Why is grass green?

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Plants contain chlorophyll for harvesting energy from sun-light.

From Wikipedia: Chlorophyll:

Chlorophylls absorb light most strongly in the blue portion of the electromagnetic spectrum as well as the red portion. Conversely, it is a poor absorber of green and near-green portions of the spectrum, which it reflects, producing the green color of chlorophyll-containing tissues. Two types of chlorophyll exist in the photosystems of green plants: chlorophyll a and b.

This can be seen from the absorption spectrum of chlorophyll a and b:

spectrum

So your teacher's statement "grass is only green and no other color" is somewhat over-simplifying. More precisely you can say: grass is a mixture of cyan/green/yellow/orange color (wavelengths from 490 to 610 nm).

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Leila Parry-Smith
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Leila Parry-Smith

Updated on August 01, 2022

Comments

  • Leila Parry-Smith
    Leila Parry-Smith over 1 year

    How come grass isn't blue or pink, but apparently, it is according to this scientist it is every color but green. I also got told by my teacher that grass is only green and no other color. So I am confused, but with an answer please try and be simple.

    • Admin
      Admin over 4 years
      Your link to "this scientist"? also have you checked out chlorophyll ?
    • Farcher
      Farcher over 4 years
      Chlorophyll absorbs all colours and does not remit them except those around the green part of the spectrum.
    • Mitchell Porter
      Mitchell Porter over 4 years
      This is not just about grass being green. It's about what you could call the 'every-color-but' theory of color. Something looks like its color is X? Actually it's every color but X! The argument is that something looks X because it reflects X-colored light, while absorbing Y-colored, Z-colored... But why does absorbing Y- or Z-colored light mean that the object's 'real color' is Y or Z? Is there some physical or color-theoretic deep justification for this way of speaking, or is it just a popular contortion of words that sounds cool because it's paradoxical?
    • Cort Ammon
      Cort Ammon over 4 years
      Go check your "the scientist" again. Did they say it is every color but green, or did they say it absorbs every color but green.
    • BioPhysicist
      BioPhysicist over 4 years
      As always, related xkcd with caption text: If you ask "why are leaves green? the usual answer is "because they're full of chlorophyl, and chlorophyll is green, even though "why does chlorophyll scatter green light?" is a great question too.
    • John Rennie
      John Rennie over 4 years
      I'm voting to close this question as off-topic because it isn't a question about physics
  • Thomas Fritsch
    Thomas Fritsch over 4 years
    Interesting point of view. See Why did chlorophyll evolve to be green as opposed to black?. It gives some more reasons why nature might have decided not to use green light for photosynthesis.