Answer:
Nerve impulse
Explanation:
A nerve impulse is transmitted through the synaptic cleft by acetylcholine. When an impulse reaches the synaptic knob, it stimulates the vesicles to move towards the presynaptic membrane releasing the acetylcholine. The transmitter substance makes the membrane permeable. An action potential is then formed along the neuron.
Answer:

Huh? You have already given the answer.......Anyways, the attached picture is an example for a stratus cloud ☁️.
Answer: According to Darwin theory of evolution the struggle for existence is considered as major part for competition among living things.
Explanation:
Coexisting species that belong to the same genera compete for same kind of resources for their survival. Some phenotypic variations gives an survival advantage over others. The superior ones dominate the inferior ones and compete for resources. The one who receives the resources like mates, food, shelter, and others the chances of survival also increases considerably.
Well the excretory system produces waste.