Three-dimensional Learning Progression This lesson provides students with experiences to observe and to collect data which will support them in their next lesson when they construct their explanations about photosynthesis and cellular respiration. They will observe that plants “breathe” (i.e., exchange gases with air) differently in the light and in the dark. This lesson includes two PEO (Predict-Explain-Observe) Inquiry Activity Sequences with the final E (Explain) occurring in the next two lessons. We will consistently focus on the idea that understanding carbon-transforming processes involves answering the Three Questions: The Matter Movement Question: Where are molecules moving? (How do molecules move to the location of the chemical change? How do molecules move away from the location of chemical change?) The Matter Change Question: How are atoms in molecules being rearranged into different molecules? (What molecules are carbon atoms in before and after the chemical change? What other molecules are involved?) The Energy Change Question: What is happening to energy? (What forms of energy are involved? What energy transformations take place during the chemical change?) The investigations in all units will make use of two essential tools: Digital balances. Students can detect movement of atoms (the Matter Movement Question) by measuring differences in mass. This Activity will ask students to harvest their plants to prepare for future dry massing. Bromothymol blue (BTB). This is a liquid indicator that changes from blue to yellow in response to high levels of CO2. Thus, changes in BTB can partially answer the Matter Change Question by detecting whether there is a chemical change that has CO2 as a reactant or product. Key Ideas and Practices for Each Activity Activity 3.1 is the Predictions and Planning Phase of the instructional model (beginning the climb up the triangle). During this phase, students record their predictions and express ideas about what happens to plants when they are in the light and the dark as well as where a plant’s mass comes from as it grows. They use the Predictions and Planning Tool to do this. Activity 3.2 will set up the Observations Phase of the instructional model for Activity 3.4. During this activity, the students will harvest their radish plants. If you are following the 2-turtle Gel Protocol, students will collect wet mass in 3.2 and set up to collect dry mass later in Activity 3.4. If you are following the 1-turtle Paper Towel Protocol, students will collect dry mass only in Activity 3.2. There are again two protocol pathways centered around the growing plants investigation for Lesson 3. These correspond to the 2-turtle (Gel Protocol) and 1-turtle (Paper Towel Protocol) that you chose in the Pre-Lesson. You will need to follow the same pathway you chose initially in order to remain consistent with the data collected from the beginning of the unit with the data students will collect here. See the Student Challenges and Teacher Choices in the Plants Unit document as a reminder. Activity 3.3 is the first part of the Observations Phase of the instructional model (going up the triangle). During this phase, the students conduct the investigation for plants in the light and in the dark, record data, and try to identify patterns in their data and observations. The important practices students focus on in this activity are 1) making measurements and observations, 2) recording their data and evidence, and 3) reaching consensus about patterns in results. They use the Observations Worksheet and Class Results Poster to do this. Activity 3.4 is the second part of the Observations Phase of the instructional model (going up the triangle). During this phase, the students conduct the investigation for plants growing by harvesting and drying their plants. The important practices students focus on in this activity are 1) making measurements and observation, 2) recording their data and evidence, and 3) reaching consensus about patterns in results. They use the Observations Worksheet and Class Results Poster to do this. Activity 3.5 is the Evidence-Based Arguments Phase of the instructional model (going up the triangle). During this phase, the students review the data and observations from their investigations of plants and develop arguments for what happened during the investigations. In this phase, they also identify unanswered questions: at this point they have collected data and observations about macroscopic scale changes (BTB color changes, mass changes), but they do not have an argument for what is happening at the atomic-molecular scale. They use the Evidence-Based Arguments Tool to record their arguments at this phase. Plants are composed of materials that they get from air and soil minerals. Given the range of experiences young children may have with plants, it is interesting that most develop the same story about plant growth—that small seeds are planted in soil and, given water, grow into mature plants over the course of weeks and months. Sunlight is also necessary for plants to grow. It is no wonder that most students believe most plant mass comes from soil and water since these are the visible inputs they see given to plants. Students are not completely wrong about soil and water. Much of a plant’s total wet mass is actually water. This water contributes to short-term mass gain, but most water does not contribute to long-term building of the large organic molecules that are plant dry mass. The dry mass is carbon-based substances. This carbon does not come from soil or water, but rather from carbon dioxide taken in from the air. Scientists have traced specific carbon atoms (Carbon-14) from glucose back to CO2. Scientists have also shown that most oxygen in glucose comes originally from CO2. The O2 plants give off comes mostly from water. Water does contribute some to biomass, through hydrogen atoms, which comprises a very small percentage of plant mass, but most of the atoms from water eventually leave the plant. Soil minerals—like nitrogen from ammonia—add to plant biomass (about 2% of dry mass) when incorporated into proteins inside the plant. Air—CO2 in air contributes carbon (45% of dry mass) and oxygen (45% of dry mass) Soil Minerals—can potentially contribute nitrogen, phosphorous, calcium, magnesium, etc. (totaling about 4% of dry mass) Water—hydrogen atoms from water are about 6% of the plant’s dry mass. There are two pathways from which to choose when teaching this lesson, depending on which turtle trail you chose in the Pre-Lesson, as well as whether or not your students’ plants seem ready at this point. See the Plants Unit Front Matter and the Student Challenges and Teacher Choices in the Plants Unit for more details. A note on mass and weight: Grams and kilograms in the SI (metric) system are units of mass—the amount of matter in a system. On the other hand, pounds and ounces in the English system are units of weight—the force of gravity on a particular mass. As long as gravity doesn’t change, these units are interconvertible: The force of gravity on a 1 kg mass is about 2.205 pounds. Since most American students are more familiar with the English units of weight, we sometimes use “weigh” and “weight,” especially when encouraging students to express their own ideas. When referring to measurements in grams, we use “mass” as both a verb and a noun. Key Carbon-Transforming Processes: Photosynthesis and Cellular Respiration Content Boundaries and Extensions
