(1) A food web is formed by interlinked of food chains and also so it is not straight.
(2) A food web provides alternative pathways of the availability of food.
(3) A food web helps in checking the over-population.
(4) A food web helps in the development of an ecosystem..

In an ecosystem food chain represents a stepwise, transfer of energy in the form of food. Green plants absorb about one percent of the solar energy and convert into food energy. From green plan& energy is transferred to consumers and then to decomposers. During the energy transfer at each trophic level 90% of energy is lost to the environment as heat. Only 10% of food eaten is turned into its own body and made available to the next trophic level. Therefore there is a gradual decrease in the amount of energy available in the successive trophic levels. All the energy transfer in a food chain follow 10% law. According to the ten percent law the energy available at each successive trophic level is ten percent of the previous level. Thus, food chains are more advantageous. Energy flow in an ecosystem is unidirectional. The energy lost as heat at each trophic level cannot be reused and always energy flows from producers to consumers and then to decomposers only.

Some of the harmful effects of agricultural practices on the environment are as follows:
Climate Change : As farming means growing a selected number of species on a large tract of land, it promotes monoculture. Thus farming affects the biodiversity of a region in a negative way.
Deforestation : Clearing of forests for agriculture has resulted in loss of habitat to wildlife. Deforestation has also affected the natural recharge process of ground water.
Soil degradation : Intensive farming robs off the soil of its nutrients. In the long run, it can lead to soil erosion and finally to desertification.
Water shortage : Over exploitation of groundwater for irrigation has resulted in acute water shortage at many places.
Pollution : Use of synthetic fertilisers and pesticides creates soil pollution, water pollution and air pollution.

(a) Effluents and harmful gases are the main wastes which are produced in a fertiliser factory.
(b) Treatment of Polluting Gases:
For reducing the amount of gaseous pollutants, catalytic converters should be fitted in the chimneys.
(c) Effluent Treatment:
Effluent from the factory should be sent to effluent treatment plant. Sedimentation, flocculation. filtration and chlorination are the various steps of effluent treatment. Once effluent is treated, the clean water can then be sent to nearest water bodies. The sludge can be allowed to decompose which can later be used as manure.

Decomposers are the microorganisms that convert the dead remains of plant and animals to humus hence, help in cleaning the environment.
The two consequences of their absence in an ecosystem are
1. Accumulation of dead plants and animals.
2. Replenishment of soil nutrients will not take place.

The flow of energy in an ecosystem happens in following sequence:
Producer\(\rightarrow \) Primary Consumer\(\rightarrow \) Secondary Consumer\(\rightarrow \) Tertiary Consumer
The flow of energy is unidirectional in the food chain due to two reasons. A predator always eats its prey but other way round is not possible. Moreover, out of the total energy consumed by an organism at a particular trophic level; 90% is utilised for its own need and just 10% is left for the organism of next trophic level. Thus, the availability of energy gets reduced at subsequent trophic level. Due to this, the flow of energy is unidirectional in a food chain.

The harmful by products are gases such as SO₂ and NO. They cause extensive air pollution and are responsible for acid rain.

(a) Walking and cycling for commute.
(b) Using jute/cloth shopping bag.
(c) using public transport.
(d) Switching off light/fans in unoccupied rooms.