Nitrogen Is Often the Limiting Nutrient in Ecosystems

Multiple Choice

Nitrogen is often the limiting nutrient in ecosystems.This is because

A) there is very little nitrogen on Earth, compared with other nutrients.
B) most nitrogen is in the form of N₂, which organisms cannot use.
C) the chemical reactions needed to produce usable nitrogen are difficult.
D) nitrogen is quickly removed from ecosystems and stored in rocks and sediments.
E) humans turn most available nitrogen into ammonia, which organisms cannot use.