Breathing as photosynthesis releases oxygen
food as photosynthesis helps the plant to grow
First, they may produce direct and relatively short-lived effects, such as stimulation of the isolated uterus or relaxation of the isolated tracheal chain preparation.
Secondly, in doses too low to produce a direct effect, they may produce a long-term potentiation of the effects of other stimulants.
I'd say it's single replacement/displacement
