24/04/2017 · Photosynthesis in the dark

Depending on a main sequence star's spectral type, even a planet with 's atmospheric composition may be colored differently. In general, larger and more massive, main-sequence ("dwarf") stars have hotter surface temperatures than our Sun, , and so they radiate more photons, particularly towards the more energetic, bluish end of the spectrum. As a result of their greater luminosity, Earth-like planets would orbit farther away from hotter dwarf stars to avoid getting scorched, but their skies would still appear bluish due to of abundant bluish photons. Around smaller, less massive and dimmer dwarf stars, however, planets would have to orbit closer in order to sustain a surface temperature that is warm enough to keep water liquid and so the star would appear larger in the sky. In addition, stars with surface temperatures of 3,300 kelvins or lower (red dwarfs of spectral type M2.5 such as , or redder) would emit so fewer photons towards the bluish wavelengths compared to Sol that the sky would appear whitish down to reddish to Human eyes (more from ). If comparatively more bluish or reddish light reaches a planet's surface than on Earth, photosynthetic plant-type life may may not be greenish in color, because such life will have evolved to different pigments in order to optimize their use of available and so color the appearance of the planet's land surfaces accordingly.

Explain how two other environmental factors may affect the rate of photosynthesis of plants

Autumnal to bluish colors. Main sequence stars brighter than the Sun (spectral types F and A and the very short-lived B and O) emit more blue and ultraviolet light than the Sun. Given sufficient time for Earth-type photosynthetic life to evolve (e.g., hundreds of millions to billions of years), planets around such stars could develop an oxygen atmosphere with a layer of ozone that blocks more energetic but potentially harmful ultraviolet but transmits more blue light to the ground than on the Earth. In response, life could evolve a type of photosynthesis that strongly absorbs blue light, and probably green as well. In contrast, yellow, orange, and red wavelengths of light would likely be reflected by such plants, so the foliage would have the bright colors found during autumn in Earth's deciduous forests all year round. On the other hand, some plants may reflect some blue light due to its overabundance and potential to "burn" photosynthetic organisms (e.g., like sunburn from ultraviolet exposure on Earth).


The Process of Photosynthesis in Plants: An Overview

Darker schemes. A main sequence star that is dimmer and redder than the Sun (spectral type K and M -- red dwarfs) could have plants that absorb more red and infrared wavelengths. Red dwarf stars, which only have some 10 to 50 percent of the Sun's mass but comprise perhaps 85 percent our Milky Way galaxy's stars, radiate most strongly at invisible infrared wavelengths and produce little blue light. By absorbing the entire spectrum of visible light more completely, such plants might look black but any color might be possible. Whatever their color, however, such plants would likely look dark to humans because little visible light would reaches the ground.