11.4.1 Protists: Archaezoa and Euglenozoa

Question 1

Protists: Archaezoa and Euglenozoa

Answer 1

• The term “protist” is a generic name for single-celled eukaryotes. The term “protist” does not imply a phylogenetic relationship.
• The candidate kingdoms Archaezoa and Euglenozoa are the most ancient eukaryotic groups to branch off the phylogenetic tree.
• Members of the Archaezoa such as Giardia sp. lack mitochondria.
• The two major groups within the kingdom Euglenozoa are the mixotrophic genus Euglena and the Kinetoplastids such as Trypanosoma gambiense.

Question 2

note

Answer 2

• Until recently, the kingdom Protista was a designation that included many single-celled eukaryotes. This group was classified into the Protozoa or animal-like protists, the algae or plant-like protists, and the fungus-like protists. Recent molecular evidence has shown that the Protista are not monophyletic. The word “protist” is now used as a generic name for single-celled eukaryotes and it does not imply a phylogenetic grouping.
• Protists are members of at least six different candidate
  kingdoms within the domain Eukarya. The most ancient of these are the Archaezoa and the Euglenozoa, both of which branched off the phylogenetic tree soon after the domains Bacteria and the Archaea.
• Although their genome contains genes that code for
  mitochondrial proteins, members of the candidate kingdom Archaezoa lack mitochondria. Giardia sp. is a common intestinal parasite that is a member of the candidate kingdom Archaezoa.
• One of the two major groups within the candidate kingdom Euglenozoa is the Euglenoids. You may be familiar with Euglenoids of the genus Euglena. Euglenoids are mixotrophic; they obtain nutrients through heterotrophic feeding as well as through photosynthesis.
• The second group within the candidate kingdom Euglenozoa is the Kinetoplastids. A structure called a kinetoplast, which consists of a mitochondrion and associated extranuclear DNA, is characteristic of this group. An example is Trypanosoma gambiense, which causes African sleeping sickness.

Question 3

Organisms that are mixotrophic

Answer 3

• are autotrophic and heterotrophic

Question 4

True or false?

The term protist implies a phylogenetic relationship.

Answer 4

• false

Question 5

Trypanosoma causes

Answer 5

• African sleeping sickness

Question 6

Organisms such as Trypanosoma have a unique organelle called the ____________________.

Answer 6

• kinetoplast

Question 7

Members of the candidate kingdom ____________________ lack mitochondria.

Answer 7

• Archaezoa

Question 8

True or false?

Giardia species lack mitochondria.

Answer 8

• true