Question

question 1

1. Your experiment used the decolorization of DCPIP to indirectly measure rates of photosynthesis in the isolated chloroplasts. Why does this work? To answer this, first provide a detailed description of the Linear Electron Flow pathway as it occurs in chloroplasts, and then explain what part of this pathway actually decolorizes DCPIP and why this only occurs when light is shining on the chloroplasts. Feel free to research this before answering. Provide the URL of any source(s) you use. (12 pts) 2. Our experimentally derived "action spectrum" seemed at odds with our directly measured Absorbance Spectrum in that blue light is absorbed more than red light, yet our chloroplasts produced a higher rate of photosynthesis when exposed to red light than when exposed to blue light. This seems backwards. One variable that was out of our control was our source of white light. Our lamps were equipped with incandescent light bulbs. Research the emission spectrum (spectral output) of incandescent light bulbs, and include an image/images of the emission spectra (spectral outputs) of incandescent bulbs versus natural daylight from the sun. Compare the light bulb emission spectrum with the absorbance spectrum you generated for the extracted spinach leaf pigments (or the one shown in the Action Spectrum data analysis recording). Discuss how the incandescent light sources could have impacted your results, perhaps explaining discrepancies noted above. Provide the URL of any source(s) you use (12 pts) 3. Anthocyanins are reddish-purple pigments found in the leaves and other organs of many plants. Research the absorbance spectrum of these pigments and include an image of it. Now compare the absorbance spectrum of anthocyanins with the action spectrum of photosynthesis either the one we generated with our data or ones that are published. Does this comparison suggest that anthocyanins participate as photosynthetic pigments? Not all plant pigments are photosynthetic-does the comparison indicate instead that anthocyanins are examples of these? Provide a logical argument to support your answer, and feel free to research the topic before answering. Provide the URL of any source(s) you use. (12 pts)

Answer 1

Answer-

According to the given question-

We know that the Green Plants, algae and some bacteria  produces their own food in the form of glucose in presence of light and water by photosynthesis . they  convert light energy into chemical energy stored in form of sugars and releases oxygen in most of the cases.

6CO2 + 6 H2O-------->>>C6H12O6 + 6O2

During photosynthesis the light energy is received by reaction centres that have pigments called chlorophyll. While in plants the reaction centres are present in chloroplasts. photosynthesis is divided into

• Light-dependent reactions or  light reaction and occur in presence of light
• Light-independent reactions or dark reactions occur in absence of light.

Light reaction is divided into cyclic and non cyclic. During non cyclic the photons are received to the photosystem II that causes release of an electron to the molecule pheophytin which serve as primary electron-acceptor and the electron further moved down through the different component.  During light reaction chlorophyll of Photosystem II or P680 receive one photon and at the same time it loses one electron also. now this electron is moved to pheophytin, which transfer it to the next molecule in sequence plastoquinone and this electron is further transferred from plastoquinone to P700 of Photosystem I through cytochrome b6f complex --->> plastocyanin >>>P700.

so the sequence of electron is as follow-

P680-- > pheophytin --->>> plastoquinone--->>>cytochrome b6f complex ----->> plastocyanin >>>P700.

This is also termed as Z-scheme. Transfer of electron from one component of electron transport chain to another in downward direction responsible for the reduction of NADP to NADPH. This also responsible for creating the  proton gradient and enzyme ATP synthase uses this gradient to form ATP molecule. water gives the electron to photosystem II and converted into oxygen.   Photosystem I is also excited by receiving the photons. The movement of electron through different acceptors of electron causes the movement of hydrogen ions from the thylakoid membrane into the lumen of thylakoid and also reduced the NADP into  NADPH. NADPH are used in the dark reaction. The cyclic reaction occur only in only photosystem I and produces ATP molecule.

- [stromal I stroma NADP+ NADOM MADP + light Cpiatons) light (photons) Cytocheme Adferredoreen Coco Pococooninocococco ooooococcoPSI COOOOOOO AT'P cocco (PST) PC I) (be f complex Synthetase 00 0000 od 6000000do Pe. My boood 600000 oooooooo 00000000 D.+(47) Plastoquinone & plas FRER & Ferrexiden-READP Yeduetase Thylakaid lumen

• DCPIP is known as 2,6-Dichlorophenolindophenol which is a chemical compound used to calculate the rate of photosynthesis as redox dye. because when the dye is oxidized oxidized,it gives blue color but after reduction it become colorless.
• During the photosynthesis on exposure to light DCPIP is become decolourized following reduction by electron which are moved through the different component from the Photosystem II to Photosystem I. electron which are released due to photolysis of water traveled through the different component of electron transport chain as described above in the diagram.
• DCPIP can be used as a substitute of NADP+ which act as final electron acceptor in the Electron Transport Chain. here in the above diagram we can observe that the ferridoxin is receiving the electron from Photosystem I but the affinity for electron is more in DCPIP than the ferredoxin due to which the DCPIP is reduces in place of NADP+  and the color of medium changes to colorless and the Absorbence of light increases during the experiment with the DCPIP which can be observed by using the spectrophotometer.
• DCPIP are belongs to the hill reagent family and used to study the electron transport chain mechanism and serve as the artificial electron acceptor and after reduction become colorless in the medium used for the experiment.
• if the DCPIP is not reduced which means that the electron are not transferred from the Photosystem II component of electron transport chain which is present in the thylakoid membrane to the final electron acceptor DCPIP and the reduction of DCPIP doesnot occurred  and the color as well as absorbance was not changed. based on this we can say that the chloroplast are not working and photosynthesis is not happening in the cell or in other word we can say that the chloroplast were damaged during extraction.
• If the DCPIP is reduced so that the electron from the Photosystem II is transferred through a series of intermediate of Electron transport chain and accepted by the DCPIP which gets reduced and changes the color to colorless and absorbance is increases. Which means that the chloroplast is working and doing photosynthesis.