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

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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


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.


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,...
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