What other two topics during the year frighten the students (and sometimes the teacher) more than photosynthesis and cell respiration? These two units really can be daunting. They don’t lend themselves to a lot of fun activities and often the teacher feels stuck listing chemical reactions on a powerpoint, using vocabulary that might as well be in Cantonese. Oxidation-reduction reactions? Phosphofructokinase? RuBisCO? Pyruvate? These words really mean less than nothing to the average 14-18 year old. What are some ways we can make this unit more approachable, more fun, and more useful in promoting the general understanding of how life works?
As a teacher, there are a few things to decide as you approach this unit:
- How much detail do you show them and how much detail do you expect them to remember?
How much detail you go into is up to you, but when teachers only show the bare minimum, I think fewer students understand the processes. If you just show them a mysterious blackbox called “glycolysis”, tell them that glucose and NAD+ go in, and pyruvate and ATP and NADH comes out, students can only memorize this short fact list. Meaningless.
My strategy to help students appreciate these processes and actually UNDERSTAND them instead of memorize a reaction is to show them some details, but only ask questions about the main ideas.
For example, I do show them all the steps of glycolysis, but I really won’t ask them more than the net reaction and a few key facts. I do want them to be able to follow the carbon atoms in a diagram from glucose all the way to carbon dioxide. I do want them to know that energy is needed in the first few steps to “kickstart” the reactions, because this helps them understand thermodynamics and kinetics later when they take chemistry/physics. I do want them to know that every reaction is catalyzed by a unique enzyme, because the enzyme pathway concept is all throughout biology. Will they need to memorize the difference between glyceraldehyde-3-phosphate and dihydroxyacetone phosphate? No way. The key is for them to UNDERSTAND, not to memorize.
- How are you going to teach these units without boring yourself to tears?
I always say that if teaching something is boring to me, it is going to be really boring to my students. If I am having fun, fun is contagious and they will too! There are a bunch of ways to deliver information to students and in my classroom, I find PowerPoint to be the least effective and the most boring, especially in this unit and especially with lower level students.
Here are a few ways I like to help my students learn in these two units:
A. Animations, animations, animations! Animations really do work wonders in helping students understand and really see any process in biology and especially these processes. Here is a brief list of the best photosynthesis and cell respiration animations I have found on the web (These work as of January 15, 2016).
McGraw Hill animation – Complete Photosynthesis Animation: http://www.mhhe.com/biosci/bio_animations/02_MH_Photosynthesis_Web/
Great Light Reactions Animation: http://www.sumanasinc.com/webcontent/animations/content/harvestinglight.html
Another light reactions animation – the intro music is quite eery and students are usually entertained: http://vcell.ndsu.edu/animations/photosynthesis/movie-flash.htm
Cellular Respiration Overview Animation: http://www.sumanasinc.com/webcontent/animations/content/cellularrespiration.html
Citric Acid Cycle: http://vcell.ndsu.edu/animations/citricacid_overview/index.htm
BEST ATP SYNTHASE ANIMATION EVER! <– All caps because it is THAT GOOD!
B. Diagrams! Good diagrams are so important for a multitude of reasons. First, they can contain the information students need to know. Second, by examining diagrams, students learn how to interpret complex diagrams. Interpreting diagrams is a reading skill that is important in many career fields. It’s great if you can get a good diagram for students to keep in their notebooks, one that isn’t too complex yet not too simple. Which leads me to the next topic…
C. Hands-on Activities! I always wished when I was teaching that I had some sort of hands-on activity, some interactive materials for my students to use while they learned about photosynthesis and respiration. So I created some! In these activities, students create their own diagram for each process: Glycolysis, Citric Acid Cycle, Oxidative Phosphorylation, Light Reactions, and Light Independent Reactions (Calvin Cycle).
Each of these activities was designed to allow students to color or cut-and-paste while they read a 2 page reading and answer some questions. The activity leads them through each step and question; the order in which they complete the reading and activity makes each process really more approachable. Here are some unique features of this set:
- They print great in black and white. So often diagrams I have found online are partially colored. When they get printed and copied in grayscale, they look awful sometimes.
- The Calvin Cycle and Krebs Cycle activities were designed using the same format, so that students can compare them after each activity is finished!
- In the Calvin Cycle and Krebs Cycle activities, there are two versions available. One shows just carbons (in black) and one shows carbons and oxygens (in white). This way, you can decide how complicated you want their diagrams to look, depending on the class you are teaching.
- The questions lead students through each step and show them how carbons either increase or decrease, depending on the cycle and stage.
- The Oxidative Phosphorylation and Light Reactions coloring pages are designed to also be compared. Students can see in the light reactions that water gives up electrons to eventually end up on NADPH AND they can see in oxidative phosphorylation that NADH gives up electrons to eventually end up on oxygen (and then water)! Similar complexes in both processes (complex 3 in oxidative phosphorylation and cytochrome b6 complex in light reactions) are drawn similarly. Also, ATP Synthase is shown as the same shape and look in both. Having great diagrams is important, but having diagrams in different units that complement each other and can be compared is terrific!
- In several of the activities, there are additional thinking/advanced questions that teachers can use with their gifted or advanced students. For example, the Light Reactions activity includes an additional Cyclic Electron Flow page that students can color and compare to the standard Non-cyclic Light Reactions page.