An ecosystem can be visualised as a functional unit in nature, where living organisms interact among themselves and with the surrounding physical environment also. The interaction of the biotic and abiotic components results in a physical structure that is characteristic of an ecosystem.
(a) Name the two features that define the structural aspect of an ecosystem.
(b) Mention the four common functional aspects of an ecosystem.

A pond is a shallow water body, which is fairly a self-sustainable unit that explains the complex interactions in an aquatic ecosystem. The water with all the dissolved inorganic and organic nutrients is the major abiotic component.
Name the three groups of biotic components in the pond and give an example for each.

The fallen parts of plants such as leaves, flowers, etc., faecal matter of animals, dead remains of animals, etc. are ultimately broken down into simpler inorganic nutrients, carbon dioxide and water.
1. Fragmentation, 2. Leaching, 3. Catabolism are some important steps in the process; they occur simultaneously.
(a) What term is given to the group of organisms that carry out the steps 1 and 3, respectively and give an example for each.
(b) Name the other two steps involved in the process.

Organisms occupy a specific place in their natural surroundings or in a community according to their feeding relationship with the other organisms. Based on the source of nutrition of food organisms occupy a particular place, called trophic level, in a food chain.
(a) What technical term is given to the organisms occupying the first, second and third trophic levels in a food chain?
(b) Choose an example for each of the above trophic levels, from the following list of organisms: Rabbit, Wolf, phytoplanktons, frog, snail, Hydrilla, jackal.

Over the years, it has been observed that some of the lakes are disappearing due to urbanisation. In the absence of human interference, depict through a flow chart, how the successional series progresses from hydric to mesic condition.