Our Environment Notes

                                              INTRODUCTION

Various components in the environment interact with each other and impact the environment. The environment consists of biotic and abiotic factors, abiotic factors includes physical surroundings like air (or atmosphere), water bodies, soil (land and biotic factors such as plants, animals, human beings and micro-organisms like bacteria and fungi (called decomposers).

 

 

ECOSYSTEM

All organisms such as plants, animals, microorganisms and human beings as well as the physical           surroundings interact with each other and maintain a balance in nature. All the interacting organisms in an area together with the non-living constituents of the environment form an ecosystem. Thus, an ecosystem consists of biotic components comprising living organisms and abiotic components comprising physical factors like temperature, rainfall, wind, soil and minerals.

Abiotic components

These are non-living components and includes :

Major abiotic factors

• • Light, temperature, pressure, humidity , soil , water , air,etc

Minor abiotic factors

• • Carbon dioxide, nitrogen, oxygen, sulfur, phosphorus, calcium, potassium, etc.

Biotic components

These are living components and includes all plants and animals in the categories as :

• • Autotrophs : all green plants which synthesize their own food.
  • Heterotrophs : all animals which depend on others for food .

TYPES OF ECOSYSTEMS

Grasses, trees; flower bearing plants like rose, jasmine, sunflower; and animals like frogs, insects and birds. All these living organisms interact with each other and their growth, reproduction and other activities are affected by the abiotic components of ecosystem. So a garden is an ecosystem.

Other types of ecosystems are forests, ponds and lakes. These are natural ecosystems while gardens and crop-fields are human made (artificial) ecosystems. An aquarium is an example of a human-made ecosystem.

ECOLOGY AND ECOSYSTEM

Ecology is the study of ecosystems and ecosystems are the units that are formed by the interaction of a community and of organisms with the environment.

Ecology is the subject that studies the interactions among organisms and between the organisms and its physical (abiotic) environment. Ecology is concerned with four levels of biological organization.

 

Producers

Organisms can make organic compounds like sugar and starch from inorganic substances using the radiant energy of the Sun in the presence of chlorophyll. All green plants and certain bacteria which can produce food by photosynthesis come under this category and are called the producers.

Consumers

Organisms which consume the food produced, either directly from producers or indirectly by feeding on other consumers are the consumers.

Decomposers

The microorganisms, comprising bacteria and fungi, break-down the dead remains and waste products of organisms. These microorganisms are the decomposers as they break-down the complex organic substances into simple inorganic substances that go into the soil and are used up once more by the plants . Like complex organic materials are broken down into carbon dioxide, water and nutrients . This process is called decomposition. Earthworm is referred to as the farmers friend because they help in the breakdown of complex organic matter as well as loosening of the soil. Dead remains such as leaves, bark, flowers and dead remains of animals are called detritus.

The important steps in the process of decomposition are :

Fragmentation :  break down of detritus into smaller particles is called fragmentation.

Leaching : going down of the water-insoluble nutrients into the soil horizon and precipitated there is called leaching.

Catabolism : the degradation of detritus into simple inorganic substances by the bacterial and fungal enzymes is called catabolism.

Humification : accumulation of a highly resistant dark colored amorphous substance known as humus is called humification.

Mineralization :  degradation of humus by some microbes and release of inorganic nutrients is called mineralization.

Food chains and food webs

This series or organisms taking part at various biotic levels form a food chain. Each step or level of the food chain forms a trophic level. The autotrophs or the producers are at the first trophic level.

They fix up the solar energy and make it available for heterotrophs or the consumers. The herbivores or the primary consumers come at the second, small carnivores or the secondary consumers at the third and larger carnivores or the tertiary consumers form the fourth trophic level.

Food chains on land

Food chains in water

The food we eat acts as a fuel to provide us energy to do work. Thus the interactions among various components of the environment involves flow of energy from one component of the system to another. The autotrophs capture the energy present in sunlight and convert it into chemical energy. This energy supports all the activities of the living world. From autotrophs, the energy goes to the heterotrophs and decomposers. One form of energy is changed to another, some energy is lost to the environment in forms which cannot be used again.

These are the examples of grazing food chain (GFC) .there is detritus food chain (DFC) also which begins with dead organic matter and made up of the decomposers, mainly bacteria and fungi. DFC may be connected with the GFC at some levels , some of the organisms of DFC are prey to the GFC animals ,and in a natural ecosystem, some animals like cockroaches, crows; are omnivores. These natural interconnections of food chains make it a food web.

ENERGY FLOW

Sun is the only source of energy for all the ecosystems on earth. 50% of this incident energy is photosynthetically active . Plants capture only 2-10 % of this active energy and this small amount of energy sustains the entire living world. Plants , photosynthetic and chemosynthetic bacteria fix suns radiant energy to make food from simple inorganic materials. The solar energy captured by the plants flows through different organisms of an ecosystem.

The flow of energy between various components of the environment has been extensively studied and it has been found that :

• The green plants in a terrestrial ecosystem capture about 1% of the energy of sunlight that falls on their leaves and convert it into food energy.
• When green plants are eaten by primary consumers, a great deal of energy is lost as heat to the environment, some amount goes into digestion and in doing work and the rest goes towards growth and reproduction.

• An average of 10% of the food eaten is turned into its own body and made available for the next level of consumers.
• Therefore, 10% can be taken as the average value for the amount of organic matter that is present at each step and reaches the next level of consumers.
• Since so little energy is available for the next level of consumers, food chains generally consist of only three or four steps.
• The loss of energy at each step is so great that very little usable energy remains after four trophic levels.
• The flow of energy is unidirectional.
• The energy that is captured by the autotrophs does not revert back to the solar input and the energy which passes to the herbivores does not come back to autotrophs.

• As it moves progressively through the various trophic levels it is no longer available to the previous level. Secondly, the energy available at each trophic level gets diminished progressively due to loss of energy at each level.
• There are generally a greater number of individuals at the lower trophic levels of an ecosystem, the greatest number is of the producers.
• The length and complexity of food chains vary greatly. Each organism is generally eaten by two or more other kinds of organisms which in turn are eaten by several other organisms.
• So instead of a straight line food chain, the relationship can be shown as a series of branching lines called a food web.
• Organisms at each trophic level depends on those at the lower trophic level for thie energy demands.
• Each trophic level has a certain mass of living material at a particular time as the standing crop.
• The number of trophic levels in the GFC is restricted as the transfer of energy follows 10%law that is only 10% of the energy is transferred to each trophic level from the lower trophic level.

 

Biological magnification

This phenomenon refers to increase in concentration of the toxicant at successive trophic levels.

• Several pesticides and other chemicals are used to protect our crops from diseases and pests.
• These chemicals are either washed down into the soil or into the water bodies.
• From the soil, these are absorbed by the plants along with water and minerals, and from the water bodies these are taken up by aquatic plants and animals.
• This is one of the ways in which they enter the food chain. As these chemicals are not degradable, these get accumulated progressively at each trophic level.
• As human beings occupy the top level in any food chain, the maximum concentration of these chemicals get accumulated in our bodies.
• This is the reason why our food grains such as wheat and rice, vegetables and fruits, and even meat, contain varying amounts of pesticide residues.
• They cannot always be removed by washing or other means.
• This phenomenon is well known for mercury and DDT.

               Environmental problems

1. Ozone depletion

Ozone layer

The ozone layer sits un the stratosphere between 15Km and 30 Km above the earth. It provides the protective shield from the suns harmful UV radiation (UV-B radiation). it can absorb more than 95% of the suns UV radiations. On depletion of ozone layer , there will be serious effects on human health and the environment. It could lead to weakened immune systems, cataracts and skin cancer if this skin weakens. A hole in the ozone layer was discovered in the Antarctica in 1985.

The Montreal Protocol was signed by the United Nations and 45 other countries on September 16,1987, on substances that depletes the ozone layer. That is why ozone day is celebrated on 16 September.

Ozone depleting substances :

1. Chlorofluorocarbons (CFCs)
2. Hydrochlorofluorocarbons (HCFCs)
3. Halons
4. Methyl chloroform
5. Methyl bromide
6. Carbon tetrachloride (CCl4).

 IMPORTANT POINTS REGARDING OZONE LAYER DEPLETION ARE :

• Ozone (O3 ) is a molecule formed by three atoms of oxygen.
• While O2, which we normally refer to as oxygen, is essential for all aerobic forms of life.
• Ozone, is a deadly poison. However, at the higher levels of the atmosphere, ozone performs an essential function. It shields the surface of the earth from ultraviolet (UV) radiation from the Sun.
• This radiation is highly damaging to organisms, for example, it is known to cause skin cancer in human beings.
• Ozone at the higher levels of the atmosphere is a product of UV radiation acting on oxygen (O2 ) molecule. The higher energy UV radiations split apart some moleculer oxygen (O2 ) into free oxygen (O) atoms.
• The amount of ozone in the atmosphere began to drop sharply in the 1980s. This decrease has been linked to synthetic chemicals like chlorofluorocarbons (CFCs) which are used as refrigerants and in fire extinguishers.
• In 1987, the United Nations Environment Program (UNEP) succeeded in forging an agreement to freeze CFC production at 1986 levels. It is now mandatory for all the manufacturing companies to make CFC-free refrigerators throughout the world.

2. Waste and its Disposal

Waste are the different type of materials we through them away. Wastes can be divided into biodegradable and non-biodegradable waste .

Biodegradable and non-biodegradable waste

Biodegradable :

• Biodegradable materials naturally degrade with time, facilitated by       natural agents such as bacteria, air, water, soil, and many others. They transform into simpler units and then we use them as fertilizers, manure, compost, biogas, etc. These substances are non-toxic.

e.g; fruits, vegetables, flowers, plants, animals, water, paper, etc.

Non-biodegradable :

• Non-biodegradable materials do not decay naturally, and the natural agents of decomposition do not affect them. They stay in the ecosystem for the longer period and even cause harm to our environment. They transform into soil waste which becomes great problem to the environment and health.

e.g; plastics, chemicals, rubber, paints, batteries, metals, etc.

The classified of waste on the basis of source and composition are as follows:

1. Solid Waste:Food waste and dry material like glass, paper, cloth or wood, tree stumps or construction and demolition waste etc.
2. Sewage Waste:Wastewater like groundwater aquifers or surface water such as rivers, lakes, estuaries and oceans, etc.
3. Electronic Waste:E-waste includes machine like refrigerators, washing machine , microwave ovens, TV, radios, computers and cellphones.
4. Hazardous Waste:Hazardous are harmful to human health and environment. They are toxic, reactive, infectious and radioactive. E.g; fissionable materials, isotopes of cobalt ,iodine etc.

Waste disposal

It is the process of collection, processing and recycling or decomposition of the waste materials of human society.

It can be done by using following methods

1. Landfilling :Non-reusable and non-replaceable substances are dug deep inside the soil.
2. Incineration:Waste is burned and garbage turns into the incombustible matter like gases and ashes. The resultants are heavy metals which are placed in landfills ultimately making air , water, and soil polluted. But we can see decreased waste quantity , production of power and heat ,pollution reduction elimination of chemical and harmful germs
3. Composting:Composting deals all organic materials including food scraps, garden waste, fruits and vegetables peels. These substances are buried and left under the soil for some days which decays by microorganisms and humus like substance called compost is formed. Vermicomposting is decomposition of waste by earthworms and other worms
4. Biogas Generation:Biogas is a mixture of gases like methane, and carbon dioxide. Biodegradable waste can broken down by bacteria and other organisms to produce biogas and these decomposed biodegradable waste serves as food to microorganisms. This process can occur anaerobically as well as aerobically .

Green House Effect and Global Warming

The greenhouse effect is a naturally occurring phenomenon that is responsible for heating of earth’s surface and atmosphere. Clouds and gases reflect about one-fourth of the incoming solar radiation, and absorb some of it but almost half of incoming solar radiation falls on earth’s surface re-emits heat in the form of infrared radiation but part of this does not escape into space as atmospheric gases (e.g; carbon dioxide, methane, etc.) absorb a major fraction of it. The molecule of these gases radiate heat energy, and a major part of which again comes to earth’s surface, thus heating up once again. Thus cycle is repeated many a times. These gases are responsible for greenhouse effect.

Increase in the level of greenhouse gases has led to considerable heating of earth leading to global warming .

Deforestation

Deforestation is the conversion of forested areas to non-forested areas. According to an estimate , almost 40% forests have been lost in the tropics, compared to only 1 % in the temperate region.