Which statement best describes the difference between primary and secondary succession?

• A. Primary succession starts on bare rock with no soil.
• B. Secondary succession starts on bare rock with no soil.
• C. Both always require soil formation before any organisms appear.
• D. They are the same process.

Answer: (A)

The key idea is how soil affects the start of recovery. Primary succession begins on surfaces with no soil at all, like bare rock exposed after a glacier melts or fresh lava flows. Harsh colonizers such as lichens and mosses move in first, slowly building up soil from their organic material and the rock's weathering, and only then do larger plants take root as the soil thickens. Secondary succession, on the other hand, happens after a disturbance that leaves soil and some seeds or roots intact, so new growth can appear more quickly because the living substrate and nutrients are already present.

So the statement that primary succession starts on bare rock with no soil matches this process. The idea that secondary starts on bare rock with no soil isn’t correct, and they aren’t the same process.