(a) An ecosystem is wherein all kinds of living things interdepend on each other to benefit their lives. The 2 main components in an ecosystem are:-
# ) Abiotic and Biotic factors
# ) Environmental conditions 

(b) In ponds and lakes their are decomposers which decay the dead and decayed matter in the pond or lake but in an aquarium no decomposer exists hence we need to clean the aquarium. 

Thank you.....!!!!
Mark as brainliest of helpful..
Yours, Jahnavi.