Chapter 2: Biological Classification

Kingdom Monera includes prokaryotic organisms. These organisms lack a true nucleus enclosed by a nuclear membrane and do not possess membrane-bound organelles.

General characteristics

• They are generally unicellular.
• The genetic material is not enclosed within a nuclear membrane.
• The cell wall, when present, varies in composition among groups.
• Nutrition may be autotrophic or heterotrophic.
• Reproduction commonly occurs through binary fission.

Archaebacteria

Archaebacteria are known for living in certain extreme environments. Their cell walls differ from those of typical bacteria.

• Methanogens: Occur in anaerobic environments, including the guts of ruminants, and produce methane.
• Halophiles: Live in highly saline environments.
• Thermoacidophiles: Live in hot and acidic environments.

Eubacteria

Eubacteria are commonly called true bacteria. Many have a rigid cell wall, and their forms include cocci, bacilli, vibrios and spirilla.

Cyanobacteria

Cyanobacteria are photosynthetic prokaryotes. They may be unicellular, colonial or filamentous. Some possess specialised cells called heterocysts that are involved in nitrogen fixation.

Mycoplasma

Mycoplasmas lack a cell wall. Many are very small organisms, and some species cause diseases in plants and animals.