Plant Processes ( Sarah Johnson)
Title: Photosynthesis Simulator, 7th Grade
Principle(s) Investigated: Students will apply their understanding of vascular plant structure to construct experiment that demonstrates the relationship of reactant to product during photosynthesis in an elodea plant ( Elodea Canadensis aka pond weed) . They will provide evidence that supports the theory that changing the amount of light directly effects the amount of oxygen released from the plant. Bubbles are released by the water plant during photosynthesis. Therefore, by measuring the rate at which the bubbles are produced it is possible to tell how fast the plant is photosynthesizing.
Standards:
MS LS1-6: Construct a scientific explanation based on evidence for the role of photosynthesis in the cycling of matter and flow of energy into and out of organisms.
SEP: Constructing a scientific explanation based on valid and reliable evidence obtained from sources ( including students' own experiments and the assumption that theories and laws that describe the natural world today operate today as they did in the past and will continue to do in the future.
DCI: Plants, algae ( including phytoplankton ) and many microorganisms use the energy from light to make sugars ( food) from carbon dioxide from the atmosphere and water through the process of photosynthesis which also releases oxygen. These sugars can be used immediately or stored for growth or later use.
CCC: Energy and Matter: Within a natural system, the transfer of energy drives the motion and/or cycling of matter.
Materials:
Virtual Lab:
http://www.reading.ac.uk/virtualexperiments/ves/preloader-photosynthesis-full.html
Virtual Lab Procedure:
ENGAGE:
1. Students begin the lab by activating background knowledge about vascular plant transport systems ( xylem and phloem, roots and shoots, and leaf structure ) and reviewing what photosynthesis is ( the process by which plants, algae, and some bacteria use sunlight, carbon dioxide, and water to make food) and its equation:
2. During this review, students locate the reactants ( carbon dioxide , water, and light energy ) and the products ( sugar and oxygen ) of photosynthesis. Students are also reminded that both land and water plants rely on photosynthesis for food production.
EXPLORE:
3. Students are then presented with a problem for discussion: If it is a cloudy day, how will it change the equation? How will it change the reactants? How will it change the products? What if it is a sunny day, will that effect the reactants and/or products?
4. Students will have difficulty answering these questions if they are focused on the amount of sugar the plant makes because it is stored. Teacher may need to guide students to consider the other product of photosynthesis.... oxygen. Oxygen production is difficult to observe with land plants, could we observe oxygen production in a water plant like elodea ? Yes, by observing bubbles.
5. Once understanding is more concrete, teacher presents the big question for today's lab report: How will changing the amount of light effect the amount of oxygen produced?
6. Students are given a tutorial on how to use the photosynthesis simulation site. Teacher models the site, showing how light can be moved from 100cm to 200cm. Students observe how the distance changes the amount of light on the elodea. Students are then shown how to use the simulators bubble counter ( BPM ). By measuring the rate at which the bubbles are produced, it is possible to tell how fast the plant is photosynthesizing.
7. Students record the procedure in their lab report. They then collect, chart, and graph their data. Students need to consider the independent and dependent variable when they label their graph. Light distance is the independent variable that would be represented on the X axis, the BPM is the dependent variable to be recorded on the Y axis.
EXPLAIN:
8. Students assess their data and form a conclusion. Students will make entries in their lab report that provide answers to the following prompts:
1. In this lab we concluded........
2. I have evidence to support this because.....
3. The reason this makes sense is because....
EXPAND:
9. To build upon this knowledge, students could be presented with another question for inquiry: Do you think plants photosynthesize at night? Explain why or why not.
********************************************************************************************************************************************
If conducting a live lab, materials and procedures:
Elodea samples, water, test tubes , clamp or flashlight, timer, ruler, magnifying glass.
1. Place elodea sprig in test tube and fill to top with water, cover.
2. Place tube in stand so that it can remain upright during experiment.
3. Position clamp light at a 30cm distance from tube, use ruler for accuracy. Record distance measurement.
4. Turn on light and shine directly onto elodea plant for 1 minute, use timer for accuracy.
5. Record the number of bubbles emitted from the plant during timeframe, use magnifying glass if needed.
6. Once minute is up, record the number of bubbles observed next to distance measurement.
7. Once trail is complete and recorded, repeat the same procedure from a 20 cm distance, , a 10cm distance, and a 5cm distance. Record and graph results.
***************************************************************************************************************************************************
Student prior knowledge:
Student will need prior knowledge of seed plants. This includes characteristics of and importance to the environment and economy. They will need to know about the structure of seeds ( particularly cotyledon and embryo, stored energy ) and seed dispersal. They will need to have knowledge of seed plant structures ( roots, shoots, stems, xylem, phloem, and leaves ) . Students also must know that photosynthesis takes place in the leaves of the plant, the roles of chlorophyll, and stomata.
Explanation:
The purpose of this lab is to enable students to apply learning of plant structure and function, and photosynthesis to a lab situation. Additionally, it gives students the ability to work authentically through the scientific process. The photosynthesis equation ( 6CO2+6H2O+light energy=C6 H12 O6 +6O2 ) can be somewhat abstract when considered as reactants and products. This lab offers students a visual mode of understanding. As oxygen is produced through photosynthesis, it travels out of the elodea leaf and displaces the water in the form of bubbles. This lab allows students to observe photosynthesis firsthand.
Photosynthesis is the process by which plants make their own food. Plants capture energy from sunlight during photosynthesis. This energy is used to make the sugar, glucose, from carbon dioxide, and water. Plant cells have organelles called chloroplasts, these are the parts of the cell that capture energy from light and facilitate photosynthesis. Inside the chloroplasts another membrane forms stacks called grana. Grana contain chlorophyll, a green pigment that absorbs light energy. Because it reflects the green wavelengths of sunlight, chlorophyll looks green. Every green part of the plant looks green because of the presence of chloroplasts and the pigment chlorophyll. The light energy captured by the chlorophyll is used to help form glucose molecules. Glucose is a simple sugar that plants use for food. As a by product, plants cells give off oxygen. Glucose molecules store energy. Plant cells use this energy for their life processes
Questions & Answers:
If photosynthesis occurs in the leaves of a plant, how do plants with no leaves, like a cactus make food?
Cacti are plants that use CAM photosynthesis, they photosynthesize in the epidermis which is why the whole plant looks green. Cacti take in carbon dioxide during the nigh so their stomata can remain closed during the day, this is an adaptation that allows the plant to retain water. Carbon dioxide is converted and stored as malic acid which is converted back to carbon dioxide during the day, Crassulasean Acid Metabolism.
What would happen if a plant had no chlorophyll?
If plants did not have chlorophyll they would brown, yellow and die, additionally they would need to become parasitic in order to consume energy for survival.
What would happen if plants could capture all wavelengths of light?
If you have ever had a sunburn you know how damaging sunlight can be, plants can also be damaged by the sun's energy. Plants are also equipped with non-chlorophyll pigments that act as a "sunscreen". Evidence of these pigments can be seen during the leaf color changing season of Fall when chlorophyll begins to break down.
Applications to Everyday Life:
ENERGY: Most of the substances we use as fuel to energize our daily needs comes from the burning or breakdown of plant material. Fossil fuels such as coal, and Ethanol, which comes from the starches in corn can be used to fuel vehicles, warm or homes, and generate electricity. Therefore, if you think about it all of the energy we use today comes from the process of photosynthesis.
MATERIALS: Many of the materials we use in our everyday lives depend directly or indirectly to photosynthesis. Paper is an obvious example, but consider plastics as well. Plastics are made from petroleum, which is a fossil fuel and is made from the breakdown of organic materials as mentioned above.
ENVIRONMENT: Without photosynthesis our planet would be a very different place. Once the first organisms began to photosynthesize, and oxygen rich atmosphere formed and this enabled aerobic organisms to thrive and evolve. However, once plant material is consumed and burned for fuel, the once stored carbon dioxide is released. Overuse of these fuels has caused an imbalance of carbon dioxide and there is now a buildup that is contributed to the warming of the Earth and climate change.
Photographs:
