Virtual lab Report: Determination of the rate of photosynthesis using Elodea plant

Introduction

Most of the aquatic plants, such as Elodea plant can be used in demonstrating the evolution of oxygen during photosynthesis process. If an aquatic plant is left in a solution that has some traces of carbon II oxide gas and there is the light of optimal intensity, such plant will undergo photosynthesis and produce effervescence that indicates production of oxygen gas. If the intensity of light is increased, the rate at which bubble is produced increases. On the other hand, decreasing the light intensity leads to a reduction in the number of bubbles observed. If the source of light is removed completely or its distance from the plant is varied to a point where the levels of energy are minimal, the production of bubbles stops completely. Light is one of the important factors of photosynthesis (IANCU & G. CHILOM, 2015). Therefore, cells of green plants left at a dark place will not undergo photosynthesis process. Increasing the amount of light results in an increased rate of photosynthesis until an optimum level of 38% is reached, above which photosynthesis does not take place.The following diagram shows a sample graph of light intensity against carbon II oxide.

 This experiment investigates the effects of light intensity on photosynthesis of Elodea plant by varying the distance of the source of light.

Hypothesis and Research question

Does the intensity of light affect the rate of photosynthesis of Elodea aquatic plants?

Hypothesis: True, the amount of light intensity affects the rate of photosynthesis in in Elodea plants. Exposing plants to too much light may cause them to burn out. On the other hand, very little light will not be enough to provide optimum photosynthesis.

Variables

Independent variable(IV): Time

Dependent Variable (DV): Number of bubbles formed

Controls and constants

Constants: Length of Elodea plant

Control: Light intensity from the lab who distance keeps on varying

Materials and software used

A computer, source of internet, and Adobe Flash Player for running the Virtual lab

Methodology

The experiment began by reading the instructions for adjusting the source of light. A data table was created to help in recording the number of bubbles after every minute and for a variety of distances. The light source was adjusted and placed at 160 mm (16cm) from the test tube containing specimen. The start button was clicked to give directions to the next screen where a close up of bubbles was seen being produced during the process of photosynthesis. The tab labeled BPM (beats per minute) was chosen to help in calculating the number of bubbles per minute. The tap button was clicked everytime a bubble was seen floating on the surface of the test tube. The process was repeated for three minutes and the data collected was recorded in the data table. The counter tab was chosen to help in giving the exact number of bubbles formed. The “+” button was clicked for every bubble that floated on top of the test tube. The process was done for three minutes, and the number of bubbles formed was recorded in the data table. A “Back” button was clicked and source of light adjusted to ensure it sits at 190 mm from the test tube. The above procedure was repeated, but this time the source of light was placed at 190 mm and 120 mm respectively. The number of bubbles observed was recorded in the data table.

Results

The table below gives an average number of bubbles recorded within three minutes after adjusting the source of light from 120 mm, 160 mm and 190 mm respectively.

The above data collected shows that the number of bubbles produced decreases with increase in the length of the source of light from the test tube that bears the specimen.

Discussion

The rate of photosynthesis is affected by different factors, but in this case, the light intensity is the only factor that was considered. The number of bubbles produced increased with a decrease in distance between the test tube and the source of light. The experiment involved recording the number of bubbles at low rates of light intensity and high levels of light intensity. For instance, when the distance between the test tube and source of light was 120 mm, 118 bubbles were observed, indicating high levels of light intensity (Virtual Lab, 2018). When light intensity is high, and below the optimum level, the rate of photosynthesis is increased resulting in increased production of air bubbles observed. However, if the rates of light intensity are very high, the process of photosynthesis reaches a saturation point and remains constant.  In such a case, the most likely cause of leveling off the photosynthesis process is saturation of active enzymes in the plant that catalyzes the reactions taking place. If the distance between the source of light and specimen is made shorter than 120 mm, the resulting limiting factor will be an ambient temperature that leads to increased rates of reaction, hence denaturing the catalyzing enzymes.

On the other hand, when the distance between the source of light and test tube was increased further to 160 mm, the number of bubbles produced decreased from 118 to 46.  In such a case, the rate of light intensity produced decreased, resulting in reduced rates of photosynthesis hence reduced the a number of bubbles. Further increase in distance to 190 mm resulted in reducing the number of bubbles produced because of reduced levels of light intensity (Virtual Lab, 2018). Therefore, the shorter the distance, the higher the light intensity and the higher the number of air bubbles process and vice versa. However, the results obtained from this experiment may not be accurate because some of the oxygen gas produced is dissolved in water or used by organisms living on the surface of Elodea plant.  Further, using the same piece of plant for the three different distances is impractical because its rate of photosynthesis decreased with time. The other source of error would have been as a result of poor observation of bubbles produced while tapping on the button before the counter records it.

Conclusion

The experiment showed that the higher the light intensity, the higher the rate of photosynthesis. This was proved by counting the number of bubbles produced at different distances between the source of light and specimen. Therefore, the experiment supports the hypothesis that the amount of light intensity affects the rate of photosynthesis in in Elodea plants.

References

IANCU, C., & G. CHILOM, C. (2015). DISCOVERING PHOTOSYNTHESIS BY EXPERIMENTS. Rrp.infim.ro. Retrieved 24 January 2018, from http://rrp.infim.ro/IP/A98.pdf

Virtual Lab. (2018). Photosynthesis - Virtual Experiment. Reading.ac.uk. Retrieved 24 January 2018, from http://www.reading.ac.uk/virtualexperiments/ves/preloader-photosynthesis-full.html