Carbon, oxygen, & hydrogen may all be elements found in ethanol, but when separated, they have completely different chemical compounds. They are pure elements where as ethanol is a mixture.
Answer:
a. The initial concentration of the substrate
Explanation:
If the researcher keeps the initial concentration of the substrate constant, it will give room to compare the reaction rates under different environmental conditions. The reaction rates will assist the researcher by providing the researcher with the necessary and important information about the enzyme's function in different environments.
I believe the answer you're looking for is photosynthesis, where plants release oxygen and humans use this to release carbon dioxide to the plants.
The difference between pH 3 and pH 4 is a 10 fold difference in the concentration of H+
