Photosynthesis Lab Report

July 13th, 2022


Light plays a crucial role in photosynthesis, especially in the splitting of water molecules to be utilized in the subsequent process. An experiment was carried out to investigate the effects of light on photosynthesis. It illustrated the impact of light by investigating the buoyancy of the leaves of the disc plates. The discs were first placed in a vacuum where they sunk since the intercellular spaces were filled with liquid instead of air. The experiment revealed that photosynthesis occurred in plants at a faster rate when the light was used compared to when the plants were placed in a darker environment. It was demonstrated by the number of plants that were buoyant at the end of the process. The study also investigated the effect of light shades and showed that they had no effect on photosynthesis. The results of the above experiment are indicative of the important role that the light-dependent process plays in photosynthesis.

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Photosynthesis Lab Report


Photosynthesis is a process in which plants use sunlight in the presence of water and chlorophyll to make food. It commonly occurs in green plants only and remains one of the dynamic methods that provide food for heterotrophic organisms (Evans, 2013). Photosynthesis is divided into two phases referred to as the light phase and the dark phase. In the former, the process occurs in the thylakoid membrane where light-dependent reactions are utilized. In this case, the different systems present in chlorophyll are employed to trap light and make ATP and NADPH (Sage, Sage, & Kocacinar, 2012). In the dark stage, the water is split, various elements are coupled with ATP, and NADPH is deployed in making a sugar molecule commonly referred to as glucose (Pallardy, 2008). The second process is classified as light-independent, and it uses specific enzymes present in the molecule (Pallardy, 2008). There are various conditions that must be present for photosynthesis to take place. These conditions include light, carbon dioxide, water, and chlorophyll in their required quantities. The absence of one compound impedes the process to a large extent. In this experiment, light-dependent reactions will be investigated through the use of disc plates. In a normal situation, the leaves of any plant are composed of intercellular spaces, which commonly contain oxygen as the main gas. When placed in any solution, plants commonly have some form of buoyancy. When these leaves are placed within a vacuum, the oxygen in the leaves is replaced making them sink and lose their buoyancy in any solution since the space of the gas is filled with liquid. When photosynthesis occurs in plants, oxygen is released as a by-product, and in the process, the leaves move from their sinking positions to their floating positions. This experiment investigates the rates of photosynthesis in plants in light and dark conditions.

Alternate Hypothesis

Photosynthesis will be observed in plants that were placed under the lamp as compared to those placed in dark conditions, or if plants are put under light, the rate of photosynthesis is expected to be higher than in those in the dark environment.

Null hypothesis

The rate of photosynthesis in the plants in light and dark conditions will be the same, or if the plants are placed in either light or dark conditions, the rate of photosynthesis is expected to be identical.


A lamp was attached to a stand, which is 25 cm high, to provide room for the use of light or dark conditions. A beaker filled with cold water was placed at the bottom of the lamp and was secured to the stand. A solution of 0.2 % sodium hydrogen carbonate was then poured into Petri dishes until they were two-thirds full. After that, 100 ml of sodium hydrogen carbonate was poured into a 250 ml flask. Several spinach disks that had been cut were then placed in the sodium hydrogen carbonate solution. The discs that contained large veins were excluded from the experiment. Then, 40-50 discs were put in the beaker while a Styrofoam board was used to make the disc plates. A water aspirator was utilized to create the necessary disc conditions and ultimately sink all the plants. Any plants that did not sink were eliminated before the next step was carried out. Forceps were used to identify such leaves. About 10-15 leaf pieces were then selected and put into several Petri dishes. The lids were placed on each of the Petri dishes before being put in different conditions. One Petri dish was placed in the dark, another one — in a light room, and the third one was put under a lamp. The leaves were left exposed to their different environments for about twenty minutes for the scientists to investigate if photosynthesis was taking place. The results of the experiment were noted in a table indicating the number of disc plates that were floating. The study was carried out in triplicate. The effect of different color shades on the rate of photosynthesis was investigated by checking the reaction of the plants to red, yellow, and blue colors.



Disks Floating

% Disc Floating




Room light



Under the lamp



Table 1. Table indicating the number of discs floating and the total percentage of discs floating when placed in different environments


Number of drops

Disks Floating

% Disc Floating













Table 2. Description of a unique experiment based on the effect of covering different Petri dishes with various colors.

Table 1 shows the number of discs that floated after changing the environment from vacuum conditions to their different settings. The table indicates that the number of discs floating under the lamp was larger than that of the present in the dark conditions.

Table 2 shows the effects of different light shades after their placement under the lamp. The numbers of the floating disks, in this case, were identical for every color, which suggests that the effect was the same across the various replicates.


The findings suggest that the null hypothesis was wrong. It implied that photosynthesis would take place at the same rate in both light and dark conditions. The results of the test indicate that the rate of photosynthesis was higher in the lighter conditions as compared to the darker conditions. It suggests that light plays a crucial role in the experiment and the process of photosynthesis overall. The alternate hypothesis suggested that the rate of photosynthesis would be greater in the plants under the light as compared to those in darker areas. Thus, the alternate hypothesis was true in this case. In principle, photosynthesis as a process has two phases. The light-dependent reaction utilizes light to break down different compounds before the products enter the dark phase (Evans, 2013; Sage et al., 2012). In this case, the presence of the light act to ensure the photosynthetic process occurs at a faster rate. The amount of light present determines the rate of photosynthesis as noted in the difference between the results of plants placed in the room light and under the lamp. The amount of light produced by the lamp was greater, thus the photosynthesis in the plants that had been placed there took place at a faster rate (West-Eberhard, Smith, & Winter, 2011). The results also indicate that different color shades have no effect on the rate of photosynthesis.

There were some possible sources of errors, especially during the creation of the vacuum condition. Thus, the vacuum conditions may have caused some leaves to fall on each other and affect the selection process. In addition, leaves that were depicted between the interphase were also selected. Another key limitation was controlling the amount of light produced by the lamp as well as the environmental light, which could be affected by any other condition that prevailed during the day. Some improvements could be made in the above experiment by ensuring that total automated vacuum conditions were utilized in the process. Moreover, the use of artificial light would be an elaborate approach to controlling any form of light. The above experiment served to highlight the important role that light plays in the photosynthetic process.

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