Which group has peptidoglycan as a major structural constituent of the cell wall (dominant stress-bearing polymer)?

Introduction / Context:
Peptidoglycan occurs in most bacteria, but its relative abundance differs dramatically between Gram-positive and Gram-negative organisms. Recognizing where it is the dominant wall component helps explain staining and antibiotic susceptibility profiles.

Given Data / Assumptions:

• Gram-positive bacteria have a thick, multilayered peptidoglycan wall.
• Gram-negative bacteria have a thin peptidoglycan layer plus an outer membrane rich in lipopolysaccharide (LPS).
• Fungal cell walls contain chitin, glucans, and mannoproteins, not peptidoglycan.

Concept / Approach:
Although both Gram-positive and Gram-negative bacteria contain peptidoglycan, it is a major (dominant) structural constituent in Gram-positive walls, where it is thick and load-bearing. In Gram-negatives, peptidoglycan is much thinner and the outer membrane plays a larger structural role.

Step-by-Step Solution:

Verification / Alternative check:
Gram staining and electron microscopy corroborate the thick peptidoglycan layer in Gram-positive bacteria.

Why Other Options Are Wrong:
Gram-negative: Do have peptidoglycan, but not as a major dominant constituent compared with the outer membrane-LPS complex. Fungi: No peptidoglycan; walls composed of chitin and glucans. None of these: Incorrect; Gram-positive clearly qualifies.

Common Pitfalls:
Assuming “presence” equals “major constituent.” The question emphasizes the dominant wall polymer, which is peptidoglycan in Gram-positives.

Final Answer:
Gram-positive bacteria