Classification of Humans
Linnaeus classified humans as animals. He recognised that people belonged with monkeys and apes in the taxonomic order Anthropomorpha, which he later renamed Primates. Linnaeus also recognised all humans as belonging to a common genus, Homo, and species, sapiens.
The Five Kingdoms
In 1969 R H Whittakar classified all living organisms into five main kingdoms. According to the system the five kingdoms are :
- Monera ( true – bacteria, bluegreen algae )
- Protista ( golden algae, yellow – green algae )
- Fungi ( slime molds, bread molds, sac fungi )
- Plantae ( plants )
- Animalae ( animals )
Bacteria are the most ancient group of organisms, having appeared about 3500 million years ago, and are the smallest organisms with a cellular structure. Bacteria range between the lengths of 0.1 to 10 micro metre. They occupy many environments such as soil, dust, water, air, in and on plants and animals. On the basis of their importance bacteria can be divided into two parts :
- Helpful Bacteria : Certain types of bacteria live in the intestines of human beings and other animals. These bacteria help in digestion and also produce vitamins for the body. Bacteria that live in soil and water play a vital role in recycling carbon, nitrogen, sulphur and other chemical elements used by living beings.
- Harmful Bacteria : Some bacteria cause diseases in humans preventing the body from functioning properly by destroying healthy cells.
Viruses are the smallest living organisms, ranging from sizes of 20 – 300 m m; on an average they are about 50 times smaller than bacteria.
Characteristics of Virus
- They are the smallest living organisms.
- They do not have a cellular structure.
- They can only reproduce by invading living cells, therefore, they are all parasitic.
- Most viruses cause disease.
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