How colors of visible light affect the activity of photosynthesis, and why LED lights are interesting for production in greenhouses. Figure 1: Blue and red LED-light on spinach leaves On the basis of Inquiry-based based science education (IBSE) students should find out what photosynthesis is about What is particularly innovative about the project? In classical photosynthesis experiments with aquatic plants you can detect photosynthesis and respiration by counting bubbles or by chemical methods where ph changes c caused by CO2 consumption or CO2 production are recorded by means of acid-base acid base indicators. In this project, photosynthesis and respiration in terrestrial plants are demonstrated by measuring the CO2 consumption and the O2-production. The measurements are performed with gas sensors (Vernier). This educational project is also new in the context of using light at different wavelength and controlling light quality. This means that the subjects of biology and physics work closely together in this educational project.
Involved disciplines: Keywords: The science teaching subjects - biology and physics, in collaboration related to issuess such as greenhouse cultivation and energy-saving production. Inquiry-based science learning Engage, Explore, Explain, Elaborate, Evaluate Age of students: 16 19 years Materials: Loggerpro data-sampling equipment (software), CO 2 -sensor (Vernier), O 2 - sensor (Vernier), Light-senor (Vernier), 250 ml Bio-chamber (Vernier), LED- spinach light bulbs, LED sockets GU-10, racks, rack clamps, fresh leaves What happens when plants makes the photosynthesis? light 6 CO 2(g) + 6 H 2 O (l) C 6 H 12 O 6(aq) + 6O 2 2(g) Kilde: http://www.ahorn.dk/asu/base/energi/energi-liv/energi-liv.asp Why are leaves green? You can get the answer looking at the chlorophyll absorbance spectrum. Looking at the chlorophyll absorbance spectrum you also see what kind of wavelength the plant will use for photosynthesis.
Figure 2: Chlorophyll a and b absorption spectrum On a small scale, it is possible in a closed chamber to measure plant photosynthesis and respiration. Photosynthetic activity is measured on basis of the photosynthesis reaction: 6 CO 2 + 6 H 2 O + Light energy C 6 H 12 O 6 + 6 O 2 Where CO 2 - consumption and O 2 - production is recorded Respiration can be measured in the plants when they are not illuminated. C 6 H 12 O 6 + 6 O 2 6 H 2 O + 6 CO 2 + ATP (energy) In the respiratory process correspondingly the CO 2 - production and the O 2 - consumption is measured. By having knowledge of these two biological processes, students can find an expression of the net production of the plant. The present photosynthesis project will demonstrate how to maintain a number of parameters, and interact with one variable (wavelength). The activity of photosynthesis is dependent on the wavelength of the light. In the leaves of the plants there is chlorophyll pigments which absorb light having a wavelength in the range of 420-480 nm (blue light), and light having a wavelength in the range of 610-690 nm (red light). The green light (520-600 nm) is reflected.
Figure 3: Spectra from light emitting diodes (LED) The students must either make measurements on two of the parameters (CO 2 and O 2 ) of the photosynthesis, or just one of them. In this context, the students should also measure the wavelength of light. Figure 4: Spinach-leaves in white light Figure 5: Spinach-leaves in blue and red light The students should measure the photosynthesis with different colors of light, and then they evaluate which colors of the light (wavelengths) that are most effective for promoting photosynthesis.
Figure 6: Spinach-leaves in 250mL Bio-chamber In Denmark, the University of Aarhus cooperates with greenhouse- gardeners to grow crops in a more energy-efficient way. This has resulted in developing special lighting fixtures with LED lights. This research also shows that plant growth and density is controlled by light at different wavelengths. Figure 7 and 8: Campanula and lettuce growing in blue light, Aarhus University (Aarslev, Funen)
Personal notes What questions about photosynthesis, could be asked by the students? The students could thereafter do experiments, which could provide the answers: Problem Hypothesis Experimenting Collecting data Analyzing data Conclusion Lektor Kenneth Alsing Bertelsen be@mfg.dk Lektor Anne Dagmar Appe pp@mfg.dk Midtfyns Gymnasium Holmehøjvej 4 DK-5750 Ringe Tlf. 6262 2577 Fax 6262 1521 post@midtfyns-gym.dk
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