Ljc Lab

Investigable Question

My investigable question for the LJOC experiment was how does the pH level of the water in the jars affect the population size of protozoans? pH level, is a scale that measures the concentration of hydrogen ions. On the pH scale, somewhat surprisingly, 7 is neutral—not 0, and anything higher than 7 is basic, and anything lower than 7 is acidic.

Background

When we (Maleek and I) setup the experiment, which involved 3 jars, we weighed some grass and put some of the grass into each of the jars. We then began to experiment combining water with vinegar (which we knew had an acidic pH around 3), and later with baking powder (which we knew had a basic pH around 9), to find the mixtures for a pH of 5 and of 9. We knew that pure

To start off, I can use a fact I have in my background knowledge—that disinfectants, cleaners, and bleaches all have a high pH (between 9 and 12)—to make sense of the dead bacteria and missing protozoans. Disinfectants, soaps, and cleaners are all used to kill off bacteria and common germs. Because pH9 is around the same pH as disinfectants, soaps, and cleaners, the dots we observed were most likely exactly what we thought them to be; dead bacteria. This all makes sense, because we know what is supposed to kill off bacteria has the same pH, so maybe anything with such a pH will kill off bacteria. Also, it makes sense that one result of this would be that the protozoans disappear, or even die. In the LJOC ecosystem, the relationship between protozoans and bacteria is a predator and prey relationship. This means that protozoans are the consumers, eating bacteria—the producers—for food. If their aquatic habitat has a higher pH than 7, then the effect disinfectants have on bacteria will likely happen; the bacteria will die. This means that the protozoans would have a shrinking food source, which is an important limiting factor that has quite a considerable effect on the carrying capacity of the population of protozoans. This explains the missing protozoans, and the appearance of unmoving bacteria—replacing the usual moving, gray swath. This makes me think that pH9 did not directly kill off the protozoans; it simply killed off their food, lowering the amount of protozoans that could be fed in the habitat. I think that this explains the lack of anything living big enough to be seen, like nematodes, because everything in the food chain that size collapsed; all of the protists probably all died, and so did the fungi, such as mold, that weren’t able to decompose of the dead protozoans and other organisms. Also, the deaths of the protozoans in pH5 make sense, because acids, such as gastric acids (found in the