ENS 233 F - Environmental Science and Engineering

MWF 10:00 - 11:00 AM

CHAPTER 1

Biogeochemical Processes

Topic: Biogeochemical Processes

Student Reporters

Cheryl Melanie Arestang

Eds Crecelle Centino

Nichole Marie Chiong

Camille Trisha Dizon

Marc Edcil Mutya

Ysabella Mae Ozoa

Meriel Torres

Dr. Irismay T. Jumawan

Instructor

September 2024
 TABLE OF CONTENTS

Introduction…………………………………………………………………………. 1

Water cycle …………………………………………………………………………... 2-5

Nitrogen Cycle ………………………………………………………………………. 6-11

Oxygen Cycle …………………………………………………………………………. 12-18

Carbon Cycle ………………………………………………………………………….. 18-23

Phosphorus Cycle …………………………………………………………………….. 23-28

Sulfur Cycle …………………………………………………………………………….. 28-32

Human Activities that Affect Biogeochemical Cycles ………………………………… 32-37

Conclusion ………………………………………………………………………………. 37

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INTRODUCTION

Biogeochemical cycles are essential processes that recycle nutrients through the Earth's

systems. These cycles allow for the continuous movement of key elements like carbon, nitrogen,

oxygen, and water between the atmosphere, biosphere, hydrosphere, and geosphere. It is the

exchange and modification of chemical elements and compounds among living creatures, the

atmosphere, and the Earth's crust. Without these natural cycles, life on Earth could not sustain

itself.

This paper will explore the fundamental concepts of biochemical cycles and their

significance. It will explain how these cycles work and their role in keeping ecosystems

balanced. Examples include the water, nitrogen, oxygen, carbon, phosphorus, and sulfur cycles.

Understanding these cycles helps to show how life stays in balance on Earth.

One of the most well-known biochemical cycles is the water cycle, also known as

hydrological cycle, which is the continuous movement of water on, above, and below the surface

of the Earth.

The nitrogen cycle involves the conversion of nitrogen into different chemical forms that

living organisms can use. The oxygen cycle, another important system, is the circulation of

oxygen between the atmosphere, biosphere, and lithosphere. This cycle ensures that oxygen

levels in the atmosphere remain balanced, supporting aerobic life. The carbon cycle is the

process by which carbon moves through the Earth’s systems, primarily the atmosphere, oceans,

soil, and living organisms. This cycle tracks the movement of carbon through the atmosphere,

oceans, plants, animals, and soils.

The phosphorus cycle is unique because phosphorus does not exist in the atmosphere as a

gas. Phosphorus is released from rocks through weathering, taken up by plants, and passed

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through the food chain. The sulfur cycle involves the movement of sulfur through the

atmosphere, hydrosphere, and biosphere. Sulfur is crucial for forming proteins and vitamins in

living organisms, and the cycle plays a role in acid rain formation due to industrial emissions.

These biochemical cycles are indispensable to life on Earth, continuously recycling key

elements through various environmental systems. However, human activities are increasingly

disrupting these natural processes. These impacts highlight the urgent need for sustainable

practices to protect and restore the balance of biochemical cycles. By understanding these cycles,

we can better appreciate the interconnectedness of life and the environment and how human

activities can impact the delicate balance of these systems.

Specific Learning Outcomes

By the conclusion of this lesson, students should be able to:

1. Understand the key components and processes of major biogeochemical cycles

2. Analyze the interactions between human activities and biogeochemical cycles

3. Evaluate the role of biogeochemical cycles in ecosystem stability and

sustainability

Prompting Questions

These questions focus on understanding the basics and general significance of

biogeochemical cycles

 What is a biogeochemical cycle, and why is it important for life

on Earth?

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  Why is it important to maintain the balance of all biogeochemical cycles on

Earth?

 What happens when one part of a biogeochemical cycle is disrupted?

Water Cycle

Water in various phases flows through the atmosphere (transportation). Liquid water

travels across land called runoff, into the ground (infiltration and percolation), and through the

groundwater. Groundwater enters plants (plant uptake) and evaporates into the atmosphere

(transpiration). Solid ice and snow can be converted directly into gas (sublimation). The opposite

can also occur when water vapor solidifies which is called deposition (National Oceanic and

Atmospheric Administration, 2019). Water vapor in the atmosphere can also condense into liquid

droplets, forming clouds, which eventually leads to precipitation in the form of rain, snow, or

hail. Water may remain for extended periods before re-entering the water cycle through

evaporation .

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Source: https://climatekids.nasa.gov/water-cycle/

Figure 1. Water Cycle Model

Water

Water is an oxygen hydride consisting of one oxygen atom covalently bonded to two

hydrogen atoms. It acts as an amphoteric solvent and is a component of greenhouse gases,

human metabolites, Saccharomyces cerevisiae metabolites, E. coli, and mouse metabolites. It is

an oxygen hydride, a mononuclear parent hydride, and an inorganic hydroxy compound. It is the

conjugate base of an oxonium. It is the conjugate acid of a hydroxide(Team, 2016).

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 Source: :https://biodynamizer.com/en/water/molecular-composition-of-water-chemical-
structure%E2%80%8B/

Figure 2. Water Molecule Model

Water influences the intensity of climate variability and change. It is a key part of

extreme events such as drought and floods. Its abundance and timely delivery are critical for

meeting the needs of society and ecosystems. Humans use water for drinking, industrial

applications, irrigating agriculture, hydropower, waste disposal, and recreation. Water sources

must be protected both for human uses and ecosystem health. In many areas, water supplies are

being depleted because of population growth, pollution, and development

Water (chemical formula: H2O) is a transparent fluid that forms the world's streams,

lakes, oceans, and rain and is the major constituent of the fluids of organisms. Water is essential

for the survival of life on Earth. Water is distributed unevenly over the Earth's surface. It is an

important solvent and dissolves almost all polar solutes. So let's look at its characteristics and

understand the reasons behind its importance.

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 Water molecules have extensive hydrogen bonds that give them unusual properties in

their condensed form where it is also a colorless and tasteless liquid. It also has a high melting

and boiling point and when compared to other liquids, it has a high specific capacity, thermal

conductivity, and surface tension. Water is an excellent solvent because it helps transport ions

and molecules necessary for metabolism. Water also has a high latent vaporization that helps in

the regulation of body temperature. These properties justify the importance of water in the

biosphere. (Linton, 2024).

Stages of Water Cycle

● Evaporation. The first step of the water cycle is evaporation. It is a process where water

on the surface transforms into vapor form. Water absorbs heat energy from the sun and

turns into vapors. Water bodies like oceans, seas, lakes, and rivers are the main source of

evaporation.

● Condensation. As water vaporizes into water vapor, it rises in the atmosphere. At high

altitudes, the water vapor changes into very tiny particles of ice /water droplets because

of low temperature. This process is called condensation. These particles come close

together and form clouds and fog in the sky.

● Sublimation. Apart from evaporation, sublimation also contributes to water vapors in the

air and is a much slower process. Sublimation is a process where ice directly converts

into water vapors without converting into liquid water. This phenomenon accelerates

when the temperature is low or pressure is high.

● Precipitation. The clouds which are composed of condensed water vapors pour down

back to the ground as precipitation due to wind or temperature changes. This occurs

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 because the water droplets combine to make bigger droplets, so when the air cannot hold

any more water, it precipitates. These water droplets fall now as rain and this is because

at high altitudes where the temperature is low, the water droplets lose their heat energy.

Water droplets could also precipitate in the form of hail, snow, or sleet depending on

temperature conditions, etc.

● Transpiration. As the water settles, some of it is absorbed into the soil. This water enters

the process of transpiration. Transpiration is a process similar to evaporation in which

plants convert liquid water into water vapor. The plant's roots absorb the water and push

it towards the leaves, where it is used in photosynthesis. The extra water is moved out of

leaves through stomata water vapor. Thus water enters the biosphere and exits into a

gaseous phase. Biosphere and leaves in the gas phase.

● Runoff. As water falls in whatever form, it causes runoff. Runoff is the process by which

water runs over the earth's surface. When snow melts into water, it creates runoff. As

water rushes over the ground, it displaces the topsoil and transports minerals with it. This

runoff combines to form channels and rivers, which eventually flow into lakes, seas, and

oceans. Here, water enters the hydrosphere.

● Infiltration. Any water that does not run immediately into bodies of water or evaporates

rapidly is absorbed by plants and soil and may be driven deeper into the earth. This is

known as infiltration. Water seeps down, raising the groundwater table. The infiltration is

measured as inches of water-soaked by the soil per hour.

Importance of Water Cycle

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 The water cycle is a critical activity because it ensures the availability of water for all

living organisms and regulates weather patterns on our planet. If water would not naturally

recycle itself, we would run out of clean water, which is necessary for survival.

Freshwater appears abundant, yet when all of the world's water is considered, it is in short

supply. Freshwater accounts for only 3% of our planet's total water. The majority of this water,

approximately 2% of the global total, is held in glaciers and ice sheets or buried underground.

The remaining one percent is found in lakes, rivers, and wetland areas, or it moves through the

atmosphere as water vapor, clouds, and precipitation.

It also helps maintain aquatic ecosystems and we know plants cannot grow without

rainwater. Our water is filtered and cleaned by infiltration. Glaciers, ice, and snow can provide

freshwater for humans and other organisms. Runoff feeds rivers, other freshwater bodies, and

eventually the ocean, maintaining both freshwater and marine life. All of these processes support

life and shape the environments around us. Certain species are extremely sensitive to changes in

the water cycle. A prolonged drought can damage a plant population, and particular salamander

species may require a specific level of soil saturation to avoid desiccation.

Nitrogen Cycle

The nitrogen cycle is a biogeochemical process through which N₂ is converted into many

forms, consecutively passing from the atmosphere to the soil to organisms and back into the

atmosphere. Nitrogen gas exists in both organic and inorganic forms. Organic nitrogen exists in

living organisms, and it gets passed through the food chain by consuming other living organisms.

Inorganic forms of nitrogen are found in abundance in the atmosphere.

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 Source: https://cdn.britannica.com/93/22393-050-41E81EB6/Nitro
gen-symbol- square-nitrogen-some-properties-periodic.jpg

Figure 3. Nitrogen Symbol

Nitrogen

Nitrogen (N) is a nonmetallic element of Group 15 [Va] of the periodic table, and it is a

colorless, odorless, and tasteless gas. It is the most plentiful element in Earth’s atmosphere and a

constituent of all living matter. Among the elements, nitrogen ranks sixth in cosmic abundance.

Nitrogen is essential to life because it is a key component of DNA, RNA, and proteins,

which are the building blocks of life. All organisms require nitrogen to live and grow, as plants

and animals need it to produce proteins. Nitrogen is present in the environment in a wide variety

of chemical forms including organic nitrogen, ammonium, nitrite, nitrate, nitrous oxide, nitric

oxide or inorganic nitrogen gas.

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 Although atmospheric nitrogen (N₂) makes up the majority of the air we breathe, most of

it is unavailable for use by organisms because the triple bond between the N atoms in N₂

molecules makes it relatively unreactive. The bond is so strong (226 kilocalories per mole) that it

is difficult to cause molecular nitrogen to enter into other combinations. However, organisms

require reactive nitrogen to incorporate it into their cells. For plants and animals to use nitrogen,

N₂ gas must first be converted into a more chemically available form through various processes

in the nitrogen cycle.

Nitrogen Cycle

This nitrogen is made available to plants by symbiotic bacteria, which can convert the

inert nitrogen into a usable form, such as nitrites and nitrates.The inert nature of N₂ means that

biologically available nitrogen is often in short supply in natural ecosystems, limiting plant

growth. For plants and animals to be able to use nitrogen, N₂ gas must first be converted to a

chemically javailable form such as ammonium (NH4+), nitrate processes such as nitrogen

fixation, nitrification, denitrification, assimilation, and ammonification. (NO3-), or organic

nitrogen (e.g., urea-NNH₂)2CO.

The nitrogen cycle is of specific intrigued to scientists since nitrogen accessibility can

influence the rate of key environment forms, counting essential generation and decay. Human

exercises such as fossil fuel combustion, utilize of fake nitrogen fertilizers, and discharge of

nitrogen in wastewater have significantly modified the worldwide nitrogen cycle. Human

adjustment of the worldwide nitrogen cycle can adversely influence the common environment

framework additionally human wellbeing. This cycle has major impacts especially to the

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environment such as its cycle that goes along with biotic and abiotic factors along through its

process.

Source: https://www.youtube.com/watch?v=vZ9b5c8BOT4&t=36

Figure 4. Nitrogen Cycle Diagram

Main Processes of Nitrogen Cycle

The nitrogen cycle involves key processes such as nitrogen fixation, where atmospheric

nitrogen (N₂) is converted into ammonia (NH₃) by bacteria, making it available to plants.

Another important process is denitrification, where bacteria convert nitrates (NO₃ ⁻) back into

nitrogen gas (N₂), returning it to the atmosphere and completing the cycle.The nitrogen cycle

consists of several processes, all occurring in stages explained below.

1. Nitrogen Fixation

It is the initial step of the nitrogen cycle. Here, atmospheric nitrogen, which is

primarily available in an inert form, is converted into the usable form of ammonia (NH 3).

During nitrogen fixation, the inert form of N₂ gas is deposited into soils from the

atmosphere and surface waters, mainly through precipitation. The entire process is completed

by symbiotic bacteria, which are known as Diazotrophs. Azotobacter and Rhizobium also

have a major role in this process. These bacteria consist of a nitrogenase enzyme, which can

combine gaseous nitrogen with hydrogen to form NH3.

This process can occur either by atmospheric fixation, which involves lightning, or

industrial fixation by manufacturing ammonia under high temperature and pressure

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conditions. This can also be fixed through man-made processes, primarily industrial

processes that create NH3 and nitrogen-rich fertilizers. The Haber Process (how fertilizers are

made) makes up approximately 30% of nitrogen-fixing. These fertilizers are used to increase

NO3- in the soil to maximize plant growth.

2. Nitrification

In this process, the NH3 is converted into NO3− by the presence of bacteria in the soil.

Nitrites (NO2−) are formed by the oxidation of NH 3 with the help of Nitrosomonas bacteria

species. Later, the produced NO2− is converted into NO3− by Nitrobacter. This conversion is

very important as ammonia gas is toxic to plants.

Many species of blue-green algae (cyanobacteria) in the ocean can also fix nitrogen.

This then provides sources of nitrogen to aquatic animals, and the nitrogen goes around a

similar cycle to what happens on land.

The reaction involved in the process of Nitrification is as follows:

2NH3 + 3O2 → 2NO2- + 2H+ + 2H2O

2NO2- + O2 → 2NO3-

3. Assimilation

Primary producers – plants take in the nitrogen compounds from the soil with the help

of their roots, which are available in the form of NH 3, NO2−, NO3−, or NH4+ ions and are used

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in the formation of the plant and animal proteins. This way, it enters the food web when the

primary consumers eat the plants.

4. Ammonification

When plants or animals die, the nitrogen present in the organic matter is released

back into the soil. The decomposers, namely bacteria or fungi present in the soil, convert the

organic matter back into NH4+. This process of decomposition produces NH3, which is further

used for other biological processes.

The process of ammonification occurs in the same manner in the marine ecosystem as

in the terrestrial ecosystem. The only difference is that it is carried out by marine bacteria.

5. Denitrification

Denitrification is the process in which the nitrogen compounds make their way back

into the atmosphere by converting NO3− into gaseous nitrogen. This process of the nitrogen

cycle is the final stage and occurs in the absence of oxygen. Denitrification is carried out by

the denitrifying bacterial species- Clostridium and Pseudomonas, which will process NO3− to

gain oxygen and give out free nitrogen gas as a byproduct.

Burning fossil fuels also adds nitrous oxide (N2O) to the atmosphere, which dissolves

in rainwater to form nitric acid (HNO3), which then adds NO3− to the soil. This upsets the

balance of the natural nitrogen cycle, polluting ecosystems and altering the ecology of entire

regions. Moreover, too much nitrogen in the soil makes it overly acidic. The nitrogen also

passes into rivers and lakes, where it is considered a pollutant. Under certain conditions, such

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 as in waterlogged soils, denitrifying bacteria in the soil break down nitrates and return

nitrogen to the air, which reduces the fertility of the soil.

Importance of Nitrogen Cycle

The nitrogen cycle is crucial because nitrogen is an essential nutrient that supports all

forms of life on Earth. Through the nitrogen cycle, atmospheric nitrogen is converted into forms

that plants and animals can use, ensuring the sustainability of ecosystems. Listed below are some

of the important roles of the nitrogen cycle.Helps plants to synthesize chlorophyll from nitrogen

compounds.

The importance of nitrogen cycle is as follows:

1. Helps in converting inert nitrogen gas into a usable form for the plants through the

biochemical process.

2. In the process of ammonification, the bacteria help in decomposing the animal

and plant matter, which indirectly helps to clean up the environment.

3. Nitrates and nitrites are released into the soil, which helps enrich the soil with the
necessary nutrients required for cultivation.

4. Nitrogen is an integral component of the cell and it forms many crucial

compounds and important biomolecules.

Nitrogen is abundant in the atmosphere but is unusable by plants or animals unless it is

converted into nitrogen compounds, a process in which nitrogen-fixing bacteria play a crucial

role by fixing N₂ into usable forms; plants then absorb these nitrogen compounds from the soil

through their roots to produce proteins and other compounds within their cells, while animals

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assimilate nitrogen by consuming these plants or other nitrogen-containing animals, and humans,

in turn, consume proteins from these sources, allowing nitrogen to assimilate into our bodies.

During the final stages of the nitrogen cycle, bacteria and fungi decompose organic matter,

dissolving nitrogenous compounds into the soil for reuse by plants, while some bacteria convert

these compounds back into nitrogen gas, returning it to the atmosphere; these processes repeat

continuously, maintaining the percentage of nitrogen in the atmosphere.

Oxygen Cycle

The oxygen cycle is a biogeochemical cycle that describes the movement of oxygen

throughout the Earth's atmosphere, land, oceans, and living organisms. It's essential for life on

Earth as oxygen is a crucial element for respiration and the existence of most organisms. Atkins,

P., & Jones, L. (2010).

The entire cycle can be summarized as, the oxygen cycle begins with the process of

photosynthesis in the presence of sunlight, releases oxygen back into the atmosphere, which

humans and animals breathe in oxygen and breathe out carbon dioxide, and again linking back to

the plants. The oxygen cycle circulates through nature in various forms. Oxygen occurs freely in

air and dissolved in water, and is the second most abundant uncombined element in the

atmosphere after nitrogen. The waters of the world are the main oxygen generators of the

biosphere; their algae are estimated to replace about 90 percent of all oxygen used.

What is Oxygen?

Oxygen is a colorless, odorless, and tasteless gas that is essential for the survival of most

living organisms on Earth. It is the second most abundant element in the universe by mass.

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Oxygen is a chemical element with an atomic number of 8 (it has eight protons in its nucleus).

Oxygen forms a molecule (O2) of two atoms which is a colorless gas at normal temperatures and

pressures.

Source:https://www.tutorialspoint.com/chemistry_part2/chemistry_oxygen.htm

Figure 5: Oxygen Symbol

Stages of the Oxygen Cycle

Stage 1: All green plants during the process of photosynthesis, release oxygen back into

the atmosphere as a by-product.

Stage 2: All aerobic organisms use free oxygen for respiration.

Stage 3: Animals exhale carbon dioxide back into the atmosphere which is again used by

the plants during photosynthesis. Now oxygen is balanced within the atmosphere.

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 Source:https://byjus.com/biology/oxygen-cycle-environment/

Figure 6: Oxygen Cycle

Components of the Oxygen Cycle

The oxygen cycle begins with the process of photosynthesis under sunlight, releasing

oxygen into the atmosphere, which is then inhaled by humans and animals and released carbon

dioxide, which then leads to plants.

Photosynthesis. Plants use sunlight to convert carbon dioxide and water into glucose and

oxygen, releasing oxygen into the atmosphere. Photosynthesis is a process used by plants, algae,

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and some bacteria to convert sunlight into chemical energy. This energy is stored in glucose, a

sugar molecule, and oxygen is released as a byproduct. Raven, P. H., Evert, R. F., & Eichhorn,

S. E. (2005).

Plants use chlorophyll, a green pigment found in their leaves, to absorb sunlight. Carbon

dioxide is absorbed from the air, and water is absorbed from the soil. During photosynthesis, the

energy from sunlight is used to split water molecules and combine carbon dioxide with this

energy to produce glucose. This process is essential for life on Earth as it provides the primary

source of oxygen in the atmosphere and the energy that fuels most ecosystems. Biology of Plants

(7th ed.). W. H. Freeman.

Source: https://www.educba.com/what-is-photosynthesis/

Figure 7: Photosynthesis

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 Respiration. Is a crucial component of the oxygen cycle. It's the process by which

organisms, including plants, animals, and microorganisms, break down glucose in the presence

of oxygen to release energy. This process consumes oxygen and releases carbon dioxide, which

is then used by plants for photosynthesis. Respiration helps maintain the balance of oxygen and

carbon dioxide in the atmosphere, ensuring a continuous supply of oxygen for life on Earth.

Campbell, N. A., & Reece, J. B. (2005). The word respiration is commonly used to describe

the process of inhaling oxygen and exhaling carbon dioxide, but more formally the term refers

to the chemical process that organisms use to release energy from food, which usually involves

the consumption of oxygen and the release of carbon dioxide.

Source: https://learningzone.oumnh.ox.ac.uk/respiration

Figure 8: Respiration

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 Decomposition. Plays a vital role in the oxygen cycle. In the oxygen cycle, oxygen is

utilized for the breakdown of organic waste. It's the process by which decomposers, such as

bacteria and fungi, break down dead organisms and organic matter. This process releases carbon

dioxide into the atmosphere, which is then used by plants for photosynthesis. Decomposition can

also consume oxygen, especially in environments with limited oxygen availability. However, the

overall effect of decomposition on the oxygen cycle is to help maintain the balance between

oxygen production and consumption. Atlas, R. M. (2009). The organic wastes obtained from

living organisms are biodegradable because some aerobic bacteria convert organic waste

materials into inorganic materials in the presence of oxygen by releasing carbon dioxide and

water.

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 Source:https://www.shutterstock.com/image-vector/process-decomposition-nature-colored-
vector-illustration-2186885695

Figure 9: Decomposition

Combustion. Is another important process in the oxygen cycle. It involves the burning of

organic matter, such as fossil fuels, in the presence of oxygen. During combustion, oxygen reacts

with the organic matter, releasing energy and producing carbon dioxide and water. While

combustion is essential for human activities, it also contributes to the increase of carbon dioxide

in the atmosphere, which can have negative environmental consequences. Chemistry (5th ed.).

The combustion of fossil fuels releases nitrogen oxides (NOx) into the atmosphere, contributing

to air pollution and disrupting the nitrogen cycle by increasing reactive nitrogen levels in

ecosystems

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Source: https://theory.labster.com/pac_flammability/

Figure 10: Combustion

Why Is Oxygen Important?

All the systems in our body rely on oxygen to make energy. If our blood didn't move the

oxygen we breathe into our organs and tissues, we wouldn't be able to carry out normal functions

such as moving our muscles, digesting food, or thinking. Blood keeps us alive.

Oxygen is a vital element for life on Earth. It is essential for respiration, the process by

which organisms convert glucose into energy. Without oxygen, most living cells would be

unable to function. Humans, animals, plants, and even many microorganisms rely on oxygen to

survive.

In addition to its role in respiration, oxygen is also crucial for other biological processes.

It is involved in the breakdown of nutrients, the synthesis of proteins and other molecules, and

the regulation of cellular functions. Oxygen also plays a significant role in the environment,

helping to maintain the ozone layer, which protects the Earth from harmful ultraviolet radiation.

Furthermore, oxygen is essential for industrial processes and human activities. It is used

in a wide range of applications, including steelmaking, welding, medical treatments, and the

production of various chemicals. Oxygen is also a component of the air we breathe, making it an

essential resource for human life and society. Campbell, N. A., & Reece, J. B. (2005).

Carbon Cycle

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 The carbon cycle is the continuous process through which carbon compounds are

exchanged among the biosphere, geosphere, pedosphere, hydrosphere, and atmosphere of the

Earth. This system involves various natural processes, such as photosynthesis, respiration,

decomposition, and the absorption of carbon dioxide (CO2) by oceans. It plays a crucial role in

regulating the Earth's temperature, as carbon dioxide acts as a greenhouse gas that helps maintain

a stable climate. Human activities, including burning fossil fuels and deforestation, significantly

impact this cycle by releasing stored carbon into the atmosphere.

One of the most important biological and environmental processes involving carbon is

the carbon cycle. This process governs the movement and exchange of carbon between the

atmosphere, living organisms, and the Earth itself. Crude oil, natural gas, black coal and lignite

are called fossil fuels. When crude oil is pumped out of the ground, refined, and used as gasoline

and diesel in engines, carbon dioxide that has been out of the carbon cycle for millions of years

is released.

The use of fossil fuels for transportation and energy releases large amounts of carbon

dioxide into the atmosphere. Human impacts on the carbon cycle lead to an increased greenhouse

effect, which causes climate change. It .an be considered a complex process that involves other

processes that can take a long period of time before again starting from the start of its cycle.

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Source:https://scied.ucar.edu/sites/default/files/media/images/carboncycle_sm.jpg

Figure 11. Carbon Cycle Diagram

Carbon

Carbon (C) is a nonmetallic chemical element found in Group 14 (IVa) of the periodic

table. Although it is widely distributed in nature, carbon is not particularly abundant, making up

only about 0.025% of Earth’s crust. Despite this, carbon forms more compounds than all other

elements combined, highlighting its unique chemical versatility. In 1961, the isotope carbon-12

was chosen to replace oxygen as the standard for measuring atomic weights. Additionally,

carbon-14, a radioactive isotope, plays a crucial role in radiocarbon dating and radiolabeling.

On a cosmic scale, carbon is the product of helium "burning," where three helium nuclei

fuse to create a carbon nucleus. While carbon is the 19th most abundant element in Earth's crust,

it is far more prevalent in the universe, with an estimated 3.5 times more carbon atoms than

silicon.

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 Source:https://cdn.britannica.com/94/22394-050-619F56C9/element-symbol-square-C-Its-
properties-some.jpg

Figure 12. Carbon Element

In Earth's crust, carbon’s elemental form is a minor component, but its compounds are

significant. Carbonates, such as those of magnesium and calcium, are found in common minerals

like magnesite, dolomite, marble, and limestone. The shells of marine organisms, including

corals, oysters, and clams, are primarily composed of calcium carbonate. Additionally, carbon is

widely present in fossil fuels like coal, petroleum, and natural gas, which are critical energy

resources.

Carbon Dioxide

Carbon dioxide (CO2) is a colorless, odorless gas composed of one atom of carbon and

two atoms of oxygen. It is stable and non-flammable under standard conditions, making up

approximately 0.04% of the Earth’s atmosphere. CO2 is produced naturally through various

processes, including respiration, combustion, and volcanic eruptions. In humans, it is generated

as a metabolic byproduct and expelled from the body during exhalation.

Despite its minor presence in the atmosphere, carbon dioxide plays a crucial role in

photosynthesis. Plants absorb CO2, converting it into organic matter while releasing oxygen as a

byproduct. This process is essential for plant growth and sustains life on Earth. In addition to its

role in photosynthesis, carbon dioxide also dissolves in oceans, where it reacts with water to

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form carbonic acid, contributing to ocean acidification—a growing concern for marine life..

There is a widespread belief that carbon dioxide is harmful and solely results from human

activities, particularly the burning of fossil fuels. Carbon dioxide is naturally present in the

atmosphere, but excessive emissions from industrial activities are accelerating the greenhouse

effect, leading to global temperature rise. However, CO2 has both natural and anthropogenic

sources, and it is vital for plant life, making it an integral part of the Earth’s carbon cycle.

………

Source:https://netl.doe.gov/sites/default/files/inline-images/carbon-dioxide-molecule.jpg

Figure 13. Depiction of a Carbon Dioxide Molecule

Process of Carbon Cycle

The carbon does not have one cycle but several, of different lengths. One day. One year.

A hundred years. Or millions of years. Through photosynthesis and cellular respiration, carbon

atoms circulate daily in a short cycle.

 Photosynthesis. Carbon dioxide (CO2) enters the atmosphere through breathing and

metabolic processes. Plants absorb CO2 during photosynthesis, using it with water (H2O)

to produce glucose, which provides energy for growth and releases oxygen back into the

atmosphere. Though CO2 makes up less than 1% of the atmosphere, it is vital for living

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 things. Photosynthesis is essential for life on Earth as it converts solar energy into

chemical energy, producing oxygen and organic compounds that fuel the food chains and

sustain ecosystems

 Respiration. Animals and humans consume carbon-rich plants, absorbing their carbon.

Through cellular respiration, they use oxygen to break down energy food, releasing

carbon dioxide back into the atmosphere. This exchange maintains the flow of carbon

between the air and living organisms.

 Decomposition. When plants and animals die, decomposition occurs. Decomposers like

bacteria and fungi break down organic matter, returning carbon to the soil and

atmosphere. This released carbon can be reabsorbed by plants. Over time, the

accumulation of organic matter forms fossil fuels like coal and oil, created under pressure

and heat.

 Combustion. Human activities, especially burning fossil fuels, add carbon dioxide back

into the atmosphere. Combustion of these fuels releases stored carbon, contributing to the

greenhouse effect and climate change. This process disrupts the carbon cycle,

highlighting the impact of human actions.

Importance of Carbon Cycle

Even though carbon dioxide (CO2) is found in only trace amounts in the Earth's

atmosphere, it plays a critical role in regulating the planet’s climate. CO2 helps to balance the

energy received from the sun by trapping long-wave radiation, which warms the Earth’s surface.

This process, known as the greenhouse effect, acts like a blanket around the planet, maintaining

temperatures that can support life. Without this natural carbon cycle, the Earth would be too cold

for life to survive. However, if the carbon cycle is disturbed—whether by excessive release of

27
carbon dioxide through human activities like burning fossil fuels or deforestation—it can lead to

serious consequences, such as climate change and global warming. These changes can result in

rising global temperatures, melting ice caps, more extreme weather patterns, and disruptions to

ecosystems.

Carbon is also an essential element in the biological makeup of every living organism. It

forms the backbone of complex molecules like proteins, lipids, carbohydrates, and even DNA,

the blueprint of life. All known life forms on Earth rely on carbon to build cells, produce energy,

and carry out vital biological processes. Since carbon is so integral to life, the carbon cycle plays

a fundamental role in maintaining the balance of carbon across ecosystems. Along with the

nitrogen and oxygen cycles, which also regulate essential elements for life, the carbon cycle

ensures that life can continue to thrive on Earth by recycling carbon between the atmosphere,

oceans, land, and living organisms.

Disruptions to the carbon cycle not only impact climate stability but can also threaten

biodiversity and ecosystem health. This is why understanding and preserving the carbon cycle is

crucial for the future of our planet and all living beings that depend on its delicate balance.

Phosphorus Cycle

The phosphorus cycle is a critical biogeochemical cycle that describes the movement of

phosphorus through the lithosphere, hydrosphere, and biosphere. Phosphorus is a vital element

for all living organisms because it plays a key role in the formation of DNA, RNA, ATP

(adenosine triphosphate), and cellular membranes.

What is Phosphorus?

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 Phosphorus is a vital chemical element with the symbol P and atomic number 15. It is

essential for life, playing a key role in forming DNA, cell membranes, and energy-carrying

molecules like ATP. Phosphorus is most commonly found in nature as phosphate, particularly in

rocks and minerals. It is widely used in fertilizers to promote plant growth. Phosphorus also has

industrial uses, such as in detergents, fireworks, and matches. It is a nonmetallic chemical

element of the nitrogen group that is a colorless, translucent, soft, waxy solid at room

temperature and glows in the dark. Phosphorus is an essential mineral that occurs naturally in

many foods and is available as a dietary supplement. Phosphorus is a component of bones, teeth,

DNA, and RNA, and ATP, playing a vital role in genetic information and energy transfer within

cells.

Sources:https://cdn.britannica.com/85/22385-050-8C724F16/Phosphorus-P-Its-phosphorus-

square-symbol.jpg

Figure 14: Phosphorus Symbol

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The Role of Phosphorus in the Environment

Phosphorus is a limiting nutrient, meaning that its availability can restrict the growth of

organisms, especially in aquatic ecosystems. It primarily exists as phosphate ions (PO₄³ ⁻) in

nature. Phosphates are essential to plants and animals for various biological functions, including

energy storage and transfer, genetic material structure, and cellular membrane integrity.

Phosphorus is most abundant in the form of phosphate minerals found in rocks and soils.

The availability of phosphorus to organisms depends on its so lubility in water, which facilitates

its absorption by plants and transfer through the food chain. Phosphorus is an element essential

to sustaining life largely through phosphates. Phosphorus has several allotropes that exhibit

strikingly diverse properties. Phosphorus also plays a crucial role in cellular energy transfer

through molecules like ATP , which stores and releases energy during metabolic processes..

Source: https://images.app.goo.gl/jyqUHKo1MHbbeVUv7

30
 Figure 15: Phosphorus Cycle

Stages of the Phosphorus Cycle

Unlike other essential elements such as nitrogen and carbon, phosphorus does not enter

the atmosphere in its biogeochemical cycle, making its movement largely dependent on the

processes within the Earth's soil, water, and organisms.

 Weathering of Rock. Phosphorus enters the phosphorus cycle primarily through the

weathering of rocks. Phosphate-rich rocks, such as apatite, undergo weathering through

physical and chemical processes. This process releases phosphate ions into the soil,

making them available for plant uptake.

 Absorption by Plants. Once in the soil, phosphate ions are absorbed by plants.

Phosphorus is a key nutrient for plant growth, playing a significant role in

photosynthesis, energy transfer, and root development. Without sufficient phosphorus,

plant growth is limited, which can reduce crop yields in agriculture.

 Movement through the Food Chain. After being absorbed by plants, phosphorus moves

through the food chain. Herbivores obtain phosphorus by consuming plants, while

carnivores obtain it by eating herbivores. In organisms, phosphorus is incorporated into

essential molecules like ATP, nucleic acids, and phospholipids, which are vital for energy

storage and genetic information.

 Decomposition. When plants and animals die, decomposers (such as bacteria and fungi)

break down their organic matter, releasing phosphorus back into the soil in the form of

phosphate ions. This recycled phosphorus can be absorbed again by plants or leached into

water bodies.

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  Leaching and Sedimentation. Some phosphorus in the soil leaches into water bodies

through runoff. Once in aquatic systems, phosphorus can either be used by aquatic plants

and organisms or settle to the bottom as sediment. Over geological time scales, these

sediments can become new phosphate-rich rocks through the process of lithification.

The Importance of Phosphorus Recycling

Since phosphorus is a non-renewable resource in the context of human timescales, there

is growing interest in recycling phosphorus, especially in agriculture. Techniques such as

composting, recovering phosphorus from wastewater, and using organic fertilizers aim to reduce

reliance on mined phosphate rock and mitigate environmental pollution.

Global Distribution of Phosphorus

Phosphorus is unevenly distributed around the world. Most of the phosphate rock

reserves are concentrated in a few countries, with Morocco holding approximately 70% of the

global reserves. Other significant producers include China, the United States, and Russia. This

uneven distribution makes phosphorus a geopolitically sensitive resource and raises concerns

about future availability, especially for countries dependent on phosphate imports for agriculture.

Challenges and Sustainable Management. One of the key challenges in managing the

phosphorus cycle sustainably is balancing agricultural productivity with environmental

protection. Some of the strategies for sustainable phosphorus management include:

Efficient use of fertilizers. Developing better agricultural practices to reduce the overuse

of phosphorus-rich fertilizers and minimize runoff into water bodies.

32
 Phosphorus recycling. Implementing technologies to recover phosphorus from

agricultural runoff, wastewater, and animal manure, can reduce dependence on phosphate

rock.

Public policy. Governments can introduce regulations to limit phosphorus pollution,

encourage recycling, and promote sustainable agricultural practices.

The phosphorus cycle is essential for sustaining life on Earth. Phosphorus is a limiting

nutrient in many ecosystems, and its availability directly influences agricultural productivity,

water quality, and biodiversity. However, human activities such as mining, fertilizer use, and

sewage discharge have greatly accelerated the release of phosphorus into the environment,

leading to significant ecological challenges such as eutrophication. Sustainable phosphorus

management practices and recycling are vital for ensuring that this critical resource remains

available for future generations.

Sulfur Cycle

The sulfur cycle is a biogeochemical cycle made up of several processes that allow sulfur

to move through different sources such as the atmosphere, biosphere, and lithosphere. The

process begins with the weathering of rocks, which releases sulfur compounds into the soil.

Microbial transformations, plant assimilation, breakdown, and air reactions complete the cycle.

The sulfur cycle is essential for the formation of vital biomolecules including amino acids and

vitamins, as well as the regulation of atmospheric and aquatic chemistry.

The cycle is restarted when the animals break down and release the sulfur back into the

atmosphere. The cycle includes both biotic (living creatures) and abiotic (non-living)

33
components. The cycle begins with rocks eroding and releasing sulfur into the atmosphere.

Sulfur then combines with oxygen in the air, forming sulfate, which plants and microbes absorb.

They convert it into organic forms and distribute it throughout the food chain

What is Sulfur?

Sulfur (S) is a nonmetallic chemical element belonging to the oxygen group (Group 16

[VIa] of the periodic table), one of the most reactive of the elements. Pure sulfur is a tasteless,

odorless, brittle solid that is pale yellow, a poor conductor of electricity, and insoluble in water.

It reacts with all metals except gold and platinum, forming sulfides; it also forms compounds

with several nonmetallic elements. Millions of tons of sulfur are produced each year, mostly for

the manufacture of sulfuric acid, which is widely used in industry. Sulfur is an element that

exists in nature and can be found in soil, plants, foods, and water.

Source: https://www.galaxysulfur.com/wp-content/uploads/2017/04/sulfur-periodictable.jpg

34
 Figure 16: Sulfur Symbol

Sulfur, an essential element for the macroSulfur, an essential element for biological

macromolecules, is released into the atmosphere by the burning of fossil fuels such as coal. As

part of the amino acid cysteine, it participates in the formation of disulfide bonds in proteins,

helping to determine the three-dimensional folding pattern of proteins and therefore their

function.

Some proteins contain sulfur in the form of amino acids. Sulfur enters the oceans via

land runoff, atmospheric precipitation, and underwater geothermal vents. Some ecosystems

depend on chemoautotrophs that use sulfur as a bioenergy source. This sulfur supports marine

ecosystems in the form of sulfate. Molecules of living things, is released into the atmosphere by

the burning of fossil fuels, such as coal. As a part of the amino acid cysteine, it is involved in the

formation of disulfide bonds within proteins, which help to determine their 3-D folding patterns,

and hence their functions.

35
Source: https://cdn.britannica.com/37/112537-050-7F7829C5/sedimentary-rocks-sources-

human-hydrogen-sulfide-gas.jpg

Figure 17: Sulfur Cycle

Process of Sulfur Cycle

 Atmosphere. Sulfur in the atmosphere is mostly found as sulfur dioxide (SO₂).

Anthropogenic activities, primarily the combustion of fossil fuels, account for the
majority of atmospheric SO₂ emissions. Volcanic eruptions play a key role in increasing
atmospheric SO₂ levels. Hydrogen sulfide (H₂S) is another important sulfur-containing
gas in the environment. The primary source of atmospheric H₂S is microbial breakdown
of organic materials from deceased and decaying organisms. These microbial processes
take place in both terrestrial and aquatic settings under anaerobic circumstances.
Microbes release H₂S during anaerobic breakdown, which is then oxidized in the
environment to produce SO₂. Microorganisms that produce H₂S by sulfate reduction are
often anaerobic. They convert oxidized forms of sulfur to H₂S. Notable sulfate-reducing
bacteria involved in this process include Desulfovibrio desulfuricans, Desulfovibrio
vulgaris, Thermodesulfovibrio yellowstonii, Desulfotomaculum nigrificans, and
Desulfobacula toluolica.
 Biosphere. Sulfur predominantly enters the biosphere via two routes: atmospheric

deposition and rock weathering. Sulfur eventually flows into the soil and then to the

ocean via both routes. Sulfur dioxide (SO₂) helps produce clouds by increasing the

number of droplets and decreasing their size. Sulfur aerosols eventually descend from the

atmosphere and settle into the biosphere.SO₂ dissolves in rainwater, generating mild

36
 sulfuric acid that contributes sulfur to the soil during precipitation. The chemical

weathering process that occurs during soil formation (pedogenesis) transfers sulfur from

rocks into the soil and water systems. Some sulfur released during weathering is

transformed into sulfate and may be released back into the atmosphere.

 Uptake by Living Organisms. When sulfur reaches the terrestrial and aquatic

biospheres, it is absorbed by plants and microbes. Green sulfur bacteria are

photoautotrophic bacteria that use sulfur for energy. Other bacteria in the soil help to

make sulfur available to plants, allowing it to be absorbed with water from the soil.

Sulfur is absorbed by living creatures and used to produce biomolecules such as proteins

and nucleotides. In the ocean ecosystem, chemoautotrophic microbes use sulfur to

generate organic chemicals such as sulfates.

 Lithification & Release. The sulfur in the biosphere then circulates through the food

chain as consumers feed on producers, eventually reaching the microbial chains. The

sulfur that does not circulate falls into the depths of terrestrial and marine ecosystems,

where it remains in the mixed form (FeS) in rocks. The sulfur in the food chain then

decomposes, transforming sulfate into sulfides that can be recycled to the atmosphere.

Sulfur-reducing bacteria convert organic forms of sulfur into inorganic forms such as

hydrogen sulfide (H2S), which is then reduced to sulfur. The sulfur in the lithosphere is

also released into the atmosphere as a result of volcanic activity.

Importance of Sulfur Cycle

The sulfur cycle is essential as it balances the concentration of sulfur in different

reservoirs to make the Earth a hospitable place for life. Sulfur forms an important component of

amino acids such as cysteine and methionine. Sulfur is found in nature in a combined state with

37
other elements like nitrogen, iron, and phosphorus, so the sulfur cycle also affects the availability

of other elements. It allows the movement of sulfur between living systems, waterways, and

rocks, maintaining the balance of sulfur concentrations across the Earth’s reservoirs.

Human Activities That Affect Biogeochemical Cycles

Human activities are indeed disrupting various biochemical processes in the environment,

particularly through industrialization, agriculture, and urbanization. Some of the most significant

disruptions include:

 Water Cycle. Human activities like deforestation, urbanization, and dam construction

disrupt the natural flow of water, impacting ecosystems and leading to water scarcity in

some areas while causing floods in others. Some human activities can cause water

pollution which resulting in less water being transfer and a much more unhygienic water

that can cause damage to humans and the environment where ecosystems are destroyed

and plants are affected by this situation as well.

38
Source:https://catimes.brightspotcdn.com/dims4/default/be259f8/2147483647/strip/true/crop/

5568x3712+0+0/resize/2400x1600!/format/webp/quality/75/?url=https%3A%2F

%2Fcaliforniatimesbrightspot.s3.amazonaws.com%2Fcf%2F2f

%2F8bcdc7244641a05cc26413c94e0c%2Fgettyimages-1245667660.jpg

Figure 18: Water Dam

 Carbon Cycle. Burning fossil fuels, deforestation, and industrial processes release large

amounts of carbon dioxide (CO2) and methane (CH4) into the atmosphere, intensifying

the greenhouse effect and contributing to climate change. Additionally, oceans and

forests act as major carbon sinks, absorbing a significant portion of carbon dioxide from

the atmosphere, but their capacity to do so is being reduced by ongoing environmental

degradation.

Source:https://images.nationalgeographic.org/image/upload/t_edhub_resource_key_image/

v1652341008/EducationHub/photos/deforestation.jpg

39
 Figure 19: Deforestation

 Oxygen Cycle. Human activities are also having significant impacts on the oxygen cycle,

which is closely tied to the carbon cycle and essential for maintaining life on Earth.

While the oxygen cycle is primarily driven by photosynthesis and respiration, human-

induced changes are disrupting the natural balance. Through photosynthesis and cellular

respiration, oxygen and carbon atoms circulate daily in a short cycle. This undergoes

several processes that involves the interactions between biotic and non-biotic factors as it

is the path where oxygen follows undergoing a continuous cycle of receiving and

emitting oxygen from plants to humans and animals for example.

Source:https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.earthandanimals.com

%2Fadvocate%2Fwild-earth%2Fparams%2Fpost%2F1285.jpg

Figure 20: Factory Burning of Fossil Fuels

40
  Nitrogen Cycle. The excessive use of nitrogen-based fertilizers in agriculture leads to

nitrogen runoff into water bodies, causing eutrophication, algal blooms, and dead zones

in aquatic ecosystems. Additionally, the increased release of nitrogen compounds into the

atmosphere can lead to air pollution and acid rain.

Source: https://media.geeksforgeeks.org/wp-content/uploads/20240115163152/Eutrophication-

image.webp

Figure 21: Eutrophication

 Phosphorus Cycle. Similar to nitrogen, overuse of phosphorus in fertilizers leads to

runoff, which can also contribute to eutrophication in water bodies, disrupting aquatic

life.

41
  Sulfur Cycle. Burning fossil fuels and certain industrial processes release sulfur dioxide

(SO2), which can lead to acid rain, harming ecosystems, soil, and aquatic environments.

These disruptions not only affect natural ecosystems but also pose risks to human health

and long-term environmental sustainability. To mitigate the risks posed by human disruptions to

biogeochemical cycles, we must adopt sustainable practices across key sectors. In energy

production, transitioning to renewable sources like solar and wind can reduce fossil fuel

emissions and slow climate change. In agriculture, reducing the overuse of nitrogen- and

phosphorus-based fertilizers, implementing organic farming, and promoting crop rotation can

help restore soil health.

CONCLUSION

Biogeochemical cycles regulate the movement of key elements like water, carbon,

nitrogen, oxygen, phosphorus, and sulfur through Earth's systems, supporting life and

maintaining environmental balance. Understanding these cycles highlights the close relationship

between life and the environment.

The water cycle, or hydrological cycle, describes the continuous movement of water

between the Earth’s surface and the atmosphere. The carbon cycle transports carbon throughout

the atmosphere, oceans, organisms, and the Earth's surface. The nitrogen cycle converts nitrogen,

a key component of proteins and DNA, into a usable form for plants. The oxygen cycle

transports oxygen between the atmosphere, living organisms, and the earth's crust. The

phosphorus cycle, unlike the carbon and nitrogen cycles, does not include the atmosphere.

42
Weathering releases phosphorus from rocks, which is then absorbed by plants and moved

through the food web. Finally, the sulfur cycle transports sulfur throughout the atmosphere, land,

and organisms.

These biogeochemical cycles are vital for maintaining the availability of nutrients

necessary for life. They maintain life by ensuring the continuous supply and distribution of

essential nutrients and gases for thriving ecosystems. However, human activities can disrupt

these cycles, leading to issues like climate change and environmental degradation. It's important

to manage natural resources responsibly to protect these cycles and ensure a healthy environment

for future generations. To maintain ecological balance and ensure the sustainability of life on

Earth, it is imperative that we take proactive measures to restore and protect these vital cycles.

Post Test Questions: 8. A biogeochemical process through which

1. What are an essential processes that N2 is converted into many forms.

recycle the nutrients through the Earth's 9. Odorless, colorless, tasteless gas, that is

systems. essential for survival.

2. An oxygen hydride consisting of one 10. A biogeochemical cycle that describes

oxygen atom covalently bonded to tel the movement of the oxygen throughout the

hydrogen atoms. Earth's atmosphere.

3. Chemical formula for water. 11. The process where plants use sunlight,

4. The circulation of water through Earth carbon dioxide and water to produce glucose

and atmosphere. and released oxygen.

5. Stages of Water Cycle

6. Most abundant gas in Earth's atmosphere. 12. A non-metallic element found in Group

7. What is the symbol of Nitrogen gas. 14. of the periodic table.

43
13. Is a colorless, odorless gas composed of 3. H2O

one atom of carbon and two atoms of

4. Water Cycle
oxygen.
5. Evaporation, condensation, sublimation,
14. A continuous process through which
precipitation, transpiration, runoff and
carbon compounds are exchange among the

atmosphere of the Earth. infiltration.

15. Process of Carbon Cycle.

6. Nitrogen
16.What is the atomic number of
7. N2
phosphorus?
8. Nitrogen Cycle
17. The first stage of phosphorus cycle.

18. Non-metallic chemical element 9. Oxygen

belonging to the oxygen group, one of the

10. Oxygen Cycle
most reactive of the elements.

19. It is made up of several process that

allow sulfur to move through different

sources such as the atmosphere.

20. The chemical symbol for sulfur.

11. Photosynthesis

12. Carbon

13. Carbon dioxide

Answers: 14. Carbon Cycle

1. Biogeochemical Cycles 15. Photosynthesis, respiration,

2. Water decomposition, combustion

44
 16. 15 20. S

17. Weathering of rocks

18. Sulfur

19. Sulfur Cycle

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