• question_answer Which one of the following wavelengths of light is most effective in photosynthesis? A)  Blue                 B)  green C)  Reflection          D)  yellow

[a] Photosynthesis is the ability of plants to absorb the energy of light, and convert it into energy for the plant. To do this, plants have pigment molecules which absorb the energy of light very well. The pigment responsible for most light-harvesting by plants is chlorophyll, a green pigment. The green colour indicates that it is absorbing all the non- green light- the blues $\left( \sim 425-450\,\,nm \right),$ the reds and yellows (600-700 nm). Red and yellow light is longer wavelength, lower energy light, while the blue light is higher energy. In between the two is green light $\left( \sim 500-550\,\,nm \right).$ It seems strange that plants would harvest the lower energy red light instead of the higher energy green light, unless you consider that, like all life, plants first evolved in the ocean. Sea water quickly absorbs the high-energy blue and green light, so that only the lower energy, longer wavelength red light can penetrate into the ocean.