Halobacterium has a photosynthetic membrane that is colored

Halobacterium has a photosynthetic membrane that is colored purple. Its photosynthetic action spectrum is exactly complementary (opposite to) the action spectrum for green plants. What wavelengths of light do the Halobacterium photosynthetic pigments absorb?

A) red and yellow

B) blue, green, and red

C) green and yellow

D) red and green

E) blue and red

Answer: E

Why?? and why not C??

Solution

Answer:

Halobacterium contains bacteriorhodopsin (integral membrane protein containing retinal) as the photosynthetic pigment instead of chlorophyll or bacteriochlorophyll. Bacteriorhodopsin absorbs most efficiently in the green region of the spectrum (peak being 568 nm) and reflects purple. So, it appears purple. The most correct option is (C) green and yellow.