Photosynthesis Prac (copy)

Research Question

What effect does the number of photosynthesizing  plants have on the pH of the surrounding environment?

Independent Variable

Number of algae balls able to photosynthesize (40,  30,  20, 10, 5, 1 and 0)

Dependant Variable

Amount of carbon dioxide used by the algae  as measured by the colour of pH indicator

Controlled Variables

amount of 2% calcium chloride solution (50ml), light source ball are left under (lumen lamp),  time left under lamp

Aim

To investigate the amount of carbon dioxide used with different numbers of photosynthesising algae balls present as measured by the colour of the pH indicator.

Hypothesis

If the amount of carbon dioxide used by the algae balls is dependant on the amount of balls present then the most carbon dioxide would be used by the 40 balls vial as opposed to the 30, 20, 20, 5, 1 and 0 as reflected by the most purple (alkaline) colour of pH indicator such as 8.6, 9.0, 9.1.

biological concepts

In the tubes with less balls, (0, 1, 5, 10) the colour of the indicator was more yellow toned indicating pHs of (7.6, 7.8, 8.1/more acidic) due to the higher amount of Co2 dissolving in the water forming carbonic acid. While the tubes with more balls (20, 30, 40) were more purple toned indicate pHs of (8.6, 9.0, 9.1/more alkaline) as there is less Co2 dissolving in the water as it is being used as an input for photosynthesis by the algae balls.

Limitations

errors

Random errors of this experiment include observer bias, photo quality and size of algae balls created.

validity

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These values, particularly the set with 3 outliers contradict the data collected by the other groups. While not deeming the entire experiment invalid, the observer bias aforementioned as well as the relatively few repeats means that the investigation of how much carbon dioxide is used with varying numbers of algae balls is not thorough enough. Particularly considering the number of outliers, questioning the reproducibility of the experiment to garner the same results.

accuracy

Accurate, expected values in this experiment would be increasing pH levels in the tubes of 0 through 40 balls. With 0 having the acidic 7.6 and 40 having the highest alkaline numbers of the 9.0-9.2 range. A value that is not accurate in this experiment is the recorded pH of 8.4 in the  30 balls tube. Which is a pH in the middle of the possible range in the tube with the second largest number of balls.

precision

One of the 40 balls tubes are not precise as there is  an outlier in the with 8.6 compared to all the other groups obtaining a 9.6. As well as in the 30 balls tubes with 8.4 compared to all the other groups obtaining a 8.8-9.2 (well in the purple, alkaline range). The 20 ball tubes had 8.2, 8.3, 8.4 compared to the other groups obtaining a 8.7-9 which meaning 3 values were listed as having a lower pH than the other 6 groups, which were much closer to the accurate, expected values

improvements

involve using the same camera when taking photos of results or recording the pH in the moment, as well as colour swatch cards of pH in order to allow the experimenters to get a close up match, as well as a set distance the syringe must be from the beaker and a swirling mechanism or technique given ahead of time