Question
Abstract
The absorption spectrum of plant pigments is essential in understanding photosynthesis, as different pigments absorb light at specific wavelengths. This experiment focused on determining the absorption spectrum of Coleus leaves by extracting pigments, calibrating a spectrophotometer, and measuring absorbance across a range of wavelengths (400–700 nm). Results indicate that the pigments in Coleus leaves absorb light most efficiently in the violet (450 nm) and red (650 nm) regions, with minimal absorption in the green spectrum (550 nm). These findings align with the function of chlorophyll in capturing light energy for photosynthesis (Taiz & Zeiger, 2018).
Introduction
Plants contain various pigments that are crucial for capturing and converting light energy during photosynthesis. Chlorophyll a and chlorophyll b are the primary pigments responsible for absorbing light in the visible spectrum, predominantly in the blue-violet and red regions (Taiz & Zeiger, 2018). Additionally, accessory pigments such as carotenoids play a role in absorbing light that chlorophyll cannot, broadening the range of usable light for photosynthesis.
Coleus leaves, characterized by their vibrant multi-colored appearance, contain chlorophyll along with anthocyanins and carotenoids (Plant Traveling Lab, TTU/HHMI at CISER, 2010). This experiment aims to identify the specific wavelengths absorbed by these pigments by extracting them from the leaves and analyzing their absorbance using spectrophotometry.
Objectives of the Experiment
1. To determine the wavelengths of light most efficiently absorbed by Coleus leaf pigments.
2. To analyze the absorption spectrum and compare findings with known characteristics of plant pigments (Taiz & Zeiger, 2018).
3. To apply spectrophotometry techniques in evaluating light absorption in photosynthetic pigments.
Materials used
Materials used are; Coleus leaf samples, Balance (0.01 g accuracy), Mortar and pestle, Ethanol (30 mL), 35 mL syringe, 100 mL beaker, Funnel with a coffee filter, Safety goggles, Cuvettes (for spectrophotometer), Spectrophotometer (range: 400–700 nm), Kimwipes’ Sharpie marker and Test tube rack
Methodology
A. Sample Preparation
1. A 0.3 g sample of Coleus leaf was weighed and torn into small fragments (Plant Traveling Lab, TTU/HHMI at CISER, 2010).
2. The leaf tissue was ground using a mortar and pestle along with 10 mL of ethanol to begin pigment extraction.
3. An additional 20 mL of ethanol was added, and grinding continued until only tiny fragments remained.
4. The extract was filtered through a coffee filter-lined funnel into a beaker to remove solid debris. And disposed the filter in the designated trash bin.
B. Calibration of Spectrophotometer
1. The spectrophotometer was set to 640 nm to ensure accurate readings.
2. A blank cuvette containing 3 mL of ethanol was prepared to act as a reference standard for calibration (Plant Traveling Lab, TTU/HHMI at CISER, 2010).
3. The blank cuvette was placed into the spectrophotometer, and 100% transmittance was set using the 0 ABS/100%T key.
4. The blank cuvette was removed, and the sample cuvette containing 3 mL of Coleus extract was inserted for absorbance measurements.
5. If transmittance was below 30%, dilution of the extract with 0.5 mL increments of ethanol was performed until a valid range was reached.
C. Measurement of Absorption Spectrum
1. Absorbance measurements were recorded for wavelengths ranging from 400 nm to 700 nm, increasing in increments of 20 nm (Plant Traveling Lab, TTU/HHMI at CISER, 2010).
2. The mode was set to absorbance (A) to obtain precise measurements.
3. At each wavelength, the blank cuvette was inserted to zero absorbance, ensuring consistency.
4. The chlorophyll extract cuvette was then inserted, and absorbance values were recorded.
5. This process was repeated at each wavelength, and all data were compiled into a table.
6. Data was plotted using Excel, generating an absorption spectrum graph.
Results
The absorbance readings obtained from the spectrophotometer are presented below:
Absorption Spectrum Data
Wavelength (nm) Absorbance Transmittance (%)
400 nm (UV/Violet) 1.534 5.1%
450 nm (Violet) 1.681 2.12%
500 nm (Blue) 0.631 23.4%
550 nm (Green) 0.398 40%
570 nm (Yellow) 0.407 39.1%
600 nm (Orange) 0.485 32.78%
650 nm (Red) 0.685 20.7 c%
700 nm (Infrared) 0.384 65.21%
Graphical representation of absorbance vs. wavelength of coleus leaf pigments
Discussion
The absorption spectrum graphts how coleus leaf pigments interact with different wavelength of light, revealing their efficiency in absorbing energy for photosynthesis. The peaks absorbance at 450 nm (violet), suggests that chlorophyll a plays a dominant role in capturing high energy blue-violet light, which is crucial for light dependent reaction of photosynthesis (Taiz & Zeiger, 2018).
A secondary peak at 650 mn (red) indicates chlorophyll b also efficiently absorbed longer wavelengths, maximizing the energy capture in the red spectrum. The drops in absorbance between 500-550 nm (blue green) shows that green light is poorly utilized by plants pigments, leading to reflection rather than absorption- explaining why leaves appear green (Plant Traveling Lab, TTU/HHMI at CISER, 2010). This pattern reinforces the importance of accessary pigments such as carotenoids, which absorb additional wavelengths and support chlorophyll in optimizing energy conversion. The gradual decline at 700 nm (far red) suggests that infrared light contribute to photosynthesis, as its lower energy limits its effectiveness in driving biochemical processes. Overall, these findings align with established photosynthetic principles, confirming that plants efficiently absorb violet and red light, while reflecting green light to create their characteristic coloration.
Sources of Error:
Inconsistent sample concentration during extract preparation could affect results.
Calibration drift in the spectrophotometer may lead to minor inaccuracies.
Human handling errors such as fingerprint residue on cuvettes affecting readings.
Conclusion
This experiment successfully determined the absorption spectrum of Coleus leaves, confirming that chlorophyll and other pigments absorb light most efficiently in the violet (450 nm) and red (650 nm) regions, while green light is minimally absorbed (Taiz & Zeiger, 2018). These findings support established knowledge of plant pigmentation and photosynthetic efficiency.
References
Plant Traveling Lab. TTU/HHMI at CISER (2010).
Taiz, L., & Zeiger, E. (2018). Plant Physiology and Development.
note: provide the references list of this practical in APA format.
The absorption spectrum of plant pigments is essential in understanding photosynthesis, as different pigments absorb light at specific wavelengths. This experiment focused on determining the absorption spectrum of Coleus leaves by extracting pigments, calibrating a spectrophotometer, and measuring absorbance across a range of wavelengths (400–700 nm). Results indicate that the pigments in Coleus leaves absorb light most efficiently in the violet (450 nm) and red (650 nm) regions, with minimal absorption in the green spectrum (550 nm). These findings align with the function of chlorophyll in capturing light energy for photosynthesis (Taiz & Zeiger, 2018).
Introduction
Plants contain various pigments that are crucial for capturing and converting light energy during photosynthesis. Chlorophyll a and chlorophyll b are the primary pigments responsible for absorbing light in the visible spectrum, predominantly in the blue-violet and red regions (Taiz & Zeiger, 2018). Additionally, accessory pigments such as carotenoids play a role in absorbing light that chlorophyll cannot, broadening the range of usable light for photosynthesis.
Coleus leaves, characterized by their vibrant multi-colored appearance, contain chlorophyll along with anthocyanins and carotenoids (Plant Traveling Lab, TTU/HHMI at CISER, 2010). This experiment aims to identify the specific wavelengths absorbed by these pigments by extracting them from the leaves and analyzing their absorbance using spectrophotometry.
Objectives of the Experiment
1. To determine the wavelengths of light most efficiently absorbed by Coleus leaf pigments.
2. To analyze the absorption spectrum and compare findings with known characteristics of plant pigments (Taiz & Zeiger, 2018).
3. To apply spectrophotometry techniques in evaluating light absorption in photosynthetic pigments.
Materials used
Materials used are; Coleus leaf samples, Balance (0.01 g accuracy), Mortar and pestle, Ethanol (30 mL), 35 mL syringe, 100 mL beaker, Funnel with a coffee filter, Safety goggles, Cuvettes (for spectrophotometer), Spectrophotometer (range: 400–700 nm), Kimwipes’ Sharpie marker and Test tube rack
Methodology
A. Sample Preparation
1. A 0.3 g sample of Coleus leaf was weighed and torn into small fragments (Plant Traveling Lab, TTU/HHMI at CISER, 2010).
2. The leaf tissue was ground using a mortar and pestle along with 10 mL of ethanol to begin pigment extraction.
3. An additional 20 mL of ethanol was added, and grinding continued until only tiny fragments remained.
4. The extract was filtered through a coffee filter-lined funnel into a beaker to remove solid debris. And disposed the filter in the designated trash bin.
B. Calibration of Spectrophotometer
1. The spectrophotometer was set to 640 nm to ensure accurate readings.
2. A blank cuvette containing 3 mL of ethanol was prepared to act as a reference standard for calibration (Plant Traveling Lab, TTU/HHMI at CISER, 2010).
3. The blank cuvette was placed into the spectrophotometer, and 100% transmittance was set using the 0 ABS/100%T key.
4. The blank cuvette was removed, and the sample cuvette containing 3 mL of Coleus extract was inserted for absorbance measurements.
5. If transmittance was below 30%, dilution of the extract with 0.5 mL increments of ethanol was performed until a valid range was reached.
C. Measurement of Absorption Spectrum
1. Absorbance measurements were recorded for wavelengths ranging from 400 nm to 700 nm, increasing in increments of 20 nm (Plant Traveling Lab, TTU/HHMI at CISER, 2010).
2. The mode was set to absorbance (A) to obtain precise measurements.
3. At each wavelength, the blank cuvette was inserted to zero absorbance, ensuring consistency.
4. The chlorophyll extract cuvette was then inserted, and absorbance values were recorded.
5. This process was repeated at each wavelength, and all data were compiled into a table.
6. Data was plotted using Excel, generating an absorption spectrum graph.
Results
The absorbance readings obtained from the spectrophotometer are presented below:
Absorption Spectrum Data
Wavelength (nm) Absorbance Transmittance (%)
400 nm (UV/Violet) 1.534 5.1%
450 nm (Violet) 1.681 2.12%
500 nm (Blue) 0.631 23.4%
550 nm (Green) 0.398 40%
570 nm (Yellow) 0.407 39.1%
600 nm (Orange) 0.485 32.78%
650 nm (Red) 0.685 20.7 c%
700 nm (Infrared) 0.384 65.21%
Graphical representation of absorbance vs. wavelength of coleus leaf pigments
Discussion
The absorption spectrum graphts how coleus leaf pigments interact with different wavelength of light, revealing their efficiency in absorbing energy for photosynthesis. The peaks absorbance at 450 nm (violet), suggests that chlorophyll a plays a dominant role in capturing high energy blue-violet light, which is crucial for light dependent reaction of photosynthesis (Taiz & Zeiger, 2018).
A secondary peak at 650 mn (red) indicates chlorophyll b also efficiently absorbed longer wavelengths, maximizing the energy capture in the red spectrum. The drops in absorbance between 500-550 nm (blue green) shows that green light is poorly utilized by plants pigments, leading to reflection rather than absorption- explaining why leaves appear green (Plant Traveling Lab, TTU/HHMI at CISER, 2010). This pattern reinforces the importance of accessary pigments such as carotenoids, which absorb additional wavelengths and support chlorophyll in optimizing energy conversion. The gradual decline at 700 nm (far red) suggests that infrared light contribute to photosynthesis, as its lower energy limits its effectiveness in driving biochemical processes. Overall, these findings align with established photosynthetic principles, confirming that plants efficiently absorb violet and red light, while reflecting green light to create their characteristic coloration.
Sources of Error:
Inconsistent sample concentration during extract preparation could affect results.
Calibration drift in the spectrophotometer may lead to minor inaccuracies.
Human handling errors such as fingerprint residue on cuvettes affecting readings.
Conclusion
This experiment successfully determined the absorption spectrum of Coleus leaves, confirming that chlorophyll and other pigments absorb light most efficiently in the violet (450 nm) and red (650 nm) regions, while green light is minimally absorbed (Taiz & Zeiger, 2018). These findings support established knowledge of plant pigmentation and photosynthetic efficiency.
References
Plant Traveling Lab. TTU/HHMI at CISER (2010).
Taiz, L., & Zeiger, E. (2018). Plant Physiology and Development.
note: provide the references list of this practical in APA format.
Answers
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GPT-4o mini
Here is the reference list formatted in APA style based on the sources provided in your practical:
**References**
Plant Traveling Lab. (2010). *TTU/HHMI at CISER*. Retrieved from [insert URL if available]
Taiz, L., & Zeiger, E. (2018). *Plant physiology and development* (6th ed.). Sinauer Associates.
(Note: If the URL for the Plant Traveling Lab source is available, please include it where indicated. Make sure to format it correctly according to APA guidelines.)
**References**
Plant Traveling Lab. (2010). *TTU/HHMI at CISER*. Retrieved from [insert URL if available]
Taiz, L., & Zeiger, E. (2018). *Plant physiology and development* (6th ed.). Sinauer Associates.
(Note: If the URL for the Plant Traveling Lab source is available, please include it where indicated. Make sure to format it correctly according to APA guidelines.)