What system is it: responding to the environment a circulatory system b repiratory system c muscular system d skeletal system e nervous system f digestive system g excretory system

Nervous system responds to the environment

Six amino acids have side chains that are polar but not charged. these are serine (ser), threonine (thr), cysteine (cys), asparagine (asn), glutamine (gln), and tyrosine (tyr). these amino acids are usually found at the surface of proteins, as discussed in the proteins 2 module.