Introduction

Relevance of the Theme

Biogeochemical Cycles are fundamental structures that maintain the balance of ecosystems and allow life on Earth. They represent the interconnection between the biotic and abiotic components of the planet. Without them, these components would exist separately, making the continuity of life as we know it impossible. Therefore, the study of these cycles is essential for understanding the dynamics and interdependence of living beings and the environment that surrounds them.

Contextualization

Within the Biology curriculum, Biogeochemical Cycles play a primordial role. They are the foundation from which more advanced and complex skills in Biology and Ecology are built. Understanding them is necessary for future topics, such as the structure and functioning of ecosystems, pollution and its consequences, global warming and climate change, and nature conservation. Therefore, this topic serves as a solid basis for the development of a broader and integrated understanding of biological and ecological processes. Here, we will unravel the functioning of four of the main biogeochemical cycles: carbon, nitrogen, phosphorus, and water.

Theoretical Development

Components

• Carbon Cycle: Carbon is an essential element for life, being a key component of organic compounds. This cycle involves the transfer of carbon between the biosphere, atmosphere, hydrosphere, and lithosphere. The main processes include photosynthesis, respiration, combustion, and sedimentation.

• Nitrogen Cycle: Nitrogen is a crucial nutrient for plant growth and, consequently, for the entire food chain. This cycle is marked by chemical transformations that convert atmospheric gaseous nitrogen into usable forms, such as nitrates and ammonium. It includes biological, physical, and chemical processes, such as fixation, assimilation, nitrification, denitrification, and ammonification.

• Phosphorus Cycle: Phosphorus is an essential element for the formation of molecules such as DNA, RNA, and ATP. Unlike other cycles, phosphorus does not pass through the atmosphere. Its cycle is characterized by the transfer between the lithosphere, hydrosphere, and biosphere, mainly through geological and biochemical processes.

• Water Cycle: Water is the universal solvent and key to most biological processes. Its constant change between liquid, solid, and gaseous states, driven by the heat of the sun, is known as the water cycle. This cycle is responsible for the circulation of water in the biosphere, atmosphere, and other reservoirs, being essential for life.

Key Terms

• Biosphere: It is the part of the planet where life is located - the sum of all ecosystems. It includes the Earth's crust, atmosphere, oceans, and other bodies of water, where living beings can be found.

• Atmosphere: It is the layer of gas that surrounds a celestial body. On Earth, the atmosphere is mainly composed of nitrogen, oxygen, and other gases in smaller quantities, including carbon dioxide.

• Hydrosphere: It is the part of the Earth composed of liquid or frozen water. It includes oceans, seas, rivers, lakes, groundwater, clouds, and ice at the poles, among others.

• Lithosphere: It is the outermost and solid layer of the planet, which includes the Earth's crust and the upper part of the mantle.

• Photosynthesis: Process by which organisms with chlorophyll (mainly plants and algae) convert the energy of the sun, carbon dioxide, and water into glucose (sugar) and oxygen.

Examples and Cases

• Soil-Plant System: Plants take carbon from the atmosphere in the form of carbon dioxide through photosynthesis, incorporating it into their structure. When plants die or are consumed by herbivores, carbon is released back into the soil through decomposition. In this cycle, carbon is transferred between the biosphere (plants), atmosphere, and lithosphere (soil).

• Fertigation: This is an example of the nitrogen cycle. In agriculture, fertigation is a practice that combines soil fertilization with plant irrigation. The fertilizer added to the soil, usually in the form of nitrate or ammonium, provides nitrogen to the plants. After plants assimilate nitrogen, it can re-enter the cycle through the decomposition of plant or animal residues by the process of ammonification.

• Acid Rain: This is a phenomenon that occurs due to high levels of sulfur dioxide and nitrogen dioxide in the atmosphere, mainly from the burning of fossil fuels. These gases react in the atmosphere to form sulfuric acid and nitric acid, which can be transported over long distances before being deposited on the Earth's surface through precipitation (rain, snow, etc). This illustrates the sulfur and nitrogen cycles, and the interconnection with the hydrosphere and lithosphere.

Detailed Summary

Relevant Points

• The Importance of Biogeochemical Cycles: These cycles are responsible for maintaining life on Earth. Without them, the components of the environment - air, water, soil, and living beings - would be completely separated, and life as we know it would not be possible. They maintain a delicate balance between the essential elements for life and the dynamics of the planet.

• Carbon Cycle: This cycle describes the movement of carbon between the atmosphere, hydrosphere, biosphere, and lithosphere. Carbon is a fundamental element for the formation of organic compounds, essential for life. Studying this cycle allows us to understand how carbon is transformed and transferred, affecting processes such as heat absorption in the atmosphere (greenhouse effect) and plant growth (photosynthesis).

• Nitrogen Cycle: This cycle describes the transformations that nitrogen, an essential component for life, undergoes as it moves from the atmosphere to the biosphere and lithosphere. Understanding this cycle is crucial to explain how nitrogen availability affects food production and ecosystem balance.

• Phosphorus Cycle: Despite being a more restricted cycle, the phosphorus cycle is of utmost importance, as this element is vital for the formation of DNA, RNA, ATP, among other essential components for life. In this cycle, phosphorus is transferred mainly between the lithosphere and hydrosphere, passing through the biosphere.

• Water Cycle: This cycle involves the continuous transfer of water between the Earth's surface, atmosphere, and oceans. It is a perfect example of how an abiotic resource (water) is constantly used and recycled by living beings and the environment.

Conclusions

• Interdependence of Components: Biogeochemical cycles demonstrate the interdependence of the biotic (living beings) and abiotic (non-living elements) components of the planet. Each cycle is a complex and interactive system, where any alteration in one component can have significant effects on the entire system.

• Importance of Preserving Cycles: Understanding biogeochemical cycles is essential for environmental preservation. Understanding how these cycles work and how human activities can influence them allows us to take measures to minimize negative impacts and promote sustainability.

Suggested Exercises

1. Carbon Cycle: Describe the main stages of the carbon cycle, including the common forms of carbon in each component (atmosphere, hydrosphere, biosphere, lithosphere) and the main transfer processes between these components.

2. Nitrogen Cycle: Explain how nitrogen fixation occurs in nature and indicate the main stages of the nitrogen cycle, including the biological and chemical processes involved.

3. Water Cycle: Using a model or diagram, represent the main stages of the water cycle, including evaporation, condensation, precipitation, and infiltration. Write a brief explanation of each stage and highlight the importance of the water cycle for living beings and for the planet as a whole.