Which statement differentiates primary from secondary succession?

Which statement differentiates primary from secondary succession?

• A. Primary succession occurs on disturbed habitats; secondary occurs on bare rock.
• B. Primary succession occurs on substrates with no prior life; secondary occurs on a previously colonized habitat that has been disturbed.
• C. Secondary succession never involves soil formation.
• D. Primary succession occurs only in aquatic systems.

Answer: (B)

The key idea is about the starting conditions of the site. Primary succession starts on a barren surface with no life and no soil—think fresh lava flows, newly exposed rock, or previously glaciated ground where nothing is established yet. In these harsh conditions, pioneer species such as lichens or hardy mosses are the first to colonize; they break down rock, form the initial organic matter, and slowly build up soil so other plants can take hold over a long time. Secondary succession, on the other hand, happens on land that already has soil and some living organisms but has been disturbed or damaged—like after a forest fire, flood, hurricane, or human disturbance such as logging or agriculture. Because soil and some seeds or remnants of life persist, recovery tends to be faster, with quicker reestablishment of vegetation and a quicker return toward the previous ecosystem. So the statement that primary succession occurs on substrates with no prior life and secondary succession occurs on a previously colonized habitat that has been disturbed best captures the fundamental difference. The other options either mix up where each process begins or claim things that aren’t true about soil involvement or aquatic context.

The key idea is about the starting conditions of the site. Primary succession starts on a barren surface with no life and no soil—think fresh lava flows, newly exposed rock, or previously glaciated ground where nothing is established yet. In these harsh conditions, pioneer species such as lichens or hardy mosses are the first to colonize; they break down rock, form the initial organic matter, and slowly build up soil so other plants can take hold over a long time.

Secondary succession, on the other hand, happens on land that already has soil and some living organisms but has been disturbed or damaged—like after a forest fire, flood, hurricane, or human disturbance such as logging or agriculture. Because soil and some seeds or remnants of life persist, recovery tends to be faster, with quicker reestablishment of vegetation and a quicker return toward the previous ecosystem.

So the statement that primary succession occurs on substrates with no prior life and secondary succession occurs on a previously colonized habitat that has been disturbed best captures the fundamental difference. The other options either mix up where each process begins or claim things that aren’t true about soil involvement or aquatic context.