Biological Classification
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(a) Photosynthetic autotrophs (E.g. Cyanobacteria):
They have chlorophyll a similar to green plants.
Cyanobacteria (blue-green algae) (AIPMT 2012) are unicellular,
colonial or filamentous, freshwater/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. (AIPMT 1994)
(b) Chemosynthetic autotrophs: (Eg. Nitrifying Bacteria)
They oxidize inorganic substances such as nitrates, nitrites &
ammonia and use the released energy for ATP production. They
help in recycling nutrients like nitrogen, phosphorus, iron and sulfur.
(c) Heterotrophs
They are the most abundant in nature.
The majority are important decomposers.
IMPACTS OF
HETEROTROPHIC
BACTERIA
Parasitic bacteria :
Some are pathogens,
causing diseases.
E.g., Cholera, typhoid,
tetanus and citrus
canker
Symbiotic
Bacteria :
Nitrogen-fixing in
legume roots etc.
(Eg. Rhizobium)
They are used to
make curd from milk.
Production of
antibiotics.