Photosynthesis Lab Report
Introduction Plants use a process called photosynthesis to covert energy from the sun into energy they can use for their activities. The plant’s chloroplasts, along with water, carbon dioxide, and light are the essential elements required for photosynthesis to take place. The “photo” part of photosynthesis is in reference to the fact that the process requires light. The simplest form of the photosynthesis equation is:
H2O + CO2 ----light----> (CH2O)N + O2
As shown in the equation, photosynthesis produces carbohydrates, but more importantly, it produces oxygen.
In 1937, Robert Hill discovered that chloroplasts in water could release oxygen if light and an electron acceptor are available. In his experiment, oxygen was still being released without the presence of CO2, meaning that it had to be coming from the water. This discovery also showed that photosynthetic reactions are different than others because they give up oxygen, whereas others use CO2. Lastly, it showed that oxidation-reduction reactions are a major part of photosynthesis. Electron-acceptor molecules are being reduced and oxidized as electrons move around during photosynthesis. As part of this movement, electrons reduce NADP+ to NADPH, which is used in light-independent reactions. A dye, DPIP, is needed to distinguish this process, where the dye’s change in color indicates electrons flowing and photosynthetic activity. Testing various conditions on their photosynthetic effectiveness is made possible by using DPIP and observing its color change (Stegenga 24-8). In class, we observed this happening using a lamp and a spectrophotometer to measure the amount of light being transmitted through a test tube. Chloroplasts were placed into test tubes along with water, DPIP, and a buffer to neutralize the pH of the solution, and then placed under a lamp with a standard 40-watt light bulb. One test tube was used to calibrate the spectrophotometer so that each transmittance reading would be
H2O + CO2 ----light----> (CH2O)N + O2
As shown in the equation, photosynthesis produces carbohydrates, but more importantly, it produces oxygen.
In 1937, Robert Hill discovered that chloroplasts in water could release oxygen if light and an electron acceptor are available. In his experiment, oxygen was still being released without the presence of CO2, meaning that it had to be coming from the water. This discovery also showed that photosynthetic reactions are different than others because they give up oxygen, whereas others use CO2. Lastly, it showed that oxidation-reduction reactions are a major part of photosynthesis. Electron-acceptor molecules are being reduced and oxidized as electrons move around during photosynthesis. As part of this movement, electrons reduce NADP+ to NADPH, which is used in light-independent reactions. A dye, DPIP, is needed to distinguish this process, where the dye’s change in color indicates electrons flowing and photosynthetic activity. Testing various conditions on their photosynthetic effectiveness is made possible by using DPIP and observing its color change (Stegenga 24-8). In class, we observed this happening using a lamp and a spectrophotometer to measure the amount of light being transmitted through a test tube. Chloroplasts were placed into test tubes along with water, DPIP, and a buffer to neutralize the pH of the solution, and then placed under a lamp with a standard 40-watt light bulb. One test tube was used to calibrate the spectrophotometer so that each transmittance reading would be
Cited: "Lab #4 - Photosynthesis." Laboratory Exercises for Biology 101. Ed. Barbara Stegenga. N.p.: n.p., n.d. 24-28. Print.