Ah, good question! Grass, like other plants, are
generally a green color (although plants can have
many colors...the bark on trees, the color of some
leaves in the fall, etc.). This color comes from
within their leaves, and even more specifically,
from within their cells. The cells that makeup the
blades of grass are the food factories for the
whole plant. They absorb light from the sun and
use this energy to produce sugars (food for the
plant, and food for us when we eat them, right?)
using water and carbon dioxide ( a waste product
that we breathe out!) This process is called
PHOTOSYNTHESIS! ( "Photo"= light, and "synthesis"
= to make a product from several different
substances). Plants release waste products from
this process and this waste is oxygen gas ( what
we breathe into our lungs and use to live!). What
does this last statement tell you about the
connection between animals and
Plants are green-colored because
within each of their cells they have pigments
(pigment is a chemical that has a visible
color...our irises in our eyes have pigments, our
skin has pigments (why do people have different
skin colors?), and plants have pigments). These
pigments, called Chlorophylls,are chemicals that
allow the cell to absorb light from the sun (so
they can photosynthesize!). Do you remember what a
rainbow looks like? A rainbow, with all of its
many colors, is really white light that has been
broken down into its many components. When we see
something that is black, it appears black to our
eyes because it is absorbing all the colors of the
rainbow and not reflecting any visible light back
to our eyes. When we see something that is white,
it appears white to our eyes because it is
reflecting all the light back to our eyes
(remember that the sum of all the different colors
of the rainbow appears as white light to us). When
we see the green pigments in the grass leaves
(blades), we see green light reflected back to our
eyes, so that means that the Chlorophyll pigments
are absorbing all the colors of the rainbow (red,
orange, yellow, blue, indigo, and violet) but NOT
GREEN. The color of light that enters our eyes and
allows us to see the grass is green.
you know this, why does an egg look white, a dog's
tongue look pink, and why is the sky blue?
The simplest answer to why plants are green is
that the parts that are green (e.g., leaves and
stems) are reflecting green light. Objects appear
certain colors to us because they reflect those
colors and absorb every other color. For example,
red things reflect red but absorb everything else.
(What colors do you think white objects reflect
and absorb? What about black objects?) Molecules
that absorb colors are usually called pigments. We
have pigments in our skin, as do most animals.
Plants have many different kinds of pigments. The
most common pigment in plants is called
chlorophyll-a, which happens to absorb red light
and reflect green.
Plants need to absorb
light because they use energy from light to
turncarbon dioxide into proteins and
carbohydrates. This is called photosynthesis.
(When we make proteins and carbohydrates, we have
to rebuild them from the digested proteins and
carbohydrates in our food. This is called
anabolism.) Plants also need water for
photosynthesis. Water is made up of two hydrogen
atoms and one oxygen atom. When plants use water
to turn carbon dioxide into proteins and
carbohydrates, water becomes split apart into its
separate hydrogen and oxygen atoms. One molecule
of oxygen gas (which is made of two oxygen atoms)
is generated for every two molecules of water that
are split. The oxygen gas is not needed by the
plant and so it is released into the atmosphere.
The hydrogen atoms are conserved within the plant
and are used to make energy (ATP).
you think many land plants would evolve to absorb
one color of light in particular (in this case,
red)? Not all plants are green. For example, some
of the single-celled plants that float in the
surface waters of the ocean are brown or orange.
Why do you think this is? (As a hint, water
absorbs some colors more than others, so sunlight
actually changes once it enters the ocean).
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