Final answer:
Photosynthesis requires pigment molecules to absorb light energy, while cellular respiration does not involve pigments as it is about metabolizing carbohydrates to release energy.
Step-by-step explanation:
The process that requires pigment molecules is photosynthesis. In the first part of photosynthesis, known as the light-dependent reaction, pigment molecules such as chlorophyll absorb energy from sunlight. This is a crucial step in converting light energy into chemical energy, which is later used to convert carbon dioxide and water into glucose during the Calvin cycle.
On the other hand, cellular respiration does not require pigment molecules; it is the process of breaking down carbohydrates to produce ATP (adenosine triphosphate), carbon dioxide, and water as metabolic byproducts, which occurs in all living organisms.