• Question: Why is the grass green?

    Asked by bread4875 to Enda, Jean, Kate, Kev, Tim on 15 Nov 2012.
    • Photo: Jean Bourke

      Jean Bourke answered on 15 Nov 2012:


      The green compound in grass (and other plants) is called chlorophyll. Chlorophyll is a little thing inside plant cell and it absorbs energy from sunlight trapping it with carbon dioxide and water to make glucose. When the glucose is broken down it results in carbon dioxide, water and energy. The plant uses this at night when it can’t get energy from sunlight and we eat it to give us energy to live.

      Chlorophyll appears green because it reflects green light. Light is a wave and its frequency determines the colour and how energetic it is (solar power). Chlorophyll absorbs other colours of light (mainly purple, blue, red and a bit of yellow) as a result the green light is reflected back at us and we see the plant as green.

    • Photo: Enda O'Connell

      Enda O'Connell answered on 16 Nov 2012:


      @bread4875

      A follow on question might be “but why is chlorophyll green and not black?” because if plants were coloured black instead of green, they would absorb even more light, including green light, which would give them even more energy from the sun.

      Scientists aren’t really sure why chlorophyll has evolved to reflect and waste green light but it is thought to have evolved early in algae, who are thought to be a common ancestor of modern day plants. By now it is probably too difficult for plants to evolve a new black pigment, after doing so well at colonising almost the entire planet using chlorophyll. Looking around at all of the grass and trees and plants everywhere, I for one am pretty happy that they’re green instead of making some kind of black world that Tim Burton might imagine.

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