Learning Outcomes
i. Understand the processes and stages of the carbon and nitrogen cycles.
ii. Describe how carbon and nitrogen circulate through ecosystems.
iii. Recognize the importance of these biogeochemical cycles for sustaining life on Earth.
i. The Carbon Cycle
The carbon cycle is the process by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth. It includes several key processes:
Photosynthesis: Plants capture carbon dioxide (CO2) from the atmosphere and convert it into glucose and oxygen.
Respiration: Animals and plants consume oxygen and glucose, which produces energy, water, and CO2, the latter of which is returned to the atmosphere.
Decomposition: Decomposers break down dead matter, returning carbon to the soil and releasing CO2 into the atmosphere.
Combustion: The burning of fossil fuels and biomass releases stored carbon back into the atmosphere as CO2.
Ocean Uptake: The oceans absorb CO2 from the atmosphere, where it can be used by marine organisms or deposited as sediment.
The carbon cycle is crucial because carbon is a building block of life and a key component of many chemical processes, including those that provide energy to organisms.
ii. The Nitrogen Cycle
The nitrogen cycle describes how nitrogen moves between plants, animals, bacteria, the atmosphere, and soil in the Earth. The main steps include:
Nitrogen Fixation: Atmospheric nitrogen (N2) is converted into ammonia (NH3) by nitrogen-fixing bacteria in the soil or by industrial processes.
Nitrification: Ammonia is converted into nitrites (NO2-) and then nitrates (NO3-) by nitrifying bacteria.
Assimilation: Plants absorb nitrates from the soil and use them to build proteins and nucleic acids.
Ammonification: Decomposing bacteria convert dead organisms and waste into ammonia.
Denitrification: Denitrifying bacteria convert nitrates back into N2 gas, releasing it into the atmosphere.
Nitrogen is a vital component of amino acids, proteins, and nucleic acids, and is therefore critical for all life forms.
iii. Importance of the Carbon and Nitrogen Cycles
These biogeochemical cycles are essential for life because they provide the elements necessary for the construction of vital organic molecules. They also regulate the availability of these elements, which can impact climate (carbon cycle) and ecosystem productivity (nitrogen cycle). The balance of these cycles is crucial; disruptions can have significant impacts on the health of ecosystems and the organisms that live within them.
In conclusion, the carbon and nitrogen cycles are fundamental processes that ensure the movement and recycling of elements necessary for life. Understanding these cycles helps explain how ecosystems function and the importance of maintaining balance within these cycles for the health of the planet.
