Archaebacteria is different from eubacteria in having

The correct option is cell membrane structure.

Archaebacteria (Archaea) and Eubacteria (true Bacteria) are both prokaryotic kingdoms that share a similar cellular organization. However, they are separated into different domains due to fundamental differences in their biochemical and molecular makeup, particularly in their cell membrane structure.
Here is a detailed explanation of this distinction:

1. Membrane Lipid Composition and Linkages:
• In Eubacteria, the cell membrane consists of a lipid bilayer where straight-chain fatty acids are joined to D-glycerol by ester bonds.
• In Archaebacteria, the membrane lipids are composed of branched-chain hydrocarbons (isoprenoids) joined to L-glycerol by ether bonds. Additionally, some archaebacteria can form a lipid monolayer instead of a bilayer. The ether linkages and branched chains are chemically more stable and resistant to disruption, which allows archaebacteria to survive in extreme environments like hot springs, hypersaline lakes, and highly acidic waters.

2. Why other options are incorrect:
• Cell shape: Both archaebacteria and eubacteria can exist in similar shapes, including rods (bacilli), spheres (cocci), and spirals (spirilla).
• Mode of reproduction: Both groups reproduce asexually, primarily through binary fission, budding, or fragmentation.
• Mode of nutrition: Both domains exhibit diverse modes of nutrition, including autotrophy (both photoautotrophy and chemoautotrophy) and heterotrophy.