14 is about 5730 years, then a fossil that has one-sixteenth the normal proportion of carbon-14 to carbon-12 should be about how many years old?

A) 2800

B) 11,200

C) 16,800

D) 22,900

D

12

13) What is true of the fossil record of mammalian origins?

A) It shows that mammals and birds evolved from the same kind of dinosaur.

B) It includes transitional forms with progressively specialized teeth.

C) It indicates that mammals and dinosaurs did not overlap in geologic time.

D) It includes a series that shows the gradual change of scales into fur.

B

13

14) If a fossil is encased in a stratum of sedimentary rock without any strata of volcanic rock (for example, lava or ash) nearby, then it should be _____.

A) easy to determine the absolute age of the fossil, because the radioisotopes in the sediments will not have been "reset" by the heat of the igneous rocks

B) easy to determine the absolute age of the fossil, because the igneous rocks will not have physically obstructed the deposition of sediment of a single age next to the fossil

C) difficult to determine the absolute age of the fossil, because the "marker fossils" common to igneous rock will be absent

D) difficult to determine the absolute age of the fossil, because radiometric dating of sedimentary rock is less accurate than that of igneous rock

D

14
card image

A sediment core is removed from the floor of an inland sea. The sea has been in existence, off and on, throughout the entire time that terrestrial life has existed. Researchers wish to locate and study the terrestrial organisms fossilized in this core. The core is illustrated as a vertical column, with the top of the column representing the most recent strata and the bottom representing the time when land was first colonized by life.

15) To assign absolute dates to fossils in this sediment core, it would be most helpful if _____.

A) we knew the order in which the fossils occurred

B) the sediments had not been affected by underwater currents during their deposition

C) volcanic ash layers were regularly interspersed between the sedimentary strata

D) fossils throughout the column were equally spaced apart

C

15

Fossils of Lystrosaurus, a dicynodont therapsid, are most common in parts of modern-day South America, South Africa, Madagascar, India, South Australia, and Antarctica. The animal apparently lived in arid regions, and was mostly herbivorous. It originated during the mid-Permian period, survived the Permian extinction, and dwindled by the late Triassic, though there is evidence of a relict population in Australia during the Cretaceous period. Some dicynodonts had two large tusks, extending down from their upper jaws. The tusks were not used for food gathering, and in some species were limited to males. Food was gathered using an otherwise toothless beak. Judging from the fossil record in sedimentary rocks, these pig-sized organisms were the most common mammal-like reptiles of the Permian.

B

16

17) What is thought to be the correct sequence of these events, from earliest to most recent, in the evolution of life on Earth?

  1. origin of mitochondria
  2. origin of multicellular eukaryotes
  3. origin of chloroplasts
  4. origin of cyanobacteria
  5. origin of fungal-plant symbioses

A) 4, 3, 2, 1, 5

B) 4, 1, 2, 3, 5

C) 4, 1, 3, 2, 5

D) 4, 3, 1, 5, 2

C

17

18) Which of these observations gives the most support to the endosymbiotic theory for the origin of eukaryotic cells?

A) the existence of structural and molecular differences between the plasma membranes of prokaryotes and the internal membranes of mitochondria and chloroplasts

B) the similarity in size between the cytosolic ribosomes of prokaryotes and the ribosomes within mitochondria and chloroplasts

C) the size disparity between most prokaryotic cells and most eukaryotic cells

D) the observation that some eukaryotic cells lack mitochondria

B

18

19) Which of the following was derived from an ancestral cyanobacterium?

A) chloroplast

B) mitochondrion

C) flagella

D) mitosome

A

19

20) 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) Animals from the late Precambrian had soft bodies.

B) There were many hard-shelled animals in the Cambrian.

C) The global climate was such that there was poor fossilization in the Precambrian.

D) There were very few animals during this period.

A

20

21) Which of the following showed their greatest diversity during the Mesozoic era, but were a small, less diverse group during the Paleozoic era?

A) gymnosperms

B) fungi

C) flowering plants

D) mammals

A

21

22) Which listing of geological periods is in the correct order, from oldest to most recent?

A) Cambrian, Devonian, Permian, Cretaceous

B) Devonian, Cambrian, Permian, Cretaceous

C) Cambrian, Permian, Devonian, Cretaceous

D) Permian, Cambrian, Cretaceous, Devonian

A

22

23) 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) a rabbit eating a daisy

B) a water lily floating in a pond

C) masses of green ferns with dragonflies hovering above them

D) a bee pollinating a flower

A

23

24) 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. As your time machine lands, you see an unusual landscape before you. As you open the door you realize you cannot breathe. You quickly shut the door, realizing you are in the _____.

A) Archaean eon

B) Cambrian period

C) Cenozoic era

D) Mesozoic era

A

24

25) An early consequence of the release of oxygen gas by plant and bacterial photosynthesis was to _____.

A) change the atmosphere from oxidizing to reducing

B) make it easier to maintain reduced molecules

C) cause iron in ocean water and terrestrial rocks to rust (oxidize)

D) prevent the formation of an ozone layer

C

25

26) What is true of the Cambrian explosion?

A) There are fossils of animals in geological strata that are older than the Cambrian explosion.

B) Only the fossils of microorganisms are found in geological strata older than the Cambrian explosion.

C) The Cambrian explosion is evidence for the instantaneous creation of life on Earth.

D) The Cambrian explosion marks the appearance of filter-feeding animals in the fossil record.

A

26

27) Which of the following characteristics are expected in the first animals to have colonized land?

  1. were probably herbivores (ate photosynthesizers)
  2. had four appendages
  3. had the ability to resist dehydration
  4. had lobe-finned fishes as ancestors
  5. were invertebrates

A) 3 only

B) 3 and 5

C) 1, 3, and 5

D) 1, 2, 3, and 4

C

27
card image

A sediment core is removed from the floor of an inland sea. The sea has been in existence, off and on, throughout the entire time that terrestrial life has existed. Researchers wish to locate and study the terrestrial organisms fossilized in this core. The core is illustrated as a vertical column, with the top of the column representing the most recent strata and the bottom representing the time when land was first colonized by life.

28) If arrows indicate locations in the column where fossils of a particular type (see key above) first appear, then which core in the figure above has the most accurate arrangement of fossils?

A) core A

B) core B

C) core C

D) core D

A

28
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29) Which factor most likely caused animals and plants in India to differ greatly from species in nearby southeast Asia?

A) The climates of the two regions are similar.

B) India is in the process of separating from the rest of Asia.

C) Life in India was wiped out by ancient volcanic eruptions.

D) India was a separate continent until forty-five million years ago.

D

29

All animals with eyes or eyespots that have been studied so far share a gene in common. When mutated, the gene Pax-6 causes lack of eyes in fruit flies, tiny eyes in mice, and missing irises (and other eye parts) in humans. The sequence of Pax-6 in humans and mice is identical. There are so few sequence differences with fruit fly Pax-6 that the human/mouse version can cause eye formation in eyeless fruit flies, even though vertebrates and invertebrates last shared a common ancestor more than five hundred million years ago.

30) The appearance of Pax-6 in all animals with eyes can be explained in multiple ways. Based on the information above, which explanation is most likely?

A) Pax-6 in all of these animals is not homologous; it arose independently in many different animal phyla due to intense selective pressure favoring vision.

B) The Pax-6 gene is really not one gene. It is many different genes that, over evolutionary time and due to convergence, have come to have a similar nucleotide sequence and function.

C) The Pax-6 gene was an innovation of an ancestral animal of the early Cambrian period. Animals with eyes or eyespots are descendants of this ancestor.

D) The need for eyes has resulted in the separate evolution of Pax-6 genes.

C

30

31) Fruit-fly eyes are of the compound type, which is structurally very different from the camera-type eyes of mammals. Even the camera-type eyes of molluscs, such as octopi, are structurally quite different from those of mammals. Yet, fruit flies, octopi, and mammals possess very similar versions of Pax-6. The fact that the same gene helps produce very different types of eyes is most likely due to _____.

A) the few differences in nucleotide sequence among the Pax-6 genes of these organisms

B) variations in the number of Pax-6 genes among these organisms

C) the independent evolution of this gene at many different times during animal evolution

D) differences in the control of Pax-6 expression among these organisms

D

31
card image

The figure below represents a cross section of the sea floor through a mid-ocean rift valley, with alternating patches of black and white indicating sea floor with reversed magnetic polarities. At the arrow labeled "I" (the rift valley), the igneous rock of the sea floor is so young that it can be accurately dated using carbon-14 dating. At the arrow labeled "III," however, the igneous rock is about one million years old, and potassium-40 dating is typically used to date such rocks. Note: The horizontal arrows indicate the direction of sea-floor spreading, away from the rift valley.

32) Assuming that the rate of sea-floor spreading was constant during the one-million-year period depicted above, on average Earth's magnetic field has undergone reversal once every _____.

A) 25,000 years

B) 100,000 years

C) 250,000 years

D) 1,000,000 years

C

32
card image

33) How many other bands of sea-floor crust in the figure above have the same magnetic polarity as the crust that directly straddles the rift valley?

A) two bands

B) four bands

C) five bands

D) eight bands

B

33
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34) Assuming that the rate of sea-floor spreading was constant during the one-million-year period depicted above, what should be the approximate age of marine fossils found in undisturbed sedimentary rock immediately overlying the igneous rock at the arrow labeled "II"?

A) 10,000 years

B) 250,000 years

C) 500,000 years

D) 1,000,000 years

C

34

35) The Permian period ended and then rapid speciation occurred as new animal and plant forms evolved. The most likely explanation for this is _____.

I) adaptive radiation

II) ecological opportunity

III) lack of competition

IV) morphological innovation

A) just one of the above

B) two of the above

C) three of the above

D) all of the above

C

35
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36) What does the circled part of the phylogenetic tree above indicate?

A) an adaptive radiation

B) a mass extinction event

C) rapid speciation

D) an adaptive radiation and rapid speciation

D

36

37) A hypothetical island lies far from any other landmasses. There are many different types of plants, but only one animal, a beetle, that can fly or walk from plant to plant and feeds by chewing leaves. Given that the beetle is not exploiting all of the resources on the island, which morphological change would be most likely to trigger an adaptive radiation of the beetles?

A) a change in wing shape that improves flight speed

B) an additional segment on a pair of legs

C) a mouthpart that can pierce fruits and seeds

C

37

38) On the basis of their morphologies, how might Linnaeus have classified the Hawaiian silverswords? Linnaeus would have _____.

A) placed them all in the same species.

B) classified them the same way that modern botanists do.

C) placed more of them in different genera than modern botanists do.

D) used evolutionary relatedness as the primary criterion for their classification.

C

38
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39) According to the theory of sea-floor spreading, oceanic islands, such as the Hawaiian Islands depicted in the figure above, form as oceanic crustal plates move over a stationary "hot spot" in the mantle. Currently, the big island of Hawaii is thought to be over a hot spot, which is why it is the only one of the seven large islands that has active volcanoes. What should be true of the island of Hawaii?

  1. Scientists in search of ongoing speciation events are more likely to find them here than on the other six large islands.
  2. Its species should be more closely related to those of nearer islands than to those of farther islands.
  3. It should have a rich fossil record of terrestrial organisms.
  4. It should have species that are not found anywhere else on Earth.
  5. On average, it should have fewer species per unit surface area than the other six islands.

A) 1, 2, and 3

B) 1, 2, and 5

C) 1, 2, 3, and 4

D) 1, 2, 4, and 5

D

39
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40) Hawaii is the most southeastern of the seven largest islands and is also closest to the sea-floor spreading center from which the Pacific plate originates, which lies about 5600 km further to the southeast. Assuming equal sedimentation rates, what should be the location of the thickest sediment layer and, thus, the area with the greatest diversity of fossils above the oceanic crust?

A) between the island of Hawaii and the sea-floor spreading center

B) around the base of the island of Hawaii

C) around the base of Kauai, the oldest of the large Hawaiian islands

D) where the islands are most concentrated (highest number of islands per unit surface area)

C

40

41) Upon being formed, oceanic islands, such as the Hawaiian Islands, should feature what characteristic, leading to which phenomenon?

A) mass extinctions, leading to bottleneck effect

B) major evolutionary innovations, leading to rafting to nearby continents

C) a variety of empty ecological niches, leading to adaptive radiation

D) adaptive radiation, leading to founder effect

C

41

Fossils of Lystrosaurus, a dicynodont therapsid, are most common in parts of modern-day South America, South Africa, Madagascar, India, South Australia, and Antarctica. The animal apparently lived in arid regions, and was mostly herbivorous. It originated during the mid-Permian period, survived the Permian extinction, and dwindled by the late Triassic, though there is evidence of a relict population in Australia during the Cretaceous period. Some dicynodonts had two large tusks, extending down from their upper jaws. The tusks were not used for food gathering, and in some species were limited to males. Food was gathered using an otherwise toothless beak. Judging from the fossil record in sedimentary rocks, these pig-sized organisms were the most common mammal-like reptiles of the Permian.

42) Which of the following is the most likely explanation for the modern-day distribution of dicynodont fossils? The dicynodonts were_____.

A) carnivores that traveled widely to find prey

B) evenly distributed throughout all of Pangaea

C) most abundantly distributed throughout Gondwanaland

D) amphibious and able to swim long distances

C

42

43) If an organism has a relatively large number of Hox genes in its genome, it most likely _____.

A) has Hox genes expressed in all cells of its body

B) has multiple paired appendages along the length of its body

C) has a relatively complex anatomy

D) belongs to one of the first groups to evolve on Earth

C

43

44) Bagworm moth caterpillars feed on evergreens and carry a silken case or bag around with them in which they eventually pupate. Adult female bagworm moths are larval in appearance; they lack the wings and other structures of the adult male and instead retain the appearance of a caterpillar even though they are sexually mature and can lay eggs within the bag. This is a good example of _____.

A) allometric growth

B) paedomorphosis

C) sympatric speciation

D) adaptive radiation

B

44

45) The loss of ventral spines by modern freshwater sticklebacks is due to natural selection operating on the phenotypic effects of Pitx1 gene _____.

A) duplication (gain in number)

B) elimination (loss)

C) mutation (change)

D) silencing (loss of expression)

D

45

A female fly, full of fertilized eggs, is swept by high winds to an island far out to sea. She is the first fly to arrive on this island and the only fly to arrive in this way. Thousands of years later, her numerous offspring occupy the island, but none of them resembles her. There are, instead, several species, each of which eats only a certain type of food. None of the species can fly and their balancing organs (halteres) are now used in courtship displays. The male members of each species bear modified halteres that are unique in appearance to their species. Females bear vestigial halteres. The ranges of all of the daughter species overlap.

46) In each fly species, the entire body segment that gave rise to the original flight wings is missing. The mutation(s) that led to the flightless condition could have _____.

A) duplicated all of the Hox genes in these flies' genomes

B) resulted in paedomorphosis

C) altered the expression of a Hox gene

D) originated in another species

C

46

47) A genetic change that caused a certain Hox gene to be expressed along the tip of a vertebrate limb bud instead of farther back helped make possible the evolution of the tetrapod limb. This type of change is illustrative of _____.

A) the influence of environment on development

B) paedomorphosis

C) a change in a developmental gene or its regulation that altered the spatial organization of body parts

D) heterochrony

C

47

48) The duplication of homeotic (Hox) genes has been significant in the evolution of animals because it _____.

A) permitted the evolution of novel forms

B) caused the extinction of major groups

C) reduced morphological diversity into simpler forms of life

D) allowed animals to survive on significantly fewer calories

A

48

49) Why would gene duplication events, such as those seen in the Hox gene complex, set the stage for adaptive radiation?

A) There are more copies of genes, meaning speciation had occurred by polyploidy.

B) The original gene copy is the outgroup, and the new gene copies are the adaptive radiation.

C) Without duplicated genes, species would be vulnerable to extinction.

D) One copy of a gene can perform the original function, while other copies are available to take on new functions.

D

49

50) All of the following events can trigger an adaptive radiation EXCEPT _____.

A) an unusual event splitting a habitat, such as a severe hurricane

B) the evolution of a new morphological feature

C) the extinction of competitors

D) Hox gene duplication events

A

50

All animals with eyes or eyespots that have been studied so far share a gene in common. When mutated, the gene Pax-6 causes lack of eyes in fruit flies, tiny eyes in mice, and missing irises (and other eye parts) in humans. The sequence of Pax-6 in humans and mice is identical. There are so few sequence differences with fruit fly Pax-6 that the human/mouse version can cause eye formation in eyeless fruit flies, even though vertebrates and invertebrates last shared a common ancestor more than five hundred million years ago.

51) Pax-6 usually causes the production of a type of light-receptor pigment. In vertebrate eyes, though, a different gene (the rh gene family) is responsible for the light-receptor pigments of the retina. The rh gene, like Pax-6, is ancient. In the marine ragworm, for example, the rh gene causes production of c-opsin, which helps regulate the worm's biological clock. Which of the following most likely accounts for vertebrate vision?

A) The Pax-6 gene mutated to become the rh gene among early mammals.

B) During vertebrate evolution, the rh gene for biological clock opsin was co-opted as a gene for visual receptor pigments.

C) In animals more ancient than ragworms, the rh gene(s) coded for visual receptor pigments; in lineages more recent than ragworms, rh has flip-flopped several times between producing biological clock opsins and visual receptor pigments.

D) Pax-6 was lost from the mammalian genome, and replaced by the rh gene much later.

B

51

52) A swim bladder is a gas-filled sac that helps fish maintain buoyancy. The evolution of the swim bladder from lungs of an ancestral fish is an example of _____.

A) exaptation

B) changes in Hox gene expression

C) paedomorphosis

D) adaptive radiation

A

52

53) Which of the following is a limit of evolution that results in exaptations?

A) Natural selection and sexual selection can work at cross-purposes to each other.

B) Evolution is limited by historical constraints.

C) Adaptations are often compromises.

D) Chance events affect the evolutionary history of populations in environments that can change unpredictably.

B

53

54) Insect wings may have begun to evolve as lateral extensions of the body that were used as heat dissipaters for thermoregulation. When they had become sufficiently large, these extensions became useful for gliding through the air. Additional selection refined them as flight-producing wings. If this hypothesis is correct, modern insect wings would be an example of _____.

A) the loss of Hox genes in the evolution of new form

B) mutations

C) an exaptation

D) an adaptive radiation

C

54

55) If one organ is an exaptation of another organ, then these two organs _____.

A) are homologous

B) are undergoing convergent evolution

C) are found in the same species

D) have the same function

A

55

56) Many species of snakes lay eggs. However, in the forests of northern Minnesota, where growing seasons are short, only live-bearing snake species are present. This trend toward species that have live birth in a particular environment is an example of _____.

A) an exaptation

B) sexual selection

C) species selection

D) goal direction in evolution

C

56

57) The existence of evolutionary trends, such as increasing body sizes among horse species, is evidence that _____.

A) a larger volume-to-surface area ratio is adaptive in many mammals

B) evolution generally progresses toward some goal

C) evolution tends toward increased complexity or increased size

D) in particular environments, similar adaptations can be beneficial to more than one species

D

57

58) If the complex protein assemblage of the prokaryotic flagellum arose by the same general processes as those of the complex eyes of molluscs (such as squids and octopi), then _____.

A) natural selection cannot account for the rise of the prokaryotic flagellum

B) ancestral versions of this protein assemblage were either less functional or had different functions than modern prokaryotic flagella

C) neither eyes nor flagella could have arisen by evolution because both are too complex to have evolved

D) the need for more complex structure must have driven evolution

B

58

59) Certain proteins of the complex motor that drives bacterial flagella are modified versions of proteins that had previously belonged to plasma membrane pumps. This evidence supports the claim that _____.

A) natural selection produces organs that will be needed in future environments

B) the motors of bacterial flagella must have originated in other organisms

C) natural selection can produce new structures by coupling together parts of other structures

D) bacteria that possess flagella must have lost the ability to pump certain chemicals across their plasma membranes

C

59

A female fly, full of fertilized eggs, is swept by high winds to an island far out to sea. She is the first fly to arrive on this island and the only fly to arrive in this way. Thousands of years later, her numerous offspring occupy the island, but none of them resembles her. There are, instead, several species, each of which eats only a certain type of food. None of the species can fly and their balancing organs (halteres) are now used in courtship displays. The male members of each species bear modified halteres that are unique in appearance to their species. Females bear vestigial halteres. The ranges of all of the daughter species overlap.

60) Which of these fly organs, as they exist in the description above, best illustrates an exaptation?

A) vestigial halteres

B) halteres

C) mouthparts

D) eggs

B

60

61) One hypothesis that has been proposed regarding the origin of life suggests that life evolved from an "RNA world" to today’s "DNA world." Considering the properties of RNA and DNA molecules, which questions would direct an investigation of the most insightful test(s) of this hypothesis?

A) Is it likely that RNA molecules functioned as ribozymes to synthesize DNA from amino acids, and that this role was reversed when DNA became the information source?

B) Is it likely that simple, yet stable RNA molecules served as a primitive precursor to a less stable DNA molecule that was more capable of storing more information?

C) Could RNA have provided a template for DNA assembly, thereby enabling a more stable molecule that is replicated more accurately?

D) Since ribozymes could freely enter and leave the vesicles, could these molecules have brought external DNA into the cell as a less stable, but more reliable storage molecule of double-stranded DNA?

C

61

62) Endosymbiosis is an evolutionary theory that explains the origin of eukaryotes and suggests a specific order in which this might have occurred. Ancestral cells engulfed and then began to use the metabolic processes of the smaller cells. Based on shared core processes and features, which statement most accurately describes the order, the theory and the evolutionary implications for all organisms within domain Eukarya?

A) Ancestral heterotrophic eukaryotes most likely engulfed both a heterotrophic and an autotrophic prokaryote, whereas ancestral photosynthetic eukaryotes probably provided the host cell for the first mitochondria. Over time, natural selection favored these relationships and these cells became ancestors of all eukaryotes.

B) All ancestral eukaryotes would have most likely consumed a nucleus-like prokaryote that eventually became the eukaryotic nucleus. These new eukaryotic cells would have had an advantage over prokaryotic cells by acquiring a nuclear command center for regulating cellular activities.

C) As carbon dioxide levels were increasing over time, natural selection would have favored organisms that acquired a photosynthetic prokaryote to convert carbon dioxide into sugars. These would have likely been the first eukaryotic cells. At which point, these ancestral cells engulfed mitochondria-like prokaryotes that would have provided an even greater advantage for cells in this environment.

D) As Earth was becoming more aerobic, mitochondria would have provided an advantage to host cells by converting "toxic" oxygen into energy for heterotrophic cells. Since mitochondria are found in all eukaryotes, these combinations likely evolved first. Photosynthetic eukaryotes probably acquired an autotrophic prokaryote, which developed an advantageous symbiotic relationship with the host cell.

D