page_title: Chlorophyll
section_title: Why green and not black?
hierarchical_section_title: Chlorophyll / Chlorophyll and photosynthesis / Why green and not black?
caption_attribution_description: The ornamental chili, Capsicum annuum cv. 'Black Pearl', from the Michigan State University Experimental Garden.
context_page_description: Chlorophyll is a chemical in the chloroplasts of plants. It allows plants to absorb and use light. Energy from the light is used in photosynthesis to make glucose. This contains lots of stored energy which the plant needs to release. It does this through respiration. This energy is then used when the plant grows or repairs damage. Chlorophyll also makes the stem and leaf of the plant green.
  Chlorophyll is a green pigment in almost all plants, algae, and cyanobacteria. It absorbs light most strongly in the blue portion of the electromagnetic spectrum, followed by the red portion. However, it is a poor absorber of green and near-green portions of the spectrum. Chlorophyll was first isolated in 1817.
context_section_description: It still is unclear exactly why plants have mostly evolved to be green. Green plants reflect mostly green and near-green light rather than absorbing it. Other parts of the system of photosynthesis still allow green plants to use the green light spectrum (e.g. through a light-trapping leaf structure, carotenoids, etc.). Green plants do not use a large part of the visible spectrum as efficiently as possible. A black plant can absorb more radiation, and this could be very useful, notwitstandanding the problems of disposing of this extra heat (e.g. some plants must close their openings, called stoma, on hot days to avoid losing too much water). More precisely, the question becomes why the only light absorbing molecule used for power in plants is green and not simply black.
  The biologist John Berman has said that evolution is not an engineering process, so it often has limits that an engineer or other designer does not. Even if black leaves were better, evolution's limitations can prevent species from becoming as efficient as possible. Berman wrote that achieving pigments that work better than chlorophyll could be very difficult. In fact, all higher plants (embryophytes) are believed to have evolved from a common ancestor that is a sort of green algae – so chlorophyll has evolved only once (common ancestor).
  Shil DasSarma, a microbial geneticist at the University of Maryland, has pointed out that species of archaea use another light-absorbing molecule, retinal, to get power from the green spectrum. Some scientists believe that green-light-absorbing archae were once the most common in the earth environment. This could have left open a "niche" for green organisms which would absorb the other wavelengths of sunlight. This is just a possibility, and Berman wrote that scientists are still not convinced of any one explanation.
caption: Black plants can absorb more radiation, and yet most plants are green
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