Final answer:
Chlorophyll a is a pigment molecule common to all photosynthetic organisms that absorbs blue and red light and reflects green light, which is why plants appear green.
Step-by-step explanation:
One pigment molecule common to all photosynthetic organisms, including the five mentioned organisms, is chlorophyll a. This molecule plays a crucial role in the process of photosynthesis by absorbing specific wavelengths of light. Pigments have an absorption spectrum, which indicates the specific pattern of wavelengths they absorb and reflect. Chlorophyll a is particularly good at absorbing light from the blue and red parts of the spectrum, while it reflects green light, which is why it appears green to the human eye. By reflecting the green wavelengths, chlorophyll a and other photosynthetic pigments give plants their characteristic colors. This action of absorbing and reflecting light enables plants to capture solar energy for photosynthesis.