Question

Archaebacteria differ from eubacteria in

• A. cell membrane structure
• B. mode of nutrition
• C. cell shape
• D. mode of reproduction

Hint:

Key differences between Archaea and Bacteria:
- Cell membrane lipids (ether vs. ester linkages, branched vs. unbranched chains).
- Cell wall composition (peptidoglycan in most bacteria, pseudopeptidoglycan or other polymers in archaea).
- Ribosomal RNA sequences.
- Gene structure and replication mechanisms.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks for a key distinguishing feature between Archaebacteria (Archaea) and Eubacteria (Bacteria).

Step 3: Detailed Explanation:
Archaea and Bacteria are two of the three domains of life (the third being Eukaryota). While both are prokaryotes, they differ significantly in several fundamental aspects, particularly at the molecular level.
* (a) Cell membrane structure: This is a major distinguishing feature.
* Eubacteria (Bacteria): Their cell membranes are composed of D-glycerol esters with unbranched fatty acid chains, and the linkages are ester bonds.
* Archaebacteria (Archaea): Their cell membranes are unique, composed of L-glycerol ethers with branched isoprene chains, and the linkages are ether bonds. This difference in lipid composition and bonding contributes to Archaea's ability to survive in extreme environments.
* (b) Mode of nutrition: Both Archaea and Bacteria exhibit diverse modes of nutrition (e.g., autotrophic - chemosynthesis/photosynthesis, heterotrophic). So, this is not a universal distinguishing feature.
* (c) Cell shape: Both Archaea and Bacteria come in various shapes (e.g., cocci, bacilli, spirilla). So, this is not a distinguishing feature.
* (d) Mode of reproduction: Both primarily reproduce asexually through binary fission. So, this is not a distinguishing feature.

Step 4: Final Answer:
Archaebacteria differ from eubacteria in cell membrane structure.

Answer 2

Checking each option against how Archaea and Bacteria actually differ at the molecular and cellular level shows exactly where the real distinction lies.

1. Cell membrane structure: Eubacterial membranes are built from fatty acid chains joined to glycerol through ester bonds, forming straight-chain lipids, while Archaeal membranes are built from branched isoprenoid chains joined to glycerol through ether bonds. This ether-linked, branched-chain lipid structure is unique to Archaea and gives their membranes exceptional stability, which is a big part of why many Archaea can survive extreme heat, acidity, or salinity. This is a genuine, fundamental point of difference between the two groups.
2. Mode of nutrition: Both Archaea and Bacteria show a wide range of nutritional strategies, including autotrophic (via photosynthesis or chemosynthesis) and heterotrophic modes, so nutrition type does not reliably separate the two groups.
3. Cell shape: Both groups include cocci (spherical), bacilli (rod-shaped), and spiral forms, so shape alone cannot be used to tell Archaea and Bacteria apart.
4. Mode of reproduction: Both groups reproduce asexually, mainly through binary fission, so this is also not a distinguishing feature between them.

Only the chemistry of the cell membrane, specifically the ether versus ester linkages and branched versus straight lipid chains, is a defining structural difference between Archaea and Bacteria.

Therefore, the correct answer is cell membrane structure.