Speaker 1: Welcome to brain Stuff production of I Heart Radio. Hey,
Speaker 1: brain Stuff, Lauren vogelbamb here, you probably don't appreciate plants enough.
Speaker 1: It's okay, none of us do. Given that plants have
Speaker 1: been the major player in the convoluted soap opera of
Speaker 1: life that landed us on this planet, we should be
Speaker 1: thanking our leafy friends every day for our existence. Honestly,
Speaker 1: the whole story is so tangled and complicated we may
Speaker 1: never know the truth about how our mean green ancestors
Speaker 1: allowed everyone else to evolve. But one aspect of the
Speaker 1: story certainly involves photosynthesis of plants ability to make its
Speaker 1: own food out of sunlight. We spoke with Gregory Schmidt,
Speaker 1: Professor emeritus in the Department of Plant Biology at the
Speaker 1: University of Georgia. He said a great way to appreciate
Speaker 1: photosynthesis is to compare Earth's atmosphere with that of our
Speaker 1: sister planets, Mars and Venus. All three planets were most
Speaker 1: likely similar when they formed and cooled, but the atmospheres
Speaker 1: of both Venus and Mars have carbon dioxide, two point
Speaker 1: seven percent nitrogen and zero point one three percent oxygen.
Speaker 1: Earth's air is seventy seven percent nitrogen, twenty one percent oxygen,
Speaker 1: and zero point four one percent carbon dioxide, although that
Speaker 1: number is rising. That means there are eight hundred gigatons
Speaker 1: of carbon dioxide in our atmosphere, but there's another ten
Speaker 1: thousand gigatons missing or buried in the form of fossil, limestone, coal,
Speaker 1: and oil. In other words, carbon has been smuggled out
Speaker 1: of the atmosphere and into Earth's crust for billions of years,
Speaker 1: which is the only reason this planet is at all
Speaker 1: habitable by multi celled organisms. Schmidt said, So, how did
Speaker 1: that dramatic atmospheric shift happen for Earth? There's only one answer,
Speaker 1: and it's pretty simple. Photosynthesis, the most amazing factor in
Speaker 1: Earth's evolution. Yes, friends, photosynthesis. A couple hundred million years
Speaker 1: after the Earth was formed, life showed up, probably first
Speaker 1: as some anaerobic bacteria, that is, bacteria that can't thrive
Speaker 1: in the presence of oxygen. These single celled organisms lived
Speaker 1: by slurping up the sulfur and hydrogen that came out
Speaker 1: of hydrothermal vents. Now we've got everything from butterflies to giraffes.
Speaker 1: But there were a few steps on the road between
Speaker 1: the first bacteria and giraffes. Those ancient bacteria had to
Speaker 1: figure out a means of finding new hydrothermal vents, which
Speaker 1: led to the development of a thermal sensing pigment called
Speaker 1: bacterial chlorophyll, which some bacteria still used to detect the
Speaker 1: infrared waves otherwise known as heat. These bacteria were the
Speaker 1: progenitors of descendants that could make chlorophyll, a pigment that's
Speaker 1: able to capture shorter, more energetic light waves from the
Speaker 1: sun and use them as a source of power. So,
Speaker 1: in essence, these bacteria created a means to capture the
Speaker 1: energy of sunlight. The next evolutionary lead necessitated working out
Speaker 1: a means of stable energy storage, creating a sort of
Speaker 1: sunlight battery that encouraged protons to accumulate on one side
Speaker 1: of their internal membranes versus the other. The true wonder
Speaker 1: of plant and algae evolution is the fact that at
Speaker 1: some point these ancient chlorophyll producing bacteria started generating oxygen.
Speaker 1: After all, billions of years ago, there was actually very
Speaker 1: little oxygen in the atmosphere, and it was toxic to
Speaker 1: a lot of early bacteria. It's still toxic to existing
Speaker 1: anaerobic bacteria that's still thrive in the oxygen free places
Speaker 1: on Earth. However, the new process of capturing and storing
Speaker 1: sunlight required the participating bacteria to burn water. The process
Speaker 1: that we call burning or combustion is basically just very
Speaker 1: rapid oxidation, the ripping off of electrons from one atom
Speaker 1: and the transfer of those electrons to another, which is
Speaker 1: called reduction. Early photosynthetic bacteria developed a way to capture
Speaker 1: photons or particles of light, and use their energy to
Speaker 1: strip water of many of its protons and electrons to
Speaker 1: use for energy production. The breakthrough of breakthroughs that happened
Speaker 1: three billion years ago was when photosynthetic machinery was perfected
Speaker 1: to the point that chlorophyll could split two water molecules
Speaker 1: at the same time. These days, we call this a
Speaker 1: photosystem to chlorophyll protein cluster. Cyanobacteria evolved once these photosynthetic
Speaker 1: bacteria figured out how to burn water and store the
Speaker 1: energy from that chemical reaction in photosynthesis, photosystem to water
Speaker 1: burning can't really be sustained without the second stage photosystem, one,
Speaker 1: which involves taking the electrons swiped off of the water
Speaker 1: molecules in the first step and making use of them
Speaker 1: before they decay. Photosystem one does this by sticking these
Speaker 1: electrons on a chemical assembly line, so the organism is
Speaker 1: able to retain that hard earned energy, which is then
Speaker 1: used to convert carbon dioxide into sugar for the bacteria
Speaker 1: to use as food. Once photosystems one and two were
Speaker 1: sorted out, cyanobacteria took over the oceans, and because oxygen
Speaker 1: was their waste product, it became plentiful in Earth's atmosphere.
Speaker 1: As a result, many bacteria became aerobic. That is, they
Speaker 1: required oxygen for their metabolic processes, or at the very
Speaker 1: least they could tolerate it. About a billion years later,
Speaker 1: Protozoa evolved as anaerobes scarfing up aerobic bacterial prey. What
Speaker 1: researchers think happened is this, at some point in at
Speaker 1: least one of these oxygen intolerant organisms, the oxygen tolerant
Speaker 1: bacteria they ate weren't completely digested, but stayed within the
Speaker 1: cell and ended up helping the oxygen intolerant anaerobic organism
Speaker 1: cope with an aerobic environment. These two organisms stuck together,
Speaker 1: and eventually the prey organism evolved into a cell organelle
Speaker 1: called mitochondria. A similar scenario occurred with cyanobacteria around one
Speaker 1: billion years ago. In this case, an anaerobic bacteria probably
Speaker 1: gobbled up a photosynthetic bacteria, which ended up setting up
Speaker 1: shop inside its host, resulting in a small membrane bound
Speaker 1: organelle common to all plants. The chloroplast as, algae and
Speaker 1: multicellular plants evolved and benefited from plentiful carbon dioxide and
Speaker 1: increasing oxygen in Earth's atmosphere. Chloroplasts became the place where
Speaker 1: photosynthesis of photosystem one, two, and even more complicated stuff
Speaker 1: went down in each cell. Just like mitochondria, they have
Speaker 1: their own DNA and spend their time busily harvesting light
Speaker 1: for the plant, creating the entire foundation for life on Earth.
Speaker 1: Today's episode was written by Joceline Shields and produced by Tyler.
Speaker 1: Playing brain Stuff is a production of I Heart Radio's
Speaker 1: How Stuff Works. For more in this and lots of
Speaker 1: other life sustaining topics, visit our home planet has Stuff
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