The mutualism type of relationship is different from a parasitic relationship because in mutualism

Step 1: Analyze the question The question asks what makes mutualism different from parasitism. So we need the feature that is true of mutualism but not of parasitism.

Step 2: Explain the concepts

• Mutualism: a close association between two different species in which both benefit. Examples: nitrogen-fixing Rhizobium bacteria in the root nodules of legumes (beans, groundnut), where the bacteria get food and shelter and the plant gets nitrates; lichens (alga and fungus); and the bacteria in the human gut.
• Parasitism: a relationship in which one organism (the parasite) benefits while the other (the host) is harmed. Examples: tapeworm in humans, Plasmodium in humans, and mistletoe on a host tree.

Step 3: Evaluate the options

• A. Both organisms involved benefit. Correct. This is the definition of mutualism, and it is the key difference from parasitism, where only one side gains.
• B. None benefits or harms the other. This describes neutralism, not mutualism.
• C. Both organisms harm each other. This is closer to competition or antagonism, not mutualism.
• D. Only one of the organisms is harmed. This fits parasitism (the host is harmed), so it is not what distinguishes mutualism.

Answer: A. In mutualism both partners benefit, while in parasitism one benefits at the other's expense.

Exam tip: Remember the pattern of "+" and "−" signs:

• Mutualism: + / +
• Parasitism: + / −
• Commensalism: + / 0

Questions like this appear often in WASSCE, NECO, and JAMB, so learn these three patterns well.