Dr. Universe: What is inside a blade of grass and why is it green? Green is my favorite color. We really like reading your articles in our newspaper. – Luke, 5, Ogden, Utah
I’ve been wondering the same thing lately. Every time I go on walks, I notice new splashes of color. Watching bugs in the grass, I pretend they’re crawling through a jungle. Everything is bright and bursting with green.
When I saw your question, I knew Michael Neff would know the answer. Green is his favorite color, too. (In fact, when we talked over video, he wore a green Hawaiian shirt.) Neff researches plants at Washington State University, and he is especially curious about grasses.
If you chopped a piece of grass and looked at it with your eyes alone, you might not see much. But if you looked at it under a microscope, you’d see tiny structures containing even tinier parts.
All living things—you and grass included—are made of cells. Cells are like little building blocks with different jobs. Every blade of grass is made of millions of them.
Plant cells contain a smaller part called a chloroplast. “Chloroplasts look like fat sausage-shaped balloons,” Neff said.
Chloroplasts have a special job: making food. Grasses can’t search for food like animals can. So instead they make it themselves, taking in sunlight and carbon dioxide.
“Food for a plant is a combination of sunlight and carbon dioxide together,” Neff explained. “And the chloroplast is the factory that turns those two pieces into energy.”
But where does the green color come from? Something else inside the chloroplast is responsible: a special pigment called chlorophyll.
Your eyes see color based on light. Many different colors make up sunlight, and objects either absorb or reflect them. When light gets absorbed, you don’t see its color. But when light reflects off objects, including grass, the color reaches your eyes so that’s what you see. That’s why the sky often looks blue. It’s absorbing all the other colors of light, except blue.
The same thing happens with chlorophyll. “Chlorophyll does a very good job of absorbing all colors of light except for green. When we look at the blade of grass, we’re seeing green light being reflected off the blade of grass,” Neff said.
But maybe you’ve noticed grass isn’t always green. Depending on the time of year and where you live, different grass grows at different speeds. Here in Washington, most grass grows in the cool spring and fall weather.
Spring grass looks especially green because it contains new cells. New cells have tons of chlorophyll, reflecting green light.
In the summer and winter, grass might turn brown or yellow. It’s still alive. It just doesn’t have as much chlorophyll. It isn’t putting as much energy into new growth.
But when spring returns, so do the ingredients for growth—lots of water, light, and carbon dioxide. The grass takes it all in, making new cells full of chlorophyll. The cycle begins again.
Tiny blades sprout. Patches of color creep in. And before you know it, green surrounds you everywhere you look.