BIO 120 Grossmont College Photosynthesis Biology Lab Report

BIO 120 Grossmont College Photosynthesis Biology Lab Report

Photosynthesis is a food making process that autotrophic plants use. The rate at which photosynthesis occurs can be based off many factors such as light intensity. In this experiment we analyzed that rate at which photosynthesis occurs by observing the time it took for Spinach (S. Oleracea) leaves to float to the top of a bicarbonate solution in comparison to different light intensities. Four treatments were observed. No light, our control, low lux, medium lux and a high lux. Results were noted and observed. Our control treatment averaged 1200+/- 0 seconds, low lux took approximately 686.3+/- 464.76 seconds , medium lux averaged 587.7 +/- 134.90 seconds and high lux treatment took on average 432.6 +/- 267.9 seconds to notice disk flotation. We hypothesized that as light intensity increased, the rate of photosynthesis would also increase. If there was a lower quality of light then photosynthesis would be slower compared to higher quality of light. Based off data, our hypothesis was supported. It can be concluded that based off this experiment plants perform photosynthesis at a much faster rate if they have a stronger light intensity than plants who have a low light intensity. Those who have a profession in the agriculture business can benefit from this study as it demonstrates an adequate way to improve the health of their crops.

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Introduction

All organisms on the earth need a way to obtain energy to survive. The process of creating energy from light is known as photosynthesis. It’s an extensive process that undergoes multiple steps that produces the oxygen we use to breathe. When light is absorbed into the leaf of a plant, electrons within each photosystem are boosted to a higher energy level (Urry et al. 2016). Once electrons are excited, adenosine triphosphate (ATP) is produced. This first step of photosynthesis is known as the Light Reactions. The Calvin Cycle is now in full effect. An anabolic process that allows carbon to enter from a CO2 source and exit as a sugar (Urry et al. 2016). The Calvin Cycle is performed in three phases. Stage one, carbon fixation attaches a five carbon sugar to to a CO2 molecule creating a new 6 carbon intermediate. It becomes too unsteady and thus splits into two three carbon molecules known as 3-phosphoglycerate. The second stage, reduction takes each 3-phosphoglycerate gets another phosphate from an ATP molecule. A group of electrons from NADPH reduces turing 3-phosphoglycerate into G3P, a sugar. Lastly the third stage known as the regeneration of the CO2 acceptor is a series in which five molecules of G3P are arranged in such a way that that they are made into three molecules of RuBP, a protein that is bountiful on earth. RuBP can accept CO2 again and the cycle repeats (Urry et al. 2016). Carbon dioxide concentration, temperature, and light can affect the rate at which photosynthesis occur (Prinsley and Leegood 1986). Having a greater amount of a carbon source can increase the rate at which photosynthesis occurs (Liu et al. 2009). In the described experiment, light intensity was our variable. In a previous study done at the University of Belgrade, a comparison of several light intensities in relation with photosynthetic activity was done. Their treatment that was placed in a dark setting of -83 lux as their control, showed a relatively low respiration. As treatments were exposed to higher lux levels, their photosynthetic rates increased (Rakic et al.

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2014). In another research done in Bremerhaven, Germany; effects of varying light intensity and photosynthesis were observed. Net photosynthesis was observed based on O2 and CO2 concentrations that accumulated. These concentration would show disk flotation. Results showed that light intensity had a desirable effect on growth rates on S.Oleracea (Trimborn et al. 2007). For the following experiment, a consideration of light and photosynthesis on  S.Oleracea examined. The relationship between the two variables may show an acute connection as how desirable light is to the rate of photosynthesis. Based on previous studies and results, we hypothesis that as light intensity increase then so will the rate at which photosynthesis occurs. If light intensity is lower on particular treatments then those treatments wont show desirable effects.

Methods Prior to the experiment, Fluorescent lights were turned on and allowed to heat. In addition, styrofoam boxes were placed beneath the lamp at different heights to emulate different light intensities. Using a hole punch, about 20 disks were cut out of the S. Oleracea leaves avoiding any stems, allowing some extra disks to be cut out incase of error. For each treatment of
bicarbonate solution 2.5%, our source of carbon, one being a control group and remaining three the experimental group, about five to seven disks were placed in a syringe that was previously capped. A generous amount of the bicarbonate 2.5% solution was added to the syringe. The plunger was reapplied and the syringe was turned upside down; cap was removed. All air was pushed out by pushing the syringe until a small bubble formed on the outside. The thumb was used on the tip of the syringe to create a suction by pressing firmly and holding the plunger with your other hand. While still pressing the thumb down, making sure no air is being released a vacuum was created by pulling the plunger portion down approximately two times but no more than five. Plunging too many could lyse the vacuole causing misleading results. Once a vacuums were created, S. Oleracea disks began falling to the bottom of the solution. Once five disks had fallen, they were moved back to their original cup of bicarbonate solution and immediately covered with aluminum foil to prevent premature photosynthesis. A lux meter was placed on each level of the light box and recorded. Following, all experimental treatments were placed at different levels of intensity and stopwatches were ready. Aluminum foil was removed and the timers were started simultaneously. Observations were made as soon as movement of disks were discovered and time was noted in seconds. Time of each disk was recorded in the corresponding treatment. An average along with standard deviation was calculated using the following formulae: