<span><span>the relevant controlled variable is the frog's body temperature, heart rate, breathing rate, and blood pressure. The controlled is a neutral pH level of 7 for the water that the frog is placed in, so that it does not obscure the effects of the water temperature on the frog's physiological factors.</span>
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Smooth muscle cells are contractile and will contract from many different agents such as hormones travelling in the blood and neurotransmitters from the autonomic nervous system. The smooth muscle cells are coupled together so that when one cell contracts, the contraction is relayed to the next. This contractile ability is important in the vascular system as it helps regulate blood pressure by changing the size of the lumen of the vessel.
<span>This contractile feature also enables the movement of food through the digestive tract. Rhythmic contractions of smooth muscle cells, called peristalsis, moves the food along.
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A polypeptide consists of a group of amino acid chains that are bonded together. The genetic code can easily locate the order of amino acids in a polypeptide because these amino acids are connected covalently to the codons of the mRNA.