What happens to what we eat Part II ? This slide marks the start of the second PP presentation focused on cellular respiration. In this section of the presentation, the specific chemical reactions of cellular respiration are introduced with an emphasis on what chemical reactions are. Specifically, this section of the presentation focuses on the following essential ideas: In the presence of oxygen glucose molecules are broken apart in the mitochondria, resulting in water, carbon dioxide. During this chemical reaction, energy is released. Some cells can break down glucose without oxygen. This is called anaerobic respiration. Many bacteria, such as those in our intestines, carry out anaerobic respiration. Muscle cells can carry out anaerobic respiration for a short amount of time, which results in lactic acid. In yeast anaerobic respiration is called fermentation and releases alcohol. The atoms that make up molecules can react with one another, coming together, breaking apart or rearranging. During some chemical reactions, energy is released.

What we covered yesterday: What happens to what we eat? Where does our food go after we swallow it and what happens to it along the way? What organs and molecules are essential to the journey? This warm up slide helps prompts students to recall information from the first part of the presentation. The emphasis is not so much on the particular organs, but helping student review the role of enzymes and remember that the food molecules travel in the bloodstream, then into individual cells and finally to the mitochondria. Student-centered presentations include slides that review previous ideas.

Enzymes in mitochondria break down glucose molecules into ATP This slide reminds students of the last leg of the journey that was discussed in the first presentation. Again, the big ideas to emphasize are: the mitochondria, like other organelles, are really just a membrane bound “rooms” where the molecules, mainly enzymes, critical to a particular function are “housed.” In the case of the mitochondria, these enzymes are important to breaking down food to get energy and many are embedded in the membranes.

How does glucose get turned into CO2? The image in this slide in intended to emphasizes that it is the Carbon atoms that are significant in cellular respiration as the carbon bonds are where the energy is. While this slide shows glucose being broken down, which is the preferred energy molecules, both amino acids and fatty acids contain carbon and can be broken down to release energy for the cell. Glucose + O2  H2O + CO2+ Energy

In the mitochondria, the food molecules are broken down by a chemical reaction This slide introduces the key terms and includes an image that is authentic to how the larger food molecules are broken down into the smaller molecules of H20 and CO2. called cellular respiration

Let’s observe a chemical reaction This slide introduces a quick demostration of a chemical reaction between baking soda and vinegar. You can see a video at https://www.youtube.com/watch?v=bP7xgV07glc Place a couple tablespoons of baking soda in a balloon and a half cup of vinegar in a flask or plastic soda bottle. Then dump the baking soda into the vinegar. The balloons will instantly fill with air when the baking soda reacts with the vinegar, which results in H2O and CO2 gas. Ask students what they think is filling the balloon and where the gas comes from. The purpose of using this reaction as a demo is that it shows students how chemical reactions can result in molecules that have very different properties from the starting molecules. Emphasize that the molecules are rearranging, which results in new substances that have very different properties. Specifically, one of the products is a gas that has filled up the balloon. This is very similar to cellular respiration where a gas is made. This correlates well with a yeast respiration demo where you place a balloon over a 2 liter bottle with a sugar solution and yeast. If the water is warm, the balloon will begin to fill within 30 minutes or less. What happened?

In a chemical reaction, the atoms that make up chemicals can: Combine Break apart Rearrange This slide highlights the fact that chemical reactions involve an rearrangement of the subunits of molecules, atoms. To review, ask students if they can think of a reaction like the first one where two things are combined to make a larger molecule (some ideas include when CO2 and H2O are combined to make glucose during photosynthesis, when amino acids are combined during protein synthesis, when nucleotides are strung together to make another strand of DNA during replication, etc. The image shows the different ways atoms can rearrange themselves in chemical reactions. They can: Combine Break apart Rearrange

Think Available To Power (the cell) The energy released from the reactions of cellular respiration is stored in molecules called ATP ATP Rechargeable This slide presents ATP molecules like rechargeable batteries and provides an acronym students might remember The way ATP works(i.e. that ATP  ADP) has been intentionally excluded to reduce complexity and increase understanding ATP : Think Available To Power (the cell)

While most energy is captured and stored as ATP, much is also released as heat This image shows how we emit heat energy since some of the energy released from the breakdown of food molecules is lost as heat. It also shows the flame as heat. Interestingly, the combustion of wood on a match and the combustion of carbohydrates is really the same reaction. The reaction in our cells is just a more slow, controlled release of the energy contained in the carbon-rich molecules. In the case of the flame, the electrons are released very quickly during the reaction and this release of energy results in heat and light. A cool, but dangerous demo is to sprinkle powder non-dairy creamer over a flame. The heat prompts the sugar molecules to rearrange just as they would in the mitochondria and energy is released, which can be seen by a big poof of flame.

So, 48 hours ago, where was the carbon you are currently exhaling? This slide revisits the driving question and reinforces the idea that we are exhaling carbon atoms that used to be a part of food molecules. The second driving question is a challenge question that prompts students to reflect on the fact that the chemical energy all started as solar energy. If students struggle, highlight the fact that energy is needed for some chemical reactions, particularly when molecules are being built. Ask them where the food molecules were originally built. In student-centered presentation, you revisit the driving questions as formative assessments to make sure students are making the appropriate connections.