Organism found on a broken beam; give oxygen (6)

I believe the answer is:

amoeba

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But I can't explain it at all! Could you help me understand?

(Other definitions for amoeba that I've seen before include "Microscopic animal found in water" , "Unicellular organism" , "little creature" , "Microscopic life form" , "Not much life" .)

I've seen this clue in The Hindu.

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