Living world 2

Micro-organisms:   Among the living organisms, microorganisms are largest in number. Hence they are classified as follows.  1. Bacteria (size – 1 mm to 10 mm): They are unicellular, independent / parasitic organisms. Sometimes many bacteria together form colonies.Bacterial cell is prokaryotic with cell wall, but distinct nucleus or cell organelles are absent.They reproduce by simple binary fission. In favourable conditions, bacteria grow vigorously and can double their number in 20 minutes. Eg: 2. Protozoa (size - approximately 200 mm): Protozoans are found in soil, fresh water and sea water. Some are found in the body of other organisms and are pathogenic.These are unicellular organisms with eukaryotic cell.There is great variation in cell structure, organs of locomotion and modes of nutrition among protozoans. These organisms reproduce by simple cell division. Eg.- Amoeba, Paramoecium - Free living in dirty water. Entamoeba histolytica - causes amoebiasis. Plasmodium vivax- ...