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The sulfur cycle

Sulfur is an essential element for the macromolecules of living things. 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. As shown in [link] , sulfur cycles between the oceans, land, and atmosphere. Atmospheric sulfur is found in the form of sulfur dioxide (SO 2 ) and enters the atmosphere in three ways: from the decomposition of organic molecules, from volcanic activity and geothermal vents, and from the burning of fossil fuels by humans.

This illustration shows the sulfur cycle. Sulfur enters the atmosphere as sulfur dioxide (SO2) via human emissions, decomposition of H2S, and volcanic eruptions. Precipitation and fallout from the atmosphere return sulfur to the Earth, where it enters terrestrial ecosystems. Sulfur enters the oceans via runoff, where it becomes incorporated in marine ecosystems. Some marine sulfur becomes pyrite, which is trapped in sediment. If upwelling occurs, the pyrite enters the soil and is converted to soil sulfates.
Sulfur dioxide from the atmosphere becomes available to terrestrial and marine ecosystems when it is dissolved in precipitation as weak sulfuric acid or when it falls directly to the Earth as fallout. Weathering of rocks also makes sulfates available to terrestrial ecosystems. Decomposition of living organisms returns sulfates to the ocean, soil and atmosphere. (credit: modification of work by John M. Evans and Howard Perlman, USGS)

On land, sulfur is deposited in four major ways: precipitation, direct fallout from the atmosphere, rock weathering, and geothermal vents ( [link] ). Atmospheric sulfur is found in the form of sulfur dioxide (SO 2 ), and as rain falls through the atmosphere, sulfur is dissolved in the form of weak sulfuric acid (H 2 SO 4 ). Sulfur can also fall directly from the atmosphere in a process called fallout    . Also, the weathering of sulfur-containing rocks releases sulfur into the soil. These rocks originate from ocean sediments that are moved to land by the geologic uplifting of ocean sediments. Terrestrial ecosystems can then make use of these soil sulfates ( SO 4 ), and upon the death and decomposition of these organisms, release the sulfur back into the atmosphere as hydrogen sulfide (H 2 S) gas.

 This photo shows a white pyramid-shaped mound with gray steam escaping from it.
At this sulfur vent in Lassen Volcanic National Park in northeastern California, the yellowish sulfur deposits are visible near the mouth of the vent.

Sulfur enters the ocean via runoff from land, from atmospheric fallout, and from underwater geothermal vents. Some ecosystems ( [link] ) rely on chemoautotrophs using sulfur as a biological energy source. This sulfur then supports marine ecosystems in the form of sulfates.

Human activities have played a major role in altering the balance of the global sulfur cycle. The burning of large quantities of fossil fuels, especially from coal, releases larger amounts of hydrogen sulfide gas into the atmosphere. As rain falls through this gas, it creates the phenomenon known as acid rain. Acid rain is corrosive rain caused by rainwater falling to the ground through sulfur dioxide gas, turning it into weak sulfuric acid, which causes damage to aquatic ecosystems. Acid rain damages the natural environment by lowering the pH of lakes, which kills many of the resident fauna; it also affects the man-made environment through the chemical degradation of buildings. For example, many marble monuments, such as the Lincoln Memorial in Washington, DC, have suffered significant damage from acid rain over the years. These examples show the wide-ranging effects of human activities on our environment and the challenges that remain for our future.

Click this link to learn more about global climate change.

Section summary

Mineral nutrients are cycled through ecosystems and their environment. Of particular importance are water, carbon, nitrogen, phosphorus, and sulfur. All of these cycles have major impacts on ecosystem structure and function. As human activities have caused major disturbances to these cycles, their study and modeling is especially important. A variety of human activities, such as pollution, oil spills, and events) have damaged ecosystems, potentially causing global climate change. The health of Earth depends on understanding these cycles and how to protect the environment from irreversible damage.

Art connections

[link] Which of the following statements about the nitrogen cycle is false?

  1. Ammonification converts organic nitrogenous matter from living organisms into ammonium (NH 4 + ).
  2. Denitrification by bacteria converts nitrates (NO 3 ) to nitrogen gas (N 2 ).
  3. Nitrification by bacteria converts nitrates (NO 3 ) to nitrites (NO 2 ).
  4. Nitrogen fixing bacteria convert nitrogen gas (N 2 ) into organic compounds.

[link] C: Nitrification by bacteria converts nitrates (NO 3 ) to nitrites (NO 2 ).

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Questions & Answers

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Burton Reply
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Burton
if an organism is cartilaginous is fully capable of a protecting the internal organs
Verah Reply
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Rose Reply
cell is the functional and structural unit of life while tissue is a group of cells aggregate to perform a similar or particular function
Tajudeen
cell is the basic unit of life while tissue is group of related cells that perform the same function Eg. the nerve tissue is made up of nerve cells
AAGifty
please what is meant by mutation
Kyere Reply
mutation is the change in DNA which results in the evolution
Shshank
what is binominal nomenclature?
Furaha Reply
the system of naming organisms depending on their xtics of origin
Vincent
The system of naming organisms using two-words Latin names
Agyeiwaa
what is the fate of reduced NAD in cell metabolism
namirembe Reply
what is plant cell
OLUWAKEMI Reply
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Kamasa Reply
it also aids in formation of pollen grain in anther and formation of ovules in ovary of flowering plant
Orawo
it also aids in formation of sperm or ova in animals
Orawo
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Jonathan Reply
skeleton is mainly the infrastructure of the organisms
Shshank
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Symon Reply
vaccination simply refers to as drugs usually injected,most times in a liquid form given to a person or an animal,while immunity refers to a source of prevention usually in a liquid form that help in disease prevention
Grace
In children
Grace
Golgi apparatus helps in the formation of lysosomes
Diana
what is the difference between placenta and umbilical cord?
Grace Reply
No difference
Onwane
what's golgi apparatus.
Grace
What is biology
Rita Reply
is the study of living things
Kisa
biology is the study of living and non living things
Tinta
Biology is the study of living things
Addai
the study of living organisms
Furaha
Biology is the study of living organism or things
Rose
Biology is the study of both living and non living things
Funteh
distinguish between sex linked characters and sex limited characters
Kisa Reply
what is active transport
Jessy Reply
why is diffusion important
Jessy
dissolved substance move with in the cytoplasm by diffusion
Kisa
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Kisa
active transport refers to the movement of certain molecules or substances from lower to higher concentration with the help of energy or ATP
Shshank
mutation occurs due to change in DNA and DNA forms our body & if DNA changes then our body also acquire some changes & these changes gradually leads to the evolution of new species
Shshank
what's the meaning of inductive reasoning and deductive reasoning
Godfred Reply
inductive reason means the method of ones experiences and observation including things learn from others are synthesized to come up with a general truth
Adoma
deductive reasoning starts with a statement or hypothesis and then test to see if it's true through observation where inductive reasoning starts with observations and moves backwards towards generalizations and theories
michelle
Deductive guarantees the truth of the conclusion,if the premises are true whereas inductive does not guarantees the truth of the conclusion,but only makes it more reasonable for us to believe the conclusion.
Mule
The phenomenon by which Protoplasm of a cell shrinks from the wall is 
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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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