Question

How many organisms in the list given below are autotrophs?
A. Lactobacillus, Nostoc, Chara, Nitrosomonas, Nitrobacter, Streptomyces, Saccharomyces, Trypanosoma, Porphyra, Wolfia
B. Five
C. Six
D. Three
E. Four

Answer 1

Hint:-The word autotroph refers to self-made food. Therefore an autotroph is an organism that feeds itself, without the assistance or help of any other organism. Autotrophs are a primary producer of organisms that can synthesize their own food themselves from organic and inorganic substances (using carbon dioxide as the carbon source) using energy from light or inorganic chemical reactions.

Complete Answer:-Out of the given examples, Nostoc, Chara, Porphyra and Wolffia are photosynthetic autotrophs. Cyanobacteria also known as Blue-green algae is a Gram-negative, photosynthetic prokaryote. It contains photosynthetic pigment chlorophyll-a, carotene, and phycobilin. The Cell membrane of blue-green algae lacks sterol. Cyanophycin protein, Cyanophycean starch, and lipid globules are used as reserve food materials. These blue-green algae are non-flagellate and move by gliding motion. Some of them can fix atmospheric nitrogen in structures called heterocysts. Examples include Nostoc and Anabaena.
Nitrosomonas and Nitrobacter are chemosynthetic autotrophs. Trypanosoma is a parasitic organism. Saccharomyces are saprophytic heterotrophic. Lactobacillus, Streptomyces are heterotrophs i.e they utilise organic compounds as a source of food.Thus from the list, autotrophic bacteria include a total of six as Chara, Nostoc, Porphyra, Wolfie, Nitrosomonas, Nitrobacter.

So, the correct option is (B) six.

Note:- Chemoautotrophs are organisms that perform chemosynthesis. These organisms use the energy released during the oxidation process in the synthesis of ATP molecules. These are often found in ocean floors as sunlight cannot reach it (due to the increased depth and the levels of water in between it and the sun). Chemoautotrophs have evolved to be independent of solar energy. Examples include Methanogenic bacteria, archaea, sulfur-oxidizing bacteria, gamma-proteobacteria, epsilon-proteobacteria, and neutrophilic iron-oxidizing bacteria.