National League for Nursing (NLN) Science Practice Exam

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Which of the following wavelengths of visible light is best absorbed by chlorophyll?

300nm
495nm
665nm
550nm

The correct answer is: 665nm

Chlorophyll, the green pigment found in plants, is essential for photosynthesis. It primarily absorbs light in the blue (around 430-450nm) and red regions (around 640-680nm) of the visible spectrum. The option that represents a wavelength best absorbed by chlorophyll is 665nm, which falls within the red spectrum. At this wavelength, chlorophyll a and chlorophyll b are highly effective at capturing light energy, which is then used to convert carbon dioxide and water into glucose and oxygen during photosynthesis. This efficiency at the 665nm wavelength highlights the importance of red light in supporting the energy needs of plants. Other wavelengths listed, such as 300nm, 495nm, and 550nm, do not align as closely with the absorption peaks of chlorophyll. Ultraviolet light (300nm) is generally not absorbed for photosynthesis since it can damage organisms. Meanwhile, 495nm is in the blue-green range, where chlorophyll does absorb light but less efficiently than at the red wavelength. Lastly, 550nm is in the green region, which chlorophyll reflects rather than absorbs, contributing to the green appearance of plants.