Deck 11: The Origin and Evolution of Early Life

Question 1

When life first evolved, ocean temperatures were ________ and there was ________ atmospheric oxygen.

A) cooler; no
B) cooler; abundant
C) hotter; abundant
D) hotter; no

Answer 1

D

Question 2

The two major cell types currently known are

A) archaea and bacteria.
B) archaea and prokaryotes.
C) prokaryotes and eukaryotes.
D) eukaryotes and archaea.

Answer 2

C

Question 3

Why did the researchers conduct serial transfers in the experiment illustrated in the figure?

A) Each serial transfer decreased the population size so that genetic drift could occur.
B) Each serial transfer was necessary to reintroduce RNA into the system.
C) Because the experiment took place in a lab, serial transfers were necessary so that the researchers could go home at night.
D) Each serial transfer is equivalent to a generation and thus provided an opportunity to study natural selection over time.

Answer 3

D

Question 4

A phylogenetic event horizon is a

A) point in the future in which species will diversify.
B) phylogeny based on extinct species.
C) point in the history of life beyond which phylogenetic analysis cannot see.
D) point at which life started.

Question 5

Natasha Paul and Gerald Joyce's experiment sought to provide evidence that supported the theory of RNA world. To show evolutionary change, there had to be variation in RNA sequences, the ability to reproduce or replicate themselves, and fitness differences between sequences. This schematic of the results illustrates which specific requirement for evolutionary change that Paul and Joyce were studying? A


B

A) It illustrates that in certain conditions, RNA was capable of replicating.
B) It illustrates variation in RNA sequences.
C) It illustrates that natural selection did not occur in RNA world.
D) It illustrates fitness differences between the RNA sequences.

Question 6

Which letter indicates where LUCA is found on this phylogenetic tree?

A) D
B) E
C) C
D) B

Question 7

The figures below illustrate two lineages with two variants: one dark gray and one pale gray. The arrows point to the descendants of the individual. Natural selection could act on the lineage on the A


B

A) left; natural selection has eliminated the spotted variant.
B) left; the number of offspring produced is independent of the mutation.
C) right; variation is heritable.
D) right; the mutation does not influence reproduction.

Question 8

Sol Spiegelman and colleagues demonstrated natural selection in RNA replications because in their experiments

A) the researchers chose which RNA molecules to replicate.
B) RNA was self-replicating.
C) RNA molecules had differential survival and reproduction rates.
D) RNA was copied into DNA.

Question 9

Encapsulation of a hypercycle would NOT be favored when

A) the costs of a membrane exceed the benefits of the cycle.
B) the membrane provides a defensive mechanism.
C) natural selection favors mutations in component members.
D) RNA components act through molecular mutualism.

Question 10

Which of the following is a reason DNA is favored over RNA as genetic material?

A) DNA makes chromosomes.
B) DNA can self-replicate.
C) DNA is more stable and thus is a more efficient transmission system.
D) DNA mutates more readily, with a weaker repair machinery.

Question 11

How can both clay and ice crystals enhance chemical reactions necessary to form complex organic molecules?

A) Both have highly reactive surfaces that help to lower the energy of activation for reactions that form complex organic molecules.
B) Both trap the water needed in reactions that result in organic molecules.
C) Both have the necessary elements to form amino acids.
D) Both have microscopic spaces that help to concentrate reagents, facilitating reactions involving those reagents.

Question 12

Ribozymes are

A) RNA enzymes.
B) proteins.
C) capable of replicating RNA.
D) capable of copying RNA into DNA.

Question 13

Which of the following is NOT a shared property of living things?

A) sexual reproduction
B) structural organization
C) homeostasis
D) response to the environment

Question 14

What was LUCA?

A) the first life-form
B) a population of life-forms that was the last common ancestor of life on Earth today
C) the only life-form present before our current lineage
D) the last universal ancestral life-form: a single individual

Question 15

The graph shown plots average ocean temperature, with two different estimates, using different methods. What has been the long-term trend over time?

A) Ocean temperature has stayed the same since Earth formed.
B) Ocean temperature has increased since Earth formed.
C) Ocean temperature has fluctuated wildly, and no discernable trend can be found.
D) Ocean temperature has decreased since Earth formed.

Question 16

Which of the following is NOT a hypothesis for the origin of viruses?

A) Viruses are escaped selfish genetic elements.
B) Viruses are escaped genes from modern genetic engineering experiments.
C) Viruses are the remnants of parasitic cellular organisms, selected for reduced size.
D) Viruses are relics of the RNA world.

Question 17

The Miller-Urey experiment is significant because it produced the first scientific evidence that

A) conditions on Earth 4 billion years ago could produce RNA.
B) conditions on Earth 4 billion years ago could produce amino acids.
C) it is possible to produce LUCA in the laboratory.
D) it is possible to produce DNA under the same conditions as on Earth 4 billion years ago.

Question 18

Which of the following was NOT a source of molecules in the "prebiotic soup"?

A) DNA
B) domets
C) meteorites
D) deep-sea hydrothermal vents

Question 19

Molecular mutualism is

A) an interaction of molecules that disrupts hypercycles.
B) an interaction of two species to the benefit of both.
C) an interaction between molecules that positively impacts the replication of each.
D) replication of RNA by another enzyme.

Question 20

How did Spiegelman et al.'s experiment on the origins of natural selection provide evidence for natural selection in an RNA-based world?

A) The RNA was originally $\backsim$ 4,000 nucleotides; after several serial transfers it was reduced to $\backsim$ 200 nucleotides as a result of faster replication of shorter sequences being advantageous.
B) The RNA sequence was originally $\backsim$ 4,000 nucleotides; after several serial transfers it increased to $\backsim$ 20,000 nucleotides as a result of faster replication of longer sequences being advantageous.
C) The experiment did not demonstrate natural selection.
D) The RNA remained at approximately is original sequence of $\backsim$ 4,000 nucleotides, demonstrating fitness in a stable environment.

Question 21

What is LUCA and why is it possible that life originated before LUCA existed?

Question 22

Consider this figure showing horizontal gene transfer and the early evolution of life. Which of the following statements is FALSE?

A) Bacteria have transferred genes to eukaryotes twice.
B) Bacteria have transferred genes to archaea many times.
C) Bacteria have transferred genes among themselves.
D) Eukaryotes have transferred genes among themselves.

Question 23

How did the discovery of ribozymes affect our understanding of the evolution of proteins and nucleic acids?

A) The discovery of ribozymes demonstrated that enzymes did not have to be proteins, and RNA enzymes (ribozymes) can be both information carrier and enzymatic molecule.
B) The discovery of ribozymes helped us understand how RNA only codes for proteins and does not act as an enzymatic molecule. This helped support the hypothesis of RNA world as an origin for living organisms on Earth.
C) The discovery of ribozymes verified that enzymes had to be proteins. This discovery helped to eliminate other theories about the origin of life in RNA world.
D) The discovery of ribozymes demonstrated definitively that ribozymes function only as an enzymatic molecule and therefore evolved before information carrier molecules.

Question 24

How has the role of horizontal gene transfer (HGT) in evolution changed over time?

A) Early life-forms had modular genomes for which HGT played a large role in adaptation. This role has decreased over time.
B) Early life-forms had modular genomes for which HGT played a large role in adaptation. This role has increased over time.
C) Early life-forms were fixed entities, and the only way to adapt was through HGT. HGT no longer occurs.
D) HGT was irrelevant for early life-forms. HGT is a more recent phenomenon and is important for current adaptations.

Question 25

How does this figure illustrate a line of evidence supporting RNA world?

A) This figure illustrates a cofactor that indicates catalytic and structural functions performed by RNAs.
B) This figure illustrates the removal of a hydroxyl group through a ribonucleotide reductase.
C) This figure shows the catalytic site of a ribosome that is formed entirely from RNA.
D) This figure illustrates one of the many essential parts of RNA present in the prebiotic environment.

Question 26

If horizontal gene transfer was predominant in early evolution, how would this affect our ability to reconstruct the tree of life?

A) Horizontal gene transfer blurs the concept of species, making it difficult to delineate ancestral species.
B) Horizontal gene transfer resulted in chloroplasts that confuse the plant lineage.
C) Horizontal gene transfer places viruses firmly at the beginning of the tree of life.
D) Horizontal gene transfer means that life-forms do not share a history of common descent.

Question 27

How do comparative data on genes of extant species help us to make estimates of what happened before the phylogenetic event horizon?

A) Common genes must have existed for a long time, possibly since the first life-forms.
B) Common functional genes imply the minimal characteristics of early cells.
C) If the first life-forms consisted of RNA, then current RNA-coding genes must be the ancestral genes.
D) The first life-forms must have been endosymbionts because most small-genome extant bacteria are endosymbionts.

Question 28

Why might the analysis of endosymbiotic bacterial genomes be misleading for understanding the minimal gene set?

A) They are bacteria and therefore have nothing in common with LUCA.
B) They may have gained genes to be able to live within another organism.
C) They may have lost genes that would have been essential to early life-forms due to their reduced metabolic requirements.
D) Their genes can be disrupted by transposons.

Question 29

How did phospholipids confer an advantage in terms of natural selection for vesicles that had higher phospholipid content?

A) Vesicles with higher phospholipid content could tolerate a wider range of temperatures in a warmer world.
B) Vesicles with higher phospholipid content were more efficient at transporting materials back and forth across the membrane.
C) Vesicles with higher phospholipid content tended to grow more than those with lower phospholipid content, giving higher phospholipid vesicles the ability to outcompete others.
D) Vesicles with higher phospholipid content were able to tolerate a more acidic environment that was typical of the prebiotic "soup" that existed at the time cells originated.

Question 30

Why would natural selection favor reduced parasitic bacterial genomes?

A) The parasitic lifestyle eliminates metabolism, leading to gene loss.
B) Parasitic bacteria are primitive and never had metabolic genes.
C) Parasites have reduced metabolic needs, which leads to gene loss.
D) Transposons have caused mutagenesis and genes have been lost.

Question 31

Explain molecular mutualism and how it is applied to the hypercycle model.

Question 32

Why does understanding the origin of life require the collaboration of biologists, chemists, geologists, and atmospheric scientists?

Question 33

Why does the theory of evolution NOT explain the origin of life?

A) The theory of evolution is a scientific theory and cannot explain supernatural phenomena such as the origin of life.
B) The theory of evolution explains how life diversified after its origin and does not address the origin of life itself.
C) The theory of evolution is only a biological theory, and the study of the origin of life also includes chemistry, geology, atmospheric scientists, and others.
D) The origin of life is typically studied by philosophers and religious scholars, not scientists.

Question 34

When researchers are trying to identify a minimal gene set, which characteristic is most critical for identifying which genes constitute the minimal gene set?

A) the overall number of genes
B) the length of the genome
C) the functions of the genes
D) the identity of genes involved in production of cell membranes

Question 35

Deletion experiments of E. coli have determined the minimal set of metabolic pathways. When these pathways were compared to a closely related species, W. glossinidia, an endosymbiotic organism that obtains resources from its host, researchers found that

A) W. glossinidia had fewer metabolic pathways.
B) E. coli was more specialized and had fewer metabolic pathways.
C) the gene sets match perfectly.
D) the genomes were not comparable.

Question 36

Identify all potential energy sources for prebiotic chemical reactions depicted in the figure.

Question 37

Which of the following was NOT identified as a basic function of genes included in a minimal gene set of Bacillus subtilis in Koonin's 2003 study?

A) translation
B) metabolism
C) photosynthesis
D) replication and repair

Question 38

Current scientific estimates indicate that Earth is approximately 4.5-4.6 ________ years old and that life began on Earth approximately 3.2-3.5 ________ years ago.

A) billion; million
B) million; million
C) billion; billion
D) million; billion

Question 39

Replicators A, B, C, and D become encapsulated by a membrane of fatty acids they produced. Building the membrane resulted in a great metabolic cost. The new membrane provides limited control over the new microenvironment, is fairly permeable, and frequently allows unneeded substances in while allowing newly made molecules to dissipate into the environment. Given this information, is it likely this new encapsulation will be favored by natural selection?

A) Yes, encapsulation always confers an advantage.
B) Yes, the metabolic costs outweigh the benefits of microenvironment control.
C) No, encapsulation is beneficial but does not affect how natural selection operates.
D) No, encapsulation had a high metabolic cost and the membrane provides little benefit for encapsulation.

Question 40

Why can we not use modern atmospheric conditions to infer the origin of life?

Question 41

Sol Spiegelman and colleagues demonstrated natural selection with RNA molecules. How did they satisfy the three conditions required for natural selection?

Question 42

Describe the four lines of evidence supporting "RNA world."

Question 43

The figure shows horizontal gene transfer and the early evolution of life. Based on this figure, order the following events from earliest to latest. A. Mitochondrial horizontal gene transfer
B. Chloroplast horizontal gene transfer
C. Plants and algae separate from animals and fungi
D. Fungi separate from animals

Question 44

The conditions in the Miller-Urey experiment produced amino acids but not peptides. Subsequent experiments have adjusted the conditions and have produced other amino acids and stable peptide bonds. What is the biological significance of stable peptide bonds?

Question 45

In the hypercycle illustrated in the figure, the four components increase their own replication and also positively affect the replication of other members. How does the presence of a membrane, uniting the four components, favor the connections between the members of the hypercycle in this case compared to a set that does not have a membrane?

Question 46

What is the evolutionary relationship between mutation rates and DNA proofreading and repair?

Question 47

To understand minimal gene sets, Csaba Pal et al. (2006) deleted genes to determine fitness effects in E. coli. How were fitness effects measured?

Question 48

Many proteins are now thought to consist of modular units that can, through exon shuffling, form new proteins. How is this situation analogous to what may have occurred in the earliest life-forms?

Question 49

List the properties typically associated with living organisms.

Question 50

What did Carl Woese hypothesize about early cell evolution and how does it affect our view of the origin of living organisms?