If the number of photosynthetic organisms on the earth decreased drastically, which would happen as a result? Less water would be available on the earth's surface. Less solar energy would reach the earth's atmosphere. More oxygen gas would be found in the atmosphere. More carbon dioxide gas would be found in the atmosphere.

More carbon dioxide gas would be found in the atmosphere.

Explanation:

Photosynthesis is a process during which green plants manufacture carbohydrates using inorganic products in the form of water and carbon dioxide. It is represented by the following equation:

Hence, if the number of photosynthetic organisms on the earth decreases drastically, more carbon dioxide (which could have been used up ordinarily) will be found in the atmosphere

the answer to your question is:

c. complementary base-pairing