Living World and Classification of Microbes Science Notes

Living World and Classification of Microbes Science Notes

Important Points:

Biodiversity and need of classification:

→ All the living organisms residing on the earth have adapted to their surroundings according to geographic regions, food ingestion, defence, etc. This causes variations among them. Even the organisms belonging to the same species also show differences.

→ About 87 million species of living organisms are seen on the land and seas on the Earth (Ref. 2011 Census). For studying their characteristics in a systematic way, they are divided into different groups. This division is based on the similarities and the differences among the different living beings.

→ Thus all the plants and animals are subdivided into groups and subgroups. This process of placing them in different groups is called biological classification.

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History of classification:

Year Scientist How many kingdoms? Method
1735 Carl Linnaeus 2 Vegetabilia and Animalia
1866 Haeckel 3 Protista, Plants and Animals
1925 Chatton 2 Prokaryotes and Eukaryotes
1938 Kopland 4 Monera, Protista, Plants and Animals
1969 Robert Harding Whittaker 5 Monera, Protista, Fungi, Plants and Animals

Whittaker’s criteria used for classification

Characteristics Type
Complexity of cell structure Prokaryotic and Eukaryotic
Complexity of organisms Unicellular or Multicellular
Mode of nutrition Plants – Autotrophic – Photosynthetic Fungi – Saprophytic – (Absorption from dead and decaying matter.)
Animals – Heterotrophic (Consumers )
Lifestyle Producers – Plants
Consumers – Animals
Decomposers – Fungi
Phylogenetic relationship Prokaryotic to Eukaryotic, unicellular to multicellular.

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Five Kingdom classification system

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As per the activities given on this page, observations of the organisms belonging to the kingdoms of Monera, Protista and Fungi can be done in the school laboratory.

Kingdom Characteristics Examples
Monera 1. All are unicellular.
2. Either autotrophic or heterotrophic.
3. Prokaryotic cell structure without distinct nucleus and cell organelles.
Bacteria Clostridium titani, Vibrio choleri, Treponema pallidum, Streptococcus pneumoniae, Legionella pneumoniae, Salmonella typhi, Staphylococcus aureus, Clostridium botulinum
Protista 1. Unicellular organisms with nucleus enclosed in a nuclear membrane.
2. Pseudopodia or cilia or flagella for locomotion.
3. Autotrophs possess chloroplast.
Euglena, Volvox, Amoeba, Paramoecium, Plasmodium, etc.
Fungi 1. Non-green, eukaryotic, heterotrophic organisms.
2. Saprotrophs, feeding upon decaying organic matter.
3. Cell wall made up of complex sugar, ‘Chitin’.
4. Thread like body with many nuclei.
Different types of fungi. Baker’s yeast, Aspergillus (Fungus on corn), Penicillium, Mushrooms

Under the jurisdiction of Indian Council of Medical Research, in 1952 National Institute of Virology was established at Pune to conduct research on the viruses.

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Classification of microbes

Microorganisms or microbes are maximum in number on this Earth in every possible environment. They can be divided into following groups.

Type Size Characteristics Examples
Virus 10 nm to 100 nm

10 to 100 times smaller than bacteria.

1. “Organisms on the borderline between living and non-living.” Extremely minute, visible only through electron microscope.
2. In the form of independent particles. A long molecule of DNA or RNA having a covering of a protein coat.
3. Can survive only in other host living cell → a produce viral proteins with help of host cell → create their numerous replica → Destruction of the host cell → Free viruses cause reinfection to other new host cells.
4. Causative agent for many plant and animal diseases.
1. Human – polio virus, Influenza virus, HIV – AIDS virus etc.
2. Cattle – picorna virus
3. Plants – Tomato – Wilt virus Tobacco mosaic virus, etc.
4. Bacteria – Bacteriophage
Bacteria 1 µm to 10 µm 1. Single cell → a independent solitary or colonial → forming Colonies .
2. Prokaryotic with cell wall. No well- formed nucleus. Cell organelles are absent.
3. Reproduction → Simple binary fission
4. Vigorous growth in favourable conditions → Number doubles in 20 minutes.
Coccus, Cocco – bacillus, Bacillus, Vibrio, Spirillum
Protozoa 200 µm 1. Present in soil, sea water and fresh water. Some pathogenic -» Present as parasites inside the host body.
2. Eukaryotic, unicellular organisms.
3. Great variation in cell structure, organs of locomotion and modes of nutrition.
4. Reproduction is by binary fission which is similar to cell division.

Paramoecium -Free living.

Entamoeba histolytica → pathogenic causing Amoebiasis Plasmodium vivax – causes malaria

Euglena → autotrophic.

Fungi Approximatly 10 µm to 100 µm 1. Eukaryotic unicellular
2. Some species are visible with naked eyes.
3. Saprotrophic, feed on decaying organic matter by absorption.
4. Found on dead and decaying organic matter.
5. Sexual reproduction or asexual reproduction by binary fission or by budding.
Baker’s yeast, Candida, Mushroom.
Algae 10 µm to 100 µm 1. Aquatic.
2. Eukaryotic, unicellular, autotrophic
3. Photosynthesizing organisms having chloroplasts.
Chlorella, Chiamydomonas

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