Grass is green because it contains a chemical called chlorophyll. Chlorophyll allows the plant to absorb energy from sunlight but not all of the energy. Because sunlight is actually composed of many colors, plants absorb energy from most all of the other colors except green and a few others--but mostly green. Where does the energy from the green in sunlight go? It gets absorbed too by the chlorophyll but then the chlorophyll re-emitts it out towards your eyes as green light and a few other rejected colors. This mixture of colors is why many plants are different shades of green.

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?

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.
Now that 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).

Why do 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).