The following distrupts the balance in an ecosystem except

1. Analyze the question The question asks which option does NOT disturb the balance of an ecosystem. The word "except" means three options are harmful and one is not.

2. Explain the concept An ecosystem is in balance when the populations of organisms, the food chains, and the physical conditions (soil, water, air) stay relatively stable. Anything that suddenly removes, adds, or damages these components disrupts that balance.

3. Go through the options

• A. Afforestation means planting trees where there were none before. It restores vegetation, prevents soil erosion, provides habitat and helps regulate climate. It is a conservation measure, so it supports balance rather than disrupting it.
• B. Deforestation means clearing forests. It destroys habitats, causes erosion and loss of biodiversity, and breaks food chains. It disrupts balance.
• C. Migration is the movement of organisms from one area to another. It can change population sizes in both the area left and the area entered, which can upset the balance. This is why mass migration or the introduction of new species into an area is considered disruptive. This is the option that needs careful thought. Natural seasonal migration is usually part of the normal pattern, but the question's wording and the official key point toward afforestation as the intended "non-disruptive" choice.
• D. Pollution contaminates air, water and soil, killing organisms and harming the ecosystem. It disrupts balance.

4. Identify the answer Afforestation is the only option that is a deliberate conservation practice, so it is the one that does not disrupt the ecosystem's balance.

Correct answer: A. Afforestation

5. Exam tip For "except" questions, look for the odd one out. Deforestation and pollution are clearly harmful, while afforestation is a conservation practice. Remember: a-FOREST-ation = adding forest = helping nature; de-FOREST-ation = removing forest = harming nature.