The Biochemical Cycles!

There are four important biogeochemical cycles of ecosystems. There is the water cycle, the nitrogen cycle, the carbon cycle, and the phosphorus cycle. These cycles play such an important part in ecosystems that if one cycle just stopped, the life that ecosystem would die.

Water Cycle

Water is the versatile liquid. Because all living things can use water in ecosystems, it plays in crucial role in life. Most life uses it as its liquid form, but some use it as a vapor.

The ocean has about 97% of earth’s water. The glaciers have only 2%, and the lakes, rivers, and groundwater have 1%. The leftover water is in the atmosphere. The sun drives water to evaporate creating condensation in the clouds to make it rain. Plants have a role in the water cycle. They have pores under their leaves that expire water vapor, which return water to the atmosphere. Groundwater returns to the sea. Thus, the cycle is complete.

Nitrogen Cycle

Nitrogen makes up most of the molecules in your body as well as other organisms. Nitrogen is a part of amino acids, proteins, and nucleic acids. Plants can use two inorganic nitrogen molecules called ammonium (NH4) and nitrate (NO3).

Bacteria can use all the molecules that form from nitrogen including nitrite (NO2). Animals, however, can only use the organic forms of nitrogen. Most of the nitrogen is in the atmosphere. There is about 78% of nitrogen free (N2) gas (in its elemental form) up there.

Inorganic and organic nitrogen like to hang out in soils and sediments of lakes, rivers, and oceans as well as surface water, groundwater, and in living things.

The best way for nitrogen to hit the ecosystem is through nitrogen fixation. Nitrogen fixation involves converting free nitrogen gas (N2) to its organic forms via bacteria, lightening, and volcanoes. Humans affect ecosystems by contributing nitrogen with fertilizers and legume crops, and by producing reactive nitrogen gas.

Bacteria make nitrogen into different forms and others involve themselves in a process called denitrification. It’s a fancy word for the process of turning nitrate to nitrogen gas.

Carbon Cycle

Because it is so critical for life, carbon (CO2) is the arguably the most important organic molecule. Photosynthetic life use carbon dioxide to drive their photosynthesis. These guys eventually eaten by consumers. Consumers, who then breathe out carbon dioxide, such as animals, fungi, and prokaryotes, complete the cycle.

The biggest supply of the carbon dioxide are fossil fuels, limestone, soils, sediments in aquatic environments, the oceans, plant and animal biomass, and the atmosphere. Photosynthesis by plants phytoplankton gets rid of a lot of carbon dioxide, which is equal to the amount of carbon dioxide added by consumers. So the burning of fossil fuels adds a lot of carbon dioxide to atmosphere, which greatly changes the climate of the earth.

Phosphorus Cycle

Nucleic acids, phospholipids, and the ATP molecules have phosphorus (P4). The most important inorganic phosphorus is phosphate (PO4 3-), which gets used by plants.

Phosphorus is found in sedimentary rocks in the sea, in the soil, and in dead organisms.

Weather-beaten rocks (usually sedimentary rocks from the sea) add phosphate so that it can drain into the water in and on land, which allow it to get into the ocean. Phosphate can also get in the ecosystem from decaying organic tissue, organismal excretions, dust, or sea-spray.

Even though there isn’t a lot of phosphorus, many animals and plants consume phosphate from producers that use it.


Reece, Jane B. Urry, Lisa A. Cain, Micheal L. Minorsky, Peter V. Jackson, Robert B (2013). Campbell Biology. (10th ed.) Boston, MA: Pearson.