3. The human body has devised an excellent method to keep the body pH under control. a. What principle underlies the constant pH of human blood, and how does the blood achieve this

The normal blood pH for adult humans is 7.40, and this pH value is vigorously defended at normal body temperature

Acid base Homeostasis is the method by which body keeps a constant ph
pH is kept under check via different systems
1. Chemical system :bicarbonate buffer system(explained below )
Respiratory component :
2. Respiratory Component: The second line of dense is rapid consisting of the control the carbonic acid concentration in the ECF by changing the rate and depth of breathing by hyperventilation or hypoventilation. This blows off or retains carbon dioxide (and thus carbonic acid) in the blood plasma as required

3.Metabolic component : third line of defense is slow, best measured by the base excess,eand mostly depends on the renal system which can add or remove bicarbonate ions to or from the ECF.Bicarbonate ions are derived from metabolic carbon dioxide which is enzymatically converted to carbonic acid in the renal tubular cells.There, carbonic acid spontaneously dissociates into hydrogen ions and bicarbonate ions.When the pH in the ECF falls, hydrogen ions are excreted into urine, while bicarbonate ions are secreted into blood plasma, causing the plasma pH to rise.The converse happens if the pH in the ECF tends to rise: bicarbonate ions are then excreted into the urine and hydrogen ions into the blood plasma.

Buffers usually consist of a weak acid and its conjugate base; this enables them to readily absorb excess H+ or OH–, keeping the system’s pH within a narrow range.

Maintaining a constant blood pH is critical to a person’s well-being. The buffer that maintains the pH of human blood involves carbonic acid (H2CO3), bicarbonate ion (HCO3–), and carbon dioxide (CO2). When bicarbonate ions combine with free hydrogen ions and become carbonic acid, hydrogen ions are removed, moderating pH changes. Similarly, excess carbonic acid can be converted into carbon dioxide gas and exhaled through the lungs; this prevents too many free hydrogen ions from building up in the blood and dangerously reducing its pH; likewise, if too much OH– is introduced into the system, carbonic acid will combine with it to create bicarbonate, lowering the pH.
Example: Antacids, which combat excess stomach acid, are another example of buffers.

ECF =Extra cellular fluid

When a virus infects a host cell, it uses the cell's machinery to make copies of its own genetic material in a process called replication. finally, during the process of self-assembly, that protein shell and the copies of the virus's genetic material are assembled into new viruses.