Hello.

It’s our very first episode of Journey to the Microcosmos, and to start, we thought some introductions were in order. I’m Hank Green.

I make YouTube channels, including SciShow and Crash Course, and this is James. James is a scientist, living in Europe, who has, what I think, is the appropriate amount of enthusiasm for microscopic life, which is to say, a lot of it. James has active, living colonies of microorganisms throughout his home.

Though, for clarity, we all do. He just has them intentionally. He keeps tardigrades fed and happy.

Gathers samples to search out new organisms for his collection and even takes samples in from elsewhere. The organisms we will explore on this channel are going to be almost entirely aquatic. This makes them easier to care for and to observe.

But, in the world of the micro, aquatic environments might be tiny droplets of water in soil, on tree bark, or the thin film of water covering the moss in your back yard. Organisms featured on this channel will be collected everywhere from soils to ponds, from puddles to seas. These ecosystems are similar to any you might find in the macroscopic world, in many ways.

Tiny organisms converting light into energy, like plants. Tiny organisms eating those organisms. And other tiny organisms eating those organisms.

Though, on the African Savannah, you will rarely see a zebra consume a tree whole, and then allow it to continue photosynthesizing through its transparent belly in order to produce sustenance for them both. Also, you very rarely see a tree eat a zebra in our world. But as we will see, the Microcosmos can be a bit strange at times.

James keeps what are called “cultures” alive and thriving in his home. These cultures are whole ecosystems with many different species living alongside each other. One is a monoculture of harmless algae that were living on blueberries from the supermarket.

And we’ll soon be getting samples from one of the last remaining untouched forests of Europe and from the Permafrost of Siberia. While this channel is going to explore remarkable diversity, we think it’s important to start out with the three main sorts of organisms you're gonna see here. First, and most simple, the prokaryotes.

Single-celled and lacking organelles, the ones you’re most familiar with are bacteria. For hundreds of millions, maybe even billions of years, prokaryotes were the only life on our planet. And, for clarity, the earth is only four and a half billion years old.

The main thing that distinguishes them from the Eukaryotes is that they don’t have membrane-bound interior structures like the nucleus or chloroplasts or mitochondria. But since they have been around for so long, prokaryotes are remarkable in their diversity. They can be huge or tiny, a magnificent variety of shapes and colors from green to red to purple.

Some contain mysterious crystals in their cells. Some reproduce by being broken into pieces, a handy trait when there are lots of things biting at you. And some of them can really move!

With the aid of flagella, long fibrous proteins that extend through the cell wall and wiggle around, some bacteria are the cheetahs of the microcosmos. The tend to be tiny, bacteria aren’t always easy to see even at 600x magnification. Though some can be comparatively huge.

And that includes cyanobacteria, that, around 2.5 billion years ago, were the first organisms to evolve the ability to turn sunlight into chemical energy. That changed the game in a lot of ways. It was very good for many organisms, including, eventually, us, and very bad for many others...but that is a story for another day.

By 1.7 billion years ago, the second sort of organism, you can expect to see here arrived... the Eukaryotes. Now, we don’t want to sound mean to our prokaryote friends, who are massively varied and complex and wonderful. But single-celled eukaryotes take it to another level.

They tend to be much larger, and so we can get a better view of their beauty and abilities. Sometimes, these organisms are even big enough for us to see without microscopes. Single-celled eukaryotes are often sometimes called protists, and we have to make the “single-celled” distinction here because there are also multi-celled eukaryotes which include a lot of different organisms including mushrooms and trees and jellyfish and you.

But since single-celled Eukaryotes only have one cell, they can’t have different cells that do different things like we do. Instead, they have different areas of their cells specialize. They have sensory systems; they can feel mechanical stimuli and react to it to avoid predators.

The red spot in this protist is an eyespot that has light-sensing structures beneath it. They can hunt actively or can avoid being eaten. They can build “shells” for themselves, and form colonies.

Some even show simple learning behaviors. The complexity of these single-celled organisms sometimes makes you feel that they have a consciousness. And we're not here to say that they don't.

Some of the eukaryotes we show are going to be photosynthetic like diatoms, which, on their own, generate 20-50% of the oxygen produced on earth and have cell walls made of glass. The best guess we have for how eukaryotic cells formed is that a single-celled prokaryote ate another prokaryote and then found that life was better for both of them if they survived together. Even today, the mitochondria in our bodies hold their own separate DNA... a relic of that ancient event.

And finally, the third category of organism we’ll be seeing a lot of on this channel... the micro-animals. These are multi-celled eukaryotes just like you and me. Animals like hydra, which can theoretically live forever.

Tardigrades that can survive the vacuum of space. Rotifers that have thousands of cells with specialized muscles, intestines, even brains...kinda. So they are in many ways, like us.

But they also have some traits that sound other-worldly. Tardigrades are hatched with the exact same number of cells in their body that they will always have, and these tiny baby water bears then only grow as their cells grow bigger. And yet, these animals are so small that sometimes a single-celled organism can swallow them whole.

Sorry little rotifer. It’s important to note that one cell can be 1000 times smaller than another cell. So a rotifer can have thousands of cells, but still be dwarfed by one protist.

Because different magnifications are better for observing different organisms, we will always have the magnification on screen, whether that’s 10x, 100x, or as much as 1000x magnification. So, prokaryotes...the simplest organisms you will see here, no organelles, but still massively varied. Single-celled eukaryotes, or protists, more varied, more specialized.

And Micro-animals, with thousands or even tens of thousands of individual cells. Those are the three main categories of the kinds of organisms you can expect to see here. If you want to see more from our "Master of Microscopes", James Weiss, check out Jam's Germs on Instagram, and if you want to see more from us, that my friends, is what that subscribe button is for.

Thank you for coming on this journey with us, as we explore the unseen world that surrounds us.