Understanding Eco-Chemical Cycles - AP Biology

Plants and animals receive carbon through photosynthesis and consumption, respectively.

Carbon that is contained in the terrestrial biosphere leaves and returns to the atmospheric biosphere through animal, plant, and soil respiration. These terms refer to the process by which food molecules (ie. glucose) are burned and converted to more usable forms of energy. The byproducts are often carbon dioxide, water, and heat. In animal respiration, carbon dioxide is produced during the transition step between glycolysis and Krebs cycle, and twice in the Krebs cycle.

Carbon from terrestrial organisms can enter into the oceanic biosphere and bodies of water through dead tissue, dissolution, or in the form of shells as calcium carbonate.

Industrialization has increased the burning of fossil fuels, such as coal and oil. This releases carbon from the geosphere into the atmosphere, increasing the carbon in the atmosphere. Carbon dioxide and methane are big contributors to the greenhouse effect and global warming.

Modern human activities greatly impact the carbon cycle. Increase in land usage decreases the presence of natural ecosystems and the ability of organisms to remove carbon from the atmosphere. Pollution damages organisms, which reenters the terrestrial biosphere and increases erosion. Deforestation directly removes carbon rom ecosystems and decreases the amount of carbon absorbed from the atmospheric biosphere.

Acid precipitation is a type of precipitation that is acidic, meaning that it has a pH of less that 7. Acid precipitation is caused by the reaction of sulfur dioxide and nitrogen oxide with water in the atmosphere, which produces acids. The production of sulfur dioxide and nitrogen oxide is directly linked with human industrialization.

The carbon cycle includes three levels: the geosphere, the terrestrial biosphere, and the atmospheric biosphere. The geosphere refers to the solid part of the earth, the terrestrial biosphere refers to all the living organisms on the land, and the atmospheric biosphere refers to the living organisms in space between the land and the outer ends of the atmosphere. Carbon is present in all levels and travels throughout the levels through various processes including photosynthesis, dissolution, and decay.

Nitrogen makes up most of the Earth’s atmosphere; however, this reserve of nitrogen is limited for biological use. Nitrogen exists in diatomic forms in the atmosphere and the process of nitrogen fixation frees atoms for biological use. As a result, nitrogen is a limiting resource in many ecosystems.

Nitrogen is necessary for all life; therefore, it is present in the territorial biosphere in living organisms, humus, and decomposing matter.

Nitrogen fixation can be described as the process in the nitrogen cycle in which bacteria “fix” atmospheric nitrogen into ammonia and usable forms of organic nitrogen.

In the process of assimilation, organic nitrogen is incorporated into plants through the roots. The type of nitrogen incorporated may be nitrate ions, nitrite ions, or ammonium ions. Symbiotic bacteria may assist this process.

During ammonification, saprobiotic bacteria convert dead organic nitrogen in the soil into ammonium.

Nitrification takes place in the soil and is the process in which ammonium is converted into nitrate. Nitrifying bacteria facilitate this process.

The processes of denitrification and nitrogen fixation both involve atmospheric nitrogen. Nitrogen fixation is the conversion of atmospheric nitrogen into ammonia and organic nitrogen by nitrogen fixing bacteria. In denitrification, denitrifying bacteria convert nitrates into nitrogen gas, which is released into the atmosphere.

Denitrification is the final process of the nitrogen cycle in which soil-dwelling denitrifying bacteria convert nitrates back into nitrogen gas. The nitrogen gas is released back into the atmosphere.

An alternative source of naturally occurring nitrogen in ecosystems is bedrock. Bedrock is nitrogen rich and can be broken down to act as a nitrogen source.

The marine nitrogen cycle is very similar to the terrestrial nitrogen cycle. In marine ecosystems, atmospheric nitrogen enters the cycle through precipitation.

Human activities such as chemical fertilizers, industrialization, and pollution significantly increase the amount of nitrogen that is biologically available in an ecosystem.

An alternative method of nitrogen fixation is a lightening strike; however, this is rare and soil-dwelling bacteria perform most of the Earth’s nitrogen fixation.