Final answer:
Photosynthetic organisms living deep underwater primarily use the pigment phycocyanin to absorb light effectively, as it captures wavelengths that penetrate water well. Other pigments, like chlorophylls and carotenoids, have distinct absorbance spectra but are not as effective for deep-water organisms. Option C is the correct answer.
Step-by-step explanation:
Photosynthetic organisms that live deep in the water must utilize light efficiently, as the intensity and quality of light decrease with depth. The pigment that photosynthetic organisms deep underwater will primarily absorb is phycocyanin (c), which is effective at capturing light in these less illuminated environments. The absorption spectrum for different pigments varies and is critical for the survival of organisms in various light conditions. For example, Chlorophyll a and Chlorophyll b absorb primarily in the blue and red wavelengths, reflecting green, which is why most leaves appear green. However, organisms in deeper water benefit from pigments like phycocyanin, which absorb different wavelengths that penetrate water effectively.
Pigments such as carotenoids and Chlorophyll c are also found in photosynthetic organisms, each with unique absorption characteristics. Carotenoids can absorb blue light and reflect longer wavelengths such as yellow, red, and orange, helping plants absorb light in a range of conditions. Chlorophyll c, similar to chlorophylls a and b, assists in light absorption, but it is not as commonly found as chlorophyll a and b, which are present in higher plant chloroplasts. Each of these pigments — chlorophylls, carotenoids, phycocyanins — are tailored to optimizing the capture of light energy under different environmental conditions.
Therefore, when considering the pigment that can absorb light used by photosynthetic organisms living deep in water, the correct option is (c) phycocyanin. This pigment allows these organisms to absorb light optimally in a habitat where specific wavelengths are more prevalent due to the filtering effect of water depth.