Notes-Class 8-Science-Chapter-1-Living World and Classification of Microbes-Maharashtra Board

Topics to be learn : Introduction Biodiversity and need of classification Whittaker’s 5 kingdom classification system Classification of microbes

Introduction :

The hierarchy for classification :

• Kingdom.
• Phylum.
• Class.
• Family.
• Genus and species.

The levels of hierarchy considered while writing the name in binomial nomenclature, are genus and species. The genus is written by the first word and the species is shown by the second word. Carl Linnaeus invented ‘binomial system’ of nomenclature.

Biodiversity and need of classification :

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

• According to 2011 census, around 87 million species of living organisms are found on the earth- including land and sea.

• 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.

 History :

1) Carl Linnaeus (1735) : Kingdom-2,

• Method : Vegetabilia and Animalia

2) Haeckel (1866) : Kingdom-3,

• Method : Protista, Plants and Animals

3) Chatton (1925) : Kingdom-2,

• Method : Prokaryotes and Eukaryotes

 4) Kopland (1938) : Kingdom-4,

• Method : Monera, Protista, Plants and Animals

5) Robert Whittaker (1969) : Kingdom-5,

• Method : Monera, Protista, Fungi, Plants and Animals.

 Whittaker’s 5 kingdom classification system :

Whittaker’s criteria used for classification :

(i) Complexity of cell structure - Prokaryotic and Eukaryotic

(ii) Complexity of organisms - Unicellular or Multicellular

(iii) Mode of nutrition –

• Plants - Autotrophic — Photosynthetic Fungi - Saprophytic - (Absorption from dead and decaying matter.)
• Animals — Heterotrophic (Consumers )

(iv) Lifestyle :

• Producers – Plants
• Consumers — Animals
• Decomposers — Fungi

(v) Phylogenetic relationship:

• Prokaryotic to Eukaryotic.
• Unicellular to multicellular.

Kingdom Characteristics:

1) Monera :

• All are unicellular.
• Either autotrophic or heterotrophic.
• Prokaryotic cell structure without distinct nucleus and cell organelles.
• Example : Bacteria Clostridium tetani, Vibrio choleri, Treponema pallidum, Streptococcus pneumoniae, Staphylococcus aureus, Clostridium botulinum, Legionella pneumoniae, Salmonella typhi.

2) Protista :

• Unicellular organisms with nucleus enclosed in a nuclear membrane
• Pseudopodia or cilia or flagella for locomotion.
• Autotrophs possess chloroplast.

• Example : Euglena, Volvox, Amoeba, Paramoecium, Plasmodium, etc.

3) Fungi :

• Non-green, eukaryotic, heterotrophic organisms.
• Saprotrophs, feeding upon decaying organic matter.
• Cell wall made up of complex sugar, ‘Chitin’.
• Thread like body with many nuclei.

• Example : Different types of fungi. Baker’s yeast, Aspergillus (Fungus on corn), Penicillium, Mushrooms.

Classification of Microbes :

Among the living organisms, microorganisms are largest in number. Hence they are classified as follows.

Classification & Characteristics of Microbes:

(1) Bacteria :

• These organisms are unicellular and may be free-living, parasitic, or may exist in some other forms. Sometimes many bacteria together form colonies.

• Bacteria are prokaryotic with cell wall, but lack distinct nucleus or other membrane bound cell organelles.
• Bacteria grow vigorously in favorable conditions. Bacteria like E. coli can divide every 20 minutes.
• These bacteria occur in different shapes – spherical (coccus), rod-shaped (bacillus), spiral (spirillum), comma-shaped (vibrio), intermediate between spherical and rodshaped (cocco-bacillus).
• The size of bacterial cell ranges from 1 μm to 10 μm.
• Reproduction is by simple binary fission.

(2) Protozoa :

• Protozoans are unicellular eukaryotes.
• They are found in soil, fresh-water and sea water. Some of them are found in the body of other organisms and are pathogenic.
• A great variation is seen amongst these organisms with respect to structure of cell, organs of locomotion and modes of nutrition.
• Protozoans can reproduce sexually and asexually. (size - approximately 200 mm)

• Examples : Amoeba, Paramoecium, Entamoeba histolytica, Euglena, Plasmodium, etc.

(3) Fungi :

• These are found on decaying organic matter and dead bodies of plants and animals.
• These are eukaryotic organisms. Some are unicellular and others are visible with naked eyes.
• Saprotrophic, absorb their food from decaying organic matter.
• They reproduce sexually and asexually by cell division or by budding.

• Examples : Baker's yeast, Candida, Mushroom. (size- approximately 10 mm to 100 mm)

(4) Algae :

• They are aquatic.
• Eukaryotic, unicellular, autotrophic organisms.
• Photosynthesis is carried out with the help of chloroplast present in the cell.

• Examples : Chlorella, Chlamydomonas (size- approximately 10 mm to 100 mm) very few species of algae are unicellular. Most of them are multicellular and visible with naked eyes.

(5) Viruses :

• Viruses are said to be the organisms at the edge of living and non-living. Generally viruses are not considered as living organisms.
• Sizes of viruses ranges from approximately 10nm to 100nm. They can be seen only with an electron microscope. Viruses are 10 to 100 times smaller than bacteria.
• Viruses are independent particles made up of a long molecule of DNA (Deoxyribo Nucleic Acid) or RNA (Ribonucleic acid) covered by a protein coat.
• Viruses infect only living plant or animal cells and produce their own proteins with the help of host cell and replicate inside the host cell. After this, they destroy the host cell and further infect new cells.
• Viruses cause many diseases to plants and animals.

• Examples : In plants − Tomato spotted wilt virus, Tobacco mosaic virus; In humans − Polio virus, Influenza virus, HIV; In cattle- Picornavirus; In bacteria − Bacteriophages.