Experiment Design: August 5, 2014

Group 4 Design

Team Violet: Colton Atkinson, Katie Ault, Rebecca Dow, Kelsey Galt

Research Question: How does the difference in green pigment transmittance, as measured through a colorimeter, in Celosia plumosa, Salvia farinacea, Salvia splendens, Crossandra infundibuliformis, and Pentas lanceolata correlate to the plants’ rate of photosynthesis?

Hypothesis: Leaves exhibiting lower transmittance of green pigments will also have lower rates of photosynthesis.  

Because the pigment chlorophyll is so strongly associated with the process of photosynthesis as it absorbs the light energy necessary for the process of photosynthesis to occur, it would seem that plants with a greater concentration of it and other green pigments would have a greater rate of photosynthesis. Furthermore, in an experiment with corn plants conducted by Zhao et al. in 2003, a lower pigment concentration correlated to a lower rate of photosynthesis due to a nitrogen deficiency in the plants with less pigment:

Zhao, Duli, K. Raja Reddy, V.G. Kakani, J.J. Read, and G.A. Carter. "Corn (Zea Mays L.) Growth, Leaf Pigment Concentration, Photosynthesis and Leaf Hyperspectral Reflectance Properties as Affected by Nitrogen Supply." Plant and Soil 257.1 (2003): 205-18. Springer Link. Web. 2 Aug. 2014. <http://link.springer.com/article/10.1023/A:1026233732507#>.

http://www.researchgate.net/publication/226515587_Corn_(Zea_mays_L.)_growth_leaf_pigment_concentration_photosynthesis_and_leaf_hyperspectral_reflectance_properties_as_affected_by_nitrogen_supply

Independent Variable: The independent variable in this experiment is the concentration (mol/L) of green pigment in the plant, represented by using five different species of plant: Celosia plumosa, Salvia farinacea, Salvia splendens, Crossandra infundibuliformis, and Pentas lanceolata.

Dependent Variable: The dependent variable in this experiment is the rate of photosynthesis for each of the plants being tested, which will be measured through the change in CO2 concentration over a period of 10 minutes.

Controlled Variables:

Variable	Impact on Experiment	Method of Control
Contained environment for photosynthesis	Differences in the environment in which the rate of photosynthesis of the plants is measured can affect the rate of photosynthesis of a plant.	The same container will be used to contain every plant while its rate of photosynthesis is measured.
Time of photosynthesis (seconds)	If one plant is allowed to photosynthesize longer than another, the measurements recorded for the rate of photosynthesis will differ.	The rate of photosynthesis for each plant will be measured for the same amount of time, 10 minutes (measured using a stopwatch in seconds).
Time of pigment extraction (seconds)	If one leaf is crushed longer than another, varying levels of pigment may be released, and this could affect the concentration readings.	Each leaf will be crushed for 3 minutes (measured using a stopwatch in seconds). All effort will be made to crush each leaf with the same intensity.
Mass of leaves (grams)	Variations in the sizes of leaves may lead to variations in the amount of pigment extracted, which may cause inaccuracies when analyzing the pigments in the colorimeter.	Leaves from which pigment is to be extracted will be massed prior to processing and cut, if necessary, so that they all have the same mass.
Water used in colorimetry	Any impurities in the water used in colorimetry may affect the readings of the pigment being analyzed.	Distilled water will be used for all colorimetry procedures.
Carbon dioxide (CO2) concentration	The dependent variable being measured is the change in CO2 concentration; therefore, the initial CO2 concentration of the environment should remain constant in order to accurately measure the change since the CO2 concentration of an environment can affect the rate of photosynthesis of a plant.	All procedures will be executed in a room kept at a constant CO2 concentration (measured with a CO2 monitor). Before measuring the rate of photosynthesis of each plant, the CO2 concentration of the air in the container will be measured to ensure that it stays at a consistent level.
Temperature (°Celsius)	The temperature of an environment affects the rate of photosynthesis of a plant.	All procedures will be executed in a room kept at a constant temperature (measured with a thermometer in °C). Before measuring the rate of photosynthesis of each plant, the temperature of the air in the container will be measured to ensure that it stays at room temperature.
Light intensity	Plants exposed to more light will undergo more photosynthesis/respiration than those exposed to less light.	All procedures will be executed in a room with constant lighting conditions (away from natural sunlight, overhead lights turned on remain turned on, lamp turned on remains turned on during procedure).

Materials:

Provided by the group:

3 Celosia plumosa plants

3 Salvia farinacea plants

3 Salvia splendens plants

3 Crossandra infundibuliformis plants

3 Pentas lanceolata plants

1 mortar and pestle

1 freestanding lamp

2 stopwatches

Provided by the school:

1 Vernier colorimeter with corresponding interface and collection of cuvettes

1 Vernier carbon dioxide monitor

1 pair scissors

1 Celsius thermometer

1 electronic balance

1 roll duct tape

1 large transparent container

1:1 acetone-hexane solution

Filter paper

Fume hood

Test tubes

Pipettes

Procedures:

These procedures are intended to take place in the Marietta High School science labs.

Setup-Chemistry Group (Rebecca and Colton):

1. Connect the colorimeter to the interface and wait until the green light on the colorimeter lights up to indicate that the colorimeter is ready to use.
2. Under the fume hood, calibrate the colorimeter by inserting a cuvette filled with distilled water and run the calibration program.
3. Remove the largest visible leaf from the plant with the smallest average leaves and determine its approximate surface area using the ruler.
4. Remove leaves of similar sizes from the other 4 plants, and use scissors to trim the leaves to match the surface area of the first leaf as closely as possible.
5. Under the fume hood, combine the acetone and hexane to make a 1:1 solution.
6. Check in with the other group before proceeding to “Colorimetry Procedures”.

Setup-Biology Group (Kelsey and Katie):

1. Measure and record initial room temperature using a thermometer.
2. Measure and record the initial room humidity using the sensor.
3. Turn on the carbon dioxide monitor; measure and record initial carbon dioxide concentration.
4. Use Saran wrap and duct tape to secure the carbon dioxide sensor underneath and within the Tupperware container.
5. Mass one of each species of plant and use scissors and hands to break down the larger plants until they have an identical mass to the plant with the smallest original mass.
6. Check in with the other group before proceeding to “Photosynthesis Procedures”.

Colorimeter Procedures-Chemistry Group:

1. Use scissors to cut the processed Celosia plumosa leaf into small slivers and place them in the mortar.
2. Use the mortar and pestle to begin crushing the leaves for 30 seconds.
3. Under the fume hood, add 5 mL of the acetone-hexane solution to the leaves and continue to crush as pigments are released.
4. Add 16 mL of the acetone-hexane solution, continuing to combine the leaves and solution, and pour the contents of the mortar into a beaker using a funnel and filter paper to remove the leaf remnants.
5. Use the pipette to remove the solution from the mortar and pestle and place it in the cuvette.
6. Run the colorimeter at each possible wavelength and see which wavelength yields the highest absorbance; record the absorbance value at the wavelength that yields the highest absorbance.
7. Discard the used solution and plant waste; clean mortar and pestle and cuvette.
8. Repeat steps 1-7 with Salvia farinacea.
9. Repeat steps 1-7 with Salvia splendens.
10. Repeat steps 1-7 with Crossandra infundibuliformis.
11. Repeat steps 1-7 with Pentas lanceolata.
12. Repeat steps 1-11 with all plants for a total of four trials.
13. If these procedures have been successfully finished before the other group has finished, check in with the other group and ask if they need help finishing their procedures before moving on to “Calculations”.

Photosynthesis Procedures-Biology Group:

1. Place lamp so that it will shine indirectly onto the completed Tupperware apparatus.
2. Place 1 Celosia plumosa underneath the Tupperware apparatus.
3. Seal off the Tupperware apparatus with the plant inside using duct tape.
4. Record the initial carbon dioxide concentration, which should match that of the room in general.
5. Start the stopwatch for 10 minutes and record the carbon dioxide concentration every 2 minutes.
6. Carefully remove the plant from beneath the Tupperware apparatus and leave the apparatus open.
7. Wait for the temperature, carbon dioxide concentration, and humidity of the environment in the Tupperware apparatus to return to that of the room.
8. Repeat steps 2-7 with Salvia farinacea.
9. Repeat steps 2-7 with Salvia splendens.
10. Repeat steps 2-7 with Crossandra infundibuliformis.
11. Repeat steps 2-7 with Pentas lanceolata.
12. Repeat steps 2-11 so that each plant has been tested five times.
13. If these procedures have been successfully finished before the other group has finished, check in with the other group and ask if they need help finishing their procedures before moving on to “Calculations”.

Calculations:

1. The chemistry group will use Beer’s law calculations to determine the concentration of green pigments in each leaf.
2. The biology group will determine the rate of carbon dioxide concentration change over time.
3. The data will be entered in Microsoft Excel to further analyze results.