Three billion years ago plants began the process of photosynthesis. Why would the appearance of plants that use photosynthesis to produce their food affect the
increase in atmospheric oxygen and the decrease in carbon dioxide?

The appearance of plants and their color would affect the atmospheric oxygen and would attract more of this chemical. The decrease in carbon dioxide would cause the plant to change in shape.

Explanation:

It depends on the type of the plant.

b. the carbon cycle ensures living things have a source of hydrogen

a- all cells come from pre-existing cells