Without the process of aerobic cellular respiration, life as we know it wouldn't exist. Simple microbes, such as anaerobic bacteria survive using the small amount of cellular food they create and subsequently break down. Large, complex, multicellular life (like humans), depend on the products of these microbes and the same cellular processes for their survival. Learning about this process helps students get a better understanding of how living things are interconnected.
Learning about Respiration
After teaching my students about photosynthesis, I go into an overview of respiration. Since my students already know the chemical equation for photosynthesis, I introduce respiration by taking that same equation and "flipping it." Often students have understood respiration as breathing in and out, but they need to understand that autotrophs use photosynthesis to capture energy from the sun and incorporate it into a molecule to be used as food by itself as well as many other organisms. Respiration is the process of a cell breaking that molecule down to release the energy.
Just as plants use energy, water, and carbon dioxide to make sugars and oxygen during photosynthesis, organisms use those sugars and oxygen that they breathe in to produce carbon dioxide, water, and energy during cellular respiration. I also remind students of the carbon cycle and the role that respiration plays in releasing carbon dioxide back into the atmosphere. Students draw diagrams to depict the carbon cycle to demonstrate their understanding of this process.
What is Cellular Energy?
It is important for students to understand the cellular process, and why it is necessary for life to exist. During the cellular process food and oxygen are broken down to release cellular energy. When I tell students about this process I say that cellular energy in the form of ATP is like small change. Just like they would have trouble getting a snack from a vending machine with a hundred dollar bill, digestive cells have to convert complex organic molecules in food into smaller molecules in order to be able to release usable energy more effectively. As I teach students about aerobic respiration, I have them compare the amount of ATP produced during each step. I've found that Internet animations are helpful in giving students a better way to understand this process.
For a hands-on demonstration of cellular respiration, I have students prove that multicellular organisms conduct aerobic respiration; not just simple microbes. First, I have everyone in my class blow into a solution of bromothymol blue to show how the color changes as the increased levels of carbon dioxide turns the solution acidic. I relate that carbon dioxide to the waste products of the respiration going on in their cells.
After that, we set up test tubes with the solution and place Elodea sprigs in half of them. The tubes are then sealed with parafilm or plastic wrap, and half of the tubes go under a light while the other half are carefully sealed in aluminum foil. After 24-hours, I have students compare the plants. The ones that were placed in the light had an energy source and so actually used the carbon dioxide during photosynthesis, while the ones placed in the dark produced carbon dioxide during respiration. This helps clear up the common misconception that plants produce oxygen just for the purpose of allowing animals to use it. What follows are more lessons about cellular respiration.
Cellular Respiration Lesson Plans:
This detailed lesson plan describes how students can work as a class using balloons, tennis balls, and signs to demonstrate the final stage of aerobic respiration.
Students create a visual comparison of photosynthesis and cellular respiration. This lesson plan features pictures of student-generated work.
In this experiment, students explore cellular respiration of a yeast culture. This can be extended into a population growth experiment as well.