Lesson 6&7: Cycles (PDF)

# Lesson 6&7 24 November 2024 15:42 ## Cycles - A series of events that are regularly repeated in the same order. - One of the major themes of the Earth subsystem. ## Biogeochemical cycle - Refers to the consideration of the biological, geological, and chemical aspects of each cycle. - "Biogeo...

# Lesson 6&7 24 November 2024 15:42 ## Cycles - A series of events that are regularly repeated in the same order. - One of the major themes of the Earth subsystem. ## Biogeochemical cycle - Refers to the consideration of the biological, geological, and chemical aspects of each cycle. - "Biogeochemical cycles are crucial for maintaining life on Earth and ensuring the health of Ecosystem." **Key aspects:** - Nutrient Recycling - Maintaining Energy - Climate regulation - Soil and plant health - Support biodiversity Sustainability ## Carbon - A common element in all known life - Found in abundance - Forms polymers and diverse organic compounds **Distribution:** - Earth's Atmosphere - 0.04% - Earth's crust - 0.025% - Mass of Human Body - 18.5% **Major locations of Carbon recycles:** - Atmosphere - Terrestrial biosphere (land) - Earth's interior - Ocean - Human influence ## Carbon Cycle **Forms:** - CO2 - CH4 **Absorption:** - Absorbed by autotrophs - Methanotrophs for CH4 - Ex: Alphaproteobacteria and Gammaproteobacteria ## Cellular Respiration - A metabolic process - Converts glucose and oxygen into energy, carbon dioxide, and water ## Photosynthesis - A process in the carbon cycle - Removes carbon dioxide from the atmosphere - Converts it into sugars that plants use for food ## Food Chain - Carbon enters the food chain through autotrophs - Self-feeders, like plants and algae - Use carbon dioxide from the air to make organic compounds - These organic compounds are passed through the food chain when other organisms, called heterotrophs, consume them. ## Decomposition **Actions:** - It releases carbon dioxide into the atmosphere. - Makes it available for plants to use in photosynthesis. - Bacteria and fungi break down the organic matter in dead plants and animals. - Consume the carbon-based compounds in the dead matter as a source of energy and nutrients - Some carbon compounds from decomposing organic matter are retained in the soil forming Humus. - Humus is a stable carbon-rich material ## Fossilization **Actions** - Dead organic material that does not decompose - This process can transform organic carbon into fossil fuels - Coal, oil, and natural gas. **Release** - When these fossil fuels are eventually burned, the stored carbon is released back into the atmosphere as CO2. ## Volcanic Activity - Volcanic eruptions releases carbon dioxide from molten rock in the Earth's crust. - Sources include the metamorphism of carbonate rocks that subduct with the ocean crust, and carbon stored in the mantle when the Earth formed. ## Ocean Absorption **Actions:** - Ocean stores about 50 times more carbon than the atmosphere. - Once CO2 is absorbed, it reacts with seawater to form carbonic acid (H2CO3). - Which then dissociates into bicarbonate (HCO3-) and carbonate ions (CO3 2-). ## Human Influence - Humans have a huge effect on the carbon cycle when we burn: - Wood - Fossil fuels (such as oil, coal, and natural gases), and other forms of carbon - Burning releases stored carbon into the atmosphere. ## Oxygen **Composition:** - Earth's mass: makes up about 30% - Mostly found in the form of oxides within minerals like silicon dioxide SiO2. - Earth's volume in the atmosphere: about 21%. - Mass of the human body: 65% of mass. ## Oxygen Cycle - Process by which oxygen moves through different parts of the Earth's ecosystem - Atmosphere, ocean, and crust. - This cycle also happens during: - Photosynthesis, cellular respiration, volcanic activity and burning of fossil fuels (combustion). ## Redox - Refers to a type of chemical reaction in which the oxidation states of atoms are changed due to the transfer of electrons between them. ## Oxidation - Refers to the process where oxygen interacts chemically with other elements in rock, minerals, and organic matter, often forming oxides. - The process in which an atom, ion, are molecule loses electrons. - When a substance is oxidized its oxidation state increases. ## Reduction - The process in which an atom, ion, or molecules gains electron when a substance is reduced, it's oxidation state decreases. **Example:** - In the reaction where iron rusts (oxidizes), iron (Fe) loses electrons to form iron oxide (Fe2O3). ## How do oxygen return to the atmosphere? 1. ** Photosynthesis** - The primary process by which oxygen is released back into the atmosphere. - Counteracts oxygen consumption in oxidation processes. 2. **Volcanic activity and geological processes** - Can release some oxygen that was found in minerals and rocks. 3. **Decomposition and aerobic respiration** - Help maintain the balance of oxygen in directly by recycling other elements in the cycle. ## Ozone-Oxygen cycle - In the upper atmosphere, oxygen plays a key role in the formation and breakdown of ozone (O3). - Ozone protects life on earth from harmful ultraviolence (UV) radiation ## Ozone Formation - Ultraviolet radiation splits molecular oxygen (O2) into individual oxygen atoms, which then bond with other O2 molecules to form ozone (O3). ## Ozone Breakdown - Ozone absorbs UV radiation and breaks down into oxygen atoms and molecules. - Discontinuous cycle of formation and break down of ozone helps shield earth's surface from UV radiation, maintaining the balance of oxygen in the stratosphere. ## Nitrogen - The most abundant naturally occurring gas is nitrogen (N2). **Distribution:** - Air: 78% - Mass of human body: 3.3% ## Nitrogen Cycle - The process by which nitrogen is converted into different chemical forms as it circulates between the atmosphere, soil, plants, animals, and microorganisms. ## The problem with N2! - Not usable by life - The three bonds between the nitrogen atoms make it very hard to break apart (unreactive). - We can't do any reactions to make DNA, RNA or proteins. - There are certain bacteria that can break this bond to make something that they can use. ## Nitrogen Fixation - Converts nitrogen gas from air into ammonia or ammonium in soil. - Found in the soil and in root nodules of certain plants known as legumes. - This bacteria (Azotobacter, Bacillus, Clostridium, and Klebsiella) great nitrogen gas apart and add hydrogen atoms to form ammonia (NH3) or ammonium (NH4+). ## Ammonification (Mineralization) **Actions** - Decomposers break down organic matter into ammonium (NH4+), which can be reused by plants. - Organic nitrogen compounds such as proteins, nucleic acid, and urea, are broken down by decomposers into simpler forms like ammonia (NH3) or ammonium (NH4+). - Can *be reused by plants or undergo nitrification to form nitrates.* ## Nitrogen Fixation by Lightning - When lightning strikes the high temperatures and energy cause nitrogen gas (N2) in the atmosphere to react with oxygen (O2) to form nitrogen oxide. - This includes nitrogen dioxide (NO2) and nitric acid (NO) - This nitrogen oxide is combined with water vapor in the atmosphere to form nitrates (NO3-). ## Assimilation **Actions:** - Ammonia and nitrate can be taken up by plants and used to make important *biological molecules like DNA and proteins*. - These proteins are then consumed by animals. ## Nitrification - The conversion of ammonium ions (NH4+) to nitrate (NO3-) by adding oxygen through nitrifying bacteria in the soil. ## Two Steps of This Process: **1. Ammonia Oxidation** - Nitrosomonas bacteria convert ammonium (NH4+) to nitrite (NH2-). **2. Nitrate Oxidation** - Nitrobacter bacteria converts nitrites (NO2-) into nitrates (NH3-). - Nitrates are highly available to plants and are an important form of nitrogen for plant growth. ## Denitrification **Actions:** - The process by which denitrifying bacteria (such as Pseudomonas and clostridium) convert nitrates (NO3-) nitrogen gas (N2) or nitrous oxide (N2O), which is released back into the atmosphere. - This process occurs under anaerobic conditions (low oxygen environment). - Waterlogged soil, wetland, and deep sediments, where oxygen is scars, and bacteria use nitrates as an alternative to oxygen for respiration. - It completes the nitrogen cycle by returning nitrogen to the atmosphere. - This maintains the balance of nitrogen in the ecosystem. ## Leaching **Actions:** - The process where excess nitrates (NO3) from the soil, often due to heavy rainfall, are carried away by water into rivers, lake and groundwater. - This can lead to water pollution. - Causing issues like eutrophication. - Eutrophication is where excess nutrients in water bodies promotes excessive plant growth, depleting oxygen and harming aquatic life. ## Biogeochemical Cycle <br> ## Weathering and Erosion ## Weathering - The physical breakdown and chemical alternation of rocks at all near earth's surface. ## Two Types of Weathering **1. Mechanical or Physical Weathering** - The breaking up of large rocks into smaller fragments without changing the rocks mineral composition. **Processes that lead to the mechanical disintegration of rocks:** - Frost wedging - When water gets inside the joints, alternate freezing and thawing episodes pry the rock apart. - Salt crystal growth - Force exerted by salt crystal that formed as water evaporates from pore spaces or cracks in rocks can cause the rock to fall apart. - Abrasion - Wearing away of rocks by constant collision of loose particles. - Biological activity - Plants and animals including humans as agents of mechanical weathering. **2. Chemical Weathering** - Decomposes rocks through chemical change **Major processes of chemical weathering:** - Dissolution: - Dissociation of molecules into ions; common example includes dissolution of calcite and salt. - Oxidation: - Reaction between minerals and oxygen dissolved in water. - Hydrolysis: - Change in composition and minerals when they react with water. ## Mass Wasting - The down slope movement of rock, regolith, and soil under the direct influence of gravity. ## Erosion and Deposition **1. Erosion** - The incorporation and transportation of material by a mobile agent such as water, wind, or ice. **2. Deposition** - The aggradation or accumulating of weathered sediments to create different landforms. ## Sulfur ## Sulfur Cycle - Non-metallic and chemical element belonging to the oxygen group (Group 16 of the periodic table). - One of the most reactive of the elements - Tasteless, odourless, brittle solid that is pale yellow in color - A poor conductor of electricity, and insoluble in water. - The tenth most abudant element by mass in the solar system. - It describes the movement of sulfur through the Earth's systems, Including the biosphere, geosphere, hydrosphere, and atmosphere. - Sulfur is a vital element in the environment and plays an essential role in lifeforms. - Particularly through the formation of proteins and enzymes. - It is also important in regulating the composition of the atmosphere - Can influence environmental processes such as acid rain. ## Sulfur in the Atmosphere **Key Reserve Locations:** - Lithosphere - Releasing into the atmosphere by: - Weathering in addition - Hydrogen sulfide (H2S) and SO2 is released into the atmosphere by: - Volcanic eruptions, hot springs and the decay of biological materials in swamps and bogs. - Dimethyl sulfide (DMS) - Emitted by oceanic organisms like phytoplankton - Another significant source of sulfur in the atmosphere. - Converted to sulfate aerosols - Affect cloud formation and climate ## Precipitation and Deposition - Sulfuric acid (H2SO4) from the atmosphere can dissolve in water droplets and fall to the ground as acid rain, bringing sulfur back to earth surface. - Sulfur compounds, including sulfates, can be deposited into soil and water bodies through precipitation. ## Sulfur in Water Bodies (Aquatic Systems) **Key Points** - Sulfate ions (SO42-) can be dissolved in water and incorporated into aquatic life. - Marine bacteria can reduce sulfate to hydrogen sulfide (H2S) - Released into the atmosphere or used by other organisms in the water. - Anoxic environments (lacking oxygen) like deep sea sediments or swamps may promote sulfate reduction, leading to the formation of hydrogen sulfide. ## Sulfur in Rocks and Minerals **Key Points** - Sulfur occurs in rocks primarily in the form of sulfide minerals (such as pyrite or FeS2) and sulfate minerals (such as gypsum, CaSO4). - Found in this minerals within the earth's crust, often as part of sedimentary rock layers or igneous rocks. ## Weathering and Erosion **Actions:** - Physical weathering and erosion of rocks break down this sulfur containing minerals, releasing sulfur into the soil and water as sulfate ions (SO42-). - Sulfur in soil can be absorbed by plants, entering the biological part of the cycle ## Assimilation by Plants **Actions:** - Plants absorb sulfate ions (SO42-) from the soil and incorporate them into organic molecules such as amino acids (cysteine and methionine) and proteins. ## Consumption by Animals **Actions:** - Animals consumes sulfur by eating plants or other animals, absorbing sulfur into their own tissues, where it plays a role in protein synthesis and cellular function. - Animals also released sulfur back into the environment through excretion and decomposition after death. ## Decomposition and Mineralization **Actions:** - When plants and animals die decomposers like bacteria and fungi break down the organic sulfur compounds in their bodies. - This process release sulfur back into the soil as sulfate ions (SO42-), this mineralization step converts organic sulfur into inorganic sulfur, making it available again to plants. ## Take Note! - Sulfate (SO42-): the primary form of sulfur in soil, water, and plants. - Hydrogen sulfide (H2S): a gas produced during the composition and volcanic activity. - Sulfur dioxide (SO2): a major pollutant released from volcanic eruptions and fossil fuels combustion. - Sulfuric acid (H2SO4): the product of SO2 reacting with water vapor in the atmosphere leading to acid rain. ## Phosphorus Cycle ## Phosphorus **Key Points** - A nonmetal that seats just below nitrogen in group 15 of the periodic table - This element exist in several forms of which white and red are the best known. - It is approximately 1% of total body weight. - Bodys phosphorus: about 85% - It is primarily found in bones in teeth as calcium phosphate. - The rest is in soft tissues and cells, playing critical roles in DNA, RNA, and ATP. - Building blocks of nucleic acid like DNA and a phosphor lipids that forms our cells membranes. - It is also essential for plant growth. ## Weathering and Erosion **Actions:** - Physical weathering of rocks and erosions break down phosphate containing rocks, releasing phosphate ions (H2PO4- HPO42-) into the soil and water. ## Phosphorus Cycle - The process by which phosphorus moves through the environment, including soil, water, organism, and rocks. - Phosphate compounds can be found on sedimentary rock. ## Phosphorus in Rocks and Minerals - Phosphorus primarily exist in earth's crust in the form of phosphate minerals such as apatite (Ca5(PO4)3(F, CI, OH). - Not readily soluble in water and is locked and rocks and sediments which can release phosphorus into the cell or water over long periods. ## Assimilation by Plants **Actions:** - Plants absorbs phosphate ions from the soil through their roots - Essential nutrients for plants, involved in processes like energy transfer (ATP), photosynthesis, and DNA/RNA synthesis. - Plants use phosphorus to grow, develop roots, flowers, seeds, and fruits. - It also helps in the formation of phospholipids for cell membranes. ## Decomposition **Actions** - When the animals excrete waste or the plants and animals die, phosphates may be taken up by detrivores(worms) or return to the soil. ## Leaching and Runoff **Actions:** - Some phosphorus in the soil is carried away by water through leaching (the process where phosphorus is washed away by the rain or irrigation) or runoff(when surface water moves phosphorus to lakes, rivers, and oceans). - This could also lead to eutrophication. - Where excess phosphorus in water bodies promotes algal blooms which deplete oxygen and harm aquatic ecosystems. ## Phosphorus and Aquatic Ecosystem **Actions:** - Phosphorus is carried into rivers, lakes, and oceans where it is used by aquatic plants and algae. - Some of the phosphorus may become incorporated into the bodies of aquatic organisms (fish and algae) ## Geological Uplift **Actions:** - Over long geological time scales, sedimentary phosphorus from ocean or lake beds can be uplifted by tectonic activity, returning phosphorus back to land. ## Take Note! - No gaseous phase: - Unlike the nitrogen and carbon cycle - Phosphorus does not have a significant gaseous phase. - Slow cycle: - The cycle is lower compared to other cycles - Because phosphorus is mostly stored in rocks and minerals - Making its movement through the ecosystem much slower. - Essential for life: - Phosphorus is critical for all living organisms - Particularly in the formation of DNA, RNA and ATP, and phospholipids. ## Water Cycle - The water cycle also known as hydrological cycle describes the continuous movement of water within the earth and its atmosphere. - It involves various processes that allow water to change states (liquid, vapor, solid) and move through different parts of the earth system including the atmosphere, oceans, land, and living organisms. ## Evaporation **Actions:** - Water from oceans, lakes, rivers, and other water bodies is heated by the sun - Causing it to change from liquid to water vapor. - Most evaporation occurs from the surface of the oceans - But it can also happen from soil, plants and freshwater bodies. ## Transpiration **Actions:** - The release of water vapor from plants into the atmosphere. - Occurs when plants absorb water from the soil through their roots and release it through tiny openings in their leaves called stomata. ## Condensation **Actions:** - As water vapor rises into the cooler upper atmosphere, it cools and condenses into tiny droplets forming clouds. ## Precipitation **Actions:** - When the water droplets in clouds combine and grow large enough they fall to the earth due to gravity - This can occur as rain, snow, hail, or sleets. ## Infiltration **Actions:** - Some of the precipitation that falls on to the land seeps into the soil, a process known as infiltration. - Infiltrated water replenishes groundwater supplies in feeds into aquifers, which can be used for drinking water or irrigation. ## Groundwater Flow **Actions:** - What are that infiltrates the soil may move downward through the ground, becoming part of underground aquifer and water tables. ## Runoff **Actions:** - Water that doesn't infiltrate the soil close across the ground as runoff eventually entering rivers, lakes, and oceans. - Runoff helps to transport water back into larger bodies of water and is influenced by factors like terrain, vegetation, and the amount of precipitation. ## Sublimation **Actions:** - In cold regions snow and ice and directly change from solid to vapor without becoming liquid. - This process is called sublimation. ## Accumulation **Actions:** - Water that falls as precipitation accumulates and body of water like rivers, lakes, oceans, and reservoirs. - This accumulation of water is what feeds the rest of the cycle ensuring that the process continues.