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Ch. 28 - Protists
All textbooksCampbell 12th EditionCh. 28 - ProtistsProblem 6
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Chapter 28, Problem 6

Based on the phylogenetic tree in Figure 28.5, which of the following statements is correct? (A)Excavata and SAR form a sister group. (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.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Phylogenetic Tree

A phylogenetic tree is a diagram that represents evolutionary relationships among various biological species based on similarities and differences in their physical or genetic characteristics. It illustrates how species are related through common ancestry, with branches indicating divergence points. Understanding how to read and interpret these trees is crucial for analyzing evolutionary relationships and determining the correct statements about groups like Excavata, SAR, and Unikonta.
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Building Phylogenetic Trees Example 2

Eukaryotic Supergroups

Eukaryotic supergroups are major lineages within the domain Eukarya, which includes all organisms with complex cells. The main supergroups are Excavata, SAR (Stramenopiles, Alveolates, Rhizarians), Archaeplastida, and Unikonta. Each supergroup encompasses a diverse range of organisms, and understanding their evolutionary relationships helps in determining the most basal groups and their common ancestors.
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Overview of the Four Supergroups of Eukaryotes

Sister Groups

Sister groups are pairs of taxa that are more closely related to each other than to any other group. In a phylogenetic tree, sister groups share a common ancestor that is not shared with any other group. Identifying sister groups is essential for understanding evolutionary relationships and can help clarify statements regarding the relative ages of common ancestors among different eukaryotic supergroups.
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Functional Groups
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Textbook Question

Which group is correctly paired with its description?


A. diatoms—important consumers in aquatic communities

B. diplomonads—protists with modified mitochondria

C. apicomplexans—producers with intricate life cycles

D. red algae—acquired plastids by secondary endosymbiosis


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Textbook Question

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

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Textbook Question

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.

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Textbook Question

EVOLUTION CONNECTION • 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.)


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