Only specially adapted micro-organisms are found in

Analyze the question: The question asks where only specially adapted micro-organisms can live. That means an environment with extreme or harsh conditions that most microbes can't tolerate.

Explain the concept: Micro-organisms (bacteria, fungi, protists) live almost everywhere, but their distribution depends on the conditions available: nutrients, moisture, temperature, pH and salt concentration. Most microbes are not adapted to extreme conditions. Those that are (e.g., halophiles, "salt-loving" organisms) are called extremophiles.

Evaluate each option:

• A. Salty water: High salt concentration draws water out of most cells by osmosis (plasmolysis/dehydration), so most microbes die. Only specially adapted ones, such as halophilic bacteria and some algae, survive. ✔
• B. Humid air: Moisture is favourable, and many bacteria and fungal spores are present, so no special adaptation is required.
• C. Moist soil: This is one of the richest microbial habitats, full of nutrients, moisture and a great variety of organisms (bacteria, fungi, protozoa).
• D. Mouth cavities: Warm, moist and nutrient-rich, so it hosts a very diverse microbial community without needing special adaptation.

Answer: Salty water is the harsh environment where only specially adapted micro-organisms are found.

Exam tip: When you see "only specially adapted" in a question, look for the extreme environment (very salty, very hot, very acidic, very cold). The other options here are all favourable, common habitats for microbes.