What are the roles of the following part of a plant:

guard cells
stoma
xylem
phloem

Guard cells becoming larger or smaller according to the pressure within the cells. stoma any of the minute pore in the epidemics or the leaf or stem of the plant. xylem the vascular tissue in plants that conducts water and dissolved nutrients. phloem is the vascular tissue that conducts sugars downward the leaves.

Neurotransmitters are messengers responsible for communication between neurons. they are released from synaptic vesicles and are received by receptors.  the communication is referred to as neurotransmission. the following statement is true about neurotransmitters: a. they're stored in synaptic vesicles in the axon.