Chapter 25 Bacteria

The first eukaryotic cell is thought to have evolved at least _____ million years ago.

1800

How many membranes are present around the chloroplast of a member of the Chlorachniophyta?

4

A young paleontologist is extremely excited. In sedimentary rocks dating from 70 million years ago, she has found some new microfossils. The shells of which organisms likely contributed to the accumulation of sediments on the seafloor (and the formation of these sedimentary rocks)? diatoms radiolarians foraminiferans coccolithophorids All of these choices are correct.

All of these choices are correct.

To which superkingdom does the organism that causes red tide belong?

Alveolata

Which of the seven existing superkingdoms includes the earliest eukaryote fossil related to living protists?

Archaeplastida

Which structural feature helps support the hypothesis that chloroplasts came from cyanobacteria? Chloroplasts and cyanobacteria have internal parallel laminae. Chloroplasts and cyanobacteria are about the same size. Chloroplast and cyanobacterial genomes are the same physical size. Chloroplast and cyanobacteria both use the same ribosomes for translation.

Chloroplasts and cyanobacteria have internal parallel laminae.

Which of the statements is evidence supporting the hypothesis that eukaryotic chloroplasts originated from cyanobacteria? Chloroplasts can leave the cell and function freely on their own. Chloroplasts and cyanobacteria have the same number of genes. Chloroplasts and cyanobacteria have similar DNA sequences for shared genes. In evaluations of phylogenies of cyanobacteria and chloroplasts, the nucleotide sequences of genes in chloroplasts appear as the sister group to cyanobacteria. The close sequence similarity between the genome of cyanobacteria and chloroplasts shows that they descended from a common ancestor.Chloroplasts and cyanobacteria both have cell walls.

Chloroplasts and cyanobacteria have similar DNA sequences for shared genes.

Phylogenies based on sequences from organellar genomes and nuclear genomes from the same group of species yield phylogenetic trees with different branching patterns. How is this possible?

Endosymbiosis makes this possible. The genome of the chloroplast is more closely related to members of the group in which it originally evolved, whereas the nuclear genome of the engulfing organism has its own evolutionary trajectory.

Eukaryotic genomes often have large amounts of non-coding DNA. A cell must expend energy to replicate all of its DNA. Which statement suggests a selective advantage over the genome organization of prokaryotic cells? Eukaryotes have a larger portion of the genome available for specific regulation of gene expression. Eukaryotes can have larger genomes because they have larger cells to hold the entire genome. Eukaryotes have multiple copies of each gene, so mutations are less likely to be expressed. Eukaryotes can express a greater number of genes at the same time relative to prokaryotes.

Eukaryotes have a larger portion of the genome available for specific regulation of gene expression.

Which of the statements is a key advantage of eukaryotic cells over prokaryotic cells? Eukaryotic cells have a rigid cytoskeleton, which allows them to withstand greater stress. Eukaryotic cells have ribosomes, which allow them to make more complex proteins. Eukaryotic cells have a cell membrane, which allows them to ship materials into and out of the cell. None of the other answer options is correct. Eukaryotic cells have a flexible cytoskeleton, which allows them to change shape and gives them the ability to engulf other materials.

Eukaryotic cells have a flexible cytoskeleton, which allows them to change shape and gives them the ability to engulf other materials.

Why have more groups within the archaeplastids not developed complex multicellularity?

Evolution is not goal-oriented, resulting in complex multicellularity; each group is successful with its current morphology.

Animals inherited a sexual life cycle from their protistan ancestors. In what way have animals modified the life cycle characteristic of most protists?

In animals, the diploid zygote undergoes multiple rounds of mitotic cell division before sexual fusion takes place.

Which statement represents evidence for the order of organelle evolution in eukaryotes? Chloroplasts evolved first because there was little to no oxygen available in Earth's early atmosphere for mitochondria to use as a final electron acceptor. The presence of some eukaryotes that lack mitochondria and chloroplasts reveals that it cannot be determined which organelle evolved first in eukaryotes. Both mitochondria and chloroplasts evolved simultaneously and resulted in different descendant evolutionary lineages. Mitochondria evolved first because all eukaryotes have mitochondria, or evidence of mitochondria, but not all eukaryotes have chloroplasts.

Mitochondria evolved first because all eukaryotes have mitochondria, or evidence of mitochondria, but not all eukaryotes have chloroplasts.

Stramenopiles, alveolates, and rhizarians all descended from the same common ancestor. Which statement is a correct representation of the presence of photosynthesis in these groups? Photosynthesis occurred from primary endosymbiosis in the Rhizaria and secondary endosymbiosis in the other two groups. Photosynthesis is the result of two separate endosymbiotic events in these groups, one of which occurred in the common ancestor of the Stramenopiles and Alveolates. Photosynthesis in these groups occurred from three separate endosymbiotic events in lineages that descended from a single common ancestor. Photosynthesis in these groups occurred from a single endosymbiotic event in a common ancestor.

Photosynthesis is the result of two separate endosymbiotic events in these groups, one of which occurred in the common ancestor of the Stramenopiles and Alveolates.

You have learned that having linear DNA has consequences, the major one being that the DNA is shortened every time it replicates. This does not happen with the circular DNA found in prokaryotes. What, then, is the advantage of having linear DNA? Linear DNA is easier to package than circular DNA. Linear DNA is less susceptible to viruses than circular DNA. Since mitochondria and chloroplasts have circular DNA, nuclear DNA had to be linear. Replication can begin from multiple sites on linear DNA, allowing rapid replication and relieving the evolutionary pressure for a streamlined genome. All of these choices are correct.

Replication can begin from multiple sites on linear DNA, allowing rapid replication and relieving the evolutionary pressure for a streamlined genome.

Imagine there is a mutation in a eukaryotic cell that affects the cell's ability to produce microtubules. Which of the answer options would you expect to be a characteristic of cells with this mutation compared to cells without the mutation? Transport rates of mRNA out of the nucleus would be slower. Production of vesicles by the Golgi would be slower. ATP production would be slower. Response rates in cell signaling pathways would be slower.

Response rates in cell signaling pathways would be slower.

The term protist lacks phylogenetic accuracy because it represents a paraphyletic group. Which of the statements reflects the paraphyly of protist taxa?

Some eukaryotic lineages evolved from protists, and they are not included in the group called protists.

To which of the superkingdoms do diatoms belong?

Stramenopila

Approximately 800 years ago paleontologists see an increase in the diversification of protists as evidenced by increased diversity of fossilized forms of organisms. Which answer option describes how this diversification may have occurred? There was a substantial increase in oxygen levels between 1000 and 800 million years ago that allowed for sessile protists to get much larger in size. The evolution of early vertebrates caused an increase in forms where selection for protection from predators increased diversity in form. A change in environmental parameters occurred such that more organisms fossilized. The change in ecological roles, for some, from filter feeders to predators resulted in selection for diverse morphologies capable of eating other organisms.

The change in ecological roles, for some, from filter feeders to predators resulted in selection for diverse morphologies capable of eating other organisms.

If you were to sequence the genome of a chloroplast and the genome of a cyanobacterial ancestor, which result would you expect to find? The genome of the chloroplast would be the same size as that of the ancestor. The genome of the ancestor would be larger. Each genome would have its own unique set of genes. Each genome would use a different set of ribosomes for translation.

The genome of the ancestor would be larger.

Most eukaryotic cells contain mitochondria, but a few single-celled eukaryotic organisms found in oxygen-free environments do not. Which of the observations led biologists to reject the hypothesis that these mitochondria-free eukaryotes evolved before the endosymbiotic event that established mitochondria in other eukaryotes? All eukaryotes have remnant chloroplast genes. The nuclear genome of these mitochondria-free eukaryotes contains relics of mitochondrial genes. Some eukaryotes have chloroplasts instead of mitochondria. All eukaryotes exhibit some sort of energy utilization.

The nuclear genome of these mitochondria-free eukaryotes contains relics of mitochondrial genes.

Imagine you are sampling unicellular eukaryotes from a lake where the environmental conditions show little variation in resource and light availability, temperature, and the diversity of other organisms that also live in the lake throughout the year. As you are collecting samples, you notice that the greatest majority of individuals sampled are haploid unicellular eukaryotes and that there are no gametes in your samples. Your hypothesis for these findings is that haploid individuals are very successful in this environment and that producing variation through sexual reproduction is not selected for in populations of unicellular eukaryotes. You sample three more lakes with the same conditions for unicellular eukaryotes. Which findings described in the answer options would refute your hypothesis? The samples from the other lakes also show the greatest number of individuals are haploid unicellular eukaryotes, but represent different species than what was found in the original lake. The samples from the other lakes show the greatest number of individuals are diploid unicellular eukaryotes, and no gametes are found in the samples. The samples from the other lakes have an equal number of individuals from haploid and diploid unicellular eukaryotes, but represent different species than what was found in the original lake. No gametes are found in these samples. The samples from the other lakes also show the greatest number of individuals are haploid unicellular eukaryotes, but represent different species than what was found in the original lake. There are gametes found in the samples.

The samples from the other lakes also show the greatest number of individuals are haploid unicellular eukaryotes, but represent different species than what was found in the original lake. There are gametes found in the samples.

What is the possible significance of the finding that genes related to bacteria and archaea occur in the eukaryotic genome?

These genes may be the result of horizontal gene transfer; An archaeon may have engulfed a bacterium to form a eukaryotic cell

T/F: Choanoflagellates are the closest protistan relatives of animals.

True

T/F: Diatoms appeared during the Mesozoic Era, and the skeletons of these organisms contributed to the accumulation of sediments on the deep seafloor.

True

T/F: For the life cycle of the vascular plant, there are two times during the life cycle where genetic variation can be introduced.

True

T/F: If you were to sequence the genome from a chloroplast found in the cyanobacteria Paulinella chromatophore and place it in a phylogeny with other photosynthetic organisms, you would get a phylogeny that shows photosynthesis originated from more than one common ancestor.

True

T/F: The nuclear genome of these mitochondria-free eukaryotes contains relics of mitochondrial genes.

True

T/F: There is no known symbiosis between a heterotrophic host and a photosynthetic partner in mammals.

True

Which of the statements best describes a symbiotic relationship between two organisms? Two organisms live in close, long-term, physical association with each other. Two organisms live in close, physical association with each other, and both organisms benefit from the relationship. Two organisms live in close, physical association with each other, and one organism benefits to the detriment of the other. Two organisms live in close, physical association with each other, and both organisms thrive, but one is the primary provider and the other is the primary beneficiary.

Two organisms live in close, long-term, physical association with each other.

Which of the statements accounts for why eukaryotic cells are typically much larger than prokaryotic cells? Using molecular motors, eukaryotic cells can transport materials throughout their cytoplasm much faster than prokaryotic cells can; prokaryotic cells have to rely on simple diffusion. None of the answer options is correct. A eukaryotic nucleus is so large that the cell has to be bigger to allow space for other organelles. Because eukaryotic cells have more DNA, their cell volume has to be larger. Reproducing sexually requires the cells to be larger so that everything in the cell can be evenly distributed to the daughter cells.

Using molecular motors, eukaryotic cells can transport materials throughout their cytoplasm much faster than prokaryotic cells can; prokaryotic cells have to rely on simple diffusion.

How does current theory explain the origin of a nucleus in eukaryotic cells?

While there are some competing theories on the origin of the nucleus, neither theory discussed in the text really explains the origin of the nucleus.

Chloroplasts are thought to have originated from a symbiotic relationship between an ancient eukaryotic cell and...

a cyanobacterium.

Which of the answer choices is the best description of a protozoan? a chemotrophic prokaryote a heterotrophic protist a chemotrophic protist a heterotrophic prokaryote a photosynthetic protist

a heterotrophic protist

Which of the answer choices is the best description of algae? a heterotrophic protist a heterotrophic prokaryote a photosynthetic protist a chemotrophic protist a chemotrophic prokaryote

a photosynthetic protist

Within the opisthokonts, animals are most closely related to...

ahoanoflagellates

Which other groups would have to be included within the protists in order for the group to be considered monophyletic? animals, plants, and fungi plants and fungi animals animals and fungi fungi

animals, plants, and fungi

Imagine there is a cell that has only long-chain saturated fatty acid tails in the phospholipids making up the plasma membranes. This would _____ the fluidity of the cell's plasma membrane.

decrease

Which of the organisms is currently one of the most important photosynthetic organisms in the oceans? red algae diatoms None of the other answer options is correct. glaucocystophytes green algae

diatoms

Chloroplasts and mitochondria have their own _____, which are _____ relative to those of the free-living bacteria to which they are closely related.

genomes; small

All of the membranes of the eukaryotic cell are in dynamic continuity except for membranes in the...

mitochondria and chloroplasts.

Which of the statements describes characteristics of eukaryotic cells but not of prokaryotic cells? two or more circular chromosomes, dynamic membrane system, compartmentalized metabolic processes two or more linear chromosomes, dynamic membrane system, diverse means of harvesting and utilizing energy under anaerobic conditions linear chromosomes, endomembrane system, nucleus, diverse means of harvesting and utilizing energy under anaerobic conditions relatively large genome, dynamic cytoskeleton, compartmentalized metabolic processes

relatively large genome, dynamic cytoskeleton, compartmentalized metabolic processes

Imagine that your uncle is a scientist who has found himself in possession of a time machine. The two of you travel back to the Paleozoic Era and are perusing the oceans for microscopic life. What will you find?

some photosynthetic organisms (cyanobacteria and green algae) and radiolarians and other heterotrophic protists

In plasmodial slime molds, what structure is responsible for producing the haploid cells that disperse into the environment?

sporangium

Of all the green algae, which are most closely related to land plants?

streptophytes