Carbon Cycle

The element Carbon has the ability to cycle globally, due to its atmospheric reservoir. In the Carbon Cycle, carbon dioxide (CO2) from the atmosphere is absorbed by plants through photosynthesis, then returned to the atmosphere via cellular respiration. In more depth, carbon dioxide in the atmospheric reservoir is taken in by plants in order to complete photosynthesis. The plants then serve two purposes: they produce oxygen (O2) and they become food for primary consumers. The oxygen in the air is breathed in by all organisms as part of cellular respiration, which returns carbon dioxide to the atmosphere. The plant food eaten by the primary consumers contains carbon, which is passed up through the trophic pyramid to all levels of consumers. In addition, dead material containing carbon is decomposed and eaten by detritivores, another part of the food chain.
imbalance in nitrogen cycle
A big problem we have going on right now is the extra emission of carbon dioxide from the burning of fossil fuels in factories, automobiles, etc. This increases the level of CO2 in the atmosphere, thus throwing the entire cycle off balance.

Abiotic reservoirs: atmosphere, soil
Biotic reservoirs: plants, animals, detritovores

36-15-CarbonCycle-L.gif
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order by machine, status, inst_id;


Nitrogen Cycle

The element Nitrogen also has the ability to cycle globally, because of its presence in the atmosphere. Nitrogen in the atmosphere is only found in the form N2. Only very few creatures can take in nitrogen in this form. Therefore, nitrogen-fixing bacteria in the soil take on the task. The bacteria come in two types: free bacteria and root nodule bacteria. Free bacteria survive on their own in the soil. These bacteria carry out the chemical reaction that changes N2 to ammonium (NH4+), called Nitrogen Fixation. Ammonium and nitrate (NO3-), another form of nitrogen, can be used by most plants and are found in Amino Acids. Nitrates come from nitrifying bacteria in the soil, which take in ammonium to create nitrates (called nitrification). These nitrates, in addition to supplying Amino Acids to plants, return to the atmospheric reservoir through a process called, incidentally, denitrification. Finally we get to root nodule bacteria. These bacteria supply legumes, or pod-producing plants, with nitrogen that they cannot recieve on their own. This is a commensalistic relationship, because the bacteria do not benefit, but the legumes could not possibly survive without them. Another process in the Nitrogen Cycle is the decomposition of animals. As stated before, animals cannot absorb N2 on their own, so they must rely on the plants they eat (or lower level consumers) to get nitrogen. When these animals die, the nitrogen stays within them, as does Carbon, and detritovores transform it into ammonium, thus continuing the cycle.

Abiotic reservoirs: atmosphere, soil
Biotic reservoirs: animals, plants, detritivores, bacteria
36-16-NitrogenCycle-L.gif

Phosphorus Cycle

Unlike the two cycles we have seen before, the Phosphorus Cycle is local, as opposed to global. This means that phosphates do not travel out of their ecosystem, because their main abiotic reservoir is in rocks. Also, the cycle mainly takes place in rocks. When rain falls on a rock, phosphates travel down the runoff and into nearby bodies of water, where they become solutes. They then separate, along with other sediments, to form precipitated, or solid, phosphates on the riverbed. They then travel up the rocks all the way to the tops of mountains, where they eventually join the runoff. All these examples of phosphates are inorganic (white boxes). However, the Phosphorus Cycle is also organic (yellow boxes). Not all phosphates in the runoff make it to the water; others simply sink into the soil. These inorganic phosphates are transformed into organic ones by plants, which are in turn eaten by animals. The dead animals, as seen with nitrogen and carbon, retain their internal phosphorus stores, and, as before, detritivores change the organic phosphates back to inorganic ones.

Abiotic reservoirs: rocks, water
Biotic reservoirs: organisms (DNA)
36-17-PhosphorusCycle-L.gif


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