The Chemistry Behind Photosynthesis: Two Easy Experiments for Middle Schoolers
written by: Dawn Marcotte
• edited by: Donna Cosmato
• updated: 8/2/2012
Students are introduced to the chemical process of photosynthesis with two easy experiments. They will observe how the introduction of chemicals into groundwater or pollution into the air affect the growth of plants.
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Middle school students already have a basic understanding of photosynthesis and can be introduced to the chemistry behind the process. Photosynthesis occurs when 6 molecules of water (Hydrogen and Oxygen) interact with 6 molecules of carbon dioxide to produce one molecule of sugar for the plant to use. This reaction also produces 6 molecules of oxygen, which the plant releases into the air. Every living organism on Earth needs Oxygen to survive. People exhale carbon dioxide into the air, which plants use and convert into oxygen. These experiments allow students to study how changing some of the elements of photosynthesis affect the growth of the plant.
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Plants absorb water through their roots and carbon dioxide through their leaves. When chemicals are introduced into the groundwater or air this can affect the ability of plants to survive. Students can test the effects of a variety of common chemicals that leach into groundwater and how they affect the growth of plants. Test paint, weed killer, fertilizer and a laundry detergent (phosphorous). Plant a quick growing vegetable such as beans, peas or spinach in 5 separate planters. Mix 1 gallon water with 1/2 cup of the substance being tested; paint, weed killer, fertilizer and laundry soap. Label each planter and each water container with the mixture being tested. The 5th planter is the control and should receive only clear water during the experiment. Water all plants with the same amount and at the same intervals. Observe and measure the plants growth for three weeks. Take notes and pictures daily to record changes. Review observations at the end of the experiment and discuss what changes occurred. This experiment can be modified to test different concentrations of a single pollutant, such as phosphorus. Students can research what types of chemicals are common in groundwater, what their sources are and how they affect the local environment.
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Humans change the environment by creating pollution that affects the amount of sunlight reaching plants. Industry has created smog in some metropolitan areas that is so thick it even affects the health of humans. Students can study the effect this reduced sunlight level has on plants with this simple experiment. Smog will be mimicked by the use of the smoke pellets commonly used in model trains. Plant three planters with peas, spinach or beans. The first planter is the control and will not be exposed to any additional pollution. The top from a hamster cage works well as a clear cover that will contain the smoke while letting sunlight through. Place the clear cover over the second planter and set off two smoke pellets each morning for the duration of the experiment. Remove the clear cover when the smoke has dissipated. Repeat for the third planter but set off two smoke pellets twice a day for the duration of the experiment. Record observations over three weeks on growth of the plants and review the results. Expand this experiment as desired with additional smoke pellets. All other variables should remain constant.
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Students interested in further study can research how much oxygen farm crops such as wheat or corn produce, and then compare to the amount of oxygen produced by a similar area of rain forest or grassland. Photosynthesis is also affected by temperature of the air and duration of sunlight during the day. Students can investigate the minimum amount of sunlight and temperature required for photosynthesis to occur.