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■ If we add a few aquatic plants and animals it can become a self- sustaining system. Can you think how this happens? An aquarium is an example of a human-made ecosystem. ■ Can we leave the aquarium as such after we set it up? Why does it have to be cleaned once in a while? Do we have to clean ponds or lakes in the same manner? Why or why not? We have seen in earlier classes that organisms can be grouped as producers, consumers and decomposers according to the manner in which they obtain their sustenance from the environment. Let us recall what we have learnt through the self sustaining ecosystem created by us above. Which organisms can make organic compounds like sugar and starch from inorganic substances using the radiant energy of the Sun in the presence of chlorophyll? All green plants and certain bacteria which can produce food by photosynthesis come under this category and are called the producers. Organisms depend on the producers either directly or indirectly for their sustenance? These organisms which consume the food produced, eitherdirectlyfromproducersorindirectlybyfeedingonotherconsumers are the consumers. Consumers can be classed variously as herbivores, carnivores, omnivores and parasites. Can you give examples for each of these categories of consumers? ■ Imagine the situation where you do not clean the aquarium and some fish and plants have died. Have you ever thought what happens when an organism dies? The microorganisms, comprising bacteria and fungi, break-down the dead remains and waste productsoforganisms.Thesemicroorganismsarethedecomposers as they break-down the complex organic substances into simple inorganic substances that go into the soil and are used up once more by the plants. What will happen to the garbage, and dead animalsandplantsintheirabsence?Willthenaturalreplenishment of the soil take place, even if decomposers are not there? Activity 13.2 ■ While creating an aquarium did you take care not to put an aquatic animal which would eat others? What would have happened otherwise? ■ Make groups and discuss how each of the above groups of organisms are dependent on each other. ■ Write the aquatic organisms in order of who eats whom and form a chain of at least three steps. → → ■ Would you consider any one group of organisms to be of primary importance? Why or why not? Our Environment 209 Reprint 2026-27