Dr. V.K.Maheshwari, M.A. (Socio, Phil) B.Sc. M. Ed, Ph.D.
Former Principal, K.L.D.A.V.(P.G) College, Roorkee, India
Ms. Arunima Maheeshwari, Student
Father Agnel School, NOIDA, India
“Your body isn’t just a body. It’s an ecosystem.”
- Douglas Coupland
Every living being however small or big depends on the environment for its existence and also competes with others for essentials in life. For survival, living beings form groups and different groups compete with each other for survival.Ecosystem is a functional unit of dynamic system of organisms interacting with each other (biotic) and with the inanimate environment (abiotic). An Ecosystem is defined as a group of plants, animals or living organisms living together and interacting with the physical environment in which they live. An Eco system has a moreor less a closed boundary and the flow of mass in and out of the system is very less as comparedto the internal movement of mass. Ecosystems can be large or small.Any Ecosystem consists of both living (biotic) and non-living (abiotic) components, whichare called Environmental or ecological components. A component is hence an ecological status, which directly or indirectly affects the life of an organism.
Abiotic Components
The physical factors of the environment (which are nonliving) have a major influence onthe life of organisms. The abiotic components are of two types. They are:(a) Climatic factors(b) Edaphic factors(a) Climatic factors consist of Temperature, rainfall and snow, wind, light, humidity etc.The climate of an area is the result of several factors such as latitude, elevation, nearness tothe sea, and monsoon activities and ocean currents.Temperature influences the rates of biochemical reactions in plants, with the reaction rates approximately doubling with every 10°C increase. Plant species require a range of temperature to survive. Below a minimum temperature they are inactive, and above a maximum temperaturebiochemical reactions stop. Normally in many plants growth is possible above 6°C. In areas with extremes of temperature, such as the tundra and tropical deserts the plants have mechanismsto adapt to such conditions.Light levels decide the magnitude of photosynthesis reactions. Different plants have their characteristic light requirements in respect of light intensity, duration and wavelength. Some plants,termed helophytes, require high levels, whereas sciophytes can grow in shady, low light conditions.Rain/Water is an essential factor for biochemical plant processes, including photosynthesis. Plants growing on lands obtain their water requirements from the soil through their roots by the osmosis process. Plants called Hydrophytes grow in fresh water and they cannot withstand drought.Xerophytes survive long periods of drought, and halophytes are able to survive in saline water.Mesophytes require moderate conditions (neither waterlogged nor drought) and are found mainlyin temperate areas.
(b) Edaphic factors or soil factors are pH, mineral and organic matter in soil and textureof soil.
Soil is the major source of nutrients and moisture in almost all the land ecosystems. Soilis formed when a rock weathers .The rocks brake down into a collection of different inorganicor mineral particles. The climate influences the type and rate of the weathering of the rocksas well as the nature of the vegetation growing on it. Nutrients are recycled in the soil by theplants and animals in their life cycles of growth, death and decomposition. Thus humus materialessential to soil fertility is produced.
Soil mineral matter is derived from the weathering of rock material. These consist oftwo types viz. stable primary materials like quartz and various secondary materials like clays andoxides of Al and Fe.
Soil texture is the different size range of mineral particles varying from fine clay to coarsegravel. The varying percentages of each size range produce soils with different characteristics.
Soil organic matter is called humus that is formed by the decomposition of plant andanimal matter. The rate of decay depends upon the nature of the material and the climate. Thehumus produced and incorporated into the soil, is known as clay-humus complexes, which areimportant soil nutrients.
Soil organisms carry out following three main groups of processes. Decomposition of organicmaterial, such as plant and animal parts by bacteria, fungi, actinomycetes and earthworms. Bacteriaand fungi also breakdown soil mineral matter generating nutrients.Transformation and fixation of Nitrogen (which is an essential plant nutrient) obtained throughrainwater or from nitrogen gas in the air. Bacteria like Azobacter and Rhizobium in the root nodulesof leguminous plants, fix nitrogen from the air. Some types of bacteria have the ability to transformpesticides and herbicides into less toxic compounds.
Structural processes are carried out by atinomycetes and fungi. Mineral particles are boundtogether forming larger structures by these organisms. Earthworms, insects and burrowingmammals, such as moles, assist in the improvement of soil porosity resulting in better aerationand water holding ability.Soil Nutrients are obtained from the weathering of rock material, rainwater, fixing of gasesby soil and the decomposition of plant and animal matter. They are available to plants in solutionand in clay humus complexes.Soil pH indicates the level acidity or alkalinity of the soil. pH is the concentration of hydrogenions in the soil. It is measured on a scale from 0 to 14, with 7 being neutral. Soil profile is the vertical sectional view of the soil. Soil consists of a series of layers,or horizons, produced by the vertical movement of soil materials. Generally soil profile consistsof four horizons.Biotic Components
The live component of an ecosystem comprises plants, animals, and microorganisms (Bacteriaand Fungi). They carry out different functions and based on their role they are classified intothree main groups. They are:(1) Producers(2) Consumers(3) Decomposers
Producers are mainly green plants having chlorophyll. They produce carbohydrates byphotosynthesis process. In effect the plants convert solar energy into chemical energy using waterand carbon di oxide. These are called Autotrophs (self-feeder) since they produce their own food.Part of the food produced by the autotrophs are utilized for their own consumption for survivaland growth while the remaining is stored in the plant parts for future consumption. This becomesthe food for other biotic components in the environment.
Consumers are living things, which do not have chlorophyll, and hence they are unableto produce their own food. They rely on the producers for their food requirements. Consumersare called Heterotrophs. Consumers are classified into four categories. They are
Primary Consumers or Herbivores: They are also called first order consumers. They eatthe producers or plants. Examples are cattle like cow and goat, deer, rabbit etc.
Secondary Consumers or Primary Carnivores: They are also called second orderconsumers. They eat herbivores Examples are snakes, cats foxes etc.
Tertiary Consumers: They are also called third order consumers. They feed on secondaryconsumers. They are large Carnivores. Example is Wolf.
Quaternary Consumers: They are also called fourth order consumers. They feed onsecondary consumers. They are very large Carnivores and feed on tertiary consumers and arenot consumed by other animals. Examples are lions and tigers.
Decomposers called, as Saprotrophs are mainly microorganisms like Bacteria and Fungi. Thedead organic materials of producers and consumers are their food. They break down the organicmatter into simple compounds during their metabolic process. These simple compounds arenutrients, which are absorbed by the producers thus completing a cyclic exchange matter betweenthe biotic and abiotic components of the ecosystem.
Energy flow in Ecosystems
The sun is the source of all our energy. It is a continuously exploding hydrogen bombwhere hydrogen is converted to helium with the release of energy. This energy is mostly in theregion of 0.2 to 4 mm (Ultraviolet to Infra-Red). Around 50% of the radiation is in the visiblerange. The energy reaches the earth at a constant rate called the Solar Flux or Solar Constant,which is the amount of radiant energy crossing unit area in unit time? This value is approximately1.4 KJ per sq. meter per second.
Chlorophyll bearing plants convert this energy from the sun into carbohydrates and sugarsusing carbon di oxide and water. This process is known as Photosynthesis. The generalized formof the photosynthetic reaction isCarbon dioxide + water —® glucose + oxygen + water
The carbohydrates produced by photosynthesis undergo further modifications such asproduction of proteins and nucleic acids by combining with nitrogen, phosphorous and sulphur.Starch polymerizes to cellulose.
The sun’s energy thus enters the living beings through photosynthetic reactions and is passedfrom one organism to another in the form of food. The flow of energy is one directional andis governed by the thermodynamic law that states that Energy is neither created nor destroyedand can transform into different forms.When energy travels from producers to different levels of consumers in an ecosystem thereis loss at each level due to the energy dissipated as heat during the metabolic processes of theorganisms. Hence as we move step by step away from the primary producers the amount ofavailable energy decreases rapidly. Hence only 3 to 5 feeding levels are possible. These are referredto as Tropic levels.
Food Chain and Food WebThe food chain is an ideal model of flow of energy in the ecosystem. According to thisscheme the plants or producers are eaten by only the primary consumers, primary consumersare eaten by only the secondary consumers and so on. The producers are called Autotrophs.A food chain has three main tropic levels viz. Producers, consumers and Decomposers. The energyefficiency of each tropic level is very low. Hence shorter the food chain greater will be the availabilityof food.
A typical food chain in a field ecosystem might be
Grass —® Grasshopper —® Mouse —® Snake —® Hawk
Food webs are more complex and are interlinked at different trophic levels. This meansthose organisms have more than one alternative for food and hence survivability is better. Hawksdon’t limit their food to snakes, snakes eat things other than mice, mice eat grass as well asgrasshoppers and so on. A more realistic depiction of eating habits in an eco system is calleda food web
As energy flows through the ecosystem there is also a constant flow of matter. Living beingstake up several nutrients from their abiotic environment and when they die they are returnedto the environment. This cyclic movement of nutrient material between the biotic and abioticenvironment is called Biogeochemical Cycle. These cycles depict the material movement andtheir conservation.
The most important and common biogeochemical cycles are:(1) Water Cycle or Hydrological Cycle(2) Carbon Cycle(3) Nitrogen Cycle(4) Oxygen Cycle(5) Sulphur Cycle(6) Phosphorous Cycle.
Water Cycle or Hydrological CycleThe water cycle, also known as the hydrologic cycle or the H2O cycle, describes the continuous movement of water on, above and below the surface of the Earth. The mass water on Earth remains fairly constant over time but the partitioning of the water into the major reservoirs of ice, fresh water, saline water and atmospheric water is variable depending on a wide range of climatic variables. The water moves from one reservoir to another, such as from river to ocean, or from the ocean to the atmosphere, by the physical processes ofevaporation, condensation, precipitation, infiltration, runoff, and subsurface flow. In so doing, the water goes through different phases: liquid, solid (ice), and gas (vapour).
There is a constant and continuous exchange of water between air, land, sea and livingbeings. Considerable part of the solar energy incident on the earth is used for the massive evaporation of water from the oceans, seas and other exposed water bodies leading to cloud formation and precipitation in the form of rainfall or snow. This is the major source of fresh water for the living beings. Surface water run off results in part of fresh water returning to the sea throughrivers and streams. Underground water or simply Ground water is replenished by surfaceAccumulated water from precipitation. Ground water depletion takes place due to exploitation ofthe same by pumping. The plants also absorb ground water. Thus hydrological cycle hence isthe continuous and balanced process of evaporation, precipitation, transpiration and runoff of water.
In short Water cycle can be summarise like this
Carbon Cycle
All living things are made of carbon. Carbon is also a part of the ocean, air, and even rocks. Because the Earth is a dynamic place, carbon does not stay still. It is on the move!The Carbon Cycle is a complex series of processes through which all of the carbon atoms in existence rotate. The same carbon atoms in your body today have been used in countless other molecules since time began. The wood burned just a few decades ago could have produced carbon dioxide which through photosynthesis became part of a plant. When you eat that plant, the same carbon from the wood which was burnt can become part of you. The carbon cycle is the great natural recycler of carbon atoms. Unfortunately, the extent of its importance is rarely stressed enough. Without the proper functioning of the carbon cycle, every aspect of life could be changed dramatically.We believe that it’s vital to understand how the carbon cycle works in order to see the danger of it not working. Therefore, let’s look at a sample carbon cycle and explore how carbon atoms move through our natural world. Plants, animals, and soil interact to make up the basic cycles of nature. In the carbon cycle, plants absorb carbon dioxide from the atmosphere and use it, combined with water they get from the soil, to make the substances they need for growth. The process of photosynthesis incorporates the carbon atoms from carbon dioxide into sugars. Animals, such as the rabbit, eat the plants and use the carbon to build their own tissues. Other animals, such as the fox, eat the rabbit and then use the carbon for their own needs. These animals return carbon dioxide into the air when they breathe, and when they die, since the carbon is returned to the soil during decomposition. The carbon atoms in soil may then be used in a new plant or small microorganisms. Ultimately, the same carbon atom can move through many organisms and even end in the same place where it began.
In short Carbon cycle can be summarised like this.
Nitrogen Cycle
The nitrogen cycle is the process by which nitrogen is converted between its various chemical forms. This transformation can be carried out through both biological and physical processes. Important processes in the nitrogen cycle include fixation, ammonification, nitrification, and de-nitrification
Nitrogen and its compounds form a vital ingredient in all forms of life in the biosphere.Availability of Nitrogen is from the atmosphere as molecular Nitrogen in the gaseous form, whichcannot be directly absorbed by the plants or producers. In order to be absorbed by the plantsit has to be converted into water-soluble compounds with elements like Hydrogen, Carbon, andoxygen. This process is known as Fixation of Nitrogen. Nitrogen fixation takes place by Bacteria,Algae and electrical storms. Synthetic fixation of Nitrogen is done by the manufacture of nitrogenousfertilizers through ammonia conversion route. The plants absorb the fixed Nitrogen from the soiland convert them into proteins and other compounds during the metabolic process. Decomposers,ammonifying bacteria and Nitrate bacteria also help in the fixing process by converting dead animaland plant parts into absorbable nitrates. The denitrifying bacteria complete the cycle, which helpsin releasing gaseous Nitrogen back to the atmosphere from the soil.
In short Nitrogen cycle can be summarised like this:-
Oxygen Cycle
The oxygen cycle is the biogeochemical cycle that describes the movement of oxygen within its three main reservoirs: the atmosphere (air), the total content of biological matter within the biosphere (the global sum of all ecosystems), and the lithosphere (Earth’s crust).
Oxygen is essential for the existence of all flora and fauna. The source of Oxygen is Atmosphere
The atmosphere is actually the smallest source of oxygen on Earth comprising only 0.35% of the Earth’s total oxygen. The smallest comes from biospheres. The largest is as mentioned before in the Earth’s crust. The Oxygen cycle is how oxygen is fixed for freed in each of these major regions.The oxygen cycle is the cycle that helps move oxygen through the three main regions of the Earth, the Atmosphere, the Biosphere, and the Lithosphere. The Atmosphere is of course the region of gases that lies above the Earth’s surface and it is one of the largest reservoirs of free oxygen on earth. The Biosphere is the sum of all the Earth’s ecosystems. This also has some free oxygen produced from photosynthesis and other life processes. The largest reservoir of oxygen is the lithosphere. Most of this oxygen is not on its own or free moving but part of chemical compounds such as silicates and oxides.In the atmosphere Oxygen is freed by the process called photolysis. This is when high energy sunlight breaks apart oxygen bearing molecules to produce free oxygen. One of the most well known photolysis it the ozone cycle. O2 oxygen molecule is broken down to atomic oxygen by the ultra violet radiation of sunlight. This free oxygen then recombines with existing O2 molecules to make O3 or ozone. This cycle is important because it helps to shield the Earth from the majority of harmful ultra violet radiation turning it to harmless heat before it reaches the Earth’s surface.In the biosphere the main cycles are respiration and photosynthesis. Respiration is when animals and humans breathe consuming oxygen to be used in metabolic process and exhaling carbon dioxide. Photosynthesis is the reverse of this process and is mainly done by plants and plankton.The lithosphere mostly fixes oxygen in minerals such as silicates and oxides. Most of the time the process is automatic all it takes is a pure form of an element coming in contact with oxygen such as what happens when iron rusts. A portion of oxygen is freed by chemical weathering. When an oxygen bearing mineral is exposed to the elements a chemical reaction occurs that wears it down and in the process produces free oxygen. These are the main oxygen cycles and each play an important role in helping to protect and maintain life on the Earth.
In short Oxygen cycle can be summarised like this:-
Sulphur Cycle
The sulphur cycle is the collection of processes by which sulphur moves to and from minerals (including the waterways) and living systems. Such biogeochemical cycles are important in geology because they affect many minerals. Biogeochemical cycles are also important for life because sulphur is an essential element, being a constituent of many proteins and cofactors. Sulphur is one of the components that make up proteins and vitamins. Proteins consist of amino acids that contain sulphur atoms. Sulphur is important for the functioning of proteins and enzymes in plants, and in animals that depend upon plants for sulphur. Plants absorb sulphur when it is dissolved in water. Animals consume these plants, so that they take up enough sulphur to maintain their health.Most of the earth’s sulphur is tied up in rocks and salts or buried deep in the ocean in oceanic sediments. Sulphur can also be found in the atmosphere. It enters the atmosphere through both natural and human sources. Natural recourses can be for instance volcanic eruptions, bacterial processes, evaporation from water, or decaying organisms. When sulphur enters the atmosphere through human activity, this is mainly a consequence of industrial processes where sulphur dioxide (SO2) and hydrogen sulphide (H2S) gases are emitted on a wide scale.When sulphur dioxide enters the atmosphere it will react with oxygen to produce sulphur trioxide gas (SO3), or with other chemicals in the atmosphere, to produce sulphur salts. Sulphur dioxide may also react with water to produce sulphuric acid (H2SO4). Sulphuric acid may also be produced from dimethyl sulphide, which is emitted to the atmosphere by plankton species.All these particles will settle back onto earth, or react with rain and fall back onto earth as acid deposition. The particles will then be absorbed by plants again and are released back into the atmosphere, so that the sulphur cycle will start over again.Diagram, 6A schematic representation of the sulphur cycle:
Phosphorous Cycle
The phosphorus cycle is the biogeochemical cycle that describes the movement of phosphorus through the lithosphere, hydrosphere, and biosphere. Unlike many other biogeochemical cycles, the atmosphere does not play a significant role in the movement of phosphorus, because phosphorus and phosphorus-based compounds are usually solids at the typical ranges of temperature and pressure found on Earth. The production of phosphine gas occurs only in specialized, local conditions.
The bones and teeth of animals including human beings contain Phosphates, which is necessaryfor their development and growth. In addition phosphates are essential for cells in the productionof DNA and RNA. Phosphates are available in the lithosphere in rocks and soil in inorganic form.Plants absorb them and convert them into organo phosphates. Phosphates are also added to thesoil through phosphatic fertilizers. Soluble phosphates reaching rivers and streams from agriculturallands made rich in phosphates causes excess algal growth leading to eutrophication. Return ofphosphates to the earth are by the decay of plant and animal matter and subsequent absorption.
The phosphorus cycle differs from the other major biogeochemical cycles in that it does not include a gas phase; although small amounts of phosphoric acid (H3PO4) may make their way into the atmosphere, contributing in some cases to acid rain. The water, carbon, nitrogen and sulphur cycles all include at least one phase in which the element is in its gaseous state. Very little phosphorus circulates in the atmosphere because at Earth’s normal temperatures and pressures, phosphorus and its various compounds are not gases. The largest reservoir of phosphorus is in sedimentary rock.It is in these rocks where the phosphorus cycle begins. When it rains, phosphates are removed from the rocks (via weathering) and are distributed throughout both soils and water. Plants take up the phosphate ions from the soil. The phosphates then moves from plants to animals when herbivores eat plants and carnivores eat plants or herbivores. The phosphates absorbed by animal tissue through consumption eventually returns to the soil through the excretion of urine, as well as from the final decomposition of plants and animals after death.
In short Nitrogen cycle can be summarised like this:
“Earth as an ecosystem stands out in the all of the universe. There’s no place that we know about that can support life as we know it, not even our sister planet, Mars, where we might set up housekeeping someday, but at great effort and trouble we have to recreate the things we take for granted here.”- Sylvia Earle
