WEBVTT - How Does Photosynthesis Power Life on Earth? 0:00:01.920 --> 0:00:06.560 Welcome to brain Stuff production of I Heart Radio. Hey, 0:00:06.600 --> 0:00:11.680 brain Stuff, Lauren vogelbamb here, you probably don't appreciate plants enough. 0:00:12.280 --> 0:00:15.480 It's okay, none of us do. Given that plants have 0:00:15.560 --> 0:00:18.079 been the major player in the convoluted soap opera of 0:00:18.120 --> 0:00:20.439 life that landed us on this planet, we should be 0:00:20.480 --> 0:00:24.480 thanking our leafy friends every day for our existence. Honestly, 0:00:24.640 --> 0:00:27.360 the whole story is so tangled and complicated we may 0:00:27.440 --> 0:00:30.240 never know the truth about how our mean green ancestors 0:00:30.240 --> 0:00:33.199 allowed everyone else to evolve. But one aspect of the 0:00:33.240 --> 0:00:37.360 story certainly involves photosynthesis of plants ability to make its 0:00:37.360 --> 0:00:41.920 own food out of sunlight. We spoke with Gregory Schmidt, 0:00:42.040 --> 0:00:44.640 Professor emeritus in the Department of Plant Biology at the 0:00:44.760 --> 0:00:48.559 University of Georgia. He said a great way to appreciate 0:00:48.560 --> 0:00:51.559 photosynthesis is to compare Earth's atmosphere with that of our 0:00:51.600 --> 0:00:55.280 sister planets, Mars and Venus. All three planets were most 0:00:55.320 --> 0:00:58.560 likely similar when they formed and cooled, but the atmospheres 0:00:58.600 --> 0:01:03.080 of both Venus and Mars have carbon dioxide, two point 0:01:03.120 --> 0:01:06.760 seven percent nitrogen and zero point one three percent oxygen. 0:01:07.520 --> 0:01:11.480 Earth's air is seventy seven percent nitrogen, twenty one percent oxygen, 0:01:11.680 --> 0:01:15.000 and zero point four one percent carbon dioxide, although that 0:01:15.080 --> 0:01:18.919 number is rising. That means there are eight hundred gigatons 0:01:18.959 --> 0:01:22.200 of carbon dioxide in our atmosphere, but there's another ten 0:01:22.240 --> 0:01:26.520 thousand gigatons missing or buried in the form of fossil, limestone, coal, 0:01:26.800 --> 0:01:31.240 and oil. In other words, carbon has been smuggled out 0:01:31.240 --> 0:01:34.160 of the atmosphere and into Earth's crust for billions of years, 0:01:34.400 --> 0:01:36.480 which is the only reason this planet is at all 0:01:36.560 --> 0:01:41.640 habitable by multi celled organisms. Schmidt said, So, how did 0:01:41.640 --> 0:01:45.760 that dramatic atmospheric shift happen for Earth? There's only one answer, 0:01:45.800 --> 0:01:49.320 and it's pretty simple. Photosynthesis, the most amazing factor in 0:01:49.360 --> 0:01:54.880 Earth's evolution. Yes, friends, photosynthesis. A couple hundred million years 0:01:54.920 --> 0:01:58.320 after the Earth was formed, life showed up, probably first 0:01:58.320 --> 0:02:02.080 as some anaerobic bacteria, that is, bacteria that can't thrive 0:02:02.160 --> 0:02:06.040 in the presence of oxygen. These single celled organisms lived 0:02:06.040 --> 0:02:08.560 by slurping up the sulfur and hydrogen that came out 0:02:08.560 --> 0:02:13.239 of hydrothermal vents. Now we've got everything from butterflies to giraffes. 0:02:13.720 --> 0:02:16.160 But there were a few steps on the road between 0:02:16.160 --> 0:02:20.160 the first bacteria and giraffes. Those ancient bacteria had to 0:02:20.240 --> 0:02:23.440 figure out a means of finding new hydrothermal vents, which 0:02:23.520 --> 0:02:26.360 led to the development of a thermal sensing pigment called 0:02:26.360 --> 0:02:30.200 bacterial chlorophyll, which some bacteria still used to detect the 0:02:30.280 --> 0:02:34.720 infrared waves otherwise known as heat. These bacteria were the 0:02:34.760 --> 0:02:38.600 progenitors of descendants that could make chlorophyll, a pigment that's 0:02:38.639 --> 0:02:41.520 able to capture shorter, more energetic light waves from the 0:02:41.560 --> 0:02:44.840 sun and use them as a source of power. So, 0:02:45.040 --> 0:02:48.240 in essence, these bacteria created a means to capture the 0:02:48.400 --> 0:02:52.720 energy of sunlight. The next evolutionary lead necessitated working out 0:02:52.760 --> 0:02:56.000 a means of stable energy storage, creating a sort of 0:02:56.000 --> 0:02:59.720 sunlight battery that encouraged protons to accumulate on one side 0:02:59.720 --> 0:03:03.440 of their internal membranes versus the other. The true wonder 0:03:03.440 --> 0:03:06.280 of plant and algae evolution is the fact that at 0:03:06.320 --> 0:03:11.400 some point these ancient chlorophyll producing bacteria started generating oxygen. 0:03:12.080 --> 0:03:14.919 After all, billions of years ago, there was actually very 0:03:14.919 --> 0:03:17.639 little oxygen in the atmosphere, and it was toxic to 0:03:17.720 --> 0:03:20.680 a lot of early bacteria. It's still toxic to existing 0:03:20.720 --> 0:03:23.800 anaerobic bacteria that's still thrive in the oxygen free places 0:03:23.840 --> 0:03:27.840 on Earth. However, the new process of capturing and storing 0:03:27.880 --> 0:03:33.720 sunlight required the participating bacteria to burn water. The process 0:03:33.760 --> 0:03:37.119 that we call burning or combustion is basically just very 0:03:37.320 --> 0:03:41.080 rapid oxidation, the ripping off of electrons from one atom 0:03:41.280 --> 0:03:43.800 and the transfer of those electrons to another, which is 0:03:43.800 --> 0:03:48.240 called reduction. Early photosynthetic bacteria developed a way to capture 0:03:48.240 --> 0:03:51.120 photons or particles of light, and use their energy to 0:03:51.200 --> 0:03:53.920 strip water of many of its protons and electrons to 0:03:54.040 --> 0:03:58.680 use for energy production. The breakthrough of breakthroughs that happened 0:03:58.720 --> 0:04:02.400 three billion years ago was when photosynthetic machinery was perfected 0:04:02.400 --> 0:04:05.600 to the point that chlorophyll could split two water molecules 0:04:05.640 --> 0:04:08.360 at the same time. These days, we call this a 0:04:08.440 --> 0:04:15.640 photosystem to chlorophyll protein cluster. Cyanobacteria evolved once these photosynthetic 0:04:15.640 --> 0:04:18.520 bacteria figured out how to burn water and store the 0:04:18.600 --> 0:04:23.440 energy from that chemical reaction in photosynthesis, photosystem to water 0:04:23.520 --> 0:04:27.680 burning can't really be sustained without the second stage photosystem, one, 0:04:28.000 --> 0:04:30.560 which involves taking the electrons swiped off of the water 0:04:30.640 --> 0:04:33.000 molecules in the first step and making use of them 0:04:33.040 --> 0:04:37.000 before they decay. Photosystem one does this by sticking these 0:04:37.040 --> 0:04:40.000 electrons on a chemical assembly line, so the organism is 0:04:40.040 --> 0:04:42.840 able to retain that hard earned energy, which is then 0:04:42.960 --> 0:04:45.880 used to convert carbon dioxide into sugar for the bacteria 0:04:45.960 --> 0:04:50.160 to use as food. Once photosystems one and two were 0:04:50.160 --> 0:04:54.520 sorted out, cyanobacteria took over the oceans, and because oxygen 0:04:54.560 --> 0:04:57.720 was their waste product, it became plentiful in Earth's atmosphere. 0:04:58.560 --> 0:05:01.920 As a result, many bacteria became aerobic. That is, they 0:05:01.960 --> 0:05:05.280 required oxygen for their metabolic processes, or at the very 0:05:05.360 --> 0:05:08.760 least they could tolerate it. About a billion years later, 0:05:09.040 --> 0:05:14.560 Protozoa evolved as anaerobes scarfing up aerobic bacterial prey. What 0:05:14.600 --> 0:05:17.919 researchers think happened is this, at some point in at 0:05:18.000 --> 0:05:22.040 least one of these oxygen intolerant organisms, the oxygen tolerant 0:05:22.080 --> 0:05:25.960 bacteria they ate weren't completely digested, but stayed within the 0:05:26.000 --> 0:05:30.159 cell and ended up helping the oxygen intolerant anaerobic organism 0:05:30.440 --> 0:05:35.080 cope with an aerobic environment. These two organisms stuck together, 0:05:35.440 --> 0:05:38.839 and eventually the prey organism evolved into a cell organelle 0:05:39.040 --> 0:05:44.440 called mitochondria. A similar scenario occurred with cyanobacteria around one 0:05:44.480 --> 0:05:48.720 billion years ago. In this case, an anaerobic bacteria probably 0:05:48.800 --> 0:05:52.440 gobbled up a photosynthetic bacteria, which ended up setting up 0:05:52.440 --> 0:05:56.279 shop inside its host, resulting in a small membrane bound 0:05:56.400 --> 0:06:01.480 organelle common to all plants. The chloroplast as, algae and 0:06:01.560 --> 0:06:05.479 multicellular plants evolved and benefited from plentiful carbon dioxide and 0:06:05.560 --> 0:06:09.520 increasing oxygen in Earth's atmosphere. Chloroplasts became the place where 0:06:09.560 --> 0:06:13.560 photosynthesis of photosystem one, two, and even more complicated stuff 0:06:13.640 --> 0:06:17.520 went down in each cell. Just like mitochondria, they have 0:06:17.600 --> 0:06:20.960 their own DNA and spend their time busily harvesting light 0:06:21.040 --> 0:06:24.400 for the plant, creating the entire foundation for life on Earth. 0:06:29.560 --> 0:06:32.360 Today's episode was written by Joceline Shields and produced by Tyler. 0:06:32.440 --> 0:06:35.000 Playing brain Stuff is a production of I Heart Radio's 0:06:35.000 --> 0:06:36.919 How Stuff Works. For more in this and lots of 0:06:36.920 --> 0:06:39.719 other life sustaining topics, visit our home planet has Stuff 0:06:39.720 --> 0:06:42.560 Works dot com, and for more podcasts from my heart Radio, 0:06:42.680 --> 0:06:45.040 you can visit the iHeart Radio app, Apple Podcasts, or 0:06:45.080 --> 0:06:46.719 wherever you listen to your favorite shows.