Unit 1 Lesson 6 Part B - The Phosphorous Cycle

Phosphorus is needed in cells to make…

ATP (adenosine triphosphate) and Nucleotides (DNA)

True or False? The Phosphorus Cycle is considered the slowest cycle.

True

Why is the Phosphorus Cycle the slowest?

It lacks a gas phase, so phosphorus moves mainly through rocks, soil, water, and organisms, making the cycle much slower than others.

True or False? Phosphorus is not a limiting factor.

False

Which factor is considered more of a limiting factor for Terrestrial Producers? Nitrogen or Phosphorus? And Why?

Nitrogen, because it is often in forms plants cannot directly use and is less available in soils compared to phosphorus.

Which factor is considered more of a limiting factor for Aquatic Producers? Nitrogen or Phosphorus? And Why?

Phosphorus, because it is scarce in aquatic systems and enters mainly through rock weathering, so even small increases can trigger eutrophication.

Fertilizers contain what two nutrients?

Nitrogen (N) and Phosphorus (P)

What are some problems that arise as a result of human impact in the Phosphrous Cycle?

Fertilizer runoff causes eutrophication, algal blooms, oxygen depletion, fish kills, and disruption of aquatic ecosystems. Mining and overuse also deplete natural phosphorus reserves.

What are the abiotic steps in the phosphorus cycle?

1. Weathering of rocks – Releases phosphate (PO₄³⁻) into soil and water.

2. Soil and water transport – Phosphate moves through runoff into rivers, lakes, and oceans.

3. Sedimentation – Phosphate settles in sediments, eventually forming new rocks over long time periods.

What are the biotic steps in the phosphorus cycle?

1. Plant absorption – Plants take up phosphate from soil or water.

2. Consumption – Animals eat plants (or other animals), transferring phosphorus.

3. Decomposition – When plants and animals die, decomposers return phosphorus to the soil.

4. Excretion – Animal waste also returns phosphorus to the environment.