Protists

First, make sure you understand how to read the comparison matrix.

Find the cell that represents the comparison of C. testosteroni andE. coli. What value is given in this cell? What does that value signifyabout the comparable rRNA gene sequences in those two organisms?Explain why some cells have a dash rather than a value. Whyare some cells shaded gray, with no value?

The equation F = e^-kt describes the fraction F of an original isotope remaining after a period of t years; the exponent is negative because it refers to a decrease over time. The constant k provides a measure of how rapidly the original isotope decays. For the decay of carbon-14 to nitrogen-14, k = 0.00012097. To find t, rearrange the equation by following these steps: (a) Take the natural logarithm of both sides of the equation: ln(F ) = ln(e-^kt). Rewrite the right side of this equation by applying the following rule: ln(e^x) = x ln(e). (b) Since ln(e) = 1, simplify the equation. (c) Now solve for t and write the equation in the form “t = ________.”

Why did the researchers choose one plant mitochondrion and five

bacterial species to include in the comparison matrix?

Using the equation you developed, the data from the table, and a calculator, estimate the ages of seed 1, seed 2, and seed 3.                

Which bacterium has an rRNA gene that is most similar to that of the wheat mitochondrion? What is the significance of this similarity?

Cite at least four examples of structural and functional diversity among protists.

Summarize the role of endosymbiosis in eukaryotic evolution.

After studying Figure 28.3, predict how many distinct genomes are contained within the cell of a chlorarachniophyte. Explain.

Why do some biologists describe the mitochondria of diplomonads and parabasalids as “highly reduced”?

WHAT IF? DNA sequence data for a diplomonad, a euglenid, a plant, and an unidentified protist suggest that the unidentified species is most closely related to the diplomonad. Further studies reveal that the unknown species has fully functional mitochondria. Based on these data, at what point on the phylogenetic tree in Figure 28.2 did the mystery protist’s lineage probably diverge from other eukaryote lineages? Explain

Explain why forams have such a well-preserved fossil record.

Would you expect the plastid DNA of photosynthetic dinoflagellates, diatoms, and golden algae to be more similar to the nuclear DNA of plants (domain Eukarya) or to the chromosomal DNA of cyanobacteria (domain Bacteria)? Explain.

Which of the three life cycles in Figure 13.6 exhibits alternation of generations? How does it differ from the other two?

MAKE CONNECTIONS Review Figures 9.2 and 10.6, and then summarize how CO2 and O2 are both used and produced by chlorarachniophytes and other aerobic algae.

Contrast red algae and brown algae.

Why is it accurate to say that Ulva is truly multicellular but Caulerpa is not?

WHAT IF? Suggest a possible reason why species in the green algal lineage may have been more likely to colonize land than species in the red algal lineage.

Contrast the pseudopodia of amoebozoans and forams.

In what sense is “fungus animal” a fitting description of a slime mold? In what sense is it not fitting?

Recent evidence indicates that the root of the eukaryotic tree may lie between a clade that includes unikonts and excavates, and all other eukaryotes. Draw the tree suggested by this result.

Justify the claim that photosynthetic protists are among the biosphere’s most important organisms.

Describe three symbioses that include protists.

WHAT IF? High water temperatures and pollution can cause corals to expel their dinoflagellate symbionts. How might such "coral bleaching" affect corals and other species?

MAKE CONNECTIONS The bacterium Wolbachia is a symbiont that lives in mosquito cells and spreads rapidly through mosquito populations. Wolbachia can make mosquitoes resistant to infection by Plasmodium; researchers are seeking a strain that confers resistance and does not harm mosquitoes. Compare evolutionary changes that could occur if malaria control is attempted using such a Wolbachia strain versus using insecticides to kill mosquitoes. (Review Figure 28.16 and Concept 23.4.)

Plastids that are surrounded by more than two membranes are evidence of 

(A) evolution from mitochondria.

(B) fusion of plastids. 

(C) origin of the plastids from archaea. 

(D) secondary endosymbiosis.

Biologists think that endosymbiosis gave rise to mitochondria before plastids partly because 

(A) the products of photosynthesis could not be metabolized without mitochondrial enzymes. 

(B) all eukaryotes have mitochondria (or their remnants), whereas many eukaryotes do not have plastids. 

(C) mitochondrial DNA is less similar to prokaryotic DNA than is plastid DNA.

(D) without mitochondrial CO₂ production, photosynthesis could not occur.

Which group is incorrectly paired with its description? 

(A) diatoms—important producers in aquatic communities 

(B) red algae—eukaryotes that acquired plastids by secondary endosymbiosis

(C) apicomplexans—unicellular parasites with intricate life cycles 

(D) diplomonads—unicellular eukaryotes with modified mitochondria.

According to the phylogeny presented in this chapter, which protists are in the same eukaryotic supergroup as plants? 

(A) green algae 

(B) dinoflagellates 

(C) red algae 

(D) both A and C

In a life cycle with alternation of generations, multicellular haploid forms alternate with 

(A) unicellular haploid forms

(B) unicellular diploid forms

(C) multicellular haploid forms

(D) multicellular diploid forms.

Based on the phylogenetic tree in Figure 28.2, which of the following statements is correct? 

(A) The most recent common ancestor of Excavata is older than that of SAR. 

(B) The most recent common ancestor of SAR is older than that of Unikonta. 

(C) The most basal (first to diverge) eukaryotic supergroup cannot be determined. 

(D) Excavata is the most basal eukaryotic supergroup.

DRAW IT Medical researchers seek to develop drugs that can kill or restrict the growth of human pathogens yet have few harmful effects on patients. These drugs often work by disrupting the metabolism of the pathogen or by targeting its structural features. Draw and label a phylogenetic tree that includes an ancestral prokaryote and the following groups of organisms: Excavata, SAR, Archaeplastida, Unikonta, and, within Unikonta, amoebozoans, animals, choanoflagellates, fungi, and nucleariids. Based on this tree, hypothesize whether it would be most difficult to develop drugs to combat human pathogens that are prokaryotes, protists, animals, or fungi. (You do not need to consider the evolution of drug resistance by the pathogen.)

Applying the “If … then” logic of deductive reasoning (see Concept 1.3), what are a few of the predictions that arise from the hypothesis that plants evolved from green algae? Put another way, how could you test this hypothesis?

Organisms interact with each other and the physical environment. In a short essay (100–150 words), explain how the response of diatom populations to a drop in nutrient availability can affect both other organisms and aspects of the physical environment (such as carbon dioxide concentrations).

This micrograph shows a single-celled eukaryote, the ciliate Didinium(left), about to engulf its Paramecium prey, which is also a ciliate. Identify the eukaryotic supergroup to which ciliates belong and describe the role of endosymbiosis in the evolutionary history of that supergroup. Are these ciliates more closely related to all other protists than they are to plants, fungi, or animals? Explain.