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If you’ve taken a biology class, at some point  you likely had to sit down to a picture of a cell.   It was vaguely oval shaped and filled with  circles and squiggly lines. And your task   was to look at those circles and lines and  assign them labels like “vesicle” or “nucleus.”  And this exercise has its benefits.

But at the  same time, the picture it paints of a cell is—by   necessity—static and uniform. The reality is  that cells may be full of analogous parts,   but their lives and physical appearance can appear  vastly different when compared to each other.   The bodies of multicellular organisms like  us are built on that principle, with a   diversity of cells dedicated to different tasks. But we can see it even more starkly in the lives   of single-celled eukaryotes.

These are organisms  who have managed to make an entire way of life   out of a single cell, taking on many  different forms to do so. Even as the   inner parts remain approximately the same,  the final results can be wildly different,   whether you’re looking at the flexible form of  an amoeba or the determined shape of a diatom.  Here on Journey to the Microcosmos,  we often focus on the organisms—on   their fascinating physiology and lives as  they navigate the world around them. But   what about the even smaller world inside of them?

If you think of a cell as its own little world, a   little society built on chemistry and biology, one  of its most important tasks is establishing its   boundaries—separating and protecting the inside of  the cell while still leaving it just open enough   to bring in essential nutrients from the outside. The essential component here is the plasma   membrane, a double layer of fatty acids that  surrounds the cell and allows some things to pass   while keeping the cell protected. But for different protists, the cell   membrane may not be quite enough to establish  the kind of boundaries it needs.

Ciliates like   these pelagotrix encase their plasma membrane  within a larger structure called the pellicle,   which has structures to define the organism’s  shape and anchor their many hairy cilia.  Other organisms supplement their plasma membrane  with another exterior wall, like this colony of   green algae called Pediastrum. Each of these  cells is encased in a protective cell wall.  What comes next after the boundaries have  been set is, well, everything. It is one   big soup of life, organelles and nutrients  swimming in the watery broth of the cytoplasm.  And just like a good soup, there is a delicate  balance to the cytoplasm.

When you’re living in   a watery environment with a thin membrane  separating you from the outside world,   water can seep through. A little bit of that water  might be fine, but too much can be dangerous.   We’ve even seen microbes burst open and die when  they’ve been pushed past their watery limits.  But microbes are not passive in the face of this  danger. If you look at the edge of this Frontonia   vernalis, you can see its solution at work.  There are canals all pointed towards the same   clear, circular region.

That area is not just  some blank space. It is a contractile vacuole,   swelling up with water until it is full.  And when it is full, you can see it contract   and push the water out of the cell through  tiny pores, leaving the world within balanced.  And as we travel further inside this world, there  is a flurry of activity, not all of which is   visible to us. Much of that activity is powered  by the mitochondria, though unfortunately they   are a bit too small for us to easily see.

But  we think that the thin rods inside this diatom   might be the famous powerhouses of the cell. The chemicals that mitochondria use to generate   power come from food. And of course, microbes  have found many creative ways to obtain food.  Some organisms make their own, turning light into  sugar through clever chemistry and chloroplasts.   And even though chloroplasts can  come in different shapes and sizes,   they’re usually easy enough to identify through  their most obvious trait: their vibrant green   color, derived from the light-absorbing  chlorophyll that powers the chloroplast.  Except…of course biology loves an exception.  There are examples of other colors in the   chloroplast realm, like in red algae that have  other pigments that stain their chloroplasts red.  Whatever the color, these are organisms  whose inner worlds can sustain themselves,   as long as they get enough light.

But other  organisms have to go out and seek their sustenance   by finding other organisms to eat. And if that  sounds like a bit much to you, I will remind you,   you are one of them. So, humans and other  organisms like us have to find a way to   introduce that food into their bodies.

In some organisms, that gate is called   the cytostome. And in this glaucoma,  the cytostome takes the form of an oval,   flapping as the organism turns  around and assesses a possible meal.  But swallowing food is only one step in the  process. After it enters the organism’s body, the   food gets wrapped up in its own little membrane  like a present—a present stuffed with digestive   enzymes that will tear its contents apart.

And just as with water, the cell doesn’t   necessarily want to keep all of this digested food  around for the rest of its life. So what doesn’t   get used gets pooped out through the cytoproct,  and if the mitochondria is the powerhouse of the   cell, the cytoproct is the butthole of the cell. And then, of course, there are other specialized   parts that help different organisms manage the  specific challenges of their lifestyle.

Like   take this Loxodes, which prefers to live in  areas of water that are lower in oxygen—areas   that are, to put it simply, down. Down  the water column, into the depths.  But to get there, the Loxodes needs to figure out  just where “down” is. So the organism relies on   its Muller vesicles, a simple structure, it’s  an organelle that allows it to detect gravity.   The vesicle holds a single mineral granule  attached to a cilium.

And as gravity pulls on the   mineral, the mineral pulls on the cilium, pointing  the Loxodes downward like an inner compass.  Now if we take a step back and survey  these little worlds inside of organisms,   it is remarkable to realize that these organisms  have built themselves, assembled and sustained   by their own reactions. They have gathered  and made their resources, and from it comes   all of these different parts that just seem to  work. There are so many bits of chemistry and   probability that have come together to make  each of these tiny remarkable lives happen.  And at the center of so much of that assembly  is the nucleus, those round organelles that hold   the DNA that describes the organism’s existence.

Nuclei are universal among eukaryotes, though of   course ciliates in all of their contrarian glory  have also managed to make their own habits out   of familiar entities. Ciliates are not content to  just have one type of nucleus, no they have two.   The larger nucleus is called the macronucleus, and  it is responsible for the day-to-day genetic needs   of the organism. Whereas the smaller nuclei are  the micronuclei, and their primary role is to pass   on genetic information during sexual reproduction.

It feels right to end with the nucleus,   the part of the cell that ensures not just the  life of this organism itself, but also of its   progeny. It is a map that is passed on and shared,  promising the creation of new worlds to come.  Thank you for coming on this journey with us as  we explore the unseen world that surrounds us.  And we would also like to say thank you  to Skillshare for supporting this video. We’ve discussed Skillshare many times, and we’ve  shared courses that can help you with everything   from learning to paint with watercolors, to  understanding how to properly cook and prepare   fish.

But what if you’re not feeling super  confident about starting down a new creative path?   Well, Skillshare is here to  help you with that as well. In the course “Confidence For Creatives”, host  Eugena Washington will help you develop some   tools to help you reconnect with your self worth  and continue to grow your confidence to do the   creative work that you love. Do you battle with  imposter syndrome?

Or are you looking for a burst   of inspiration? Well, if you answered “Yes” to  either of these questions, this class is for you! Skillshare is an online learning community that  can help you make 2022 a year of new learning,   growth, and connection through creativity.

With so  much to explore and real world projects to create,   Skillshare empowers you to accomplish real  growth. It’s curated specifically for learning,   meaning there are no ads to distract you, and  they’re always launching new premium classes,   so that you can stay focused  on leveling up your skills. And also if you’re one of the first 1,000  people to click the link in the description   can get a 1 month free trial of  Skillshare’s Premium Membership.

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