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Saturday, 27 June 2015



Substances that are broken down by the biological processes are said to be
biodegradable. These substances are decomposed through the actions of fungi,
bacteria and other living organisms. Temperature and sunlight also play an important
roles in the decomposition of biodegradable plastics and other substances.
A ‘biodegradable’ has the ability to break down, safely and relatively quickly, by
biological means into the raw materials of nature and disappear into the environment.
These products can be solids biodegrading into the soil or liquids biodegrading into
Biodegradable plastic is intended to break up when exposed to micro-organisms.
Examples : Food refuse, tree leaves urine and faecal matter, sewage agricultural
residue, paper, wood, cloth, cow-dung, etc.

Substances that are not broken down by biological processes. These substances may
be in solid, liquid or gaseous form. These substances are inert and simply persist in
the environment for a long time or may harm the various members of the ecosystem.
Example ; these includes DDT, insecticides, pesticides, mercury, lead, arsenic,
aluminium, plastics, polythene bags, glass, radioactive wastes.
These non-biodegradable wastes are major pollutants of the environment.

1. This waste destroyed the natural beauty and surroundings become dirty.
2. Decomposition of these wastes results in the production of foul smell, which
spreads to surroundings areas.
3. These wastes may also block the drains creating pools of waste which becomes
the breeding sites of mosquitoes. The letter is carriers of diseases like malaria
and dengue.

1. These wastes are very harmful. They enter the food chains and their
concentration goes on increasing from one trophic level to the next. This leads to
biological magnification and result in harmful effects in human beings and other
2. Dumping these wastes affects the soil fertility and subsequently reduces the crop
3. These substances are inert and persist in the environment for a long time or may
harm the various members of the ecosystem

Ecosystem can be defined as followings:
Ecosystem is a structural and functional unit of the biosphere consisting of a
community of living beings and the physical environment; both interacting exchanging
materials between them also, an ecosystem is a relatively self containing and distinct
community of organisms (plants and animals) and their environment. In an ecosystem,
energy and matter are continuously exchanged between living and non-living
An ecosystem can be both natural or man-made. Some examples of natural
ecosystems are grass land, a forest, a sea, a river, a desert, a mountain, a pond, a lake etc.

The desert, grass land and mountain represent the terrestrial ecosystem 
(land based ecosystem).
The ponds, rivers, lakes and sea represent the aquatic ecosystem 
(water- based ecosystem).
Man – made or artificial ecosystems are garden, crop fields, park aquarium, etc.


Every ecosystem has two main components:

(i) Abiotic components and 
(ii) Biotic components.

These are non- living components of an ecosystem. 
These include:
Physical environment:
(i) Edaphic factors like soil texture, topography, water and air.
(ii) Inorganic substances like carbon dioxide, nitrogen, oxygen, water, phosphorus,
sodium, potassium, and calcium. These are involved in the cyclic of materials
in the ecosystem.
(iii)Organic compounds like proteins, carbohydrates, and lipids. These largely form
the living body and link the abiotic and biotic components.

Climatic factors: these are sunlight, temperature, pressure, humidity, moisture,
rainfall, etc. these factors affect the distribution of the organisms.


The biotic component of an ecosystem is a community of living organisms (like plants, animals and microbes). The biotic community of an ecosystem includes the following:

These are the organisms which are able to synthesise their food. They are mainly green plants which make their food with the help of solar energy. All green plants have the capability to absorb the sun energy and convert simple inorganic raw materials like carbon dioxide and water into carbohydrates, which give them food. This process is called photosynthesis. Therefore, all green plants are called producers. They are also called autographs.

They are organisms which consume other organisms or their products as their food. All animals belong to this category. The consumers depend upon producers for their food directly or indirectly. They get their food either by eating other organisms or their products. For example, man, goat, deer, fish, lion, cow, buffalo, etc., are common consumers.

The consumers can be classified into the following three types:

(i) HERBIOURS:-These are organisms (animals) which get their food by eating the
producers (or plants) directly. Herbivores are also called first order consumers
Some common examples of herbivores are: deer, rabbit, rat, squirrel, goat, cattle, etc.

(ii)CARNIVORES:- These are organisms (animals) which consume other animals.
Therefore, carnivores feed on the flesh of harbivores. These are also called
primary carnivores or second order consumers. Some common examples are
snake, wild cat, jackal, frog, some birds, fishes, etc.

There are animals which pray upon primary carnivores. They are called second order
consumers or third order consumers. For example, owl, peacock, tiger, lion, etc. some
second order carnivores may be eaten by third order carnivores. The carnivores which
are not preyed upon further are called top carnivores. For example, lion is a top

(iii)OMNIVORES:- The organisms which feed on both plants and animals are called
omnivores. Human beings are common example of omnivores because they
eat both plants (e.g., pulses, grams, oil seeds, fruit, etc.) animal products
(milk, meat, egg, etc).

These are organisms which feed on the dead bodies of plants and animals. These are
micro-organisms like bacteria and fungi which break down the complex organic
compounds present in dead organisms like plants and their products into a simpler
substance. These are also known as micro-organisms or saprotrophs. These are also
called reducers.


(I) Decomposers help in disposing off the wastes and dead bodies of plants and
animals. Therefore, they clean the environment and create space for living of
newer generations of organisms.

(II) The decomposers release minerals and other raw materials trapped in organic
matter. These are picked up by plants. This also help to maintain the fertility
of soil.

(III) The decomposes produce some acids which are useful in solubilisation of
some minerals.

(IV) Decompose rs help in recycling the materials in the biosphere so that the
process of life may go on and on like an unending chain.

(i) Ecosystem indicates available solar energy and the efficiency of an ecosystem to
trap the same.

ii)It gives information about the available essential minerals and their recycling

(iii)It provides knowledge about the web of interactions and inter relationship amongst the various populations as well as between the populations and the abiotic environment.

(iv) It helps human beings to know about conservation of resources, protection from
pollution and inputs required for maximizing productivity.

(v) In the ecosystem, two processes of energy flow and biogeochemical cycles
(nutrients movement) proceed side by side. The energy flow is uni-directional
while the movement of nutrients is cyclic.


In the biosphere, food relationships exist between different living organisms. 
They interact with one another for their food preparation as well as food consumption. 
Some organisms consume other organisms and they are in turn consumed by others, thereby forming a chain. In this chain, energy transfer takes place, and it is called a 
food chain.
A food chain can be defined as follows:
Food chain is sequential process which represents “who eats whom”. In terms of
energy, sequence of living organisms in a community in which one organism consumes
another organism to transfer food energy is called a food chain
In a food chain, unidirectional transfer of energy takes place.

Simple food chain operating in a grass land or forest:
Grass Deer Lion
(Producer) (Herbivore) (Carnivore)
In this food chain, grasses represent the producers (first tropic level). Grass synthesize their own food by the process of photosynthesis. Grass are eaten up by deer, which represent the herbivores or the primary consumers. Deer in turn are consumed by lions, the carnivores or the secondary consumers.
A food chain in grassland which has four steps is: Grass Insect Frog Eagle
(Producers) (Herbivores) (Carnivores) (Secondary Carnivore )


(i) The study of food chains helps in understanding food relationships and
interactions among the various organisms in an ecosystem. The food chains
transfer energy and materials between various living components of an ecosystem.

(ii) The food chains transfer energy and materials between various living
components of an ecosystem or biosphere.

(iii)The food chains give dynamicity to an ecosystem or biosphere.

(iv) The movement of toxic substances like pesticides, weedicides, etc., through food
chains can prove very harmful.

The various food chains, operating within an ecosystem or the biosphere cannot
function in isolation. Many of these food chains are interconnected by organisms which are a part of more than one food chains form a network with interconnections and linkages
The network of various food chains which are interconnected at various tropic
levels is called food web.
In a food web, one organism may occupy position is more than one food chain.
An organism can obtain its food from different sources and in turn may be eaten up by different types of organisms.

The various levels or steps in a food chain at which the transfer of food or energy takes place from one generation to another are called trophic levels. The number of triohic levels in a food is equal to the number of trophic levels in a food chain is equal to the number of steps in the food chain.
The various trophic levels are given below:
i. The plant or the producers constitute the first trophic level.
ii. The herbivores or the primary consumers form the second trophic level.
iii. Carnivores or the secondary consumers make up the third trophic level.
iv. Large carnivores or the taritiary consumers which feed upon the small carnivores
constitute the fourth trophic level.

Energy is used and conveyed from one trophic level to another is a food chain. This is
called flow of energy. Green plants capture about 1% of the solar energy incident on
the earth through the biochemical process of photosynthesis. A part of this trapped
energy iss used by plants in performing their metabolic activities and some energy is
released at heat into the atmosphere. The remaining energy is chemical energy stored in the plants as ‘carbohydrates’.
When plants are eaten up by herbivores, the chemical energy stored in the plants
is transferred to these animals. These animals (herbivores) utilize some of this energy
for metabolic activities, some energy is released as heat and the remaining energy is
The process of energy transferred is similarly repeated with carnivores and so on.

The following are the characteristics of energy transfer in the biosphere:
(i) Energy is supplied by the sun and it is not created in the biosphere. Energy is
only converted from one form to another in the biosphere.
(ii) There is a continuous transfer of energy from one trophic level to the next in a
food chain.
(iii)At each trophic level, some of the energy is utilized by the organisms for their
metabolic activities.
(iv) At each trophic level, some amount of energy is utilized for the composition of
(v) At each trophci level, there is loss of energy, which goes into the environment
and remains un-utilized.
(vi) At each trophic level, the amount of energy available is less than that available at
the previous level.

According to this law only ten percent of the energy entering a particular trophic level
is stored and the remaining is lost during energy transfer. In the words, the energy
available at each successive trophic level is only 10 percent of the previous level.
e.g.,Sun energy 1000 J Plant 10 J Dear 1 J Lion
For example, suppose 1000 J of solar energy is received by green plants, then only 1% of solar energy available on earth is utilized by plants. So only 10 J (1% of 1000 J) is trapped by plants and the rest 990 J of energy is lost to the environment. So, plant
utilizes only 10 J of energy.
Next, only 10% off the 10 J energy of plants, that is, 1 J, is available to the
herbivore animal while 9 J is lost to the environment.
Against, just 1% of the 1 J of energy of herbivore animals is utilized by carnivore
animals. Thus, carnivore animals have only 0.1 J of energy while 0.9 J is lost to the

The upper reaches of the atmosphere extend up to 600 km above the earth. At about
10-50 km above the earth is a region called the ozonosphere, where there is a relative abundance of the gas called ozone. The ozone layer protects life on the earth by blocking most of the sun’s harmful ultraviolet rays.
The ozone molecule is made up of three atoms of oxygen. The chlorine atom
attacks ozone and takes one oxygen atom away from ozone, to chlorine monoxide
combines with another oxygen atom to form oxygen and chlorine.
When chlorine becomes free, it will combine with another molecule of ozone and
break the bonds between its oxygen atoms, thus, reducing the amount of ozone. 
The newly formed oxygen molecules cannot prevent the sun’s ultraviolent rays from
reaching the earth. Exposure to these rays can lead to various diseases like cataract
and skin cancer.
The source of chlorine are compounds like fluorocarbon and chlorofluorocarbon
(CFC). Chlorofluorocarbon wafts up to the atmosphere. Very high up in the
atmosphere, this compound breaks up and starts the demolition of ozone.

Chemicals like DDT are widely used to kill pests. These chemicals can get into the food chain and cause great harm. They enter the food chain through aquatic life forms like plankton, which are eaten by fishes, which in turn might be eaten by birds and other consumers higher up in the food chain. These chemicals are not metabolised in the body of animals and hence accumulate in their tissues. As the chemical passes on from one level to the next in the food chain, the concentration of the chemical retained by organisms at each level increases. This is called biological magnification. This kind of process was observed around Lake Michigan in North America. DDT was sprayed extensively around the lake in 1942 to kill mosquitoes, which caused malaria. After almost twenty years, ie., in the early sixties, a dramatic fall in the number of pelicans (a type of bird) was noticed.

The disposal of waste should be done scientifically. There are different
techniques of waste disposal, which depends upon the nature of the waste.
Most solid wastes are buried in urban areas as land fills.
Some solid wastes like plastics, metals, papers are recycled. Industrial wastes
are treated in special plants and valuable wastes are recycled.
Domestic wastes are used as manure for plants, including trees after
Waste coming out of industries, such as metals can be melted and recycled into
solid metal once again.
Molten plastic waste mixed with asphalt can also be used for making roads.
These reduce pollution.
The volume of the waste can be reduced by incineration or burning at high
Biogas and manure can be prepared from the biodegradable waste, which cost
much less than other fuel and fertilizers.

The damage of ozone layer leads to variation in rainfall, ecological disturbances and
other effect in global food supply. To limit this damage, U.N.E.P, United Nations
environment programme has forged an agreement to freeze for CFC production at
1986. All t he developed and developed countries are taking keen interest to work in 
this regard to save the ozone layer from further depletion.

Also read.

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