Homeschool Science: How to Make a Molecular Model of Photosynthesis

The kids and I are using CK-12's 9th/10th grade Biology textbook as the spine for this year's biology curriculum--for Will, who is in the eighth grade but who is taking high school-level coursework, this will be recorded as Honors Biology on her transcript.

In addition to that textbook, we're using The Illustrated Guide to Home Biology Experiments as our lab manual, and of course we've got a plethora of other reading/viewing/listening resources and hands-on activities to enrich our study.

We're progressing through the book a LOT more slowly than I thought we would, but that's okay, as biology is in both of the kids' areas of interest, so we might as well be thorough and enjoy ourselves, and unlike AP European History, which Will and I are also enjoying, there's no deadline for finishing, so I'll be happy simply to have us finish by next September, when Will will begin 9th grade coursework.

All that is to explain why after almost two months of study we're only in chapter 4, lol! And we've taken nearly a month to get through chapter 4, as some of the labs that I wanted the kids to do called for special supplies that I had to order. But finally we've got our elodea cuttings, our bromothymol blue, our hydrochloric acid, our test tube stoppers, and our heat lamp bulb, and so so our study of photosynthesis and cellular respiration is finally almost complete.

This molecular modeling of the process of photosynthesis is a hands-on enrichment activity that I had the kids complete after reading the chapter, but before we did our first experiment on actual plants. Modeling the process helps your kid see that it really is just a math formula, not magic: carbon dioxide plus water plus light energy equals glucose and oxygen.

Oh, who am I kidding? Science IS just another name for magic!

Got some molecular modeling tools? You can make the magic happen yourself!

To model photosynthesis, you'll need your favorite molecular modeling kit, or a DIY version. We have Zometools, and last year I bought the Molecular Mania set when we were doing a brief chemistry study. I like the Zometools set because it includes color-coded buckyballs and molecule building cards, but since we have the larger set, too, when I needed more of a particular element all I had to do was lightly spray paint one of our regular white buckyballs and there you go! Paint a ball red and it still works with the regular kit, but now it also represents oxygen!

Here is the chemical formula of photosynthesis:

6CO₂ + 6H₂O + sunlight ------> C₆H₁₂O₆ + 6O₂


To model photosynthesis, then, each kid needs to build six carbon dioxide molecules and six water molecules:

In Zometools, carbon is black, oxygen is red, and hydrogen is white. I told the kids not to worry about single or double bonds, since I just wanted them to witness the conservation of matter throughout the process itself.

We used our imagination to add sunlight, and then the kids then had to figure out how to use what they already had to build glucose: C₆H₁₂O_6:

This is Syd's version of glucose:

I didn't ask them to put it together the "right" way, because I didn't want them to have to research an answer. Just getting all of the correct elements collected into a glucose molecule was enough for me.

Nevertheless, look what Will came up with, all on her own!


Well, the dog may have been giving her tips...



But check out the symmetry of her glucose molecule!

It's really not that far off!

As you could see in the lower half of Will's photo above, when you've finished reassembling the water and carbon dioxide molecules into glucose, you'll have some oxygen atoms left over. This is the waste product, but oxygen doesn't like to be a single atom--it likes to have an oxygen buddy, so give all of your oxygen atoms an oxygen buddy:

And you'll have a perfectly even number!

It's ready to be exhaled, so that humans can inhale it and exhale carbon dioxide, which is what plants inhale so that they can exhale 02, so that humans can inhale it.

P.S. If you don't want to buy a molecular modeling kit, that's cool. I've actually collected links for some nice-looking DIY molecular modeling sets, so here they are:

• I haaaaate the idea of Styrofoam balls, but it would be cheap!
• Gumdrops and marshmallows could work--you'd just need to color code the elements.
• You've probably already got what you need for this LEGO version.
• This biochemistry teacher uses pipe cleaners, beads, and paper clips.