Curare is a potent neurotoxin extracted from the Strychnos toxifera plant in Central and South America. Indigenous peoples of South America apply curare to arrows, which they used to hunt and kill animals. Curare acts at synapses between motor neurons and skeletal muscle cells. When a motor neuron synapses with a skeletal muscle cell, the skeletal muscle cell may be stimulated or inhibited just like postsynaptic neurons are. Curare acts by binding temporarily to acetylcholine receptors on the postsynaptic cell and prevents acetylcholine from binding.

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Explanation:

The curare acts at the level of the assimilation of acetylcholine, which is a neurotransmitter responsible for uniting the excitation of the neuron with the muscle fiber, the union of Ach released by the nerve terminal that entered the action potential with the receptor on the surface of the smooth muscle are those that cause muscle contraction to happen, if this neurotransmitter is not able to unite with its receptor then the inability of muscle contraction will occur.

"d.) carbon dioxide and hydrogen sulfide"

the fossil record provides evidence of a common ancestor to many species.