Kaplan Nursing Entrance Practice Exam

Which two wavelengths of light are ideal for photosynthesis?

1. 480 nm, 650 nm

2. 420 nm, 660 nm

3. 400 nm, 700 nm

4. 500 nm, 750 nm

The correct answer is: 420 nm, 660 nm

The choice of 420 nm and 660 nm as ideal wavelengths for photosynthesis is based on the light absorption characteristics of chlorophyll, the primary pigment involved in the photosynthetic process. Chlorophyll a, which plays a significant role in photosynthesis, absorbs light most efficiently at these wavelengths. At approximately 420 nm (in the blue region of the spectrum), chlorophyll absorbs light energy that is essential for initiating the photochemical reactions of photosynthesis. Similarly, around 660 nm (in the red region), chlorophyll also absorbs light effectively, allowing the plant to convert this energy into chemical energy. This absorption of light in the blue and red parts of the spectrum is crucial for maximizing the energy capture that sustains the process of photosynthesis, enabling plants to synthesize glucose and oxygen from carbon dioxide and water. While other wavelengths are present in the options, they do not correspond as closely to the peaks of chlorophyll absorption, making them less effective for driving the photosynthetic machinery of plants. Therefore, focusing on the specific wavelengths of 420 nm and 660 nm provides a clear understanding of how plants optimize their light absorption for photosynthesis.