Yes, RESPIRATION is a Scrabble word!

Letter values in Scrabble US: R 1, E 1, S 1, P 3, I 1, R 1, A 1, T 1, I 1, O 1, N 1.

Is it a valid word?

RESPIRATION is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

the metabolic processes whereby certain organisms obtain energy from organic molecules; processes that take place in the cells and tissues during which energy is released and carbon dioxide is produced and absorbed by the blood to be transported to the lungs
a single complete act of breathing in and out
the bodily process of inhalation and exhalation; the process of taking in oxygen from inhaled air and releasing carbon dioxide by exhalation

Also: internal respiration, cellular respiration, external respiration.