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Name: Date: Hour: Mrs. Fenech........Biology………Ch 8: The Cellular Basis of Activity Optimizing photosynthesis & why are plants green? Can you increase the rate of Photosynthesis? Will stronger light lead to more growth? Are certain wavelengths of light more effective? And why are plants green?? 1. Examine the complete set of data for an experiment testing light intensity as a variable in photosynthesis. Graph the data, draw a conclusion and explain why this would happen. Light intensity % 0 5 10 15 20 25 30 35 40 45 O2 produced mL 0 4 8.2 12.6 17.1 21.6 26.1 30.5 31.3 31.3 Conclusion and explanation: 2. Examine the complete set of data for an experiment which tests wavelength as a variable in photosynthesis. Graph the data, draw a conclusion and explain why this would happen. Wavelength 375 400 425 450 500 525 550 575 600 625 650 nm O2 produced 32 36 44 36 32 20 12 14 16.8 24 34 mL Conclusion and explanation: 50 31.3 Introduction A pigment is a molecule that absorbs light in the visible portion of the electromagnetic spectrum. The leaves of most plants are rich in pigments. These pigments absorb light and convert it into chemical energy to fuel the production of sugars. The primary photosynthetic pigment is chlorophyll a. Other pigments such a chlorophyll b and carotenoids are referred to as accessory pigments. Different pigments absorb different type (wavelengths) of light. Some pigments might absorb blue light better that other wavelengths of light, for example. Others may absorb all the colors well, or none. A spectrophotometer is a machine used by scientists to measure absorbance of light by substances. The better pigment absorbs a color (wavelength) of light, the higher its percent of absorbance reading. The data table below gives possible spectrophotometer absorbance readings for the two plant pigments. Process & Procedure 1. Graph the data for chlorophyll a and chlorophyll b on the same graph. The line for each is an approximation of the absorption spectrum for that pigment. As always, be sure to SPACE OUT your graph, write a descriptive TITLE, label the AXES and make a KEY! Wavelength of Visible Chlorophyll a Chlorophyll b Light % absorption % absorption 400 nanometers 32 8 425 nanometers 60 29 450 nanometers 10 62 475 nanometers 3 51 500 nanometers 0 8 525 nanometers 0 0 550 nanometers 4 3 575 nanometers 2 4 600 nanometers 4 2 625 nanometers 3 20 650 nanometers 21 29 675 nanometers 44 4 700 nanometers 12 0 Process & Procedure…. 2. Use the EM spectrum to find the colors of light that correspond to each wavelength on your graph. Some wavelengths may fall in the transition range between two colors. Color-code your graph in a way that clearly shows the color range between 400 and 700 nanometers. Analysis 1. At what wavelength does chlorphyll a absorb the most light? a. What color does this correspond to? 2. At what wavelength does chlorphyll b absorb the most light? a. What color does this correspond to? 3. What wavelength of light is NOT absorbed by chlorophyll a or b? a. What color does this correspond to? 4. Based on the data and your graphs, what can you conclude about the two chlorophylls and their absorption spectra? In what ways are the two similar? Different? 5. Chlorophylls are the predominant pigments in leaves. Based on the data and your graph, give a possible explanation for why plants are green. 6. If some wavelengths (colors) of light are absorbed by chlorophylls, what happens to the wavelengths that are not absorbed? Give any possibilities you can think of. 7. Based on the data and your graph, which type of light is most important to plants for photosynthesis? Explain. 8. Design an experiment to collect evidence that supports you answer for question 7 above.