Total Duration: |
61 to 90 Minutes |
Materials and Resources: |
(Some items can be at a central location for all groups (e.g. stock baking soda solution, stock titanium dioxide solution, stock dye solution) For each team: 1: 1 plastic knife (or stirrer) 2: 1 plastic spoon 3: 2g baking soda 4: 2 transparent plastic cups or beakers 5: 3 50 ml test tube 6: 4 L regular water 7: 1 fresh spinach bag 8: 1% TiO2 titanium dioxide nanoparticle solution (stock solution recommended) 9: 3 1/16’’ ID rubber tube connected to a black rubber stopper for test tube 10: 3 1/16 ‘’ glass capillary tube 11: color indicator solution with Rhodamin B dye solution (stock solution) 12: 100 Watt desk lamp 13: clock for timing 14: 1 waste bottle or a class waste container 15: gloves 16: plastic transfer pipette 17: graduated cylinder 18: graph paper (cm units) |
Technology Resources Needed: |
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Background/Preparation: |
Students should be familiar with measurement for conducting the experiments and should have some basic background with chemical equations/reactions and symbols for chemicals. Students should be familiar with the structure of plant cells and their organelles. Students should be aware that visible light is comprised of spectrum of wavelengths (ROYGBV) of varying wavelengths.
TIPs for Teachers: (saves time) Teachers will need to either make a stock solution of baking soda (recommended) or have baking soda, filter paper, and balance available for the teams. Teacher take a sharpie to mark the cups at the 4/5 fill line. Teachers need to make a 1% TiO2 stock solution Teachers may put capillary tubing into the stoppers
Teachers need to prepare the capillary pipette tubes for student teams used in the measurement of O2 .
Teacher Background: Photosynthesis is an energy conversion process taking place in plants that utilizes sun light to produce food (energy) for all kinds of activities of an organism. Typically, CO2 and water are converted in the presence of chlorophyll and sunlight into glucose, water while oxygen is released to the atmosphere to be used by other living organisms including ourselves. At the microscopic level, photosynthesis takes place by absorbing sun light using the plant’s photosynthetic reaction centers, the chloroplasts. The photosynthetic center contains chlorophylls that capture solar energy and starts the process by splitting water with oxygen being given off through stomata. Hydrogen is then chemically combined with carbon dioxide to form a simple sugar (C6H12O6) and water. During cellular respiration glucose in the cells is oxidized to release energy which is used to convert adenosine diphosphate to adenosine triphosphate (ATP), the energy currency of the cells. ATP releases energy for cellular activity when a phosphate is split off and it become ADP. (Balance equation for photosynthesis)
Light 6CO2 + 12H2O _____________ C6H12O6 + 6H2O + 6O2
Photosynthesis is considered an efficient energy conversion process that stores solar energy in chemical bonds that can be used for many applications. Similar to several artificial energy conversion systems (e.g., solar cell, and photoelectrochemical water splitting catalysts), photosynthesis produces useful energy that can be used to keep organisms alive and to power cell activities. In comparison to photosynthesis, artificial energy conversion systems use more stable inorganic or organic materials with much simpler charge storage/conversion configuration upon light absorption. Energy conversion process of 25 nanometer (in diameter, 1 nanometer=10-9 meter) TiO2 nanoparticles is
Light (UV and blue) + TiO2 + CO2+ H2O_________H2 + CH4 + O2
TiO2 nanoparticles only absorb ultraviolet (UV) light with wavelengths less than 400 nm. When the short wavelengths are absorbed by TiO2, the electrons in TiO2 are excited to higher energy levels and they can reduce CO2 and/or water to produce methane and/or hydrogen gas, while the positive charges left would oxidize hydroxide to produce oxygen. Hydrogen production is important as it can be used as energy storage to be supplied to fuel cells with high energy intensity, and the product of burning hydrogen in oxygen is water so it serves as a clean energy source without producing CO2.
The lesson demonstrates gas production of TiO2 which is not as efficient as photosynthesis of spinach. This is because: 1) TiO2 absorbs only the portion of the light near ultraviolet end of the spectrum which is only a very small portion of solar energy (or our lamp). Chlorophyll in spinach captures a range of wavelengths in the visible light region; 2) spinach uses more sophisticated chemical reactions upon light absorption to convert water and CO2 to food and oxygen effectively; and 3) the structure of TiO2 nanoparticles are not optimal for effectively storaging charge into chemical bonds. In addition, the TiO2 sample of small nanoparticles has a total surface area that is much larger than spinach, this often result in the scattering of light by the nanoparticles which can decrease the actual light absorption by the nanoparticle.
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Engage As a team of scientists working on the Mars, the production of oxygen is critical to survival. You and your team members are working toward creating inexpensive, sustainable and efficient ways to generate oxygen gas quickly. You are currently considering plants, like spinach for the production of oxygen or other substances such as particular nanoparticles. Teams of 3-4 students should consider the following questions: Why would your team consider using plants to generate oxygen? What would be needed for the plants to generate oxygen? After teams write their responses to the scenario questions, as a class students should discuss their ideas.
Or you may choose to do the following first and then ask why a mission to the Mars would consider using photosynthesis for oxygen production. What is the advantage of do so?
Ask students what they know about photosynthesis, in particular what materials are needed for photosynthesis and what products of the important energy conversion system. Allow them to discuss their ideas to ascertain their prior knowledge of the photosynthetic process. These can be drawn on the board and the teams describe what should be included with each sphere. Explore (Note: tools and items for the activity are indicated by the numerical label shown in the materials list.)
As a team, students will conduct the following activity to find out which of the materials: Which substances produce more oxygen in a given time frame. In other words, which tube exhibits the highest efficiency of oxygen production.
Students follow the instructions:
Figure 2. Alignment of the pink color indicator in capillary tube with a paper ruler.
Table 1. Record the location (by cm) of the pink color indicator column in each of the capillary tube from A to C under light.
Explain After completing the experiment and recording data. Use the following questions to guide the discussion regarding the concepts and findings. (1) Do you see any location change for any of the three pink color indicators? Explain how you think the colored liquid in an empty capillary tube moves? Rank the speed of the three pink colored liquids from fastest to slowest when they move inside the capillary tubes under light. (2) Which, if any, colored liquid did not move? How can you explain this? (3) Which test tube (A, B and C) did the color liquid move fastest? What are the contents in the test tube? Using the tube contents in your explanation, what do you think is occurring? (4) Explain why test tube A is compared to B to explain the movement of their corresponding pink colored liquids? What is test tube A called in an experiment? (5) Compare test tube A and B, which one has a chemical reaction occurring under light? Why do you need spinach leaf? Is spinach considered biotic or abiotic? (6) What important plant process is occurring in test tube B? What are the products of the reaction? What are the reactants? What does the chemical equation of the photosynthetic process look like? (7) What is the role of baking soda (sodium bicarbonate) in the test tubes? (8) Examining test tube B, what is the purpose of the light in photosynthesis? (9) Light energy is converted into what type of energy in photosynthesis? What is the key product of photosynthesis? (10) What structures are present in plant cells like spinach capture light energy? (11) What is the purpose of baking soda (sodium bicarbonate) in test tube B? (12) Compare B and C, which indicator moves faster? Did both of them move? (13) Explain what might be produced in C if the pink colored liquid moves? (14) What might be a reason (test tube C) titanium dioxide nanoparticles are less efficient in producing gas? (15) Which of the tubes is more efficient in producing oxygen?
Elaborate/Extend
Part 1: Graph the data for Test tubes A, B, and C (Distance vs Time) Compare and contrast the data plotted on the graph. Part 2: Now that you have carried out you experiments for examining the efficiency of oxygen production with spinach versus titanium dioxide. As a scientific team member based on what you have learned, write up a short report about which of the two designs photosynthetic systems (using plants to produce oxygen) versus artificial systems (using chemicals like TiO2) would be most effective for oxygen production on a Mars station. In the report include describe photosynthesis and details about the plant structures where it occurs. What aspects will you have to consider to make the system on Mars sustainable (reusable), least expensive and a long term solution for oxygen production.
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Assessment Strategies |
Informal assessment occurs during the engage, explore and explanation phases. The teacher asks appropriate questions as students conduct the experiment. Questions listed for the teacher to ask during the explain portion of the lesson more thoroughly assess students knowledge of photosynthesis and the role of light energy to produce glucose (food as stored energy) leading to cellular respiration which leads to the discussion of energy flow (glucose plus oxygen releases energy for cell function) .
Formal Assessment: Each student will answer the following questions:
1. Which of the following is not a product or by-product of photosynthesis? a. carbon dioxide b. water c. glucose d. oxygen
2. What is organelle carries out photosynthesis? a. chloroplasts b. cytoplasm c. vacuole d. ribosomes
3. What pigment in spinach captures light to start photosynthesis? a. chromoplast b. chloroplasts c. chlorophyll d. leucophyll
4. In photosynthesis light energy is captured in the green plant cells and converted in which of the following: a. chemical energy b. mechanical energy c. electrical energy d. none of these
5. What gas is needed for photosynethis? a. water vapor b. oxygen c. carbon monoxide d. carbon dioxide
6 During photosynthesis what product stores energy for cell use? a. water b. oxygen c. glucose d. none of these 7. During the experiment what role did the sodium bicarbonate (baking powder) play in photosynthesis? a. source of carbon dioxide b. source of oxygen c. source of energy d. none of these
8. Complete the following equation for photosynthesis?
6CO2 + 12H2O C6H12O6 + 6H2O + 6O2
9. Which Test tube in the experiment represents an example of an abiotic and biotic system?
10. Give one characteristic of titanium dioxide nanoparticles that make it less efficient than the photosynthesis of spinach in the production of oxygen in this experiment?
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Acceleration: |
Students could use a variety of resources to explore the light/dark reactions of photosynthesis as well as the detailed structure of chloroplasts (including stroma, grana, thylakoids). Building a model of the structure is a visual, creative way to share their understandings. Other options could be to have students build parts of the chloroplast and photograph them with a narrative showing the structures and their functions. |
Intervention: |
Students may struggle with the equation of photosynthesis. Students could actually build models of the reactants (e.g. 6 molecules of carbon dioxide, 12 molecules of water) the reconstruct them to make models of the products. (one note: the water reactant is different than the water product. The oxygen in the water product is from the carbon dioxides. This approach allows them to visualize the process and see the conservation of the matter in the reaction by using only the reactant molecules to make the product molecules. |
View the Special Education resources for
instructional guidance in providing modifications and adaptations
for students with significant cognitive disabilities who qualify for the Alabama Alternate Assessment.
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