Subject Chemistry
Paper No and Title 4, Environment Chemistry
Module No and Title 3: Biogeochemical cycles of sulphur, phosphorus, oxygen and bio distribution of elements Module Tag CHE_P4_M3
CHEMISTRY PAPER No. 4: Environmental chemistry MODULE No. 3: Biogeochemical cycle of Sulphur, Phosphorus, Oxygen and bio distribution of elements
TABLE OF CONTENT
1. Learning Outcomes 2. Introduction 3. Sulphur cycle 4. Oxygen cycle 5. Phosphorus cycle 6. Bio-distribution of elements 7. Summary
CHEMISTRY PAPER No. 4: Environmental chemistry MODULE No. 3: Biogeochemical cycle of Sulphur, Phosphorus, Oxygen and bio distribution of elements
1. Learning Outcomes-:
After studying this module, you shall be able to
Know about most important biogeochemical cycles like sulphur, oxygen, and phosphorus. Understand different steps involved in biogeochemical cycles. Know about reactions involved in sulphur, oxygen, and phosphorus. Know about effects of biogeochemical cycles on environment. Know different components of biogeochemical cycles. Know about different functions of phosphorus cycle.
2. Introduction-:
You are already aware that a cycle is a series of change which comes back to the starting point and which can be repeated. Biogeochemical is combination of biological, geological, and chemical and are part of larger cycle. Biogeochemical cycle is very important in nature. Cycling of water, carbon, oxygen, sulphur, phosphorus, nitrogen, etc. are cycled by biogeochemical cycle. It is also called nutrient cycle. Biogeochemical cycle is very important for environment and it is a spontaneous chemical cycle. In this cyclic process, chemical elements and molecules are moved through segments of environment (atmosphere, lithosphere, biosphere, and hydrosphere). Matter converts one form to other form by biogeochemical cycle. There are some important biogeochemical cycles like nitrogen, phosphorus, carbon, oxygen, water, sulphur, etc. Let us study some of them in this module.
3. Sulphur cycle
Sulphur cycle is important for geochemical cycle and life. Many minerals are affected by this cycle. Sulphur is an essential element and is an important nutrient for organisms. Oxidation reaction takes place in sulphur cycle. There are some broad steps or processes involved in sulphur cycle. They are:
a) Mineralization process-: Organic sulphur converts into inorganic sulphur (H2S) by mineralization process.
2- b) Oxidation process-: In this process, hydrogen sulphide oxidizes into sulphate, SO4
c) Reduction process-: In this process, sulphate reduces into sulphide.
d) Incorporation of halide-: In this process, sulphide converts into organic sulphur.
CHEMISTRY PAPER No. 4: Environmental chemistry MODULE No. 3: Biogeochemical cycle of Sulphur, Phosphorus, Oxygen and bio distribution of elements
Plants take their nutrient from mineral compound of environment. In this process, sulphate of sulphur are taken by roots. Animals get the sulphur by eating plants, or other animals. Sulphur is essential component of some of the amino acids. Sulphur is huge component of living organism. In atmosphere, sulphur is present in the form of sulphur dioxide.
3.1 Reactions involved in sulphur cycle-:
Formation of sulphuric acid-:
퐇ퟐ퐒 + 퐎ퟑ → 퐇ퟐ퐎 + 퐒퐎ퟐ
퐒퐎ퟐ + 퐎 + 퐌 → 퐒퐎ퟑ + 퐌
Where, M= oxygen molecule
퐒퐎ퟑ + 퐇ퟐ퐎 → 퐇ퟐ퐒퐎ퟒ
Sulphuric acid falls down as rain.2
3.2 Effect of sulphur cycle in environment Sulphur cycle is natural processes, which affect the environment in various ways. There are many types of reactions that occur in environment which change the form of sulphur. In each segment of environment, sulphur is present in different form like; sulphur dioxide, hydrogen sulphide, sulphates, etc. Also, there are some formation that affect environment in huge amount.
3.2.1 Acid rain-: Acid rain is a polluted rain in which sulphur fall on earth in form of sulphuric acid. Sulphur dioxide comes from factory, industrial areas, etc. now, sulphur dioxide react with moisture and form sulphuric acid. Acid comes from atmosphere along with rain and it harms the corps, soil and all living organisms. Acid rain severely affects the plants and the composition of soil. The affected wild plants and corps are characterized with injury and become prone to multiple infections and ultimately die out.
3.2.2 Water-: Sulphuric acid increases acidity of water and also increases amount of aluminum in water by which pH of water decreases continuously. Fish and aquatic animals are damaged by high concentration of aluminum and pH imbalance. Due to acid rain, the acidity in 70 percent of lakes and 30 percent of streams has increased.
3.2.3 Soils-: Soils are damaged by acid rain. Acidity of rain increases toxicity of soil and decreases the amount of nutrient in the soil. High altitude forests, which are surrounded by fog and clouds, receive more acidic rain. Due to loss of nutrients in the soil, corps damage also occurs in large amount.
CHEMISTRY PAPER No. 4: Environmental chemistry MODULE No. 3: Biogeochemical cycle of Sulphur, Phosphorus, Oxygen and bio distribution of elements
Thus sulphur damages all i.e, soil, plants, water, and different segments of environment.
4. Oxygen cycle-:
The oxygen cycle is a biogeochemical cycle, which is very important for environment. Oxygen cycle is a natural process in which oxygen moves into different spheres of environment. In atmosphere, oxygen and its product play an important role. Oxygen is present in different spheres of environment like; lithosphere, atmosphere, biosphere, and hydrosphere. In this process, oxygen moves through animals, plants and atmosphere. Plants release oxygen by photosynthesis reaction in presence of sunlight. But at night, plants release carbon dioxide.
4.1. Steps and reactions involved in oxygen cycle
There are some important steps and reactions:
4.1.1 Photosynthesis-:
Plants make its food in presence of sunlight with help of chlorophyll. In this process plants release oxygen in atmosphere and take carbon dioxide from animals.
ퟔ퐂퐎ퟐ + ퟔ퐇ퟐ퐎 → 퐂ퟔ퐇ퟏퟐ퐎ퟔ + ퟔퟎퟐ
4.1.2 Respiration-:
In this step, animals take oxygen and in turn, release carbon dioxide in the atmosphere. This process continuously moves in repeating manner.
퐂퐇ퟐ퐎 + 퐎ퟐ → 퐂퐎ퟐ + 퐇ퟐ퐎 + 퐄퐧퐞퐫퐠퐲
4.1.3 Formation of ozone-:
Oxygen and its products are present in the atmosphere. Ozone is an important product of oxygen. In stratosphere, ozone layer plays a preventive role. Dangerous ultraviolet rays are prevented to reach at earth by ozone layer because ultra violet rays are very harmful for animals, plants, and whole part of earth.
퐎ퟐ + 퐡훎 → ퟐ퐎
퐎ퟐ + 퐎 → 퐎ퟑ
Ozone is a secondary pollutant if it is produced in troposphere than stratosphere.
CHEMISTRY PAPER No. 4: Environmental chemistry MODULE No. 3: Biogeochemical cycle of Sulphur, Phosphorus, Oxygen and bio distribution of elements
4.2.Effect of oxygen on health
1. Accelerates/ supports combustion, major hurdle in fire-fighting. But choking the fire of oxygen supply extinguishes the fire.
2. Reacts with almost all the metals to form oxides and bring about corrosion. Generally known as rusting in the context of iron.
3. Humans breathe oxygen, but if we try to inhale pure oxygen. It could prove harmful to our internal organs. This is because of oxidizing nature of oxygen.
4. Animals and plants survive due to presence of oxygen into different segment of environment.
5. Phosphorus cycle-:
The phosphorus cycle is other type of biogeochemical cycle in which phosphorus move through part of environment. Phosphorus found in water, soil, rock, etc. it is also referred as mineral cycle and is very important for normal growth and development of all living organisms. Phosphorus is component of our body; teeth, bones, and DNA. Phosphorus does not exist in gaseous state. Phosphorus is absorbed by soil water and plants easily, and it produces from rocks.
Animals absorb phosphates by eating plants or plant-eating animals. When animals and plants die, phosphates return to the soils or oceans due to decomposition. After that, phosphorus will end up in sediments or rock formations again, remaining there for millions of years. Eventually, phosphorus is released again through weathering and the cycle starts over.
Phosphorus is an essential element. It is an important part of ATP molecule. It also found in DNA and RNA. Phosphorus is important for every living organism for growth.
5.1 Steps and reactions involved in phosphorus cycle-:
Phosphorus moves in different areas of environment in phosphorus cycle. Animals get phosphorus from plants. Aquatic plants obtain phosphorus directly from water and animals get it from drinking water. Phosphorus are absorbed by earth in different way. Animals release their phosphorus through waste. Phosphorus containing waste break down and due to decomposition and mineralization the phosphorus goes back to water or soil systems.
There are three phosphorus atoms present in ATP molecule as shown below.
CHEMISTRY PAPER No. 4: Environmental chemistry MODULE No. 3: Biogeochemical cycle of Sulphur, Phosphorus, Oxygen and bio distribution of elements
5.2 Human impact on phosphorus cycle
Phosphorus cycle is largely affected by human activities. For example, the excessive use of fertilizer and detergents contribute very high amount of anthropogenic phosphorus.
5.3 Functions of phosphorus There are various different types of function of phosphorus
5.3.1 Biological function-: Formation of ATP takes place every day in human body. Phosphates are component of nucleotides. These nucleotides play an important role in biological function. Energy is saved inside the body due to phosphorus in the form of ATP in the cells. Structure of DNA is possible as helix because helix of DNA is joined to each other through Phosphate Bridge. Phospholipids are found in biological membrane, which are significant to maintain the acid base homeostasis in body.
5.3.2 Ecological function-: Phosphorus is an important macro element required for normal growth and development of animals, plants and other living organisms. Therefore, phosphorus forms life sustaining molecules. For aquatic ecosystems, phosphorus is limiting nutrient and affect the biological productivity. Mainly, phosphorus is not found in atmosphere in gaseous form, rather, is commonly found in soils, rocks and water. Fertilizer is made by phosphorus in huge amounts. In nature, phosphorus most commonly exists in form of phosphates.
6. Bio distribution of elements
The distribution of metal elements in the biological system has functional significance. There are many factors like pH, redox potential (in particular local environment), ambient aqueous conditions, etc. on which the availability of metal elements have changed with time in biosystem.
The condition of primitive earth was reducing than that demanded by living organisms. The concentration of oxygen has continuously increased in environment with time.
Metal ions present in the biosphere have their functional values. In 1826, Wohler recognized that organism have organic chemicals hydrogen, carbon, nitrogen and oxygen. Essential requirement for nitrogen, sulphur, potassium, calcium, magnesium and iron were firstly suggested in 1860, however occurrence of “heme” in the living system was recognized using spectroscopic method
CHEMISTRY PAPER No. 4: Environmental chemistry MODULE No. 3: Biogeochemical cycle of Sulphur, Phosphorus, Oxygen and bio distribution of elements
in the year 1895. In fact, Warburg (1935) wrote a book entitled “Metal Prosthetic Groups” (especially heme enzyme).
In 1948, Irving-William series of transition metal stability constant was given. However, theories of general understanding of complex ion stabilities including Na⁺, K⁺, Mg²⁺ and Ca²⁺ was studied during 1950-60’s.
7. Summary
Biogeochemical cycles are essential for functioning of earth system During biogeochemical cycles, elements like; oxygen, sulphur, and phosphorus move through different spheres of (lithosphere, biosphere, atmosphere, hydrosphere, etc.) of environment. These cycles play significant role to create a balance in environment, but at the same time are cause of environmental pollution, especially sulphur. Oxygen cycle helps to survive animals and plants. Ozone layer in stratosphere protects living organisms on earth by harmful ultra violet rays.
CHEMISTRY PAPER No. 4: Environmental chemistry MODULE No. 3: Biogeochemical cycle of Sulphur, Phosphorus, Oxygen and bio distribution of elements