Final answer:
The biological process that produces most of the dry mass of a plant is called photosynthesis. It uses sunlight, carbon dioxide, and water to create glucose and oxygen, which plays a key role in the plant's development and the oxygen we breathe.
Step-by-step explanation:
The biological process that produces 96% of the dry mass of a plant is called photosynthesis. Photosynthesis is a fundamental process in which plants use sunlight, carbon dioxide, and water to produce glucose and oxygen. This process not only contributes to the dry mass of plants by producing carbohydrates, but it is also essential for the production of oxygen that we breathe.
In comparison, the transpiration process in which plants give off water vapor through tiny pores, called stomata, in their leaves is mainly involved in the water cycle and doesn't contribute to the dry mass of plants. While respiration, oxidation, cation exchange are all important biological processes, they do not contribute as significantly to the dry mass of plants as photosynthesis does.