The Effect of Light Quality and Light Quantity on a Photosynthetic Plant

Photosynthesis can be defined as light energy being converted into chemical energy, which is a very important process for plants and other organisms. Light can be described in terms of light quantity and light quality. Both of these have an affect on photosynthesis. The more light a plant absorbs the more the plant is able to photosynthesize. This light is absorbed though pigments which have specific interactions with certain light waves (colors). The goal of my first experiment was to test the effect that which different colors have on photosynthesis, in other words the amount of oxygen that is produced.

As previously mentioned, oxygen is a product of photosynthesis. In my second experiment, I tested whether light intensity has an affect on photosynthesis, in other words the release of oxygen. µmol m-2 s-1 Methods: Light quality: First, I cut off the Egeria of a plant and placed in a bicarbonate solution. Then, I started by placing a green filter in front of the test tube turning on the projector. Next, I set the PAR at 70 µmol m-2 s-1 by moving the projector closer or farther from the plant. At that time, I brought the test tube with the Egeria in closer and exposed the green light on to it starting me stop watch at the same time.

I allowed the stem to photosynthesis for three minutes and recorded the amount of oxygen which was released. I repeated the same process with the blue, red and white filters. After I took all the measurements with all the filters and weighed my plant on a scale. Light quantity: With this experiment I used two plants, a light plant and a shade plant. First of all, I switched on the projector so that I could adjust my light intensity to my liking by placing the projector closer or further away from my plant.

Then, I placed a transparent water bath in between the projector and test tube. Next, I took the light plant and placed it in the test tube and began the stop watch simultaneously. I let the plant photosynthesis for a certain amount of time and then shut off the projector and stopped the stop watch. I then, recorded the amount pf oxygen released that was shown in the pipette. I test the same process for all the different PAR levels (i. e. 21, 30, 40, 50, 61, 80, 100, 120, 141, 160, 200, 300 and 401). I then repeated the experiment with my shade plant.

After I recorded my results, and weighed both my light and shade plant. Discussion: Plants react different to different color lights. I experimented with different colors of light including red, blue, green and white to test how the plant reacts to each. From my results in this experiment, I noticed that blue light produced the most photosynthesis. The red light caused the plant to produce the second highest oxygen while the white light was third and the green light produced the least oxygen. There are two types in chlorophyll, chlorophyll A and B.

Chlorophyll A is a pigment that absorbs light and converts it in to energy. Chlorophyll B also absorbs light but it absorbs the light that chlorophyll A can not absorb. Chlorophyll B works secondary. The pigments in the plant are responsible for absorbing the green light. Chlorophyll A successfully absorbs light on the red side of the spectrum, whereas chlorophyll B successfully absorbs light on the blue side of the spectrum. Plants absorb red and blue light, but reflect green light. White light consists of red, blue and green light.

A photon can be defined as moving energy. Light has photons but of different wave lengths, resulting in different colors. Red light has the longest wave length with 650 nm, while green light is slightly shorter with 560 nm; however blue light has the shortest wave length with 430 nm. The shorter the wave length, the more energy is produced. Blue light results in the most energy and green light the least, but absorption plays a much bigger role in photon absorption. When it comes to light intensities, plants do not always react the same.

A light plant photosynthesis’ better in a high light intensity whereas the dark plant reacts better at a low light intensity. The light plant began to photosynthesis slowly, but it increased on a PAR of 61 and reached its maximum at PAR 100 and stayed constant at 141. The amount of oxygen released by the shade plant at a low light intensity was higher in the beginning in comparison to the light plant, but it reached a constant amount of oxygen being released at a faster pace. The shade plants oxygen produced at a high light intensity is less than the light plant.

The reason that the photosynthesis tempos differ at a low light intensity is because the shade plants cells function at low light intensity while the light plant needs more light in order to photosynthesis at the same rate. The light plant is more functional and photosynthesizes faster than the shadow plant when the PAR level rises above 60. The shade plant reaches its maximum photosynthesis temp at around 70 µmol m-2 s-1 and cannot photosynthesis faster because the plants maximum light capacity has been reached.

The light plant reaches its maximum photosynthetic temp by 100 µmol m-2s-1 because its cells are used to store more light, thus more light is needed for maximum photosynthesis. Results: Effect of color of light on rate of oxygen evolution Color FilterTime (min)PAR (µmol m-2 s-1)Oxygen produced (µl)Mass (g)Photosynthesis rate Red3 m70148 µl2. 901 g17. 01 g Green3 m7080 µl2. 901 g9. 19 g Blue3 m70178 µl2. 901 g20. 45 g White3 m70120 µl2. 901 g13. 79 g **Graph attached “Light plant” PAR (µmol m-2 s-1)Time (min)Oxygen produced (µl)Mass (g) 218:26 m21 µl2. 83 g 303:37 m20 µl2. 83 g 403:05 m23 µl2. 3 g 502:04 m24 µl2. 83 g 611:49 m28 µl2. 83 g 801:05 m22 µl2. 83 g 1001:06 m30 µl2. 83 g 12035 (s)20 µl2. 83 g 14132 (s)21 µl2. 83 g 16032 (s)21 µl2. 83 g 20132 (s)21 µl2. 83 g 30032 (s)21 µl2. 83 g 40032 (s)21 µl2. 83 g **

Graph attached “Shade plant” PAR (µmol m-2 s-1)Time (min)Oxygen produced (µl)Mass (g) 214:35 min21 µl3. 25 g 302:44 min21 µl3. 25 g 401:58 min21 µl3. 25 g 501:45 min21 µl3. 25 g 611:40 min22 µl3. 25 g 801:30 min23 µl3. 25 g 1001:24 min22 µl3. 25 g 1201:25 min21 µl3. 25 g 1411:10 min21 µl3. 25 g 1601:14 min21 µl3. 25 g 2001:12 min21 µl3. 25 g 3001:12 min21 µl3. 25 g 011:12 min21 µl3. 25 g **Graph attached Addendum A: A. 1. Why immerse the leaf in a bicarbonate solution and not simply water? The leaf is placed into a bicarbonate solution and not just simply water because plants use the carbon from the solution in the process of photosynthesis. A. 2. Why is a transparent water bath placed between the projector and the tube containing the shoot? A water bath is placed in between the projector and the test tube so that the water bath prevents the heat caused by the projector to play an affect on the experiment, allowing the results to be as accurate as possible.

Conclusion: My experiments clearly show that light quality and quantity have a direct affect on photosynthesis in plants. My results show that blue light produces the most energy where as green light produces the least amount. The amount of oxygen produced varies from plant type to plant type. Light plants produce more oxygen than shade plants, but shad plants reach their optimum photosynthesis level quicker as light intensity increases.


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