Deck 11: The Origin and Evolution of Early Life

Question 1

Why were the first RNA replication experiments insufficient support for the RNA world hypothesis?

A)The experiments did not demonstrate natural selection.
B)RNA could not adapt to environmental challenges.
C)The RNA produced was not self-replicating.
D)No mutations occurred in the RNA.
E)Mutations occurred, but they were not heritable.

Answer 1

C

Question 2

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

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

Answer 2

C

Question 3

Why was it necessary to do serial transfers in the experiment illustrated above?

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

Answer 3

A

Question 4

Ribozymes are

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

Question 5

The schematic diagram above of a simple self-replicating system demonstrates that

A)natural selection is occurring.
B)replication is occurring given specific substrates.
C)replication can occur independent of substrates.
D)variation can be induced in a system.

Question 6

Molecular mutualism is

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

Question 7

When life first evolved the oceans were

A)hotter and there was more oxygen than today.
B)hotter and there was less oxygen than today.
C)cooler and there was more oxygen than today.
D)cooler and there was less oxygen than today.

Question 8

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

A)Meteorites
C)Prebiotic soup reactions
B)Comets
D)DNA

Question 9

The graph below plots average ocean temperature,with two different estimates,using different methods.What has been the 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 decreased since Earth formed.
D)Ocean temperature has fluctuated wildly, and no discernable trend can be found.

Question 10

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

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

Question 11

The figures below illustrate two lineages with two variants: with and without a black spot.The arrows point to the descendants of the individual.In which situation can natural selection work?

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

Question 12

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

A)Homeostasis
B)Structural organization
C)Sexual reproduction
D)Growth
E)Response to the environment

Question 13

Why is DNA favored over RNA as genetic material?

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

Question 14

The two major cell types are

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

Question 15

In early cell evolution,why would natural selection favor division into equal-sized daughter cells?

A)Splitting into two equal parts is the most energetically efficient method.
B)Two daughter cells is the most efficient way to reproduce sexually.
C)Splitting into two daughter cells is more efficient for horizontal gene transfer.
D)Hypercycles can be maintained by splitting into two.

Question 16

A phylogenetic event horizon is

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

Question 17

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

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

Question 18

What was LUCA?

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

Question 19

Where on this tree is LUCA found?

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

Question 20

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 21

Fission is likely a method of reproduction in early cells because

A)the easiest way to divide genetic material is to split it in two.
B)hypercycles that become unstable split apart.
C)modular genomes transfer well between cells.
D)the physical constraints of a sphere cause it to become unstable and break when it becomes too big.

Question 22

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

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

Question 23

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

Question 24

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

Question 25

Why might life be much older than LUCA?

Question 26

What is most critical for understanding the minimal gene set and the origin of life?

A)The number of genes
B)The functions of the genes
C)The stable environments of bacteria with the most reduced genomes
D)The identity of genes involved in fatty acid/lipid metabolism to understand the origin of cell membranes

Question 27

What does the abbreviation LUCA stand for and what is it?

Question 28

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

Question 29

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 significance of stable peptide bonds?

Question 30

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

Question 31

Based on the figure below,showing horizontal gene transfer and the early evolution of life,which of the following statements is not true?

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

Question 32

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

Question 33

Why would natural selection favor reduced parasitic bacterial genomes?

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

Question 34

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

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

Question 35

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

Question 36

Identify all of the potential energy sources for prebiotic chemical reactions in this picture.

Question 37

In the hypercycle illustrated below,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 38

Give an example of a modern hypercycle.

Question 39

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

Question 40

How does 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.
B)If the first life-forms consisted of RNA, then current RNA-coding genes must be the ancestral genes.
C)Common functional genes imply the minimal characteristics of early cells.
D)Because so many small genome bacteria are endosymbionts, the earliest cells must have been endosymbionts.

Question 41

Pal and colleagues deleted genes to determine fitness effects in E.coli.How were fitness effects measured?

Question 42

The figure above 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