Question

How many organisms in the list given are autotrophs?
Lactobacillus, Nostoc, Chara, Nitrosomonas, Nitrobacter, Streptomyces, Trypanosoma, Porphyra, Wolffia
A) Four
B) Five
C) Six
D) Three

Answer 1

Hint:The word “autotroph” derives its meaning from the two root words “auto” meaning self and “troph” meaning food. Autotrophs are organisms that can synthesize their own food by using organic or inorganic materials and sunlight as their source.

Complete answer:
Certain bacteria and fungi along with plants and algae are categorized as autotrophs.
>Let us study each organism given in the question individually and determine whether or not they are autotrophs.
>Lactobacillus is a gram positive, rod shaped anaerobic bacteria. It utilises sugar as its carbon source and ferments it to lactic acid. It does not synthesize its own food by photosynthesis. Therefore it is not an autotroph.
>Nostoc is a cyanobacteria which has the ability to fix nitrogen in specialized cells called heterocysts. Along with other pigments, Nostoc contains chlorophyll that enables it to carry out photosynthesis. Therefore, it is an autotroph.
>Chara is a genus of green algae. Algae are autotrophic in nature.
>Nitrosomonas is a gram negative, rod shaped chemoautotrophic bacteria. It converts ammonia into nitrite in a process known as nitritation. The chemoautotrophic nature of this bacteria classifies it as an autotroph.
>Nitrobacter is a gram negative, rod shaped chemoautotrophic bacteria. It converts nitrite to nitrate which is a primary source of inorganic nitrogen in plants. The chemoautotrophic nature of this bacteria classifies it as an autotroph.
>Streptomyces are a genus of gram positive, filamentous bacteria whose shape resembles filamentous fungi. This bacteria gains nutrition by scavenging from the substrate it grows on and it is the most important source of antibiotics. Since it is a scavenger, it cannot be classified as an autotroph.
>Trypanosoma is a unicellular parasitic flagellate protozoa. Parasites are organisms that scavenge on other organisms for nutrition; therefore, trypanosoma is not an autotroph.
>Porphyra is a seaweed which grows in cold, shallow seawater. It contains chlorophyll as well as other major photosynthetic pigments in its gametophytic blades. Therefore it is an autotroph.
>Wolffia is a genus of free floating thalli which includes the smallest flowering plants on Earth. All plants are autotrophs.

From the above description of the organisms mentioned in the question, we can clearly see that Nostoc, Chara, Nitrosomonas, Nitrobacter, Porphyra and Wolffia are autotrophs.

Therefore the correct answer is option (C) six.

Note: Autotrophs are of two types. They can either be photoautotrophs or chemoautotrophs. While photoautotrophs like plants and green algae convert electromagnetic energy from the sun into chemical energy; chemoautotrophs like extremophile (organisms that live in hostile environments) bacteria or archaea convert organic or inorganic compounds in their environment into energy.