Lab Report Example: A Full Biology Lab Report With Data and Notes

Abstract

Catalase, the enzyme that breaks down hydrogen peroxide into water and oxygen, is present in nearly all aerobic organisms and is easily extracted from potato tissue for classroom study. This report measures catalase activity across five temperatures (4, 22, 40, 50 and 60 degrees Celsius) using a filter-paper disc float assay, in which a faster float indicates faster oxygen production and therefore higher enzyme activity. Discs soaked in a standardized potato extract were submerged in a 1.5% hydrogen peroxide solution held at each target temperature, and float time was recorded across three trials per temperature. Mean float time was shortest at 40 degrees Celsius (22 seconds) and increased sharply above and below that point, with discs at 60 degrees Celsius failing to float within a 300-second cutoff. Results match catalase's expected mid-range temperature optimum and its loss of activity through heat denaturation.

Introduction

Catalase (EC 1.11.1.6) is one of the fastest enzymes known, converting hydrogen peroxide, a toxic byproduct of aerobic metabolism, into water and oxygen gas at a rate approaching the diffusion limit (Chelikani et al., 2004). Because catalase activity is easy to observe visually through oxygen bubble production, it is a standard subject for an introductory enzyme-kinetics lab. Like most enzymes, catalase's activity depends on temperature: reaction rate typically rises with temperature up to an optimum, then falls as heat disrupts the protein's folded structure, a relationship general biochemistry texts describe for enzymes broadly (Nelson & Cox, 2017). This experiment tests that relationship directly in potato-derived catalase.

Hypothesis: catalase activity, measured as float time in a filter-paper disc assay, will be fastest (shortest float time) at a mid-range temperature near 40 degrees Celsius, and will slow sharply at both a refrigerated temperature and a temperature at or above 60 degrees Celsius, where the enzyme is expected to denature.

Materials and methods

Materials. Russet potato, blender, cheesecloth, filter paper (6 mm discs), 1.5% hydrogen peroxide solution, five water baths held at 4, 22, 40, 50 and 60 degrees Celsius and checked with a calibrated thermometer, 250 mL beakers, stopwatch, forceps.

Extract preparation. 50 g of peeled potato was blended with 100 mL of cold distilled water for 30 seconds, then filtered through two layers of cheesecloth to remove solids. The filtrate was kept on ice and used within 30 minutes of preparation to limit activity loss before testing.

Procedure. For each temperature, 100 mL of 1.5% hydrogen peroxide was equilibrated in its water bath for five minutes. A filter paper disc was submerged in the potato extract for 10 seconds, lifted with forceps to drain excess liquid, then dropped to the bottom of the hydrogen peroxide solution. A stopwatch recorded the time from submersion to the disc floating to the surface, which happens once enough oxygen gas has collected under the disc to overcome its weight. Each temperature was tested in three trials with a fresh disc and fresh hydrogen peroxide solution each time, and the observation window was capped at 300 seconds.

Results

Mean float time was shortest, meaning catalase activity was highest, at 40 degrees Celsius, and increased at both the lower and the higher temperatures tested (Table 1, Figure 1). At 60 degrees Celsius, no disc floated within the 300-second cutoff in any of the three trials, consistent with denaturation rather than simply slower activity.

Table: Mean time to float (seconds) by temperature, potato catalase in 1.5% hydrogen peroxide (illustrative data created for this sample; n = 3 trials per temperature)

Figure 1 (described): a line graph plots mean float time in seconds (y-axis, lower means faster) against temperature in degrees Celsius (x-axis). The line falls from 4 to 40 degrees Celsius, then rises steeply from 40 to 50 degrees Celsius; the 60-degree point is plotted off-scale, past the 300-second cutoff, to mark denaturation rather than a slow but measurable rate.

Discussion

The results support the hypothesis: float time was shortest at 40 degrees Celsius and increased on both sides of that point, the rise-then-fall pattern described for enzymes generally (Nelson & Cox, 2017). Catalases from different organisms vary widely in properties such as heat stability (Switala & Loewen, 2002), so the optimum measured here applies to this potato extract and this assay only. The sharp jump between 50 and 60 degrees Celsius, rather than a gradual slowdown, is consistent with denaturation: past a threshold, heat unfolds the enzyme's active site fast enough that activity collapses within the trial instead of merely slowing.

Between 4 and 40 degrees Celsius, mean float time fell from 168 to 22 seconds, a more than sevenfold difference. That falling segment reflects faster molecular motion: enzyme and substrate collide more often at higher temperature, so the reaction speeds up until the protein's structure begins to fail. The 50-degree result, slower than 40 but still measurable, suggests partial denaturation, with some enzyme molecules still active. By 60 degrees Celsius, too few remained active to lift a disc within 300 seconds.

Error analysis. The 4-degree trials showed the largest spread (SD = 10.5 s), most likely because condensation on the cold beaker made the disc's exact submersion moment harder to time consistently across trials. A second limitation is that float time is an indirect proxy for reaction rate: it depends on the disc's oxygen-holding capacity as well as the reaction itself, so the assay ranks relative activity across conditions rather than measuring catalase kinetics in absolute units. A titration-based or spectrophotometric assay would remove that indirectness, at the cost of equipment a typical introductory lab does not have.

Conclusion. Potato catalase, assayed by filter-paper disc float time, showed its fastest activity near 40 degrees Celsius and lost measurable activity by 60 degrees Celsius, supporting the hypothesis that catalase activity in this system follows the same rise-then-fall temperature pattern documented for enzymes broadly. Because catalases differ in structure across organisms (Chelikani et al., 2004), a follow-up run at 35, 40, and 45 degrees Celsius would locate this extract's optimum more precisely.

References

Chelikani, P., Fita, I., & Loewen, P. C. (2004). Diversity of structures and properties among catalases. Cellular and Molecular Life Sciences, 61(2), 192-208. https://doi.org/10.1007/s00018-003-3206-5

Nelson, D. L., & Cox, M. M. (2017). Lehninger principles of biochemistry (7th ed.). W. H. Freeman.

Switala, J., & Loewen, P. C. (2002). Diversity of properties among catalases. Archives of Biochemistry and Biophysics, 401(2), 145-154. https://doi.org/10.1016/S0003-9861(02)00049-8