a) Recycling
(b) Sewage treatment
(c) Preparing compost
(d) Landfill
(e) Incineration

Ozone is formed in upper atmosphere by the reaction of ultraviolet (UV) radiations on oxygen (O₂) molecule.
The damage to ozone layer is a cause of concern to us as due to its damage, more ultraviolet rays reach the earth's surface causing various health hazards.
               \({ O }_{ 2 }\overset { UV }{ \longrightarrow } O+O\\ { O }_{ 2 }+O\longrightarrow \underset { Ozone }{ { O }_{ 3 } } \) 
A cause of this damage is the presence of large amount of chlorofluorocarbons in the atmosphere.

Grass→Grasshopper→Frog→ Peacock Peacock will have maximum cone.

The two step chains in which man is close to producer are advantageous. For example. Producer → Man.

Ozone and its chemical formula is O₃

Biodegradable wastes are those substances which are broken down into simpler, harmless substances in nature in due course of time by the biological processes such as action of micro organisms.

Chlorofluorocarbons (CFCs) are the chemicals which are used in refrigerators and air conditioners as coolant when released into the air react with ozone gas present in the ozone layer and destroy it gradually. If the ozone layer in the atmosphere disappears completely, then all the extremely harmful ultraviolet radiations coming from the sun would reach the earth and cause skin cancer and other ailments in humans, animals and plants.

In a crop field, plants do not grow naturally rather most of the plants are grown by humans. An ecosystem is nevertheless present in a crop field, but it is an artificial ecosystem as a major component of the ecosystem comes into origin because of human intervention.

Certain substances are easily acted upon by the action of enzymes of saprophytes and get converted into simpler substances, hence are called biodegradable. Whereas certain substances like plastic, etc., cannot be degraded by the action of enzymes and thus, are called non-biodegradable.

The transfer of food or energy takes place through various levels in the food chain, which are known as trophic levels, e.g.
Trees                   \(\rightarrow\)    Rabbit                \(\rightarrow\)         Snake      \(\rightarrow\)        Hawk
(First trophic level)    (Second trophic level)     (Third trophic level)    (Fourth trophic level)
  [Producers]               [I consumer]                       [II consumer]             [III consumer]

(a) A food chain involves interaction between the living organisms of an ecosystem.
(b) A food chain is always straight.
(c) A food chain has a unidirectional flow of energy from sun to producers and then to consumers.
(d) A food chain has three or four or five trophic levels.
(e) According to law of thermodynamics, 80 - 90% of energy is lost as heat. 

(i) Based on the nature, the ecosystem is classified into types namely.
(a) Natural ecosystem: The ecosystem that has been developed in the nature without any human interference is called natural ecosystem. The natural ecosystem is are of two types namely.
(i) Aquatic ecosystem: Aquatic ecosystem occurs in water bodies such as ponds, lakes, rivers, marines, estuaries etc.
(ii) Terrestrial ecosystem: Terrestrial ecosystem: Terrestrial ecosystems occur over land such as forest, grassland, desert etc. 
ecosystem: The ecosystem created and maintained by man to maintain the natural balance by the addition of energy and planned manipulations. Hence, the artificial ecosystems are also called man-made or man-engineered or anthropogenic ecosystem. Examples: Aquarium, garden etc. Agro-ecosystem is the largest man-made ecosystem.
(ii) Based on the duration, the ecosystem is classified into two types namely.
(a) Temporary ecosystem: The ecosystem which are short lived are called temporary ecosystem.
(b) Permanent ecosystem: The ecosystem which are self-supporting natural ecosystem that maintain itself for a longer duration are called permanent ecosystem.
(iii) Based on the size, the ecosystem is classified into two types namely,
(a) Small ecosystem: These are small sized ecosystems which are also termed as micro ecosystems.
(b) Large ecosystem: These are very large sized ecosystems which are also termed as macro ecosystems.