The world is turning little by little into an urban environment. People are concentrating more in large cities and depleting the natural resources of the earth (Walker, 1993: 249-252). This single reality should encourage the creation of urban gardens in cities across the world. Plants in the city do so much good for all of us equally. Could we think of a New York City without Central Park? It is also necessary to conserve the natural environments that are left over from the onslaught of a greedy invasion by human beings in the last five hundred years. Students at all levels of education have to learn the context of this problem. There is an urgency to create urban gardens and to instill in students and the community respect for nature so as to safeguard natural resources for future generations. Through the various components of gardening students at all levels can become aware of ways to change the current trend of waste disposal, pollution, the use of nuclear power and the consequences for the future. It is also imperative to address the scientific knowledge of the process of photosynthesis. Life, as we know it on our planet, is at the center of our discussion.
Experiment # 1: The Essential Elements of Photosynthesis
In the classroom, the information of the seminar, “The Chemistry of Photosynthesis,” is essential because it brings new light and the latest developments in the field.
This subject matter falls into the curricular material of the New Haven Public School System. Photosynthesis is at the meeting point of just about everything that has to do with life in our planet. Let’s take for example the process of photosynthesis itself in order to understand the growth of plants. Light is essential for the process, so is water, air (carbon dioxide) and soil. Photosynthesis is a process that involves many steps. In an experiment in the class, we could challenge the students by making them come out with the necessary elements for the process of photosynthesis (Project Wet, 1996: 76-78). In an empty box, we place a cup of soil measured in milligrams, and a cup of water measured in milliliters. Covering the box we could ask the students to come out with the elements of life necessary in plant growth. There are four elements of life. Apparently, the box contains two of them. Which are the elements missing? If we cover the box we eliminate one of the ingredients. Which is this ingredient? Students could challenge each other trying to come out with the essential elements. One of them will realize that light is one of the elements necessary for a plant to grow. By covering the box we cover the source of light. Then, which is the fourth element necessary in the process of life? Again, without telling them directly, in an instructional conversation, they will sooner or later realize that the element not accounted for is carbon dioxide present in air.
This exercise is also written while the discussion is on. Sometimes it is easier for students to write when they have a strong partner. Whichever might be the case, the opportunity for writing is enhanced by the step-by-step procedure of the experiment. This serves as an anchor for their attention and concentration. The hands-on experience is vital in the development of strategies for expression. Generally, it is expected that students in the fifth grade level should develop strategies for expository writing. As such, it is central to consider a main idea and details, keeping in mind the organization, the fluency and expression. In our case, the writing for the experiment has elements applicable in expository writing. The main idea is the elements of life for plant growth. If students do not know this information they might write in the form of a prediction or even a hypothesis. Testing and recording information with rich details would be one of the ways to organize their writing exercises. Students in this way could compare notes, results, drawings and solutions. This lends itself for an application of the scientific process (See above,
The Use of the Scientific Process
).
By this time students are already very excited to have come out with the answers. The classroom is full of sounds and conversations; the next step is the analysis of the photosynthesis process itself. How does this happen? Plants fabricated sugar in the process of photosynthesis using these four elements. But how does this miracle take place? The key lies in the composition of air, in water and in the energy of the sun. The elements are present in the air. The carbon dioxide, the oxygen and the water are elements indispensable for the production of sugar. This process could be best illustrated once the soil and the water are put to use together with air and light. All we need is a seed in the soil and some good care. Once the plant starts growing we could visualize the process of the production of sugar in the leaves of the growing plant. A brief background of the history of the discovery of the process of photosynthesis would be appropriate at this point (Conant, 1957). The history itself is fascinating since it is not too long ago that we did not have much information about the elements and the procedure involved in photosynthesis. In fact, it is in the beginning of the XIX century that De Suassure came up with a fairly clear picture of the dynamics of photosynthetic materials (Conant, 1957: 420). “Gas” became part of the common parlance of the scientific community in the beginning of the XVII century by the experiments of the Belgian physician Baptista van Helmont (Conant, 1957: 327-328). Students would be able to put the process in perspective and be able to visualize it much clearly. The fact of having discovered the various substances involved in photosynthesis through various stages of experimentation no doubt gives the students a sense of comfort with their own ideas and constructs of science. The discovery of the functions of oxygen, water and carbon dioxide in the production of sugar is one step into the understanding of the complex steps of photosynthesis. At the same time, the exposure of this discovery lends the opportunity in the classroom to make a transition from the general to the more specific. That is to say that now the students are ready to discuss the process including more detailed accounts of its components.
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Experiment #2: Growing Popcorn in the Classroom
In order to illustrate the production of sugar by plants we could use six small pots with uniform soil (one produced in the classroom from recycled material is best). We are going to plant nine seeds in equal pots and soil. We separate them in sets of three. Each set is going to get different amounts of water. Formulate a hypothesis: The seeds with more water are going to grow larger than the others (we follow the steps for the scientific process). Students record information, graph, give results and come to conclusions after rigorous analysis. The plants with larger leaves and flowers are the ones with more food--sugar.
In this way students are more ready to visualize the process of photosynthesis as a formula where what goes in has to come out on the other side balanced.
CO2 + H2O + ENERGY FROM THE SUN AND CHLOROPASTS ’! SUGAR + O2
In other words, the photosynthetic apparatus in the chloroplast makes the following chemical reaction occur:
6CO2 + 6H2O + LIGHT ENERGY ’! C6H12O6 + 6O2 (Flowering Plants. 1991: 27).
Later on, as the understanding and enthusiasm of the student has increased, we could get into the more complex relations of photosynthesis and respiration and some of the details of oxidation and reduction. (Walker, 1993: 13, 16-17). At this stage of the game in the fifth grade classroom it would suffice to talk about the nature of the balance of both sides of the formula. We started with 6 carbons, 18 atoms of oxygen, and 12 of hydrogen and we end up with the same amount on the other side, which really corresponds to the sugar molecule, C6H12O6, and the oxygen bond. O2. The use of manipulatives to present the formation of molecules to the class can also contribute to the understanding of the process of sugar production by plants. This will also explain the law of conservation of matter.
Experiment # 3: Playing with candy
We use for this experiment gummy drops, toothpicks and the formula for photosynthesis. We make the molecules needed for photosynthesis and then, after formulating a prediction, we test it by re-using the same candy to make sugar and oxygen molecules.
The exploration of themes related to photosynthesis ranging from pigmentation to the evolution of the Earth’s atmosphere is important for the class. I find this very fascinating and necessary, particularly when these ideas are going to be presented with a hands-on approach. Students in the elementary level need to be guided through a particular lesson with a tangible process, step by step, to a point where they could actually begin to build a construct for further learning and exploration on their own. The experiments conducted in the seminar can be adapted for the classroom situation where we could align the guidelines of the standards and the curriculum to accomplish our objectives. Experiments such as the production of carbon dioxide and oxygen to make students visualize the differences and similarities of the elements involved in the production of sugar. These experiments would also help to understand the concepts of oxidation, combustion, and reduction as a good start. The production of CO2 can easily be accomplished with baking soda, or from dry ice, whereas oxygen could be isolated by the direst process of photosynthesis in the growth of elodia canadensis (Anacharis) trapping the gas in a cylinder (Stodola, 1987: 97, 99). The differentiation of the two materials can best be illustrated by putting a fire out, or by keeping it going with carbon dioxide and oxygen respectively.