An undulating blanket of green grass provides one of the sensory pleasures of summer. Meadows, lawns, ball fields and public parks all become vibrantly green with the arrival of spring. While many people associate green grass with life and vitality, many do not know that this, in fact, has a basis in science and that, without grass and related plants, there would be no life as we know it on Earth.
Grass belongs to the plant kingdom, a classification of living organisms defined by genetic similarity, the presence of a cell wall and the ability to convert energy from the sun into sugars that can be used as food by the plant. The latter is of particular importance when understanding why plants, including grass, are almost always predominantly green in color.
"The most important characteristic of plants is their ability to photosynthesize, in effect, to make their own food by converting light energy into chemical energy," writes researcher Michael W. Davidson of Florida State University. This vital activity is carried out inside of small cellular structures called chloroplasts that contain the green pigment chlorophyll. Chloroplasts are so dense in the leaves of plants--and blades of grass are leaves--that a half-million may be found in an area not much larger than a period on a page.
When light strikes the chloroplast, it excites atomic particles inside of the structure and sets off a chemical reaction called photosynthesis. The energy absorbed from light rearranges molecules of carbon dioxide and water to produce glucose, a high-energy sugar that plants burn as food. Grass contains not only billions of chloroplasts but tiny pores called stomata that absorb carbon dioxide. The water needed for photosynthesis is drawn up from the grass's roots.
Chloroplasts are excellent at absorbing light, and their green coloration demonstrates that. Chloroplasts absorb all wavelengths of light except for green. Because they do not absorb green, it reflects from the chloroplasts and makes the grass appear green. Grass is never blue or red because the chloroplasts absorb those colors of light and use them to power photosynthesis.
If the green color of grass signifies energy production, then the green color of grass is also vital for the survival of the plant. However, photosynthesis in green plants extends in importance beyond individual survival. Grass is the basis of many food webs, feeding organisms that, in turn, feed other organisms. Outside of the plant kingdom, organisms are unable to use the sun's energy to produce their own food and must obtain chemical energy from other sources. Without plants like grass, life on Earth would not exist.