How does pH affect respiration rate?
First of all the pH of your blood plays the major role in controlling the respiration rate. Blood pH is directly linked to C02 levels as H+ + HC02- = C02 + H20 so as C02 levels rise the pH decreases. Your respiratory system is the body's number one way to immediately control pH while the kidneys and intestines are important for longer range control.
Secondly when one hyperventilates they breath off their CO2 making the blood basic creating a metabolic alkalosis rather than an acidosis. People are told to breath into a paper bag, so that they can re-intake the CO2 they are breathing out to restore the appropriate pH before they pass out.
yes, pH could affect the rate of photosynthesis as most enzyme reactions are pH sensitive. However, it should be remembered that any drastic change in the pH levels of the plants leaf would most certainly kill the or damage the plant in any case - so the rate of photosynthesis then becomes really an academic issue
If the pH is too acidic or too basic, the rate at which photosynthesis occurs will decrease. If the pH is just right for a specific plant (different plants work better at different pH levels), the rate will increase to an optimum point. This is because photosynthesis involves the operation of enzymes, which are affected by many factors, such as changes in pH.