Question

Photoautotrophs form the base of food webs on both land and in the sea. Ultraviolet and red wavelengths do not penetrate water as deeply as green and blue wavelengths do. Natural selection favored the evolution of different pigments at different water depths. Red algae lives deep in the sea. Green algae live in shallow water, their chlorophyll absorbs red wavelengths of light, some of their accessory pigments shield against ultraviolet radiation. (1) Why/how did natural selection favor the evolution of different pigments at different depths? (2) Why is red algae located at a deeper depth than green algae? (3) Lastly, explain the relationship between pigments, color perceived, and color of light absorbed.  

Answer 1

Ans 1-  Ultraviolet and red wavelengths do not penetrate water as deeply as green and blue wavelengths do. Natural selection favored the evolution of pigment which will absorb green and blue wavelength.

Ans 2- red algae has phycoerythrin pigment, which absorb green and blue light, thus it can live under deep water.

Ans 3- different pigments absorb different light, and light which they reflect is visible to us. For example phycoerythrin is a red colour pigment, because it reflects red light and absorbs blue and green light.