Q26 of 31 Page 1

Taking the example of a lake as a simple aquatic ecosystem, interpret how various functions of this ecosystem are carried out. Make a food chain that is functional in this ecosystem.

Various functions of a lake ecosystem:


Productivity: Autotrophs such as floating plants, phytoplanktons convert inorganic substances into organic material with the help of solar energy.


Energy flow: Energy always flows from producers to top consumers therefore, energy flow is unidirectional. Some of the energy is lost as heat to the environment during energy transfer.


Decomposition: Dead and decaying organic matter is decomposed by bacteria, fungi and flagellates through these process fragmentation, leaching, catabolism, humification, and


Nutrient cycling: Nutrients released during decomposition released back to be re-used by the autotrophs.


Food chain in aquatic ecosystem. Example a lake:



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The graph given below shows the variation in the levels of ovarian hormones during various phases of menstrual cycle:


(a) Identify ‘A’ and ‘B’.


(b) Specify the source of the hormone marked in the diagram.


(c) Reason out why A peaks before B.


(d) Compare the role of A and B.


(e) Under which condition will the level of B continue to remain high on the 28thday?

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Which methodology is used while sequencing the total DNA from a cell? Explain it in detail.

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(a) Colonization of a rocky terrain is a natural process. Mention the group of organisms which invade this area first. Give an example.

(b) Over the years, it has been observed that some of the lakes are disappearing due to urbanization. In absence of human interference, depict by making a flow chart, how do the successional seres progress from hydric to mesic condition.


(c) Identify the climax community of hydrarch and xerarch succession.