Understanding Eco-Chemical Cycles - AP Biology

Water, carbon, nitrogen, sulfur, and phosphorus have cyclic pathways that allowing them to flow within an ecosystem. Iron is not involved in very many ecological processes, and does not follow a defined chemical cycle.

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.

Precipitation is when condensed water vapor falls to Earth. Common types of precipitation include rain, sleet, and snow. In contrast, runoff is water flow across the Earth’s surface.

In the precipitation stage of the water cycle, condensed water vapor falls to the Earth’s surface; however, a tree canopy, for instance, may block this precipitation, preventing the precipitation from reaching the Earth’s surface. The intercepted precipitation then evaporates back into the Earth’s atmosphere.

Snowmelt is a type of runoff that results from melting snow.

Runoff, or surface runoff, is the flow of water over the Earth’s surface. Runoff occurs when there is an excess of water on the surface due to excessive precipitation. The excessive precipitation leads to the full saturation of soil, resulting in water flowing over the surface.

Infiltration is a process in the water cycle in which water on the ground’s surface enters the soil.

Both cellular respiration and photosynthesis are involved in the carbon cycle and the oxygen cycle. They both require carbon and oxygen in order to complete their mechanisms of action.

During photosynthesis, carbon is taken by the plant and converted into energy. As a result, oxygen is released. This oxygen can be used by cellular respiration to generate energy, which produces a carbon dioxide product. This carbon dioxide product can be recycled and eventually used for photosynthesis.

Energy, in an ecological context, refers to its flow in an ecosystem. Energy is passed from trophic level to trophic level; however, each time this occurs about ten percent of this energy is lost to the environment or as digested food. Energy is thus not recycled in this context.

In contrast, water, carbon, oxygen, nitrogen, and hydrogen are passed from one organism to another as organic material. This material is digested and incorporated into the organism's own biology, or released back into the ecosystem for continued use by other organisms in the environment. Energy can be passed from one organism to another in the form of chemical bonds and is released in the form of heat, but cannot be used by other organisms once it is returned to the environment and does not follow an ecological cycle.

In Earth’s atmosphere, carbon can be found in two forms: carbon dioxide and methane. Both are responsible for the greenhouse effect as they absorb and retain heat.

Carbon leaves the atmosphere and enters the terrestrial biosphere through photosynthesis and dissolution. Thus, carbon enters bodies of water and plants, where it is incorporated into organisms as organic molecules. Then the different trophic levels will consume these organic molecules. Upon their death, the carbon will be recycled within the terrestrial biosphere.

Carbon leaves the atmospheric biosphere and enters the terrestrial biosphere through photosynthesis and dissolution into bodies of water. Recall that carbon dioxide is a reactant of photosynthesis, and it gets converted into glucose.

When carbon enters into bodies of water through precipitation, it reacts with water to form carbonic acid. Carbonic acid then is absorbed into rocks in the sedimentary biosphere. Carbonic acid is very soluble in water, and is the form that most of carbon is in when dissolved in water.

The burning of fossil fuels has increased the amount of carbon in the atmosphere, contributing to the greenhouse effect and global warming. Burning fossil fuels mainly involves combustion reactions in which the fuel is oxidized, producing carbon dioxide and water. While the other answer choices may add to the carbon dioxide levels of the atmosphere, the question asks for a direct cause.

In the terrestrial biosphere, carbon can be found in all living and dead organisms, stored in the soil, and in inorganic forms. Inorganic carbon refers to carbon in minerals and ores. It is often said that life on earth is carbon-based due to its versatility and ubiquity.

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.