Lab Report: Photosynthesis

Abstract

The purpose of this experiment was to determine the need for light in the production of starch in plants. The predictions were that light is one of the conditions that necessitate the process of photosynthesis and thus, of starch production, in the leaf of geranium. Two pots were filled with geraniums, one of which was kept in light and the other in darkness. The two plants were boiled and extracted by using ethanol, and then stained using iodine to determine the presence or absence of starch in the leaves. The results indicated that the leaf which had been in the light was positive for starch, therefore indicating that starch was produced in the light. The starch present in the dark-exposed leaf could not be seen, suggesting the theory that light is needed during the process of photosynthesis. This experiment confirms again that light is required in the photosynthesis process and the formation of starch in plants.

Introduction

The process is called photosynthesis and deals with the process by which plants convert sunlight energy into products, i.e., chemicals in the form of glucose and other substances, such as starch (Simkin et al., 2022). This is performed in chloroplasts, whereby the light-to-dark reactions gain energy using sunlight to generate glucose. The role of light in the process of photosynthesis was already heavily documented, and light triggers the chloroplasts to perform the repetitive duty of turning carbon dioxide and water into glucose (Cronan, 2023). In the provided experiment, starch, as one of the photosynthesis products, will be examined in the geranium leaves. Glucose and light are hypothesized to be used in the experiment in order to produce glucose, and the presence of starch could be tested by the fact that, as the paint (the iodine), the starch could turn blue. The research question is: Does light play any role in the production of starch in geranium leaves?

Methods/Procedures

Materials

• China marker
• Lugol's iodine solution
• 2 Petri dishes
• Geranium plants
• Forceps
• DH₂O
• 2 400-ml beaker
• Hot plate
• 3-4 boiling chips
• 95% ethanol

Procedure

1. Two geranium plants were pre-selected. A single plant was left in the light throughout the experiment, whereas another was left in the dark.
2. One leaf was extracted from every plant, which was tagged to differentiate between the two.
3. In order to denature it and get rid of excessive pigments, each leaf was boiled in water for 223 min.
4. The leaves, which had been boiled, were transferred into a beaker with ethanol and then heated on a hot plate until the leaves were decolorized.
5. After the decolorization of the leaves, they were then transferred to a beaker containing Lugol's iodine solution and left to stand there for 2-3 minutes.
6. Following the iodine treatment, the leaves were washed and left to be examined for starch presence, which would result in a bluish-black color of the leaf.
7. The results were noted down, and the presence and absence of starch in the solution were recorded.

Observations and Results

The following were the observations made from the lab;

Table 1: Test for products

The blue-black iodine-stained light-exposed leaf (Geranium plant grown in the light) indicated the presence of starch in the leaf. The iodine stain did not cause the dark-exposed leaf (Geranium plant kept in darkness) to turn color, meaning it did not contain starch in it.

Discussion

The results of this experiment are noticeable and demonstrate that starch can be produced only in the presence of light. The plant exposed to light showed the presence of starch, and this aligns with the certainty of the known cycle of photosynthesis, where energy of light is captured and used in the synthesis of glucose, which is stored later as starch (Ribeiro et al., 2022). Dark-grown plants that were not allowed to see light did not make starch. Such an observation affirms the adoption of light in the catalysis of the chemical reaction that culminates in the generation of glucose and other by-products of photosynthesis (Stephens et al., 2021; Wang et al., 2022). When the dark exposed leaf lacks the starch content, it is evidence that in the absence of light, the process of photosynthesis does not take place, thus glucose and starch are not synthesized.

This experiment has validated the conclusions in previous experiments conducted on the relevance of light in the process of photosynthesis. It was just an easy experiment, but more extensive when trying with tester wavelengths of light to identify whether the particular light spectra is more influential on starch production than others. It is also possible to take the experiment to a greater extent by subjecting it to a sample of plant species to support the conclusion.

Conclusion

The experiment results proved that plants required light to produce starch. A positive outcome of the presence of starch was demonstrated in the leaf in the presence of light, thus validating the hypothesis that light is instrumental in photosynthesis. These findings support the necessity of light for the metabolism of plants and their capacity to stimulate the conversion of water and carbon dioxide to sugar in the form of glucose that is saved as starch. This experiment is another indication of how vital light is in photosynthesis and the formation of organic molecules in plants.

Answers to questions

1. Which wavelengths in the visible light spectrum provide the highest energy? Which wavelengths provide the least energy?

From the visible light, violet has the longest wavelengths, between 380nm and 450 nm, and the light with the shortest wavelength is red.

1. Explain the difference between the spectra produced by a green filter and by the plant extract.

The green filter blocked other types of light from penetrating it and allowed the green light to pass, whereas the plant extract only blocked green light from penetrating.

1. Explain why a leaf appears dark in color after being treated with iodine.

The leaf appears dark in color because iodine reacts with starch to form a blue-black substance.

1. Why is starch production an indication that photosynthesis is occurring?

It is an indication that photosynthesis occurred.