11.2.1 The Archaea

Question 1

Archaea

Answer 1

• The Archaea, organisms formerly grouped with Bacteria, are now placed in their own domain because they differ both genetically and biochemically from Bacteria.
• There are four major groups within the domain Archaea: the methanogens, the extreme halophiles, the extreme thermophiles, and the Thermoplasma.

Question 2

note

Answer 2

• The cladogram shows the current three-domain system, which reflects the important molecular and biochemical differences between Bacteria and Archaea. The rRNA sequences of Archaea are more like Eukarya than Bacteria. They contain many genes that are not found in either Bacteria or Eukarya. As shown in the diagram, members of the domain Archaea have unusual cell membranes made up of long-chain hydrocarbons with glycerol at both ends. Finally, Archaean cell membranes do not contain peptidoglycan, while bacterial cell membranes do.
• There are four groups within the Archaea: the methanogens, the extreme halophiles, the extreme thermophiles, and the Thermoplasma.
• The methanogens are responsible for producing all of the methane on the planet through the reduction of CO2. They are obligate anaerobes. Methanogens live in the guts of ruminants and in protozoans that inhabit the guts of termites where they digest cellulose.
• The extreme halophiles are found in extremely saline
  environments such as the Great Salt Lake and Mono Lake. These environments can be as much as 10 times saltier than the ocean. This group of archaeans has evolved physiological adaptations to maintain osmotic stability under these extreme conditions.
• The extreme thermophiles are archaeans that live in extremely hot environments, some of which attain temperatures as great as 105° C. They are found in hot springs and deep sea vents. The deep sea vent worm, Riftia pachyptila, obtains all of its nutrients from an endosymbiotic sulfur thermophile.
• The fourth group of Archaea is made up of a single genus, Thermoplasma. They are thermophyllic and acidophyllic, and occur in coal deposits.

Question 3

Which of the following does not belong to the domain Archaea?

Answer 3

• cyanobacteria

Question 4

The ____________________ are found in extremely saline environments such as the Great Salt Lake.

Answer 4

• extreme halophiles

Question 5

The methanogens produce methane by ____________________.

Answer 5

• reducing carbon dioxide

Question 6

What aspect of the Archaean cell membrane is unique?

Answer 6

• long-chain hydrocarbons with glycerol at both ends

Question 7

____________________ inhabit the guts of termites where they digest cellulose.

Answer 7

• Methanogens

Question 8

True or false?

The rRNA sequences of Archaea are more like Eukarya than Bacteria.

Answer 8

• true