Experiment to Test the Role of Phosphorus in the Growth of Algae and




In an experiment to determine where the phosphorus in the phosphoruscycle goes, the two bar graphs, Figure 1 and Figure 2, were producedfor the sake of analyzing the data collected.

C.Graphs, Tables, and Calculations

Producing bar graphs with mean Total Phosphorus

The table used to generate the bar graph was:

Table1: Mean and standard deviation of Total Phosphorus

Total phosphorus



standard deviation
















algae+ daphnia





Figure1: Bar graph for the means Total Phosphorus showing the error barsbased on the standard deviations

Producing a bar graph showing the means of Phosphates

To generate the bar graph, Table 2 was first developed.

Table2: Mean and Standard deviation of Phosphate

PO4 (Dissolved)



standard deviation
















algae+ daphnia





Figure2: Bar graph for the mean Phosphate concentration showing the errorbars related to the standard deviations.

B. Questions

Quiz 1: Hypotheses

The experiment was conducted to test two hypotheses

H1: limited amounts of phosphorus and phosphates increase plantgrowth including that of zooplanktons while excess phosphorus andphosphates lead to an increase in algal growth and a reduction in thepopulation of daphnia.

H0: The amount of phosphates and phosphorus does not affect thepopulations of algae and daphnia.

According to the data collected from the experiment and theinformation displayed by the bar graphs, the Hypothesis H1 wasconfirmed while the H0 was rejected.

Quiz 2: Interpretation of the bar graphs

With reference to the error bars in Figurer 1, it is possible tostate that for the algae and the control samples, the absorption waslimited because phosphorus is limited in supply. Even after thetreatment, algae still do not use much phosphorus. However, for thesample that contains the mixture of zooplanktons and the algae, theabsorption was low before the treatment but increased significantlyafter the treatment. This reveals that the increased amount ofphosphorus increases the algal population that in turn leads to adecline in the population of daphnia.

The error bars also reveal that the increased amounts of phosphatespromote even more of the growth of algae, which decompose and depletedissolved oxygen thus suffocating the zooplanktons. This explains thetremendous decline in the bar of algae + daphnia in Figure 2.

Phosphorus ends up in the bodies of organisms through absorption. Asalgae absorb phosphorus in the form of phosphates, they increase intheir population. When phosphorus and phosphates are in limitedsupply, the daphnia are also able to absorb them and grow. However,as the amount of phosphorus is increased, the population of algaeincreases tremendously thus hindering the growth of the daphnia byusing up all of the available dissolved oxygen. The daphnia thereforesuffocates. This is called eutrophication.

Quiz 3: Properties of phosphorus

Phosphorus can be too much of a good thing. As the amount ofphosphorus is kept at minimum, phosphorus can be absorbed by plantsand animals for many beneficial uses. It a major plant nutrient thatpromotes plant growth in fresh water habitats, it is used by mammalstogether with calcium to make teeth.

However, as the amount of phosphorus increases in the water bodies,they end up causing algal blooms, which means that algae will growtremendously and becoming too much in the water. As the algae dieoff, they are decomposed by bacteria, taking up to much dissolvedoxygen from the water. The aquatic plants like daphnia will thensuffocate and die. This is called eutrophication.

Quiz 4: Experimental Errors

Errors are inevitable in experiments. There are some errors that canbe avoided while there are some that are just part of everyexperiment. Errors that result from the environmental conditions likeweather would be very difficult to deal with.

Contamination of samples is one of the sources of errors that is noteasy to control. The water that might have evaporated from the samplecontainers over the experiment duration may also not have beenaccounted for. Addition of more phosphorus or phosphates than therequired amounts could have also produced results with errors. Theuse of less amounts was also a possible source of errors. Defectivemeasuring devices could also have led to the production of errors.Some people also have reading problems, called parallax, which canlead to slight changes in the amounts measured, which can in turnlead to deceiving results.

Quiz 5: Particulate Phosphorus

At the end of the experiment, with the algae only treatment, the meanconcentration of particulate phosphorus was 90.9µg/L located in thewater. The phosphorus was initially within the algae but when lateron the algae died off, they decomposed to release the particulatephosphorus into the water and into the bodies of decomposers. Withinthe cells of the algae, it existed as a phosphate. This was confirmedthrough further research.

Quiz 6: Effects of Evaporated Water on Readings

The amount of water that evaporated from the treatment flasks duringthe experiment carried out for a whole week must be accounted for inorder to gain the right measurements. As the water in the solutionreduces, the concentration of phosphorus increases. If the researcherdoes not account for the evaporation, it is possible to take highermeasurement readings of concentrations of Total phosphorus and thephosphates than the actual values. The evaporated water may not havereadings of Total Mass of phosphorus in the flask since as waterevaporates, it leaves behind the phosphorus due to the fact thatphosphorus is not gaseous.

Quiz 7: The law of physics

Matter cannot be created nor destroyed. With regard to the results ofTotal Phosphorus in the algae + daphnia treatment, this law ofphysics is not violated. This is because the phosphorus is absorbedby the excess algae and exist in their cells in the form ofphosphates. When these algae will be decomposed, the phosphates willagain become phosphorus in the same amounts that were initiallyabsorbed by the algae.


In the experiment that was conducted to test the benefits ofphosphorus to aquatic environments, it was discovered that it leadsto increased growth of aquatic plants. However, this was found to beonly for the limited supply of phosphorus. When the amount ofphosphorus is increased, the algae will grow fast and as they die andare decomposed, the decomposers use up all the dissolved oxygenleading to the suffocation of the aquatic plant.