Volvox and pH
The Effect of pH Change on Motility of Volvox Flagella
Abstract
In this experiment, I am interested in testing out the effect of pH on the functionality of enzymes of the extracellular matrix in the photosynthetic algae Volvox Carteri. Optimal pH is required for proper enzymatic function, which facilitates synchronized motion of the two flagella located on one side of each Volvox cell. If the pH of the environment is too deviated, then enzymes are denatured. Since enzymes catalyze reactions producing ATP, which is the powerhouse of energy for motion of eukaryotes including Volvox cells, is vital to ensure that the cells are exposed to the pH contained in their freshwater habitats- that is, a pH of around 7.4. I approached testing the functionality of enzymes required for motion of flagella by observing the changes in movement of the colony when introduced to variations in pH- that is, the motility of the cells. This involved exposure to 10 ml apple cider vinegar (an acid with pH of 4), NaOH (a strong base with pH of 13), and fertilized freshwater as our control ( pH of close to 7.4). I dispersed 1 drop of each on all three slides and observed the motility of Volvox for 10 second intervals. It was found that motility of the colony when exposed to both acids and bases remained stagnant, while most active when exposed to freshwater. This supports the hypothesis that enzymes required for flagella motility function best at the optimal freshwater pH.
Introduction
Volvox Criteri is a photosynthetic algae that thrives in freshwater environments such as ponds, creeks, and other damp water habitats. Volvox form round or oval hollow colonies that contain around 500 to 60,000 cells embedded in a gelatinous wall and that are often visible with the naked eye. The flagella are pointed outwards and move in unison to ultimately create locomotion. A large eye-spot is present in the anterior pole section of each cell, which enable these cells to detect light. This is the reason why volvox moves towards the direction of light. The extracellular matrix of the Volvox cells consists of molecules secreted by support cells that provides structural and biochemical support to the surrounding cells.These include enzymes such as phosphatase, a lysozyme/chitinase, and an arylsulfatase. One of the prerequisites to promote the transition from unicellularity to multicellularity during evolution was the development of a complex extracellular matrix (ECM) from a simple cell wall (Shiraishi, 2008). The ECM of a multicellular organisma is a complex organelle that serves structural and enzymatic functions. It mediates many developmental responses including regulation of growth and differentiation, growth repair, and pathogen defense. The ECM also plays a key role when adaptations to environmental changes are required (Hallmann, 1999). In this experiment, the environmental change observed was a deviation from optimal pH. Thus, we hypothesized that if the Volvox Criteri colony is exposed to a strong base or an acid, then the motility of the colony as a whole would noticeably decrease.
Materials and Methods
- 10ml apple cider vinegar (pH of 4)
- 3 labeled slides with volvox culture in each
- Microscope with 40X magnification
- 1 drop of 1 molar NaOH (pH of 14)
- 10 ml nutrient based freshwater (pH of 7.4)
- 3 pipets
Throughout the experiment, the temperature and volume of the solutions used were kept constant. The independent variable was the pH of the solutions. The control group was Volvox in freshwater. A drop of pond water containing Volvox was placed on a glass depression slide using a disposable pipette and sealed with a coverslip. Three slides were prepared separately. Throughout the microscope, live moving Volvox were observed. Each prepared slide was individually tested with NaOh, apple cider vinegar, and nutrient based freshwater. A micropipette was used to dispense 1 drop of corresponding solution to a slide, and changes in behavior were observed and recorded. One drop of NaOh was added to the prepared slide with Volvox. One drop of apple cider vinegar was added to the second prepared slide with Volvox. The last prepared slide with Volvox was tested with fresh water. Changes in motility were observed, timed with 10 second intervals, and recorded in Table 1.
Data/ Results
During the observation, we can see that before the addition of sodium hydroxide, the motility of the Volvox was high. However, when the sodium hydroxide was introduced, the Volvox no longer moved as can be seen in figures 4–5. Similarly, when we added the apple cider vinegar, the Volvox stopped in its tracks when the apple cider vinegar was integrated into its environment seen in figures 9–10. However, when the water was introduced, there was no effect in the movement of Volvox before and after as seen in figures 11–15. Table 1 below depicts which variables affected motility. In order to quantify observations into a line graph for a clearer representation of Volvox movement in different pH values, we measured the average distance moved in mm per pH value based on the images shown below in Figures 1–15.
Figures 1- 3: Volvox motility in 10 sec. interval in absence of NaOH
Figures 4–5: Volvox motility in 10 sec. interval with addition of NaOh
Figures 6–8: Volvox motility in 10 sec. interval in absence of Apple Cider Vinegar
Figures 9–10: Volvox motility in 10 sec. interval with addition of Apple Cider Vinegar
Figures 11–13: Volvox motility in 10 sec. interval in absence of water
Figures 14–15: Volvox motility in 10 sec. interval with addition of water
Figure 16:The Effect of pH Change on Volvox Motility
*In order to quantify our data, the average distance moved in mm was measured and recorded in Figure 16. We can see that the water had a steady incline in movement compared to the acid and base. This was a randomized measurement in 10 sec. intervals and measured based on Figures 1–15.
Conclusion
If a Volvox Criteri colony is introduced to an acid or a strong base, the colony’s motility will notably decline. This hypothesis was supported in terms of the motility decline. When the environmental pH changes, it directly affects the functionality of Volvox cells. Additionally, when introduced to such alterations in environment, homeostasis is affected. A plausible explanation for these results is that the change in optimal pH of the environment denatured enzymes responsible for catalyzing motility of the two flagella. In a study which observed different pH environments and their effects on algae such as Spirogyra, Volvox, and Micrasterias, it was revealed that in a different pH environment with a high and low acidic pH, Volvox did not grow and thrive well either (Munden, 2005). An application of this experiment brings to light the issue of acid rain and its effect on organisms such as algae, which are a source of food for many other organisms such as Escherichia coli. A possible error in conducting this experiment may have been the choice of independent variables as a strong acid, strong base, and neutral pH as opposed to an additional inclusion of a weak acid or a weak base for a more detailed data collection. In addition, there may be alternative reasoning besides pH change as to why the Volvox cells did not appear to move when exposed to acids and bases. That is an area of further exploration.
References
Assadi-Rad, A. (2017, February 22). Amir Protista 3. Prod. Amir A. Rad. Perf. YouTube. San
Joaquin Delta College, 16 Feb. 2018. Web.
Hallmann, A. (1999, January 15). Enzymes in the Extracellular Matrix of Volvox: an Inducible,
Calcium-dependent Phosphatase with a Modular Composition*. Retrieved February 22,
2018, from http://www.jbc.org/content/274/3/1691.full
Munden, A. D. (2005, February). Algae and Acid Rain. Retrieved February 22, 2018, from http://cssf.usc.edu/History/2005/Projects/J1325.pdf
Shiraishi, H. (2008, August 26). Hatching enzyme of Volvox: a possible implication in the evolution of multicellularity . Retrieved February 22, 2018, from http://www.jbiochemtech.com/index.php/jbt/article/viewFile/JBT115/18
