Photosynthesis

Algal Photosynthesis of Hurricane Creek

__**Introduction**__

Photosynthesis is a process that converts carbon dioxide into organic compounds using the energy from the sunlight. Photosynthesis is absolutely fundamental to the sustainability of life on Earth. The food we eat for nourishment, growth, and energy, as well as the air we breathe so our hearts continue pumping and our brains continue thinking – all of this is part of a large cycle that is perfect for our sustenance. For example, the air we breathe turns out to be, in part, the oxygen produced by plants and algae during photosyntheis and the carbon dioxide respired by plants and animals, and vice versa – altogether giving the image of an infinite loop. Energy, which is persistently required for the cycle of life to continue, and is acquired when the sun’s light is absorbed by photosynthetic organisms, is then converted into chemical energy that can be transfered up the food chain.

During this process of chemical conversion in photosynthesis, carbon dioxide and water are transformed into oxygen and glucose in the presence of sunlight. These photons of energy present in sunlight arrive as various wavelengths, some of which are absorbed by chloroplasts (pigments) in plants. For example, plants appear green because it is the color being reflected by the plant, while the other colors of the visible light spetrum are being absorbed by the plant's pigments. When substances appear colored, it is as a result of the absorption of specific wavelengths of light in the visible spectrum and the reflection of others. In this experiment the lab group used paper chromatography of photosynthetic pigments to determine the polarity of the pigments found in leaves in addition to using a spectrophotometer to measure the absorbance spectrum of different leaf pigments. The four pigments that were observed in this experiment were Chlorophyll A, Chlorophyll B, Xanthophyll, and Carotene. To determine polarity the lab group looked at the molecular structure of each pigment and counted the number of oxygen molecules. In knowing that the Chromatography paper is a polar substance the group hypothesized that the most polar substance will be attracted to the paper, meaning that it will travel the least far up the paper (staying close to the pencil line), while the most non polar substances will move the furthest up the paper.

__**Photosynthesis at Hurricane Creek**__ Photosynthesis is vital to the ecosystem of Hurricane Creek and is the base of its food chain. The algae must be able to receive the amount of sunlight needed to produce oxygen and glucose via photosynthesis, which can then be used by other organisms in the creek. Adequate wavelength absorption by the algae means adequate photosynthesis in the area, and adequate photosynthesis means sustainable life. Therefore, we conducted this exercise to examine the relative importance of algal photosynthesis in different habitat types of the creek. There are many threats to Hurricane Creek and the life it contains -- including natural disasters and man-made disasters -- and hence the importance of such tests. Furthermore, given the importance of photosynthesis in the carbon cycle (Figure 1), we were also able to examine the importance of photosynthesis in a broader context.



__**Methods of Experiment**__
 * 1) **Algae samples were taken from nine different rocks in Hurricane Creek – three from a run, three from a riffle, and three from a pool (but all from the same transect of the creek near Highway 216). **
 * 2) Pigment was collected in filters, and then scraped it into a dish where we combined it with pure acetone, using a mortar and pestle.
 * 3) Pipettes were used to transfer non-residue-inclusive solution to graduated cylinder to measure out 4 mL, and then transferred to a cuvette (i.e. a test tube) in preparation for measurement of absorption using the spectrophotometer (Figure 2).
 * 4) When the spectrophotometer was ready, we selected the beginning wavelength as 400 nanometers (nm).
 * 5) We then zeroed the instrument so that the needle indicated 0% transmittance.
 * 6) After inserting our control sample of acetone, we aligned the meter to 100% transmittance (0 absorption) and measured the absorption of the algal pigment in soultion.
 * 7) This process was continued for all nine samples and at every 20nm from 400 to 720nm, or for the entire visible light spectrum.

*The following precautions were taken: Kimwipes were used on all cuvettes before inserting into the spectrophotometer; cuvettes were only grabbed at the top rim to avoid fingerprints; cuvettes were shaken slightly before measuring (each and every time); finally, the spectrophotometer was re-scaled with each round of measurements*



__**Results**__ Multiple measurements of abitioc variables were taken from all nine locations where the algae samples were collected (Table 1).

Table 1: Abiotic variables measured at sample collection points in Hurricane Creek. Temperature (C) || 19.57 || 19.53 || 19.5 || Oxygen (%) || 121.13 || 123.97 || 110.33 ||
 * Abiotic Variables || Run Avg || Riffle Avg || Pool Avg ||
 * Water Depth (cm) || 54.5 || 22.67 || 41.33 ||
 * Velocity (m/s) || 0.19 || 1.19 || 0 ||
 * Water
 * Water pH || 7.78 || 7.72 || 7.84 ||
 * Dissolved

For a better illustration of the measurements above, below are some visualizations of the average for the run, riffle and pool habitats.

Next are the relative wavelength absorption measurements of algae taken with the spectrophotometer (Table 2). Again, these are the individual stream habitat averages.

Table 2. Average absorption of algal pigments in each habitat type.
 * Wavelength (nm) || Run Avg || Riffle Avg || Pool Avg ||
 * 400 || 0.5 || 0.49 || 0.44 ||
 * 420 || 0.57 || 0.45 || 0.49 ||
 * 440 || 0.5 || 0.44 || 0.43 ||
 * 460 || 0.4 || 0.38 || 0.38 ||
 * 480 || 0.31 || 0.33 || 0.31 ||
 * 500 || 0.2 || 0.28 || 0.28 ||
 * 520 || 0.16 || 0.23 || 0.24 ||
 * 540 || 0.16 || 0.23 || 0.24 ||
 * 560 || 0.15 || 0.21 || 0.24 ||
 * 580 || 0.15 || 0.2 || 0.22 ||
 * 600 || 0.15 || 0.18 || 0.2 ||
 * 620 || 0.15 || 0.17 || 0.22 ||
 * 640 || 0.16 || 0.2 || 0.23 ||
 * 660 || 0.23 || 0.21 || 0.26 ||
 * 680 || 0.15 || 0.16 || 0.2 ||
 * 700 || 0.09 || 0.13 || 0.16 ||
 * 720 || 0.09 || 0.12 || 0.14 ||

To better understand the measurements above, have a look at the graph below. The graph above demonstrates the average wavelength absorption of algae samples taken from all three stream habitats.

__**Discussion** __ First, it is important to illustrate that the spectrum of visible light ranges from 380 nm to 780 nm, from higher energy violet to lower energy red, respectively (Blanch). In each geomorphic unit the relative absorption was greatest in the higher energy range of 400 nm to 520 nm. This shows that the algae get the most energy from the shorter wavelengths in the violet range. There were also peeks at 660 nm in the runs, riffles, and pools, meaning that they utilize energy from the longer wavelengths in the red range. From 500 nm to 620 nm, which is in the green range, relative absorption is low and steady.

Please refer to the below graphic for visualization of the relationship between wavelength and energy:

In addition to light availability, there are several factors that could influence the amount of algae in the creek. The water velocity indicates the speed at which water is moving in meters per second. It can greatly effect algal growth by increasing/decreasing the probability of displacement and mixing of algal nutrients.

Water temperature is also a main factor in the production of algae via photosynthesis because the process will slow in cooler temperatures, but thrive in warmer temperatures up to a point.

Aquatic organisms may also be affected by pH. It is unlikely that pH affected algae in this case, as the pH levels all remained within a cirucmneutral range near 7.

Dissolved oxygen concentrations (%) denotes the amount of oxygen present in the water. Because the riffle's and run’s averages are both higher than the pool's, we can assume that the pool is exposed to a lesser degree of oxygenated molecules. It is not apparent, however, that this affected the abundance of algae in the pools.

__**Conclusion**__

** The experiment showed that **  different pigments transmit a different amount of energy depending on the wavelength of the light transmitted**.** <span style="color: #000000; font-family: arial,helvetica,sans-serif; font-size: 9pt; font-style: normal; font-weight: normal; line-height: 200%;">** This different pigments allow a higher level of transmittance to help facilitate photosynthesis. Chlorophyll A had the highest level of transmittance proving that it is the most significant in carrying out photosynthesis. In conclusion, the algae seem to be equally absorbing wavelengths regardless of habitat type, thus indicating successful photosynthesis in multiple areas of the creek. Of course, this does not mean there are no threats to the creek. Both natural and man-made disasters could easily change things for the worse in the creek. Obviously, we wish that not to happen. In order to best ensure Hurricane Creek's longevity, we suggest this experiment be regularly conducted to monitor photosynthesis over time. After all, Hurricane Creek's survival is, in turn, linked to our own survival. **

__<span style="font-family: Helvetica,sans-serif; margin-bottom: 0in;">**References** __ Blauch, David. "Spectrophotometry: Absorbance Spectrum." (2009). Web. <http://www.chm.davidson.edu/vce/spectrophotometry/absorbancespectrum.html>

<span style="font-family: Helvetica,sans-serif; margin-bottom: 0in;">Claydon, Stephen. "Photosynthesis." //Science Aid// (2006): 1. Web. 18 Oct 2010

<span style="font-family: Helvetica,sans-serif; margin-bottom: 0in;">Jones, Andrew. "What is a Photon?." About Physics n. pag. Web. 17 Oct 2010.