Quick note: today is the last day to enter our giveaway of the Charley Harper poster. Just post your bird tallies in comments by midnight Eastern time (U.S.) and we will spot them. The winner will be announced tomorrow, February 25.
We’re (finally!) starting to see a bit of activity in our microbe biosphere. At the very top of the mud there’s a new, thin black layer. The water is now brown and cloudy, and sitting on top of the water is a thin shiny film.
Anne's family also has a biosphere that is really perking along. Here's a photo she took almost 10 days ago--lots of things growing in there!
Let’s turn to our ingredient of the week, light, which works with water in a special way (beyond what we discussed in Week 1) to make food for some microbes.
Ingredient of the Week: Light
You’ll recall that our final step in creating microbe biospheres was to place our jars in indirect sunlight. Grownups can guess why: some microbes (though not all), act just like plants by using sunlight and water to change carbon dioxide from the air into food for the plant.
You can show a young child how plants rely on the sun by taking two small green plants. Put one in a dark closet, the other on a window sill. Water them both as the plants need it. Which plant survives—and thrives?
So we know plants need the sun. But what is sunlight, anyway? When the sun shines, it’s sending us light in super tiny pieces we call photons. The photons our eyes see as rays are the same photons that plants—and some microbes--use as energy to make food.
You might think microbes that use sunlight to make food are tiny plants. In fact, scientists have carefully studied these microbes and found them to be very different from plants in almost ever other way. Microbes that use sunlight to make food are living creatures, but they belong to their own family (or scientific group) that is separate from plants and animals.*
Still, we can learn a lot about how microbes use sunlight by studying plants. You’ll notice that most plants are green—it comes from a substance we call chlorophyll. Plants use chlorophyll in their leaves to stop photons and capture them. The photons’ energy is then used to make food. Microbes, like plants, use chlorophyll to capture light, too.
How does the chlorophyll in plants catch the photons in sunlight? The photons travel from the sun with different amounts of energy. In a stream of sunlight, the photons are travelling all together and we see the color of the light as almost white. But if the photons are separated by their energy levels, either by drops of water in the sky or with a glass prism, we can see that light is a rainbow of photons.
Back to green plants. As confusing as it seems, a green plant isn’t really green. Instead, photons at “green speed” are bouncing off the plant and back to our eyes, so we see the plant as green. But light is made of lots of several different colors—so what’s happening to the other colors of photons from the rainbow? Most of them are staying inside the plant, captured by the chlorophyll which stopped them in their tracks.
Microbes that use sunlight to make food do the exact same thing. Their color (“pigment”) stops the bits of light we call photons so their energy stays inside the microbe.** The microbe then uses the photon energy, together with air (carbon dioxide), as well as water, to mix the carbon and water into sugars called carbohydrates. (We talked about carbon in Week 2.)
Eventually, we may see large groups of these microbes in our jars. Even as we speak, microbes are using sunlight to help make sugars. These sugars will give the microbes energy to make more microbes until their families are big enough for us to see.
* There are microscopic plants called algae. Microbes that mimic algae in some ways (by living in water and using light to grow food) were once thought to be algae, but DNA studies show that they are not very similar to each other otherwise.
** Microbes that use chlorophyll to catch light usually aren’t green. Their colors range from black, to blue-black and blue-green, even orange and purple. The green chlorophyll is still in there, but other substances keep us from seeing the familiar green we see in plants.