Question

The mode of nutrition of bacteria is usually
A. Photoautotrophic
B. Chemoautotrophic
C. Heterotrophic and autotrophic
D. None of the above.

Answer 1

Hint: Bacteria are the sole member of the kingdom. According to the five kingdom classification system they are prokaryotic organisms. They are both autotrophic and heterotrophic, that is they make their food by their own and also dependent on others. There are two types of bacteria namely:-
> Archaebacteria- They are usually autotrophic in nature. Some of them are methanogens that live in the gut of ruminant animals.
> Eubacteria- They are photosynthetic autotrophs like blue green algae and some are chemosynthetic autotrophs like Anabaena. Some are heterotrophic like lactobacillus.

Complete answer:
> Photoautotrophic:- they are photoautotrophic, that is they synthesise their food by using light. This option is somewhat correct but these are also chemoautotrophs. Hence this option goes wrong.
> Chemoautotrophs:- they synthesise their food by using chemical energy. So this option goes correct but they are also heterotrophs. Hence the option goes wrong.
> Heterotrophic and autotrophic:- they are dependent on others for food and also prepare their food by their own. Hence the option is correct.
> None of the above:- As option c is correct. This option goes wrong.

Our required answer is c that is heterotrophic and autotrophic.

Note:
Chemosynthetic autotrophic bacteria oxidises various inorganic substances such as nitrates, nitrites and ammonia and uses the released energy for ATP production. They play a great role in recycling nutrients like nitrogen, phosphorus, iron and sulphur.
Some of them fix atmospheric nitrogen in specialised cells called heterocyst.