Choose one nuerotransmitter and describe how an external substance effects that neurotransmitter

Johnny rode his bike to a friend's house 4 blocks down the street in his neighborhood. he immediately rode back home once he realized his friend was not able to play. what was his displacement for the total bike ride? how did you determine this? what could we use as a reference point to determine he was in motion during his bike ride? why can you use it as a reference point

Coral have a symbiotic relationship with what in order to eat?

These are the components of the reservoirs of carbon that are exchanged in our environment.