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Ch. 28 - Protists
Campbell - Campbell Biology 12th Edition
Urry12th EditionCampbell BiologyISBN: 9785794169850Not the one you use?Change textbook
All textbooksUrry 12th EditionCh. 28 - ProtistsProblem 6
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

Verified step by step guidance
1
Understand the concept of a phylogenetic tree: A phylogenetic tree is a diagram that represents evolutionary relationships among various biological species based upon similarities and differences in their physical or genetic characteristics.
Identify the key components of the phylogenetic tree: Look for the nodes, branches, and the root of the tree. Nodes represent common ancestors, branches show evolutionary paths, and the root is the most ancestral form.
Examine the relationships between groups: Determine which groups are sister groups, meaning they share a common ancestor not shared by other groups. Look for the branching points that indicate these relationships.
Analyze the age of common ancestors: Compare the positions of nodes to determine the relative ages of common ancestors. Nodes closer to the root are older, while those further away are more recent.
Determine the basal group: The basal group is the one that diverged first from the common ancestor. Look at the branching pattern from the root to identify which group diverged first.

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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. The tree's branches indicate how species or groups are related through common ancestors, with the root representing the most recent common ancestor of all entities on the tree.
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Building Phylogenetic Trees Example 2

Sister Groups

Sister groups are two descendants that split from the same node in a phylogenetic tree, indicating they share an immediate common ancestor. Understanding sister groups is crucial for interpreting evolutionary relationships, as they help identify which groups are more closely related to each other compared to others on the tree.
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Functional Groups

Basal Group

A basal group in a phylogenetic tree refers to the earliest diverging lineage within a clade, often depicted as the first branch from the root. Identifying the basal group helps in understanding the evolutionary history and ancestral traits of the clade, although it can sometimes be challenging to determine due to incomplete data or complex evolutionary histories.
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Functional Groups
Related Practice
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, 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

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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