Kingdom Monera

Bacteria are the sole members of the Kingdom Monera. They are the most abundant micro-organisms on the planet and occur almost everywhere. Hundreds of bacteria are present in just a handful of soil, and they also thrive in extreme habitats such as hot springs, deserts, snow and deep oceans where very few other life forms can survive. Many live in or on other organisms as parasites.

Bacteria are grouped under four categories on the basis of their shape:

• the spherical Coccus (plural: cocci)
• the rod-shaped Bacillus (plural: bacilli)
• the comma-shaped Vibrium (plural: vibrio)
• the spiral Spirillum (plural: spirilla)

Though the bacterial structure is very simple, bacteria are very complex in behaviour. Compared to many other organisms, bacteria as a group show the most extensive metabolic diversity. Some bacteria are autotrophic — they synthesise their own food from inorganic substrates, and may be either photosynthetic autotrophic or chemosynthetic autotrophic. The vast majority of bacteria, however, are heterotrophs: they depend on other organisms or on dead organic matter for their food.

Bacteria reproduce mainly by fission. Sometimes, under unfavourable conditions, they produce spores. They can also reproduce by a primitive kind of sexual reproduction, in which DNA is transferred from one bacterium to another. …