LAb report

Effect of light color on the rate of photosynthesis in Algal Beads Using Absorbance and pH

Sixto Sanchez

June 30, 2025

BSC2010L.9

Beatrice Chostel, Mareena Spiridis and Jasmelyn Barrera

Abstract

Four different light conditions were investigated and how they can affect the rate of photosynthesis in the alga beads. The light used was red, green, blue and white, this was the control that was used, and the light source was LED at about ten cm. Each cell contained ten algae beads with two ml of CO2 indicator solution. The photosynthesis was measured and thus the solvency was recorded as well as the changes in pH at 550 nm, these were every three minutes for thirty minutes. In the beginning it was hypothesized that red light would provide the highest rate of photosynthesis and green light would cause the lowest rate of photosynthesis in the chlorophyll solution spectrum. The results were able to confirm the hypothesis. The samples which were exposed to red light and those which were white showed that they had a higher increase in absorbance and pH, which did not indicate that more photosynthetic activity was taking place. On the contrary, what was green light which produced the smallest and somewhat negative changes, that was not indicating that it is the limited CO2 training and what those lower rates of photosynthesis. Observations were obtained with the naked eye, and this confirms the results also, seeing that the increase in color intensity is more pronounced in red and white light conditions.

Introduction (2-3 Pages reference the source)

Photosynthesis is the biochemical process by which plants, algae, and some bacteria convert light energy into chemical energy. Chlorophyll, the primary photosynthetic pigment, absorbs light most efficiently at red and blue wavelengths and reflects green light. As a result, green light is typically the least efficient for promoting photosynthesis. In this lab, we investigated how different colors of light affect the rate of photosynthesis in pearl algae. Photosynthesis rate was measured using a spectrophotometer to track changes in absorption at 550 nm and to monitor pH over time. Our hypothesis was that red light would yield the fastest photosynthesis rate and green light would yield the slowest rate.

Independent variable: light color.

Dependent variable: photosynthesis rate.

Control: white light.

Hypothesis:

The rate of photosynthesis will be highest under red light and lowest under green light because chlorophyll absorbs the red wavelength.

Materials and methods: (in my own words no list in past tense 1-2 pages long)

-2 Cuvettes

-10 Algal beads per cuvette

-2 ML CO2 indicator for blank

-Spectrometer set at 550 NM

-Led light source

-Ruler to ensure the light is at 10 cm

-Stopwatch

-Notes

1. Prepared 4 cuvettes with 10 algal beads each and 2 mL CO₂ indicator.

2. Assigned each to a different light condition (red, green, blue, white).

3. Placed all samples 10 cm from the LED light source.

4. Measured absorbance at 550 nm every 3 minutes for 24 minutes.

5. Recorded pH at the same time points.

6. Controlled for external variables such as temperature and light intensity.

Results:

Time	Red	Green	Blue	White (Control)
3	0.457	0.800	0.867	0.342
6	0.815	0.873	0.579	0.469
9	1.485	0.343	0.386	0.497
12	1.222	0.426	0.293	1.197
15	1.282	0.255	0.603	0.913
18	0.914	0.528	0.511	0.786
21	1.554	0.312	0.601	0.648
24	1.222	0.511	1.091	0.717

Table 1: Absorbance over time in four different light Conditions

Time	Red	Green	Blue	White (Control)
3	8.300	8.100	8.900	8.300
6	8.300	8.300	8.600	8.300
9	8.300	8.500	8.300	8.300
12	8.300	8.500	8.300	8.700
15	8.500	8.500	8.700	8.700
18	8.500	8.500	8.700	8.700
21	8.600	8.600	9.100	8.900
24	8.500	8.300	9.100	8.900

Table 2: Ph color over time in four different light Conditions

	∆ abs/time
Time (Minutes)	Red	Green	Blue	White (Control)
3	0.119	0.024	-0.096	0.042
6	0.223	-0.177	-0.064	0.009
9	-0.088	0.028	-0.031	0.233
12	0.020	-0.057	0.103	-0.095
15	-0.123	0.091	-0.031	-0.042
18	0.213	-0.072	0.030	-0.046
21	-0.111	0.066	0.163	0.023
24	0.045	-0.065	-0.024	0.055

Table 3: Absorbance over time in four different light Conditions

Figure 1: Absorbance in four different light conditions This graph is referring to the table 1 data

Figure 2: Change of pH over the time This graph is referring to the table 2 data

Figure 3: Absorbance over time in four different light conditions. This graph is referring to the table 3 data

Quantitative results. The absorbance readings were evaluated in the four light conditions throughout the 30-minute period. Referring to table 1, the algae beads that were exposed to the red light showed the greatest increase in absorbance with a peak of 1,554 at 21 minutes, indicating the greatest photosynthetic activity. Blue light produced a moderate increase in absorbance, with a late peak of 1.091 at 24 minutes. In contrast, green light showed the lowest and most inconsistent absorbance values. White light showed somewhat moderate and relatively stable absorbance changes.

Qualitative results. A visual inspection of the pH color changes in the algal beads was made and this supports the absorbance of data. Referring to table 2 the beads under red and blue light had noticeable changes towards more alkaline colors due to the time they were exposed to the light. These were being consumed by CO2 consumption due to photosynthesis. The green light made a minimal visible color change, while the white light samples showed a somewhat constant but moderate change and this indicates that their role is that of balanced control.

Discussion:

The hypothesis that red light would produce the highest photosynthesis rate and green light the lowest was confirmed by the data. Red and white light produced the most significant increases in absorption and pH, indicating higher photosynthesis rates and greater CO2 utilization. Green light, reflected by chlorophyll, showed a decrease in absorption and stable pH, confirming its ineffectiveness in stimulating photosynthesis. Blue light yielded average results. Possible sources of error include uneven distribution of rays, small changes in light intensity, and temperature fluctuations. Future experiments will include repetitions and a wider range of light intensities.

References:

Bottrill DE, Possingham JV, Kriedemann PE. 1970. The effect of nutrient deficiencies on photosynthesis and respiration in spinach. Plant Soil. 32(2):424–438.

Evans JR. 2013. Improving photosynthesis. Plant Physiol. 162(4):1780–1793.

Upadhyaya A. 2025. Cellular processes. In: BSC2010 lab manual, Summer 2025. Tampa (FL): USF ProCopy. p. 84.

Urry LA, Cain ML, Wasserman SA, Minorsky PV, Orr RB. 2020. Campbell biology. 12th ed. New York (NY): Pearson Education.

pH in four different light Conditions

Red 3 6 9 12 15 18 21 24 8.3000000000000007 8.3000000000000007 8.3000000000000007 8.3000000000 000007 8.5 8.5 8.6 8.5 Green 3 6 9 12 15 18 21 24 8.1 8.3000000000000007 8.5 8.5 8.5 8.5 8.6 8.3000000000000007 Blue 3 6 9 12 15 18 21 24 8.9 8.6 8.3000000000000007 8.3000000000000007 8.6999999999999993 8.6999999999999993 9.1 9.1 White (Control) 3 6 9 12 15 18 21 24 8.3000000000000007 8.3000000000000007 8.3000000000000007 8.6999999999999993 8.6999999999999993 8.6999999999999993 8.9 8.9

Time (Minutes)

pH

Absorvance over time in four different light Conditions

Red 3 6 9 12 15 18 21 24 0.11933333333333331 0.22333333333333338 -8.7666666666666712E-2 2.0000000000000018E-2 -0.12266666666666666 0.21333333333333335 -0.11066666666666669 5.0916666666666666E-2 Green 3 6 9 12 15 18 21 24 2.4333333333333318E-2 -0.17666666666666667 2.7666666666666655E-2 -5.6999999999999995E-2 9.1000000000000011E-2 -7.2000000000000008E-2 6.63333333333 33341E-2 2.1291666666666667E-2 Blue 3 6 9 12 15 18 21 24 -9.6000000000000016E-2 -6.4333333333333312E-2 -3.100000000000001E-2 0.10333333333333333 -3.0666666666666658E-2 2.99 99999999999988E-2 0.16333333333333333 4.545833333333333E-2 White (Control) 3 6 9 12 15 18 21 24 4.2333333333333313E-2 9.333333333333341E-3 0.23333333333333336 -9.4666666666666677E-2 -4 .2333333333333334E-2 -4.6000000000000006E-2 2.2999999999999982E-2 2.9874999999999999E-2

Time

Absorbance

Absorvance in four different light Conditions

Red 3 6 9 12 15 18 21 24 0.45700000000000002 0.81499999999999995 1.4850000000000001 1.222 1.282 0.91400000000000003 1.554 1.222 Green 3 6 9 12 15 18 21 24 0.8 0.873 0.34300000000000003 0.42599999999999999 0.255 0.52800000000000002 0.312 0.51100000000000001 Blue 3 6 9 12 15 18 21 24 0.86699999999999999 0.57899999999999996 0.38600000000000001 0.29299999999999998 0.60299999999999998 0.51100000000000001 0.60099999999999998 1.091 White (Control) 3 6 9 12 15 18 21 24 0.34200000000000003 0.46899999999999997 0.497 1.1970000000000001 0.91300000000000003 0.78600000000000003 0.64800000000000002 0.71699999999999997

Time (Minutes)

Absorvance