Page 214 - NCERT Science Class 10 English Medium

n 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.
n 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,
either directly from producers or indirectly by feeding on other consumers
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?
n 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
products of organisms. These microorganisms are the decomposers
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
animals and plants in their absence? Will the natural replenishment
of the soil take place, even if decomposers are not there?

Activity
Activity 13.213.2
Activity 13.2
Activity
13.2
Activity 13.2
n While creating an aquarium did you take care not to put an aquatic
animal which would eat others? What would have happened
otherwise?
n Make groups and discuss how each of the above groups of
organisms are dependent on each other.
n Write the aquatic organisms in order of who eats whom and form
a chain of at least three steps. → →
n Would you consider any one group of organisms to be of primary
importance? Why or why not?

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