the answer is relative frequency ^^
The answer is the endogenous opiate.
The human body naturally produces its own opiates like substances and uses them as neurotransmitters. These substances include endorphins, enkephalins, and dynorphin, often collectively known as endogenous opioids. Endogenous opioids modulate our reactions to painful stimuli.
Organism, organ system, Organ, Tissue, Cell
Biosphere, organisation, ecosystem, community, population
Population, organism, organ system, tissue, cell
Biosphere, ecosystem, community, population, organism
