What is autotrophic nutrition?

Step 1: Analyze the question The question asks for the definition of autotrophic nutrition. The key is to break down the word itself.

Step 2: Explain the concept

• Auto = self
• Troph = nourishment or feeding

So autotrophic means "self-feeding": the organism makes its own food from simple inorganic substances.

There are two main types:

1. Photoautotrophs use light energy (sunlight) to make food by photosynthesis. Examples are green plants, algae and some bacteria. 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (in the presence of light and chlorophyll)
2. Chemoautotrophs use energy from chemical reactions involving inorganic substances, such as sulphur or ammonia. Examples are nitrifying bacteria (Nitrosomonas, Nitrobacter) and sulphur bacteria.

Step 3: Check each option

• A. Breaking down complex organic compounds describes saprophytic/heterotrophic nutrition (e.g. fungi, mushrooms, bread mould). ❌
• B. Obtaining food from other organisms describes heterotrophic nutrition in general (parasites, holozoic feeders). ❌
• C. Consuming both plants and animals describes omnivores, which are a type of heterotroph. ❌
• D. Producing their own food using energy from the sun or from inorganic substances is exactly what autotrophs do. ✅

Step 4: Answer The correct option is D.

Exam tip: Link the prefix to the meaning:

• Auto = self, so it makes its own food.
• Hetero = other, so it feeds on others.

If an option mentions "making food from inorganic substances", think autotroph straight away.