Why is the grass green

The leaves of plants, trees and other fauna exhibit many colours, often changing with the seasons, but by far the most common colour seen in healthy vegetation, particularly grass, is green. The green appearance of grass, and many other higher plant forms, is due to a natural pigment known as chlorophyll. Chlorophyll plays a vital role in the growth and development of all plant life as it is pivotal in the process of photosynthesis. Photosynthesis is the fundamental process through which green plants (and some other organisms) capture incident light and use it to convert water, mineral and carbon dioxide in to organic and energy-rich compounds. Photosynthesis is fundamental to the existence of life on Earth and it is thought that chlorophyll, or a chemical compound very similar, was instrumental in the first steps in the evolution of self-sustaining life.

Photosynthesis is broken in to stages: light absorption, oxygen formation, and the reduction of carbon dioxide to form glucose and other nutrients. In higher plants, chlorophyll binds to proteins and the lipids aschloroplastin in definite and specific modes forming chloroplasts. Chloroplasts are often considered the photosynthetic building blocks of plants. When examined under an electron microscope, chloroplasts exhibit a series of internal membranes called lamellae. Individual lamella, which house the photosynthetic pigment, are typically 12 to 15 nanometres thick and exist in layered flat sheets of varying sizes. As the composition of chloroplasts alters over time, the hue of the grass reflects this change. Lamella comprise approximately equal portions of proteins and lipids. About a quarter of the lipids part of lamellae are pigment bearing. About 20% of the lipids within the lamellae are chlorophyll molecules. The cholorophyll molecules are bound to small proteins and most of these chloropyll-protein combinations are pigments used to capture light.

Other coloration in higher plants forms can result from several other similar pigments that bind to form chloroplasts. Chlorophyll A is responsible for the common green or blue-green coloration seen in many plants. Chlorophyll B is the second most common pigment and leads to yellow-green coloration. Xantophyll is the third most popular pigment and exhibits a yellow colour. While Carotene is the pigment responsible for orange colouring seen in some plants, carrots are a prime example.
Other rarer forms of chlorophyll have been found to exist in special vegetation or environments. Chlorophyll C and chlorophyll D have been found, along with chlorophyll A, in algae. Chlorophyll E is even rarer and found in some golden algae. While bacterio-chlorophyll occurs in some bacteria. Chemically, chlorophyll is very similar to another compound fundamental to life: haemoglobin.

Although chlorophyll is the principal light-absorbing molecule in green plants and grass, other pigments such as carotene and carotenoids may supplement chlorophyll in this action. Chlorophyll is also instrumental in the formation of fossil fuels, such as oil, gas and coal. Although the question ‘why grass is green?’ seems very simple, it is clear that the answer to this basic question sheds light on the fundamental processes of all life on earth.