Bacteria; which derive energy by oxidizing certain inorganic compounds, are said to be

Step 1: Analyze the question The question asks about bacteria that get energy by oxidizing inorganic compounds such as ammonia, hydrogen sulphide, sulphur or iron compounds.

Step 2: Explain the concept Organisms obtain food or energy in different ways:

• Chemosynthesis: Energy comes from the oxidation of inorganic substances. It is used to make organic food from CO₂ and water. Examples are Nitrosomonas (oxidizes ammonia to nitrite), Nitrobacter (oxidizes nitrite to nitrate), and sulphur bacteria.
• Photosynthesis: Energy comes from light, as in green plants, algae and cyanobacteria.
• Holozoic: Ingestion of solid food and its internal digestion, as in humans and most animals.
• Parasitic: Feeding on a living host and harming it.
• Saprophytic: Feeding on dead organic matter, as in many fungi and decay bacteria.

Step 3: Apply to the options

• A. Chemosynthetic: the energy source is chemical (oxidation of inorganic compounds). ✔
• B. Holozoic: no, this involves ingesting food.
• C. Parasitic: no, this needs a living host.
• D. Photosynthetic: no, this uses light energy.
• E. Saprophytic: no, this uses dead organic matter.

Step 4: Answer Bacteria that derive energy by oxidizing inorganic compounds are chemosynthetic.

Tip: Link the word parts. "Chemo" means chemical and "photo" means light. Whenever you see "oxidizing inorganic compounds" together with bacteria, think of Nitrosomonas and Nitrobacter in the nitrogen cycle, and choose chemosynthetic.