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Uploaded:2021-04-05
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(HANK) This episode was brought to you  by the Music for Scientists album,   now available on all streaming services.

You  can check out the music video for the song   “The Idea” at the link in the description. Here at Journey to the Microcosmos, we have a  small team of people working to make these videos   for you every week.

First, there’s me. Hi, I’m  Hank Green, your narrator. And then there’s James   Weiss our Master of Microscopes, providing all  of the beautiful footage you see on your screen.   Matthew Gaydos is our producer and editor, taking  my narration and James’s footage and turning them   into actual videos that you can watch.

And last,  but certainly not least is Deboki Chakravarti,   our writer on Journey to the Microcosmos, the  person who brings the Microcosmos to life with   her storytelling and her exhaustive research. Deboki has been with the channel since almost   the very beginning. In fact, the first script she  ever wrote for Journey to the Microcosmos, was our   episode about diatoms back in 2019.

And since  we’re here today to discuss diatoms once again,   we thought it would be fitting to use this  opportunity to introduce Deboki’s new role,   as another host of Journey to the Microcosmos. I’ll still be here, narrating most of the   episodes, but from time to time, you’ll hear  Deboki hosting a video instead of me. With   her experience, not only in writing over  70 episodes of Journey to the Microcosmos,   but also with her PhD in Biomedical Engineering  and as a host on Crash

Course: Organic Chemistry,   I could not be more excited to  have her join me on this journey.  So, now I am going to hand the microphone over to  Deboki so she can teach you more about diatoms! (DEBOKI) Wherever you are on your  journey to the microcosmos,   the odds are high that you’ll run into a diatom.   They’re both abundant and easy to spot because  of the shells they encase themselves in. The   results are beautiful, exacting geometries that  create a living kaleidoscope in the microcosmos.  And even if you lived your entire life  without ever seeing a diatom, without   ever hearing the word “diatom,” you would still  be living a life that’s shaped by them...all   the way down to the oxygen you breathe,  thanks in no small part to their outsized   contribution to the world’s photosynthesis. But what remains captivating about diatoms is,   well, the thing that remains even when the  diatom itself is gone: the hard silica shell   they once lived in, also known as the frustule.  We’ve talked about frustules a bit before,   and how they’ve given diatoms the nickname  “jewels of the sea.” And today we’re going   to dive a bit more into how those frustules  are made, and the role they play in our world.  Diatoms are the architects of their own  glass houses. And the scale of this project   is immense.

These silica shells aren’t just a  smooth, uniform exterior. There are pores and   elongated channels creating ornate, microscopic  patterns that the organism depends on to survive.  The source of the diatom’s building blocks  is geology. As rocks and land get weathered   and eroded, silica enters the water,  where it dissolves into silicic acid,   which can then diffuse into the  diatom and get converted into silica.  But if diffusion isn’t  bringing in enough material,   the diatoms can also rely on silicon transporter  proteins in their membranes to gather more.  Inside the diatom is a special area  called the silica deposition vesicle.   And it’s there that the silica bits get linked  together to form bigger and bigger pieces.  But while we know that this is where  the silica walls get put together,   the chemistry and biology of how they  get put together is still unclear.   We know that silica can itself form a gel-like  network, so that could make up a key assembly   step.

But there may also be other organic  molecules like proteins that bind to the   silica and help to create the final structure. While scientists are still untangling those   mechanisms, they have observed the way that the  silica deposition vesicle and other structures   in the cell, including the mitochondria, can help  to mold the shape of the final silica structure.  For example, elongated, symmetric diatoms—also  called pennate diatoms--often have a slit called   the raphe. This slit helps the diatom move  around, serving as an opening through which   they can secrete a viscous fluid to glide on.  And one of the ways that diatoms make the raphe   is by physically molding it through  the arrangement of their microtubules.  Many diatoms are nonmotile,  meaning they don’t move around.   And the lack of visible movement from the  outside is striking when you consider all   of the activity that has gone on inside  of them to make those frustules happen.  Like we said earlier, they’re doing more than  creating a smooth, transparent surface.

They’re   creating a molded, ornate structure personalized  to their own shape, like a house couture.  And not only is this process a lot of work,  it renders diatoms dependent on silica,   a chemical they can’t make themselves. So why do it? Well, for one, it’s cheaper   than both making and assembling your own  materials.

The silica is already out there,   so why not take advantage of it? One study found  that the materials in the diatom’s frustules   might help the organism take in carbon dioxide,  improving their photosynthetic capabilities.  These advantages seem to translate over  into the immense capacity of diatoms to grow   and dominate over other algae that share  their waters. But taking over a body of water   is all fun and games until the silica runs out.  Diatoms are known for their ability  to form large, visible blooms,   whether in your local lake or the Arctic Ocean.  But scientists studying those Arctic blooms found   that as the diatom population expanded, they  also depleted their waters of silicic acid.  And that, in turn, halted their growth and  began to increase the number of dead diatoms.   And both of these things—the  lack of growth and the dying—have   another impact on diatom populations: sinking.  Healthy, growing diatoms can up their buoyancy   to keep them afloat, while dying cells cannot.

It might be sad to imagine those blooms dying   and descending to lower depths, the ornate  jewels collapsing like a microbial empire.   But nature doesn’t trade in  inconsequential tragedies.  The death of diatoms leaves  behind frustules like this one,   which means it leaves behind silica. Some of  that silica can be recycled by other diatoms,   but over time, it will eventually descend further  and further down until it gathers on sediments.  When a diatom takes in silicic acid, it’s taking  in the remnants of a geological process—the   weathering and erosion that brought the  silicon to water in the first place.  And then through the construction of its shell, it  recycles and transforms the dissolved silicon into   a form that can become geological once again. And how that silica gets used again can vary.   But as always with the diatom, your  chances of running into it again are high.  Scientists found that dust from a  diatom shell-rich sediment in Chad   might travel as far as the Amazon.

The  diatom itself may not be making the trip,   but the microcosmos and the things built  in it have a way of sticking around.   Thank you for coming on this journey with us as  we explore the unseen world that surrounds us.  This episode is brought to you by the Music  for Scientists album, which was created by   composer and musician Patrick Olson. The album is  inspired by the intersection of science and art.  And if you’re looking to explore that intersection  more, check out the music video for one of the   tracks on the album called ‘The Idea’. The  music video for this track was produced from   a sequence of 15,000 photographs of three  traditional paintings by artist Jon Todd.  His painting style was then transferred  to a video performance by using a form   of machine learning.

And the song itself  is all about exploring how we form ideas.  If you think this sounds like something you  might enjoy, click the link in the description   to see the video or stream the  music on all major music services.  The names on the screen right now,  those are our patreon patrons.   Without them, we could not make this show and we  are so thankful to them. If you like what we do,   and want to help us keep making it, you can  join those people at patreon.com/journeytomicro.  If you want to see more from our  Master of Microscopes James Weiss,   check out Jam & Germs on Instagram. And if you want to see more from us,   there’s always a subscribe  button somewhere nearby.