Question

Bacteria in the soil converts this nutrient into a usable form. Plants take up the usable nutrient through the soil and assimilate it into proteins, making it part of the plant. An animal eats the plants, and the nutrient becomes part of the animal. When the animal dies, it decomposes, returning the nutrient back to the soil. Which cycle is being described?

water cycle

carbon cycle

nitrogen cycle

phosphorous cycle

Answer 1

The cycle being described is the **nitrogen cycle**. In this cycle, bacteria in the soil convert nitrogen from the atmosphere (or organic matter) into forms that plants can use, such as ammonia or nitrates. Plants assimilate this nitrogen into proteins. When animals eat the plants, the nitrogen is incorporated into their bodies. Upon decomposition of the animals (and plants), nitrogen is returned to the soil, where it can once again be converted by bacteria into usable forms for plants.