Answer: adenylyl cyclase inositol triphosphate mainly known as IP3 causes the release of Calcium ions directly from the inracellular stores and causea contraction.
Explanation:
IP3, inositol phosphate is a second messenger a signaling molecule. It is made by hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2), a phospholipid that is located in the plasma membrane, by an enzyme phospholipase C.
IP3 binds to the calcium channels and opens Ca2+ channels that are embedded in the ER membrane, releasing Ca2+ into the cytosol. Calcium ions released may cause contraction and regulate the Ca2+ channels in the membranes.
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B) Oxygen may not have been able to accumulate in the atmosphere
The two semilunar valves, the pulmonary and aortic valves, are closed, preventing backflow of blood into the right and left ventricles from the pulmonary trunk on the right and the aorta on the left.