Which one of the following organisms is used as an indicator of water quality?

What is the role of bacteria present in the rumen of cattle?

Penicillin is the first antibiotic. It was discovered by

$A$ scientist associated with the discovery of the first 'antibiotic' is

Assertion $(S)$: Alexander Fleming was the discoverer of antibiotics.
Reason $(R)$: Penicillin was obtained from $Penicillium \text{ } notatum$.

Give scientific reasons: In the rumen of cattle,components having high cellulose content get digested easily.