Ecosystem and Food Chain Class 10 Notes | EduRev

Our environment

Environment
Environ - surrounding - Everything which surrounds and influences the organism directly or indirectly is included in the environment.
or

Fig: Envieonment

The environment is the sum total of all living and non-living factor that surround and influence an organism.

It has two components :-

The study of environment includes the study of its various components, and their protection, preservation & management.
Ecology :- Greek word Oikos - home + logos - to study
Ecology means study of habitat or living place of organisms or study of organisms at home.
or

Fig: Ecology Environment

"The study of inter relationships of organisms between the biotic and abiotic components of their environment.
The 'Ecology' term was coined by Ernst Haeckel (1868).

Ecosystem:

• Ecosystem is the structural & functional unit of biosphere.
• It has a property of self perpetuation.
• It is an open system and depend on sun light.
• It may be small and also very large.
• Ecosystem term coined by Sir Arthur Tansley (1935).

Definition: According to Eugene P. Odum- Ecosystem is the basic unit of ecology and the biotic and abiotic components present in it influence each other. Both the components are essential for the sustenance of life.
or
A self-contained unit of living things [Plants, animals & decomposers] and their non-living environment [soil, air & water].
Types of Ecosystem:
In the biosphere, ecosystem may be classified on the basis of their nature, duration and size :

(A) Nature: On the basis of nature, ecosystem may be classified as:
(1) Natural ecosystem
(2) Artificial ecosystems
(1) Nature ecosystem: These ecosystem operate in the nature by themselves without any human interference. Common examples of natural ecosystem are : a pond, a lake, a meadow, a desert, a grassland, a forest, an ocean etc.
(2) Artificial ecosystem: These are maintained by man and hence are also termed man-made or man-engineered ecosystem. In these ecosystem, main maintains / disturbs the natural balance by the addition of energy and planned manipulations Common examples of artificial ecosystem are croplands, orchards, gardens, aquarium etc

(B) Duration: On the basis of duration, ecosystem may be classified as:
(1) Temporary ecosystem: e.g. _ short lived ecosystem, rainfed pond
(2) Permanent ecosystem: e.g. _ a lake, a forest, a desert

(C) Size:
(1) Small ecosystem: eg:- flowerpot, water in a dish.

(2) Large ecosystem: eg:- forest, desert, ocean.

Components of Ecosystem :

Fig: Biotic and Antibiotic

The various components of any ecosystem may be grouped into two main types:
(A) Abiotic (non-living) components
These include the non-living physico-chemical factors of the environment.
Abiotic factors include: 
(1) Inorganic substance (2) Organic compounds (3) Climatic factors
(1) Inorganic substance: Inorganic substances, e.g., carbon, nitrogen, oxygen, calcium, phosphorus etc. and their compounds (water, carbon dioxide, etc.) constitute the main abiotic component.
(2) Organic compounds: These include carbohydrates, proteins, lipids, nucleic acids etc.
(3) Climate factors: These include light, temperature, humidity, wind, rainfall, water etc. and also
edaphic factors (e.g., soil and substrate, topography, minerals, pH etc.)
Example of Ecosystems- (i) Grass land [meadow] ecosystem, (ii) Forest ecosystem, (iii) Desert ecosystem (iv) Mountain ecosystem (v) Pond ecosystem

Biotic Components:
The biotic community of an ecosystem includes 3 types of organisms :-
1. Producers: The organisms which can prepare their own food from simple inorganic substances like carbondioxide and water by using sunlight energy in the presence of chlorophyll. e.g. Green plants & Certain blue green algae. 

2. Consumers: Those organisms which consume food or eat food prepared by producers are called consumers. The consumers depends on producers for food, directly or indirectly. All the animals are consumers.

Consumers can be further divided into three groups 

(a) Herbivores- Those animals which eat only plants are called herbivores. e.g. Buffalo, Goat, Sheep, Horse, Deer, Camel.
Since herbivores obtain their food directly from plants or producers, therefore herbivores are primary consumers.

Fig: Herbivores

(b) Carnivores- Those animals which eat only other animals as food are called carnivores.
or
Those animals which eat the meat [or flesh] of other animals are called carnivores. e.g. Lion, Tiger, Frog, Vulture, Kingfisher.
The small carnivores which feed on herbivores [primary consumers] are called secondary consumers. e.g. Grasshopper, Rat, Frog.
The large carnivores [or top carnivores] which feed upon the small carnivores [secondary consumers] are called tertiary consumers. e.g. Lion, Tiger, Hawk
(c) Omnivores: Those animals which eat both, plants & animals, are called omnivores.
or
Those animals which eat plant food as well as the meat (or flesh) of other animals. e.g. Man, Dog, Crow, Sparrow, Bear & Ant.

(3) Decomposers: The micro-organisms which break down the complex organic compounds present in dead organisms like dead plants and animals and their products like faeces, urine into simpler substances are called decomposers. e.g. Bacteria & Fungi.

Fig: Decomposers

The decomposers help in decomposing the dead bodies of plants and animals and hence act as cleansing agents of environment.

Due to the presence of decomposers the various nutrient elements which were initialy taken by plants from the soil, air and water are returned to the soil, air and water after the death of plants animals thus decomposer organisms help in recyling the materials.

Importance of decomposers
They decompose the dead bodies of animals and plants, thus acts as cleansing agents of the environment.
They help in recycling the material in biosphere thus play a vital role in biogeochemical or nutrient cycles. They maintain the fertility of soil.
If there were no decomposers, the earth would have been a heap of dead organisms.

Food Chain
It is a sequence of ogranisms through which energy is transfered in the form of food by the process of one organism consuming the other.
or
List of organisms [living beings] showing "who eats whom" is called a food chain.
→A food chain represents unidirectional transfer of energy.
→ All the food chains begin with a green plants.
(i) Grass →      Deer →         Lion
(Producer)    (Herbivore)     (Carnivore)
(ii) Grass →    Insects →      Frog →         Birds
(Producer)    (Herbivore)   (Carnivore)   (Top carnivores)

Fig: Food Chain

Characteristics of Food Chain
1. A food chain involves a nutritive interaction between the living organisms (biotic components) of an ecosystem in a food chain, there occurs repeated eating, i.e., each group eats the other group and subsequently is taken by some other group organisms.
2. A food chain in always straight and proceeds in a progressive straight line.
3. In a food chain, there is unidirectional flow of energy from sun to producers and subsequently to series of different types of consumers.
4. Usually, there are 3 or 4 trophic levels in the food chain. In few chains, there may be maximum of 5 tropic levels.
5. Some organisms are omnivores. These occupy different trophic positions in different food chains.
6. At each transfer, generally 80-90% of energy is lost as heat in accordance with second law of thermodynamics.

Two types of food chain:

(a) Grazing type food chains

(B) Detritus food chain

Significance of Food Chains
The significance of food chains can be seen with the help of following functions:-
(i) It is a means of transfer of food from one trophic level to another.
(ii) It provides information about the living components of an ecosystem.
(iii) It helps us in understanding the interactions and interdependence amongst different organisms in an ecosystem.
(iv) It is a pathway for the flow of energy in any ecosystem.
Plants → Men (Two trophic levels)
Plants → Goat →  Men (Three trophic levels)
Plants →  Mice →  Snakes →  Peacocks (Four trophic levels)
Plants →  Insects →  Frogs →  Snakes → Eagles (Five trophic levels)
Plants →  Grasshoppers →  Frogs → Snakes →  Hawks (Five trophic levels)

Trophic levels:- The distinct sequential steps in the food chain where transfer of energy occurs are referred to as different trophic levels. For example, green plants (producers) form the first trophic level _ the producer level ; the plant eaters (herbivores), also called primary consumers, belong to second trophic level _ the primary consumer level ; and the flesh eaters (carnivores), also called secondary consumers, represent the third consumer level _ the secondary consumer level and so on.

Producers - T₁ - First trophic level
Herbivores - T₂
Primary carnivores - T₃
Secondary carnivores - T₄ 

Food web
The inter - connected food chains operating in an ecosystem which establish a network of relationships between various species is called a food web.
or
The network of a large number of food chains existing in an ecosystem is called a food web.

Fig: Food Web

 DIFFERENT BETWEEN FOOD CHAIN AND FOOD WEB: 

Different between Food Chain and Food Web

Ten Percent law
It was put forth by Lindeman (1942). It is also termed as second law of thermodynamics or law of entropy. According to this law, transfer of energy from one trophic level to other trophic level is never 100 percent. It is so because most of energy gets lost as heat in the environment during each transfer. On an average, about 10% of energy is actually available to the next trophic level.

Flow (Transfer) of energy in an ecosystem
Each organism needs energy to carry on vital activities, and for building up and repairing the body tissues.

• The ultimate source of entire energy, used by living organisms, is the sun
• In a community, each food chain, in fact, represents stepwise transfer of food (energy).
• Of the total solar radiations falling on the earth, only about 1% are captured by green plants in a terrestrial ecosystem and converted into food energy by photosynthesis. This energy is stored as chemical energy of food.
• When green plants are eaten by herbivores (primary consumers), a great of energy is lost as heat to the environment in accordance with the second law of thermodynamics. On an average, 10% of the food (energy) is turned into body of herbivores. In the same way, 10% of total energy available to the herbivores is made available for the next level of consumers. In other words, on an average, 10% of the amount of organic matter that is present at each step reaches the next consumer level.
• Since, amount of available energy goes on decreasing at each trophic level, food chains usually consist of only 3 or 4 steps and rarely maximum of 5 steps.
• In an ecosystem, generally the producers are maximum in number. As we move along the chain, the number of individuals at each trophic level decreases.