Question

why is phosphorus considered a slow - moving biogeochemical cycle?
a there is not much phosphorus available, so it moves slowly.
b since there is not much phosphorus present in the atmosphere, it moves slower than any other biogeochemical cycle.
c most phosphorus is locked up in rocks, and releasing it requires erosion, which is a lengthy process.
d most phosphorus is unavailable for uptake by plants and animals, causing the cycle to move slowly.

Explanation:

The phosphorus cycle is a sedimentary cycle. Phosphorus is mainly stored in rocks. For it to enter the biotic part of the cycle (available for plants and animals), rocks need to undergo erosion (a slow geological process). Option A is incorrect as the amount of phosphorus is not the key factor for its slow - moving nature. Option B is wrong because the main reservoir of phosphorus is rocks, not the atmosphere. Option D is not the fundamental reason as the unavailability is due to its storage in rocks.

Answer:

C. Most phosphorus is locked up in rocks, and releasing it requires erosion, which is a lengthy process.