Chemicals released by the synaptic vesicles that travel across the synaptic space and affect adjacent neurons are called a. pathogens b. androgens c. neurotransmitters d. ions

i believe it is "they are not used up by reactions" as the answer to your question, text me back if this is correct because i just learned this.

several tissues working together form an organ, and several organs together make up an organisms.

the group of cell that carries out special jobs are tissue.