Most things can't be explained or it hasn't been discovered yet. Science is all about asking questions and figuring out how things are the way they are.
Answer:
D. Allosteric activator
Explanation:
In an enzyme, the allosteric site is a site/motif different from the active site, (i.e., the site with catalytic activity) which is able to interact with regulatory effector molecules in order to activate or inhibit enzymatic activity by influencing the tridimensional (3D) structure of the enzyme. An allosteric activator is an effector molecule with the ability to bind to a specific enzyme at a different site than the active site, thereby modifying the shape of the enzyme and increasing the affinity of this enzyme for its substrate. Moreover, Adenosine monophosphate (AMP) is a nucleotide composed of a phosphate group, a sugar ribose, and an Adenine (A) base. This effector molecule (AMP) has shown to allosterically stimulate diverse enzymes in physiological conditions (e.g., AMP-activated protein kinase).
Chemical factors: This is due to internal stimuli. Changes in the blood such as decrease in O2, increase in CO2 and decrease in PH cause impulse in the carotid artery which stimulates the respiratory centers in the medulla and cause breathing.
Mechanical factors: also called external stimuli. Compression of the fetal chest during delivery forces small amount of lung fluid out of the lungs. This increase in pressure in the chest draws air into the lungs.
