27. Protists

Why are protists considered paraphyletic? a. They include many extinct forms, including lineages that no longer have any living representatives. b. They include some but not all descendants of their most recent common ancestor. c. They represent all of the descendants of a single common ancestor. d. Not all protists have all of the synapomorphies that define the Eukarya, such as a nucleus.

What is a transition state? a. the shape adopted by an enzyme that has an inhibitory molecule bound at its active site b. the amount of kinetic energy required for a reaction to proceed c. the intermediate complex formed as covalent bonds in the reactants are being broken and re-formed during a reaction d. the enzyme shape after binding an allosteric regulatory molecule

Evaluate the following statements regarding motility in protists. Select True or False for each statement. T/F Amoeboid motion is common in species with cell walls. T/F Some protists use flagella to swim. T/F Some protists use cilia to swim, which are shorter and more numerous than flagella. T/F Amoeboid motion requires ATP and interactions between the proteins actin and myosin.

If you were to expose cells that are undergoing aerobic respiration to a radioactive oxygen isotope in the form of O2, which of the following molecules would you expect to be radiolabeled? a. pyruvate b. water c. NADH d. CO2

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.

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.)

Complete the sentence: All protists ____________.

Which of the following is a common feature of all protists?