As teachers, we all have that one topic we hate to teach. For me, it’s photosynthesis and cellular respiration. They learn the basics in middle school: plants need water, carbon dioxide, and sunlight, and in turn they create oxygen and glucose. Eventually glucose gets broken down and turns into energy. End of story.
In college or AP biology, students have to learn the nitty gritty of the light dependent and light independent reactions. The biochemistry can make your eyes glaze over. It has always been a struggle for me to figure out what exactly to cover for the average high school student. What is that “happy medium” I can cover that will give them more than the basic formula, but not so much they get overwhelmed?
I’ve decided that that happy medium looks like this:
Students need to memorize the overall formula for photosynthesis. They should recognize the products for photosynthesis are the reactants for cellular respiration and vice versa.
Students should understand the inputs and outputs of the light dependent and light independent reactions, but don’t need to understand all the biochemical reactions.
Students should be able to apply photosynthesis concepts to real world situations. Why do stomata open at night? Why do leaves drop in the fall/winter? Why do plants lean towards the sunlight? Where does the mass of the tree come from? (Notice now none of these questions involve students explaining what NADPH is or how photosystems work?)
Here is a round-up of what I consider “happy-medium” photosynthesis lessons.
1. You’ve probably seen this spinach disc lab floating around the internet. It is fun and produces good data… when students set it up correctly. You can find a summary of the lab with pictures here.
It can be difficult for them to get all the spinach discs to sink in the syringe. Sometimes after students finally get them to sink, they get terrible data (and often times the discs won’t rise at all). Tip: I tell students if they don’t get the discs to sink after 3 tries, dump them and start over with new discs.
2. If you have access to some aquatic plants and bromothymol blue, this carbon cycle lab is fun with easy set-up. Students place some aquatic plants (elodea works great, but any aquatic plant will work) in test tubes and fill with water and bromothymol blue, which is a pH indicator. Placed in the light, the plants will produce oxygen and students will see the color change from green to blue in one test tube. If the test tubes are wrapped in tin foil to block any light, the plants will only do respiration and the color will change from blue to green in one vial. If you’d like to read more about how I set up this lab, head to this blog post.
3. Similar to the lab above- algae beads are a great option. As you place the algae beads with a pH indicator under a light source, students will see a color change as carbon dioxide is converted to oxygen. While you can make your own, it is easier to just order them. The kit pictured is from Wards.
5. This interactive diagram has clickable slides for both photosynthesis and cellular respiration. Students can click on each step and learn about what occurs, as well as watch video clips and try out some interactive websites. Also included is a google form self-grading quiz students can take following the activity. You can find it on my website or on TpT.
6. This station activity was created with the intent to give students an opportunity tounderstand and apply big picture photosynthesis concepts, not memorize biochemistry steps. Stations include things like observing stomata under the microscope, learning about why leaves change color in the fall, and learning about some animals that are able to photosynthesize. High interest and low prep! You can find it on my website or on TpT here.
7. Here is a virtual (non-flash!) lab that students can complete. They are able to change the light intensity, light distance, and light color to see the impact on the rate of photosynthesis.
8. Chlorophyll absorbs red and blue wavelengths really well, and does no absorb green (which is why it appears green). In this “bloody chlorophyll” demo, students can see how chlorophyll appears red under a black light. Check out a video here, and an explanation of how it works here.
9. Want to try some fall leaf chromatography? Here is a site that includes lab directions.
11. This photosynthesis modeling activity from Cal Academy uses ping pong balls and egg cartons. While it takes a while to set up, it helps students visualize how molecules move through the processes of photosynthesis (and respiration).
12. If you want something students can glue into an interactive notebook, you might be interested in this photosynthesis flip book. Students cut out the 6 flaps, staple them together, and identify the major components of the light dependent and light independent reactions. You can find it on my website or on TpT.
I hope one (or two!) of those activities help you with this tough topic!
Looking for cellular respiration resources? Head to this blog post.