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Difficulty: MediumKingdom Monera: Bacteria and Cyanobacteria

A culture of unicellular organisms isolated from a freshwater lake sample is analyzed under an electron microscope. The cells lack a membrane-enclosed nucleus and membrane-bound organelles, possess circular DNA floating freely within a nucleoid region, and are surrounded by a rigid cell wall composed of peptidoglycan. Which group of organisms does this specimen belong to?

  1. BacteriaAnswer
  2. B
    Green algae
  3. C
    Yeasts
  4. D
    Viruses

Answer

The organism belongs to Bacteria because it exhibits prokaryotic cellular organization with a peptidoglycan cell wall and circular DNA in a nucleoid region.
Bacteria are prokaryotic organisms in Kingdom Monera that feature circular DNA unattached to histones in a nucleoid region, lack membrane-delimited organelles, and possess cell walls reinforced by peptidoglycan.

Step-by-Step Solution

1
Analyze cellular organization from the stem description
The absence of a membrane-enclosed nucleus and membrane-bound organelles indicates the organism is a prokaryote belonging to Kingdom Monera.
Prokaryotes are defined by the lack of internal membrane-bound compartments.
2
Evaluate cell wall chemical composition
Peptidoglycan (murein) is the defining structural cross-linked polymer of bacterial cell walls.
Distinguishes bacterial cell walls from eukaryotic plant/algal walls (cellulose) and fungal walls (chitin).
3
Match characteristics to the correct taxonomic group
Unicellular prokaryotes with peptidoglycan walls and naked circular DNA are classified as Bacteria.
All listed features align precisely with bacterial Moneran characteristics.

Key Concept

Structural organization and cell wall composition of Kingdom Monera (Bacteria)
Estimated Time:1m 0s
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Topics

Kingdom Monera: Bacteria and Cyanobacteria

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