Question

Autotrophs are:

• A. those microbes that utilizes organic carbon
• B. those microbes that utilizes inorganic carbon
• C. those microbes that utilizes organic nitrogen
• D. both A & C

Hint:

Remember: {Auto = self}, autotrophs make their own food using inorganic carbon.

Answer 1

The Correct Option is B

Step 1: Understanding autotrophs.
Autotrophs are organisms that can synthesize their own organic food from inorganic substances. They use inorganic carbon, mainly in the form of carbon dioxide, as the carbon source.
Step 2: Source of energy and carbon.
Autotrophs obtain energy either from sunlight (photoautotrophs) or from chemical reactions (chemoautotrophs), but their carbon source always remains inorganic.
Step 3: Analyzing the options.
(A) Incorrect, utilization of organic carbon is a characteristic of heterotrophs.
(B) Correct, as autotrophs utilize inorganic carbon such as CO\(_2\).
(C) Incorrect, nitrogen source does not define autotrophic nature.
(D) Incorrect, since option A itself is incorrect.
Step 4: Conclusion.
Autotrophs are correctly defined as organisms that utilize inorganic carbon.

Answer 2

The word "autotroph" itself gives a strong clue here, since it breaks down into "auto" meaning self and "troph" relating to nourishment, so the reasoning should centre on how these organisms obtain their carbon rather than on nitrogen or organic sourcing.

1. Utilizes organic carbon: Organisms that depend on ready-made organic carbon compounds from their environment are heterotrophs, since they cannot build their own food from inorganic starting material.
2. Utilizes inorganic carbon: Autotrophs build their own organic molecules starting from simple inorganic carbon sources such as carbon dioxide, using either light energy or chemical energy to drive the process, which is exactly the self-feeding behaviour the name implies.
3. Utilizes organic nitrogen: The nitrogen source an organism uses does not determine whether it is autotrophic or heterotrophic, since that classification is based on carbon and energy source, not nitrogen.
4. Both A & C: Since option A does not correctly describe autotrophs, a combination that includes it cannot be correct either.

Because the defining feature of an autotroph is building organic matter from inorganic carbon, the option describing inorganic carbon use is the one that matches the definition.

Therefore, the correct answer is those microbes that utilize inorganic carbon.