Biogeochemical Cycles: Carbon, Nitrogen, and Phosphorus

Importance of Carbon: Carbon is identifying as the key element of life on Earth.
Carbon Sources in the Lithosphere: Carbon is stored within the Earth's crust in several forms: - Dead and Decaying Organic Matter: Organic materials that are in the process of breaking down. - Fossil Fuels: Created from organisms decomposed by heat and pressure from the Earth's crust over long periods. Specific types include: - Oil - Coal - Natural Gas

Photosynthesis: - Performers: Only plants perform this process. - Function: It is the method by which plants create their own energy in the form of glucose ( $C_6H_{12}O_6$ ). - Essential Aspect: A byproduct of photosynthesis is oxygen ( $O_2$ ), which is critical for human survival. - Chemical Reaction: - Word Equation: Carbon dioxide + water ${\rightarrow}$ glucose + oxygen - Chemical Equation: $CO_2 + H_2O \rightarrow C_6H_{12}O_6 + O_2$
Cellular Respiration: - Performers: All cells, including those in both plants and animals, perform respiration. - Function: This is how organisms use their stored energy. Humans utilize energy from food combined with oxygen to perform daily functions. - Chemical Reaction: - Word Equation: Glucose + oxygen ${\rightarrow}$ carbon dioxide + water - Chemical Equation: $C_6H_{12}O_6 + O_2 \rightarrow CO_2 + H_2O$
Decomposition: - When an animal or plant dies, decomposers break down the dead tissues. - This process releases $CO_2$ back into the ground. - Examples of Decomposers: - Fungi (e.g., fungi decomposing a log). - Bacteria (e.g., bacteria decomposing a tomato).

Disruption of Cycle Balance: - Clearing Vegetation: Leads to an increase in atmospheric $CO_2$ because it removes a "carbon sink" (plants that absorb carbon). - Burning Forests: Directly increases $CO_2$ levels in the atmosphere. - Burning Fossil Fuels: Human industrial activities release significant amounts of $CO_2$ into the air. - Consequence: Any increase in atmospheric $CO_2$ contributes to global warming.
Restoring Balance: - Planting Trees: Helps decrease atmospheric $CO_2$ levels to restore balance between photosynthesis and respiration. - Transportation Choices: Walking or carpooling helps cut down on $CO_2$ emissions resulting from fossil fuel combustion.

Questions and Discussion: - Q1: What is the carbon cycle? - A: The repeated movement of carbon between Earth’s atmosphere and organisms. - Q2: How do producers use carbon dioxide? - A: They use it to make food during the process of photosynthesis. - Q3: How is carbon dioxide released into the air by consumers? - A: It is released during cellular respiration. - Q4: What are fossil fuels? - A: Fossilized remnants of plants and animals. - Q5: How do fossil fuels release carbon dioxide into the atmosphere? - A: Through the process of burning, also known as combustion. - Q6: Name three types of fossil fuels. - A: Oil, coal, and gas. - Q7: What led humans to burn more fossil fuels? - A: Industrialization, specifically the making of more goods in factories. - Q8: What is deforestation? - A: The excessive removal of forests.

Atmospheric Composition: Nitrogen ( $N_2$ ) is extremely abundant, making up approximately $78\%$ of the Earth's atmosphere.
Biological Importance: - Nitrogen is a primary building block of all life. - It accounts for approximately $3\%$ of total human mass. - It is a critical component of all proteins and DNA.
Usability: Most organisms cannot use diatomic nitrogen ( $N_2$ ) directly from the air.
Nitrogen Acquisition: - Producers: Obtain nitrogen by taking it up through their roots from the soil, a process known as assimilation. - Consumers: Obtain nitrogen by eating producers (plants).

Microbial Role: All major chemical transformations in the nitrogen cycle are performed by bacteria.
Nitrogen Fixation: The conversion of atmospheric nitrogen ( $N_2$ ) into ammonia ( $NH_3$ ).
Nitrification: The process where ammonia ( $NH_3$ ) is converted into nitrate ( $NO_3$ ) by soil bacteria.
Denitrification: The process that returns nitrogen to the atmosphere by converting nitrate ( $NO_3$ ) back into nitrogen gas ( $N_2$ ).

Fertilizer Usage and Eutrophication: - Humans produce fertilizers (e.g., Ammonium Nitrate with $34.40\%$ N content, often sold in large weights like $500\,kg$ ). - Fertilizer runoff leads to leaching into water systems. - Process of Eutrophication: - Excessive nutrients cause Algae blooms. - Algae blocks sunlight from reaching deeper water. - Algae eventually dies. - Decomposing algae consumes oxygen, causing fish to suffocate.
Burning Fossil Fuels and Acid Rain: - Burning fossil fuels releases sulfur dioxide and nitrogen oxides. - These gases combine with moisture in the atmosphere to form acid water droplets (sulfuric and nitric acid). - Deposition Types: - Wet deposition (rain/snow). - Dry deposition (particulates/gases). - Effects of Acid Rain: - Forest and vegetation deterioration. - Corrosion of statues and buildings. - Death of fish in acidified water bodies.
Other Impacts: - Mining activities. - Deforestation.

True or False Exercise: - 1. About 87% of the atmosphere is made up of nitrogen gas. - Result: False (it is approximately $78\%$ ). - 2. The process of combining nitrogen with other elements in order to make usable compounds is called the nitrogen cycle. - Result: True. - 3. In the nitrogen cycle, nitrogen gas is changed into a usable compound called lightning. - Result: False. - 4. Plants and animals use nitrogen compounds to build proteins and other complex substances. - Result: True. - 5. Bacteria break down the nitrates and release oxygen. - Result: False (they release nitrogen gas during denitrification). - 6. The nitrogen cycle is the using and reusing of nitrogen in an ecosystem. - Result: True.

Unique Characteristic: Unlike the carbon or nitrogen cycles, phosphorus is not found in the atmosphere as a gas.
Reservoirs: Phosphorus is found in rocks, sediments, and soil.
Biological Roles: Phosphorus is found in all living things, specifically in: - DNA: Instructions for cell function. - Cell Membranes: Component of the outer layer of cells. - Skeletons and Teeth: Found as calcium phosphate.
Cycle Mechanisms: - Weathering: Long exposure of rocks to air releases phosphate ions ( $PO_4$ ) into the soil and water. - Assimilation: Plants take in these phosphate ions from the soil to use as nutrients for growth. - Consumption and Excretion: Herbivores and carnivores consume plants/prey and excrete phosphorus as waste in urine and feces. - Decomposition: After death, phosphorus returns to the soil as plant or animal matter is broken down by detritivores. - Geological Uplift: Geological forces carry phosphorus-containing materials back to the Earth's surface.

Pollution Sources: - Mining phosphate for industrial use. - Production of fertilizers. - Production of laundry detergents.
Environmental Consequence: - Runoff of these products into water systems introduces excessive nutrients. - This leads to eutrophication, increasing plant and algae growth to the detriment of aquatic ecosystems.