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Man has a varied diet. When on a vegetarian diet, they are primary consumers and when on a non-vegetarian diet, they are secondary consumers.

A trophic level refers to the position of an organism in the food chain. The number of trophic levels is equal to the number of steps in the food chain. The green plants (producers) occupying the first trophic level (T₁ ) are called producers. The energy produced by the producers is utilized by the plant eaters (herbivores) they are called primary consumers and occupies the second trophic level (T₂ ).

Herbivores are eaten by carnivores, which occupy the third trophic level (T₃ ). They are also called secondary consumers or primary carnivores. Carnivores are eaten by the other carnivores, which occupy the fourth trophic level (T₄ ). They are called the tertiary consumers or secondary carnivores. Some organisms which eat both plants and animals are called as omnivores (Crow). Such organisms may occupy more than one trophic level in the food chain.

Detritus food chain is a type of food chain which begins with dead organic matter which is an important source of energy. A large amount of organic matter is derived from the dead plants, animals and their excreta. This type of food chain is present in all ecosystems. The transfer of energy from the dead organic matter, is transferred through a series of organisms called detritus consumers (detritivores)- small carnivores – large (top) carnivores with repeated eating and being eaten respectively. This is called the detritus food chain.

Fallen leaves → Earthworm → Blackbird → Hawk Detritus Detritivores Small carnivores Top carnivores

Main source of energy for the grazing food chain is the Sun. It begins with the first link, producers (plants). The second link in the food chain is primary consumers (mouse) which get their food from producers. The third link in the food chain is secondary consumers (snake) which get their food from primary consumers. Fourth link in the food chain is tertiary consumers (eagle) which get their food from secondary consumers

Grass → Mouse → Snake → Eagle

Producers Primary consumers Secondary Consumers Tertiary consumers

1. The first link of grazing food chain is plants (Producers). 

2. The first link of detritus food chain is dead remains and excreta of plants and animals.

The transfer of energy in an ecosystem between trophic levels can be termed as energy flow. It is the key function in an ecosystem. Energy flow is always unidirectional in an ecosystem.

Second law of thermodynamics states that energy transformation results in the reduction of the free energy of the system. Usually energy transformation cannot be 100% efficient. As energy is transferred from one organism to another in the form of food, a portion of it is stored as energy in living tissue, whereas a large part of energy is dissipated as heat through respiration. The transfer of energy is irreversible natural process.

First law of thermodynamics states that energy can be transmitted from one system to another in various forms. Energy cannot be destroyed or created. But it can be transformed from one form to another. As a result, the quantity of energy present in the universe is constant.

The movement of energy from producers upto top carnivores is known as food chain, i.e., in any food chain, energy flows from producers to primary consumers, then from primary consumers to secondary consumers, and finally secondary consumers to tertiary consumers. Hence, it shows linear network links.

Ten percent law states that only 10% of the energy is transferred from one trophic level to the next trophic level through food chain.

Ten percent law states that during transfer of food energy from one trophic level to other, only about 10% stored at every level and rest of them (90%) is lost in respiration, decomposition and in the form of heat.

• The base of the pyramid of energy is occupied by producers, which have the maximum amount of energy.
• When energy flow from one trophic level only 10% is transferred, there is always loss of some energy in the form of heat.
• So, the amount of energy at higher trophic level will always be less than the lower trophic levels and pyramid of energy will be upright and be inverted.

Kavitha showed values like love for nature, responsibility & care for animals. If frogs are killed it will have an adverse effect on the other organisms. The insect population will increase and the snake population will decrease and the whole ecosystem will be disturbed.