To Submit This Assignment Students Will Complete The Lab Wor ✓ Solved

To Submit This Assignment Students Will Complete The Lab Worksheet On

To submit this assignment, students will complete the Lab Worksheet on pages 7-10, then upload their completed document as a DOC or PDF file in Canvas. Objectives: Determine the effects of light on the rate of photosynthesis; Determine the absorption spectrum of leaf pigments. Background: Sunlight provides the majority of energy for organisms living in most ecosystems, however only a subset of organisms are capable of harvesting this energy. Plants use their chloroplasts to absorb the energy from sunlight. This energy is then stored in the covalent bonds of glucose, a simple sugar, and can be used by the plant for structural purposes (cellulose), as usable energy (ATP generation), or for energy storage (starch). Animals can eat plants to obtain glucose and produce energy through a process called cellular respiration. The overall reaction for photosynthesis is represented by the chemical equation: 6 CO2 + 6 H2O + sunlight → C6H12O6 + 6 O2. The entire process is complex and involves many enzymatic reactions. You may notice that the photosynthesis reaction is nearly the exact reverse of cellular respiration.

From the equation above, the three key elements for photosynthesis to occur are carbon dioxide (CO2), water (H2O), and light. If any of the three are missing from the system, photosynthesis will not occur, and glucose production in the plant will be negatively affected. There are two phases of photosynthesis: 1) In the light-dependent phase, chlorophyll molecules located in the thylakoid membrane stacks of the chloroplasts absorb the energy from light resulting in the production of ATP and NADPH. 2) In the light-independent reactions (the Calvin Cycle), the energy stored in ATP and NADPH is used to ultimately convert carbon dioxide to sugar. The process of taking carbon dioxide from the air to build carbohydrates is called carbon fixation.

In solution, CO2 can be converted to carbonic acid (H2CO3) when dissolved in water. The carbonic acid will then release hydrogen ions (H+), causing the pH of the solution to decrease. Bromothymol blue is a pH indicator that changes color based on the pH of a solution. Bromothymol blue turns yellow at lower pH and blue as the pH is increased. This indicator can be used to track respiration (turns yellow as CO2 is added to the system) or photosynthesis (turns blue as CO2 is consumed). Different colors of Bromothymol blue at the indicated pH conditions include yellow in acidic conditions and blue in basic conditions.

Light energy is a small part of the electromagnetic spectrum which is visible to the eye. The wavelength of visible light lies between 380 nm and 760 nm. In order to obtain the energy from light, plants must absorb light energy using pigments, namely chlorophyll a, chlorophyll b, carotene, and xanthophyll. These pigments show characteristic colors because they do not absorb all light equally. By measuring the absorbance at different wavelengths, the absorption spectrum of the leaf pigments can be obtained.

Materials: Internet Safety: Follow all standard laboratory safety procedures. Procedure: Experiment 1 involves observing photosynthesis by using bromothymol blue as a pH indicator in water, with Elodea plant cuttings, and exposing them to light. The experiment aims to observe changes in the indicator's color, indicative of CO2 consumption during photosynthesis. It includes wrapping the plant in green film to restrict the wavelength of light reaching it and recording observations before and after light exposure. Experiment 2 involves measuring the absorption spectrum of leaf extract using a spectrophotometer, scanning across multiple wavelengths, and plotting absorbance data. The goal is to determine which wavelengths are most effectively absorbed by leaf pigments, informing about the best light conditions for plant growth.

In the analysis, students will interpret how photosynthesis affects pH changes, analyze the absorption spectrum data to identify peaks and valleys, and draw conclusions about ideal light wavelengths that promote photosynthesis. The experiment emphasizes understanding the relationship between light wavelength, pigment absorption, and photosynthetic efficiency, linking molecular processes to ecological and agricultural contexts.

Sample Paper For Above instruction

Effects of Light Wavelengths on Photosynthesis and Pigment Absorption Spectrum

Photosynthesis is a vital biological process that converts light energy into chemical energy within autotrophic organisms, primarily plants. Its efficiency is influenced by the wavelength of light available to the plant. This study explores how different light wavelengths affect the rate of photosynthesis and examines the absorption spectrum of leaf pigments to identify the most effective wavelengths for promoting photosynthetic activity.

Introduction

Sunlight serves as the primary energy source for photosynthetic organisms in ecosystems. Plants utilize chlorophyll pigments to absorb specific portions of the electromagnetic spectrum, primarily within the visible range, to fuel the photosynthetic process. Not all wavelengths of light are equally effective; certain wavelengths are absorbed more efficiently, impacting the overall rate of photosynthesis. This research investigates the relationship between light wavelength and photosynthetic efficiency, focusing on the absorption characteristics of chlorophyll a, chlorophyll b, and accessory pigments such as carotene and xanthophyll.

Methodology

The experiment consisted of two main parts. The first involved observing the effect of different light conditions on photosynthesis by using bromothymol blue in water with Elodea plant cuttings. The second involved measuring the absorption spectrum of leaf extracts using a spectrophotometer across a range of wavelengths from 380 nm to 760 nm.

In the first experiment, students prepared water solutions with bromothymol blue and used Elodea cuttings submerged in these solutions. The plant was either exposed to full-spectrum light or restricted to green light using a green film. Changes in the indicator's color indicated CO2 consumption or production, correlating with photosynthetic activity. The observations were recorded before and after one hour of light exposure.

The second experiment involved calibrating the spectrophotometer with an alcohol blank and measuring the absorbance of leaf extracts at multiple wavelengths. The data collected was used to generate an absorption spectrum, indicating the wavelengths most strongly absorbed by the pigments present.

Results

The bromothymol blue results showed that in the presence of the Elodea under full-spectrum light, the indicator turned blue, indicating CO2 consumption and active photosynthesis. When light was restricted to green using the green film, little to no color change occurred, suggesting that green light is less effective for photosynthesis. The control tube without the plant maintained its color, confirming that the change was due to the plant's activity.

The absorption spectrum revealed peaks in the regions around 430 nm (blue) and 660 nm (red), which coincide with the absorption maxima of chlorophyll a. Chlorophyll b showed similar absorption peaks, with accessory pigments absorbing in other regions of the spectrum. Valleys in the spectrum corresponded to wavelengths with minimal pigment absorption, such as green, corresponding to the color reflected by chlorophyll.

Discussion

The data confirms that chlorophyll pigments strongly absorb blue and red wavelengths, correlating with the observed peaks in the absorption spectrum. These wavelengths are most effective in driving photosynthesis because they provide the energy needed to excite electrons in chlorophyll molecules, initiating the conversion of light into chemical energy.

The experiments with the bromothymol blue indicator demonstrated that photosynthesis effectively reduces atmospheric CO2 during exposure to favorable wavelengths, evidenced by the color change from yellow to blue. The limited activity under green light supports the theory that chlorophyll reflects green and absorbs poorly at this wavelength, making green less effective for photosynthesis.

Conclusion

Based on the absorption spectra and photosynthesis observations, wavelengths within the blue (around 430 nm) and red (around 660 nm) regions of the visible spectrum are the most effective for plant growth. These findings align with the known absorption characteristics of chlorophyll pigments. Therefore, using light sources rich in blue and red wavelengths maximizes photosynthetic efficiency and promotes plant health and productivity.

References

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