1 00:00:08,820 --> 00:00:26,379 The process of photosynthesis produces ATP from ADP and PI by using the energy from light 2 00:00:26,379 --> 00:00:30,359 to excite electrons that are passed along an electron transport chain. 3 00:00:31,679 --> 00:00:36,079 Coupled with the transfer of electrons is the pumping of hydrogen ions and the splitting 4 00:00:36,079 --> 00:00:37,280 of water molecules. 5 00:00:38,859 --> 00:00:43,119 The following complexes are found in the photosynthesis electron transport chain. 6 00:00:44,420 --> 00:00:53,420 Photosystem II, Cytochrome B6F, Photosystem I, 7 00:00:53,420 --> 00:00:58,920 Ferredoxin NADP reductase, and the complex that makes ATP, 8 00:00:58,920 --> 00:01:01,420 ATP synthase. 9 00:01:01,420 --> 00:01:04,420 In addition to the complexes, three mobile carriers 10 00:01:04,420 --> 00:01:12,219 are also involved, Plastiquinone QB, Plastocyanin, 11 00:01:12,219 --> 00:01:14,780 and ferredoxin. 12 00:01:14,780 --> 00:01:22,650 Other key components include photons, chlorophyll molecules, 13 00:01:22,650 --> 00:01:34,099 protons, water, molecular oxygen, NADP and the electrons 14 00:01:34,099 --> 00:01:45,180 to form NADPH, and ADP and PI, which combine to form ATP. 15 00:01:45,180 --> 00:01:48,599 Photosynthesis occurs in the chloroplasts of plants 16 00:01:48,599 --> 00:01:49,379 and algae. 17 00:01:49,379 --> 00:01:56,079 The process is also found in single-cell organisms, such as cyanobacteria, that do not have chloroplasts. 18 00:01:56,079 --> 00:02:04,879 Like its mitochondrial counterpart, the chloroplast electron transport chain consists of several protein complexes and mobile electron carriers. 19 00:02:04,879 --> 00:02:10,780 First, a photon of light hits a chlorophyll molecule surrounding the photosystem II complex. 20 00:02:10,780 --> 00:02:16,580 This creates resonance energy that is transferred through neighboring chlorophyll molecules. 21 00:02:16,580 --> 00:02:23,300 When this energy reaches the reaction center embedded in photosystem II, an electron is released. 22 00:02:23,300 --> 00:02:28,340 The reaction center chlorophyll contains electrons that can be transferred when excited. 23 00:02:28,340 --> 00:02:34,699 One photon is needed to excite each of the electrons in this chlorophyll. 24 00:02:34,699 --> 00:02:42,860 Once excited, two electrons are transferred to plastiquinone QB, the first mobile carrier. 25 00:02:42,860 --> 00:02:47,900 In addition to the two electrons, QB also picks up two protons from the stroma. 26 00:02:49,740 --> 00:02:55,340 The two electrons lost from photosystem II are replaced by the splitting of water molecules. 27 00:02:56,620 --> 00:03:03,340 Water splitting also releases hydrogen ions into the lumen. This contributes to a hydrogen ion 28 00:03:03,340 --> 00:03:07,819 gradient similar to the one created by mitochondrial electron transport. 29 00:03:08,620 --> 00:03:14,080 After two water molecules have been split, one molecule of molecular oxygen is created. 30 00:03:20,069 --> 00:03:26,090 Plastiquinone QB then transfers the two electrons to the cytochrome B6F complex. 31 00:03:26,650 --> 00:03:30,710 The two protons it picked up are released into the lumen. 32 00:03:32,189 --> 00:03:39,110 These transfers are coupled with the pumping of two more hydrogen ions into the lumen space by cytochrome B6F. 33 00:03:39,650 --> 00:03:42,870 The electrons are next transferred to plastocyanin. 34 00:03:43,030 --> 00:03:45,150 another mobile carrier. 35 00:03:45,150 --> 00:03:48,409 Next, the electrons are transferred from plastocyanin 36 00:03:48,409 --> 00:03:51,310 to the photosystem I complex. 37 00:03:51,310 --> 00:03:55,710 It is here that photons again energize each electron 38 00:03:55,710 --> 00:03:59,590 and propel their transfer to ferredoxin. 39 00:03:59,590 --> 00:04:02,449 Ferredoxin then transfers the electrons 40 00:04:02,449 --> 00:04:09,110 to the ferredoxin NADP reductase, also known as FNR. 41 00:04:09,110 --> 00:04:12,270 After two electrons are transferred to FNR, 42 00:04:12,270 --> 00:04:16,269 NADPH is made by adding the two electrons and a hydrogen 43 00:04:16,269 --> 00:04:19,509 ion to NADP. 44 00:04:19,509 --> 00:04:22,750 The gradient created by the electron transport chain 45 00:04:22,750 --> 00:04:29,269 is utilized by ATP synthase to create ATP from ADP and PI. 46 00:04:29,269 --> 00:04:32,110 This is similar to the way ATP is synthesized 47 00:04:32,110 --> 00:04:33,829 in the mitochondria. 48 00:04:33,829 --> 00:04:39,709 ATP, NADPH, and molecular oxygen are the final vital products 49 00:04:39,709 --> 00:04:40,990 of photosynthesis.