Our Environment
In this Chapter...
!
Ecosystem
!
Food Chain, Trophic Levels,
Energy flow and Food Web
! Environmental Problems
All those things and set of conditions that influence the life of
2. Artificial Ecosystem
an organism like their growth, survival, development and
reproduction, constitute the environment.
An ecosystem which is created and maintained by humans
is called as artificial or man-made ecosystem. It rely on
It is composed of physical surrounding (e.g. air, water), living
human efforts to sustain. It does not possess a self-regulating
beings (e.g. plants, animals) and climatic conditions (e.g.
mechanism.
rainfall, temperature) of the region.
e.g. Aquariums, botanical gardens, field crops, etc.
Agro-ecosystem is the largest man-made ecosystem.
Ecosystem
It is the structural and functional unit of biosphere. It is a
Components of Ecosystem
stable ecological unit where regular input of energy and
The ecosystem encompasses both living (biotic) and
circulation of matter takes place. The term ecosystem was
non-living (abiotic) components of the earth.
coined by AG Tansley (in 1935).
All the interacting or living organisms (biotic components) in
1. Biotic Components
an area together with the non-living constituents (abiotic
These include all the living organisms present in the
components) of the environment form an ecosystem, e.g. a
ecosystem, i.e. plants, animals and microorganisms.
lake, a field or a forest.
On the basis of food, they consume the different living
organisms can be categorised into three groups. These are as
Types of Ecosystem
follows
There are two types of ecosystem, i.e. natural and artificial
(i) Producers All green plants and certain blue-green
ecosystem.
algae which can produce food by the process of
photosynthesis are producers. These are also called
1. Natural Ecosystem
autotrophs. These are the source of nutrition for rest of
The naturally existing ecosystem without any human support is
ecosystem.
called as natural ecosystem. Depending upon the habitats,
(ii) Consumers These are dependent on producers for
natural ecosystem may be terrestrial (desert, grassland and
their nutritional requirement and consume food prepared
forest) and aquatic (ponds, lakes, estuaries and marine).
by producers. These are also called heterotrophs.
Consumers can be further divided into the following three
Trophic Levels
categories
The transfer of food or energy takes place through various
● Herbivores These are primary consumers which feed
steps or levels in the food chain known as trophic levels.
directly on the producers, i.e. plants. e.g. Grazing
animals.
The producers (autotrophs) are present at the first trophic
level. They fix solar energy, making it available for
● Carnivores The carnivores which feed on herbivores
consumers (heterotrophs). The herbivores or the primary
are called secondary consumers.
consumers are found at the second trophic level.
● Some are predators which attack and kill their prey and
feed on their bodies. Some are scavengers that feed on
Small carnivores or secondary consumers are present at the
dead animals that they find. These are called tertiary
third trophic level. The large or the tertiary consumers
consumers.
form the fourth trophic level.
● Omnivores These are animals that feed on both plants
and animals, e.g. humans and bears.
Trophic
(iii) Decomposers These are microorganisms which feed on
levels
decaying and dead organic matter. They breakdown the
Tertiary
IV
remains of dead animals and plants, to release simpler
consumers
inorganic materials, making nutrients available to
Secondary
III
producers.
consumers
Primary consumers
II
e.g. Bacteria and fungi.
Producers
I
2. Abiotic Components
The abiotic components of an ecosystem are the non-living
Trophic levels in an ecosystem
components on which living organisms depends. These
components are light, temperature, water, atmospheric gases,
Energy Flow
wind, etc.
● The green plants in a terrestrial ecosystem capture about
1% of the energy of sunlight (light energy). They convert
Food Chain
it into food (chemical energy).
It is a linear network of living organisms in a community
● When green plants are eaten by primary consumers, a
through which energy is transferred in the form of food.
great deal of energy is lost as heat and an average of 10%
It describes relationship of organisms about ‘who eats whom’.
of the energy of food eaten by an organism is turned back
into its own body and made available for the next level
of consumers. This is known as the 10% law (Lindemann
in 1942).
Therefore, 10% can be taken as the average value for the
amount of organic matter that is present at each step and
reaches to the next trophic level.
● The loss of energy at each step is very large. Only a little
energy is available for the next level of consumers, food
chains generally consist of three or four steps.
Top carnivores
(a)
(b)
(c)
Carnivores
Food chain in nature; (a) in forest,
Herbivores
(b) in grassland and (c) in a pond
On the basis of choice of habitat, food chains are of two types
Producers
(i) Terrestrial food chain It is the food chain present on
Sunlight
land.
e.g. Grass → Insects → Snake → Hawk.
Flow of energy in an ecosystem
(ii) Aquatic food chain It is the food chain present in
● The flow of energy is unidirectional, i.e. the energy which
different water bodies.
passes to the next trophic level, does not come back to the
e.g. Phytoplankton → Zooplankton → Fish → Shark
lower trophic level.
In the atmosphere, UV radiations breakdown CFCs
Food Web
molecules and release chlorine atom. These atoms on
It is the interconnection of different food chains, which correlate at
reacting with ozone, dissociate ozone molecules into
various trophic levels operating in an ecosystem. Each organism is
oxygen.
generally eaten by two or more other kinds of organisms. They in
Thus, it leads to depletion of ozone layer.
turn are eaten by several other organisms.
Managing the Garbage We Produce
The household waste is called garbage. Every
household produces a lot of garbage on daily basis.
Improvements in our lifestyle have resulted in
greater amounts of waste material generation.
These waste substances can be divided into two main
groups
(i) Biodegradable substances The substances which
can be disposed off naturally by the action of
microorganisms like bacteria, fungi, etc., are called
biodegradable substances.
e.g. Tea leaves, waste paper, left over food, etc.
(ii) Non-Biodegradable substances The substances
that cannot be converted into harmless simpler
Food web consisting of many interlinked food chains
forms by the action of microorganisms are called
non-biodegradable substances. These are toxic,
Environmental Problems
harmful, may be inert and accumulate in the
environment or food chain.
Human are an integral part of the environment. Various human
e.g. Plastics, insecticides, heavy metals, etc.
activities pollute the environment in various ways and pose.
Serious environmental problems such as biomagnification, ozone
Methods of Waste Disposal
layer depletion, waste accumulation are as follows
Various methods of waste disposal are as given below
Biological Magnification or Biomagnification
(i) Recycling It is the processing of waste materials to
It is the phenomenon of progressive increase in the concentration
form new products.
of non-biodegradable toxicants in organisms at each successive
(ii) Composting Biodegradable domestic wastes
trophic level. It is also called bioconcentration. These toxic
can be buried in a pit, dug into ground and
chemicals enter the food chain through pesticides like DDT.
are converted into compost and used as manure.
The maximum concentration of these chemicals gets accumulated
(iii) Incineration It is burning of a substance at high
in humans as they occupy the topmost place in any food chain.
temperature to form ash. It is commonly used to
dispose hospital waste.
Depletion of Ozone Layer
(iv) Landfills Solid waste is dumped into a low lying
Ozone (O )
3
is a molecule formed by three atoms of oxygen. It is
area and covered with soil.
found in the stratosphere. It shields the surface of the Earth from
(v) Sewage treatment Organic material in the sewage
harmful ultraviolet (UV) radiations of the Sun.
is allowed to settle down and decompose in large
tanks. The water from these tanks is cleaned and is
Formation of Ozone Layer
released into waterbodies.
Ozone is a product of UV radiations acting on oxygen (O
)molecule.
2
(vi) Biogas production In some places, sewage is
The high energy UV radiations split apart some molecular oxygen
decomposed anaerobically to yield biogas and
(O )into free oxygen (O) atoms. These atoms are very reactive and
2
manure.
combine with the molecular oxygen to form ozone.
UV
Note Disposable paper cups which are biodegradable in nature
O
⎯→
O + O;O + O
⎯→
O
2
2
3
are now being used in trains instead of plastic cups and
(Ozone)
kulhads.
Ozone Depleting Substance
As the production of kulhads at a large scale resulted in the
The increasing use of synthetic chemicals like Chlorofluorocarbons
loss of top fertile layer of soil which leads to soil erosion,
whereas, plastic cups are non-biodegradable in nature,
(CFCs) which are used in refrigerants as coolant and in fire
therefore cause environmental problems.
extinguishers are responsible for ozone layer depletion.
