Which of the following relationships does not involve two organisms?

Analyze the question: We need the relationship that does not involve two living organisms interacting with each other.

Explain the concepts:

• Commensalism: Two organisms live together; one benefits and the other is neither harmed nor helped (e.g., orchids growing on trees).
• Symbiosis: Two organisms live in close association, usually to mutual benefit (e.g., nitrogen-fixing bacteria in legume root nodules).
• Parasitism: Two organisms, where the parasite benefits and the host is harmed (e.g., tapeworm in humans).
• Saprophytism (spelled "saprophitism" in the question): An organism (such as a fungus or bacterium) feeds on dead and decaying organic matter. The food source is dead material, not a second living organism, so only one living organism is involved.

Solution:

1. Check each option for two interacting living organisms.
2. A, C and D each need two living partners.
3. Saprophytism involves only one living organism (the saprophyte, e.g., mushroom or Rhizopus on bread), feeding on dead matter.

Answer: B. Saprophitism

Tip: Think "SAP = dead stuff." Saprophytes feed on dead material, so no living partner is involved. For relationships like commensalism, symbiosis and parasitism, always ask, "Who is the partner?" If the answer is a living organism, it involves two organisms.