The question focuses on how the body maintains homeostasis when the acidic level of human blood increases. Let’s break down the options and analyze each one to determine the correct mechanism.
a) [tex]$H ^{+}$[/tex] ion-donor levels increase:
- Increasing [tex]$H ^{+}$[/tex] ion-donor levels will actually introduce more hydrogen ions into the bloodstream, making the blood more acidic. This option does not help in maintaining homeostasis when the blood becomes too acidic.
b) Bicarbonate [tex]$\left( HCO _3^{-}\right)$[/tex] releases [tex]$H ^{+}$[/tex] ions that combine with excess [tex]$OH ^{-}$[/tex] ions to form [tex]$H _2 O$[/tex]:
- This option only addresses the scenario where there is an excess of [tex]$OH ^{-}$[/tex] ions, which would make the blood more basic rather than acidic. Therefore, this option is not relevant to our situation of increased acidity.
c) Bicarbonate [tex]$\left( HCO _3^{-}\right)$[/tex] accepts [tex]$H ^{+}$[/tex] and forms carbonic acid:
- This is a plausible mechanism because bicarbonate ([tex]$HCO _3^{-}$[/tex]) is a base and can neutralize excess [tex]$H ^{+}$[/tex] ions (protons) in the blood. When bicarbonate accepts hydrogen ions, it forms carbonic acid ([tex]$H_2CO_3$[/tex]), which can then be converted to carbon dioxide ([tex]$CO_2$[/tex]) and water ([tex]$H_2O$[/tex]) and exhaled through the lungs. Hence, this process helps in reducing the acidity of the blood and maintaining homeostasis.
d) Bicarbonate [tex]$\left( HCO _3^{-}\right)$[/tex] releases [tex]$H ^{+}$[/tex] ions that combine with excess [tex]$OH ^{-}$[/tex] ions to form [tex]$H _2 O. H ^{+}$[/tex] ion-donor levels increase. Bicarbonate [tex]$\left( HCO _3{ }^{-}\right)$[/tex] accepts [tex]$H ^{+}$[/tex] and forms carbonic acid:
- This option combines various statements, but it contains inconsistencies. Releasing [tex]$H ^{+}$[/tex] ions would increase acidity rather than decrease it. Although it also states that bicarbonate accepts [tex]$H ^{+}$[/tex] and forms carbonic acid, the presence of conflicting statements makes this option confusing and not entirely accurate.
Based on the analysis, the most accurate choice is:
c) Bicarbonate [tex]$\left( HCO _3^{-}\right)$[/tex] accepts [tex]$H ^{+}$[/tex] and forms carbonic acid.
This mechanism accurately describes the role of bicarbonate in neutralizing excess hydrogen ions and thus maintaining the pH balance (homeostasis) of blood.
