Tamilnadu BoardEnglish MediumSTD 11BIO BOTANYLiving World5 Marks
Question
Explain the mode of nutrition in bacteria.
✓
Answer
On the basis of their mode of nutrition bacteria are classified into two types namely autotrophs and heterotrophs.
I. Autotrophic bacteria:
Bacteria which can synthesis their own food are called autotrophic bacteria. They may be further subdivided as
A. Photoautotrophic bacteria – Bacteria use sunlight as their source of energy to synthesize food. They may be:
Photolithotrophs: In Photolithotrophs the hydrogen donor is an inorganic substance.
Green sulphur bacteria: In this type of bacteria the hydrogen donor is $H_2S$ and possess pigment called Bacterioviridin. Example: Chlorobium.
Purple sulphur bacteria: For bacteria belong to this group the hydrogen donor is thiosulphate, Bacteriochlorophyll is present. Chlorophyll containing chlorosomes are present. Example: Chromatium.
Photoorganotrophs: They utilize organic acid or alcohol ‘as hydrogen donor. Example: Purple non-sulphur bacteria – Rhodospirillum.
B. Chemoautotrophic bacteria – They do not have photosynthetic pigment hence they cannot use sunlight energy. These type of bacteria obtain energy from organic or inorganic substance.
1. Chemolithotrophs: This type of bacteria oxidize inorganic compound to release energy.
Examples:
Sulphur bacteria – Thiobacillus thiooxidans
Iron bacteria – Ferrobacillus ferrooxidans
Hydrogen bacteria – Hydrogenomonas and
Nitrifying bacteria – Nitrosomonas and Nitrobacter.
2. Chemoorganotrophs: This type of bacteria oxidize organic compounds to release energy.
Examples:
Methane bacteria – Methanococcus
Acetic acid bacteria – Acetobacter and
Lactic acid bacteria – Lactobacillus
II. Heterotrophic bacteria:
They are parasites (Clostridium and Mycobacterium), Saprophytes (Bacillus mycoides) or symbiotic (Rhizobium in root nodules of leguminous crops).
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