Advanced Placement (AP) Biology Practice Exam

What role do plant pigments play in photosynthesis?

1. They reflect all wavelengths of light

2. They absorb water and nutrients

3. They absorb some wavelengths and reflect others

4. They inhibit chlorophyll production

The correct answer is: They absorb some wavelengths and reflect others

Plant pigments are essential for photosynthesis because they selectively absorb specific wavelengths of light while reflecting others. Chlorophyll, the most well-known pigment, primarily absorbs blue and red light, which is vital for driving the photosynthetic process. The absorbed light energy is then converted into chemical energy during the process, while the reflected wavelengths contribute to the green coloration of plants. This selective absorption is critical because different pigments can capture various wavelengths of light, allowing plants to utilize a broader spectrum of sunlight for photosynthesis than they would be able to with chlorophyll alone. Some pigments, such as carotenoids, absorb light in the blue and green parts of the spectrum and reflect yellow, orange, or red light, thus complementing the light absorption of chlorophyll. In contrast, reflecting all wavelengths of light would render the plant incapable of harnessing light energy effectively for photosynthesis. Absorbing water and nutrients is a function of root systems, not pigments, while inhibiting chlorophyll production would detract from the plant's ability to perform photosynthesis. Therefore, the role of plant pigments in selectively absorbing certain wavelengths of light and reflecting others is integral to optimizing the photosynthetic efficiency of plants.