Biological Classification - Notes | Class 11 | Part 2: Kingdom Monera



-    Bacteria are the most abundant microorganisms.

-    Hundreds of bacteria are present in a handful of soil.

-    They also live in extreme habitats such as hot springs, deserts, snow & deep oceans. Many are parasites.

-  Based on shape, bacteria are 4 types: Coccus (Spherical), Bacillus (Rod-shaped), Vibrium (Comma-shaped) & Spirillum (Spiral).

-    Some bacteria are autotrophic (synthesize food from inorganic substrates). Majority are heterotrophs (they do not synthesize food but depend on other organisms or on dead organic matter for food).

I. Archaebacteria

-   They live in harshest habitats such as extreme salty areas (halophiles), hot springs (thermoacidophiles) and marshy areas (methanogens).

-    Archaebacteria have a different cell wall structure for their survival in extreme conditions.

-   Methanogens are present in the guts of ruminant animals (cows, buffaloes etc). They produce methane (biogas) from the dung of these animals.

II. Eubacteria (‘true bacteria’)

-    They have a rigid cell wall and a flagellum (if motile).

-    They include Autotrophs (photosynthetic and chemosynthetic) and Heterotrophs.

a. Photosynthetic autotrophs (E.g. Cyanobacteria):  

-    They have chlorophyll a similar to green plants.

-    Cyanobacteria (blue-green algae) are unicellular, colonial or filamentous, marine or terrestrial algae.

-    The colonies are generally surrounded by gelatinous sheath.

-    They often form blooms in polluted water bodies.

-    Some of them fix atmospheric nitrogen in specialized cells (heterocysts). E.g., Nostoc & Anabaena.

b. Chemosynthetic autotrophs:

- They oxidize inorganic substances such as nitrates, nitrites & ammonia and use the released energy for ATP production.

-    They help in recycling nutrients like nitrogen, phosphorous, iron and sulphur.

c. Heterotrophic bacteria:

-    They are the most abundant in nature.

-    The majority are important decomposers.

Impacts of Heterotrophic bacteria on human affairs:

·   They are used to make curd from milk.

·   Production of antibiotics.

·   Fixing nitrogen in legume roots etc.

·   Some are pathogens causing diseases. E.g. Cholera, typhoid, tetanus and citrus canker.

Reproduction in Bacteria:

·   Bacteria reproduce mainly by fission.

·   Under unfavourable conditions, they produce spores.

·   They also reproduce by a sort of sexual reproduction (DNA transfer from one bacterium to other).

Mycoplasmas are organisms without a cell wall. They are the smallest living cells. They can survive without oxygen. Many are pathogenic in animals and plants.


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