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

The key distinction in biology between autotrophs and heterotrophs is the carbon source, not the nitrogen source. Heterotrophs rely on organic carbon compounds made by other organisms, while autotrophs, whether they are photoautotrophs using sunlight or chemoautotrophs using chemical energy, always start from an inorganic carbon source such as carbon dioxide and build their own organic molecules from it. Nitrogen utilisation, whether organic or inorganic, is a separate topic entirely and does not define this classification, which rules out any option built around nitrogen.

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

Answer 2

Grouping organisms by how they obtain both energy and carbon makes this question straightforward to resolve.

1. Organic carbon: Relying on organic carbon already made by another organism is the hallmark of a heterotroph, the opposite of what is being asked about here.
2. Inorganic carbon: Photoautotrophs fix carbon dioxide using light energy and chemoautotrophs fix it using energy from inorganic chemical reactions, but both groups share the same inorganic carbon starting point, which is the unifying feature of all autotrophs.
3. Organic nitrogen: Nitrogen handling varies independently of whether an organism is autotrophic, so this cannot be the defining trait being tested.
4. Both A & C: Since neither organic carbon nor organic nitrogen use defines an autotroph, combining them does not produce a correct description either.

Looking at the common thread across both photoautotrophs and chemoautotrophs confirms that inorganic carbon utilisation is what defines the group.

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