Which statement correctly describes a key difference between Bacteria and Archaea?

• A. Archaea are always multicellular, whereas Bacteria are always unicellular.
• B. Archaea use ester-linked fatty acids in their membranes, whereas Bacteria use ether-linked isoprenoids.
• C. Archaea have a membrane-bound nucleus, whereas Bacteria do not.
• D. Archaea lack peptidoglycan in their cell walls, whereas most Bacteria have peptidoglycan.

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the basic cellular structure of Bacteria and Archaea. Both are prokaryotes, meaning they lack a membrane-bound nucleus, so any statement claiming one has a nucleus and the other does not is incorrect.
2. Step 2: Examine the cell wall composition. Most Bacteria have cell walls containing peptidoglycan, a polymer that provides structural strength. Archaea, however, do not have peptidoglycan; instead, they have other unique cell wall components such as pseudopeptidoglycan or other polymers.
3. Step 3: Consider membrane lipid differences. Bacteria typically have membranes with ester-linked fatty acids, while Archaea have ether-linked isoprenoid chains. This is a key biochemical difference but not related to the cell wall.
4. Step 4: Address the misconception about multicellularity. Both Bacteria and Archaea are generally unicellular organisms; neither group is characterized by being always multicellular.
5. Step 5: Conclude that the key distinguishing feature relevant to the question is the presence or absence of peptidoglycan in the cell wall, which correctly differentiates Bacteria from Archaea.