What is the effect of pH levels on the net production, given by the change in dissolved oxygen, in Chlorella pyrenoidosa?

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What is the effect of pH levels on the net production, given by the change in dissolved oxygen, in Chlorella pyrenoidosa?


        Chlorella pyrenoidosa is a special type of green micro algae that grows in fresh water, and is common throughout much of the world. In this experiment, the species pyrenoidosa is the Norton Lake 170 variation was cultured ex situ. Chlorella pyrenoidosa has a reproductive cycle of about 2 days and is known for its high yield rate, where one parent cell divides into 4 daughter cells daily. Furthermore, it is considered to have the highest chlorophyll concentration of any known plant (about 28.9g/kg) and is used for health benefits. Chlorella pyrenoidosa, because of its high concentration of chlorophyll, has an overall pH optimum at around pH 8, while it is found usually in environments with pH ranges 6-7.

 Oxygen is critical to the maintenance of life processes of nearly all organisms. Its concentration in the air and water is dependent upon chemical  processes but even more so on the biological processes like photosynthesis and respiration. Primary producers like the phytoplankton Chlorella pyrenoidosa are generally photosynthesizers and yield a gross productivity in oxygen while using some oxygen produced from hydrolysis of water in respiration. The result is generally a positive net production of dissolved oxygen levels (when isolated samples of photosynthetic organisms are used). Therefore, dissolved oxygen becomes an important measure of water quality and health of a population of species. Acid rain and industrial pollution has caused pH changes in the environment since the Industrial Revolution, and pH must be stable in order to keep integrity of protein) secondary and tertiary structures from polar interactions. Moreover, large pH fluctuations may be disastrous for O2 evolving thylakoid membranes of chloroplasts, or inner membranes in mitochondrion, affecting total net production rates. But then the question becomes, to what pH level can Chlorella pyrenoidosa be tolerant and yield higher net production values? In this experiment, the effects of pH on the net production, from change in dissolved oxygen, were studied.

Question: What is the effect of pH levels on the net production, given by the change in dissolved oxygen, in Chlorella pyrenoidosa?


If the test bottles (150 mL containers) are filled with about 20 mL of cultured Chlorella pyrenoidosa sample and 130 mL of pH solutions from pH 6, 7, 8, 9, and 10, and the test bottles are exposed to conditions suitable for survival of Chlorella pyrenoidosa , then the test bottles that contain the optimum pH, that is the pH 8 for Chlorella pyrenoidosa, will have the highest amount of net production, or change in DO levels from final (after a 48 hour period) to initial (time of setup) measurements, because Chlorella pyrenoidosa has been shown to have the highest photosynthetic productivity (and resultantly primary productivity) ex situ in environments with pH 8. Moreover, if test bottles have cultured Chlorella pyrenoidosa samples with pH values deviating from the optimum pH of 8, there will be a significant decrease in the net productivity. This is due to the charge fluctuations impacting the structure of proteins and enzymes that support photosynthetic reactions and respiration, which are pivotal processes in determining net production. In other words, keeping pH of solution of Chlorella pyrenoidosa within the optimal pH of 8 will allow the phytoplankton to maintain homeostasis, increasing net production (relative to other experimental groups).

The rationale for this hypothesis is that all enzymes have an optimal pH in which their catalytic function is maximized. Changes in pH of a solution (generally both decreasing and increasing pH) may change the state of ionization of amino acids in a protein, yielding a net loss in keeping 3-D structure, and results in enzyme inactivity or altered protein recognition. Moreover, change in pH may change the substrate shape or charge properties of substrate as to induce inability to undergo enzyme facilitated catalysis. Thus a change in pH levels (both increased and decreased) from the optimal pH of 8 in solutions containing Chlorella pyrenoidosa will result in a decreased amount of enzyme catalytic processes in photosynthesis and respiration (Gross Productivity – Respiration = Net Production). Thus over a 48 hour interval, yields a lower net production.

Independent Variable: pH level of solution (in test, large DOD bottles) containing Chlorella pyrenoidosa

Dependent Variable: Net production in mg/L (given by the change in DO concentration measured with probe ware as calculated using final measurements taken after 48 hours subtracted from initial measurements from set up time)

Controlled Variables:

Tap water was used in all trials in order to allow for maximized growth ex situ. Note: The tap water was from the same source. (water content can affect growth of phytoplankton)

Phytoplankton were all cultured in same BOD bottles for testing procedures.  (The bottle itself provides the same boundaries for all the phytoplankton to grow and the type of surface allows for same light refraction)

All Chlorella pyrenoidosa containing solutions were placed in the same system. This meant that all Chlorella pyrenoidosa faced the same variations in temperature, salinity, and other environmental factors. By placing the phytoplankton in a constant light in room temperature environment, regardless of the conditions, all samples would have been affected. As a result, the affect of environmental condition can be negated. Results are relative.

Temperature was monitored each 24 hour period in samples to make sure temperature was not changed from sample to sample.

Salinity was monitored each 24 hour period in samples to make sure salinity readings were same across all samples.

The amount of pH buffer solution (130 mL + 5 mL) used to keep pH at + 0.5 of pH values.

Species variation within cultured phytoplankton samples was kept at minimum by ordering pure Chlorella pyrenoidosa samples from SK& Boreal Laboratories©. But the same sample was distributed across all 25 BOD, 150 mL test bottles so the variation from bottle to bottle would be about the same.

Control Group: Chlorella pyrenoidosa in pH 8 buffer solution.

Experimental Groups: Chlorella pyrenoidosa in pH 6,7,9,and 10 buffer solutions.


25 BOD, large bottles (closed using black cap) capable of holding up to 150 mL of liquid

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Graduated  cylinder for measuring pH buffer solution quantities and Chlorella pyrenoidosa sample quantities (uncertainty +/- 1mL)

Probe Ware for DO readings

650 mL +/- 10 mL of pH 6 buffer solution (potassium hydrogen phosphate) uncertainty of +/- 0.1 in pH fluctuation from pH 6. 130 +/- 5 mL per trial used.

650 mL +/- 10 mL of pH 7 buffer solution (Sodium Hydroxide-Potassium Dihydrogen Phosphate) uncertainty of +/- 0.1 in pH fluctuations from pH 7. 130 +/- 5 mL per trial used.

650 mL +/- 10 mL pH 8 buffer solution (Potassium Phosphate-Sodium Hydroxide) uncertainty of +/- 0.1 in pH fluctuations ...

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