To consider that the important issue is not to calculate the emissions for each car model and engine, but to find a way to represent the vast array of data and how to find representative values for them. To calculate emissions produced by cars and to develop models (tables, graphs and/or formulas). Results obtained here will be taken up again at the end of the project in order to produce the final report, once the amount of CO2 a tree can compensate for has been investigated. Appendix II: experiment using Elodea canadensis– task 3 Photosynthesis is a process in which carbon dioxideand light are combined to generate carbohydrates and oxygen. Normally, special instruments are needed to observe the process and to measure it. Usually, these instruments cannot be found in a school laboratory. However, there are some special cases in which the process is visible and some rough measurements can be made. In this experiment, students will work with a type of aquatic plant: Elodea canadensis. The mainadvantage of this is that, when oxygen is produced, it produced little bubbles that are visible. We can use the amount of oxygen given off by the plant as a measure of how much photosynthesis is taking place. In some versions of this experiment, baking soda is used in order to get a higher concentration of CO2. You can explore this option, but consider that extra bubbles mayappear and they must be removed before the experiment starts. We will suggest other ways of increasing the CO2 concentration in water, such as using exhaled air throughout straws. Students should work in groups and share their observations and conclusions at the end of the experiment. The teacher should promote and manage collaborative classroom discussion and reflections about CO2 consumption. Lab materials Plant Elodea Canadensis,beakers (250 ml), test tubes (30 mm Ø), water, sodium hydrogen carbonate solution (10 % w/v),
This process can be described in a very simplified way as Light + water + carbon dioxide sugar + oxygen Through a non-balanced equation using chemical symbols Light + H2O + CO2 Sugar + O2 Or even the balanced chemical equation 6 CO2 + 6 H2O + photons → C6H12O6 + 6 O2 In any case it is important in this point to be aware about a common misconception students’ develop: the oxygen produced in the photosynthesis comes directly from the CO2 molecule. That is, during the photosynthesis the CO2 molecule is divided into two different parts: the carbon atoms go somewhere and the oxygen molecules are excretedinto the atmosphere. This misconception is normally reinforced by simplified formulas like “Light + water + CO2 Sugar + O2”. It may be interesting therefore to askyour students about this in order to determine if this misconception is emerging. This will enable you to react accordingly. The experiment renders photosynthesis visible, enabling students to be introduced to the process and provide the motivation to study photosynthesis and the fact that it is affected by external conditions (concentration of CO2, in this case). This will be the bridge to the next activity, where other factors will be explored. Some pedagogical guidelines Allow students enough time to carry out the experiment in the three different versions, to observe phenomena, to formulate a hypothesis, to try to explain them, and to discuss and debate. In order to promotediscussion and debate, you could organise a plenary where students explain and defend their findings. Another possible strategy is to let students organise their findings asa “scientific poster” and havea poster session (such as would be found at a scientific conference). You might also consider asking students to prepare a brief PowerPoint presentation to communicate and debatetheir findings. Some guiding questions you use (included in the students’ worksheet): What do you think the bubbles are? What is the gas that is collected in the test tube? Give reasons for your answers. Is the number of bubbles significantly different for the three experiments? Do you think that “water quality” affects the rate of photosynthesis for aquatic plants? Do you think these observations should be carried out with a land plant? Give reasons.