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

Complete the sentence: All protists ____________.