Kingdom Monera

Bacteria are the only members of kingdom Monera. They are the most plentiful micro-organisms, found almost everywhere: hot springs, deserts, snow, deep oceans, and inside other living things. By shape, they are coccus (round), bacillus (rod), vibrio (comma-shaped) and spirillum (spiral).

Bacteria have the widest variety of ways of getting food. Some are autotrophs: they make their own food, either by photosynthesis or by chemosynthesis (using energy from chemical reactions). But most bacteria are heterotrophs: they depend on other organisms.

Archaebacteria live in the harshest places. Halophiles live in very salty water; thermoacidophiles in hot springs; methanogens in marshes and in the gut of cows and buffaloes, where they make methane. That is how cow dung gives biogas (gobar gas). A cell wall different from other bacteria helps them survive these conditions.

Eubacteria (true bacteria) have a rigid cell wall. Cyanobacteria (blue-green algae) have chlorophyll a like plants; they can cover polluted water as blooms. Some, like Nostoc and Anabaena, fix nitrogen from the air in special cells called heterocysts. Heterotrophic bacteria are decomposers; they help make curd from milk and give us antibiotics. Some cause diseases: cholera, typhoid, tetanus in humans and citrus canker in plants.

Bacteria mostly reproduce by fission (splitting in two). In bad conditions they form spores, and they can also pass DNA from one to another. Mycoplasma have no cell wall at all. They are the smallest living cells known, and can live without oxygen.