Phosphorus Cycle

Lecture Content Introduction Phosphorus is a vital nutrient required for DNA, RNA, ATP, and cell membranes. Unlike carbon and nitrogen, phosphorus does not cycle through the atmosphere in significant amounts. The phosphorus cycle describes how phosphorus moves through rocks, soil, water, and living organisms.

Definition The phosphorus cycle is the biogeochemical cycle that describes the movement of phosphorus through the lithosphere, hydrosphere, and biosphere.

Major Reservoirs of Phosphorus

• Lithosphere: Rocks and minerals (phosphate deposits).

• Soil: Phosphate ions available for plants.

• Hydrosphere: Dissolved phosphates in rivers, lakes, and oceans.

• Biosphere: DNA, RNA, ATP, phospholipids in plants and animals.

Steps in the Phosphorus Cycle

1. Weathering of Rocks

   • Releases phosphate ions into soil and water.

2. Absorption by Plants

   • Plants take up phosphates from soil.

3. Consumption by Animals

   • Animals obtain phosphorus by eating plants or other animals.

4. Decomposition

   • Microbes recycle phosphorus from dead organisms back into soil.

5. Sedimentation

   • Phosphates may settle in water bodies, forming new rocks over time.

Ecological Importance

• Essential for nucleic acids (DNA, RNA) and energy molecules (ATP).

• Maintains soil fertility and agricultural productivity.

• Supports plant growth and ecosystem stability.

• Human activities (fertilizer use, mining, pollution) disrupt the cycle, causing eutrophication in water bodies.

Quick Revision Table

Summary / Key Takeaways

• Phosphorus cycle = movement of phosphorus through rocks, soil, water, and organisms.

• Driven by weathering, absorption, consumption, decomposition, and sedimentation.

• Essential for DNA, RNA, ATP, and cell membranes.

• Human activities disrupt the cycle, leading to eutrophication and pollution.