The report is due tomorrow
The report is due tomorrow. Here on Earth we’ve got it all - plants that eat spiders, spiders that eat birds, and birds that drink blood. There are trees that live for thousands of years and some mayflies that live for only 12 hours, and that seemingly immortal mold in the corner of your basement that you’d rather not think about. Variety is the spice of life, but in all its spiciness, life also has order. It’s organized in layers, each one rich, complex, and connected - like the most delicious multi-layer dip you’ve ever tasted. We call those layers the levels of biological organization, and we are all swimming in them - from the cells in our bodies to the totality of all living things on our planet. And understanding this organization is important to understanding life as we know it.
Hi, I’m Dr. Sammy, your friendly neighborhood entomologist, and this is Crash Course Biology. Now, where’s my theme music?
You may not see the family resemblance, but you and I both share our family tree with the Venus flytrap, the blobfish, and yes, even our old friend the platypus. That’s because all life on Earth shares a common ancestor, and that makes for some interesting family reunions - with Grandpa Bacterium dozing off in the corner, Aunt Fungi recalling the good old days before mammals showed up, and all the youngins crawling and flying around, getting skinned knees and crying and stuff. Good times, good times.
As we page through life’s family album, some shared properties pop up again and again - which we’re calling the themes of life. Cue dramatic music First, life’s physical forms tend to fit their function, like how a shark’s tail helps it swim through the water. Second, life is governed by regulation mechanisms that keep life’s processes in check. And third, life depends on a flow of information, energy, and chemicals.
As we explore biology, we’ll encounter these themes over and over to see how this plays out across the levels of biological organization. Let’s start here with our distant cousin, the humpback whale. She, like you and I, is an organism - an individual life form. Yeah, she’s alive, all right. But zoom in and out on our whale, pan up and down, and you’ll find layers of life. I’m not just talking about the barnacles growing on her chin, either. Although, wow, those are some strange designs. Is that the Mona Lisa?
Starting from the bottom, the levels of biological organization begin on the microscopic level with the molecules inside your cells, and they end with the sum of every living thing on our planet. Quality is called emergent properties arise at each of these levels. They’re kind of like special powers appearing only when all the parts are together, like how a boy band’s harmonies only work if all the members are there.
You here to watch me film again? It’s so sweet. Sweet. Life itself is an emergent property. It starts with cells, the basic building blocks of all living things - way before we have an entire whale in front of us. But all living things have cells, or are cells, in the case of single-celled organisms like bacteria. And groups of similar cells make up tissues, tissues make up organs, such as the whale’s heart or brain. As groups of organs work together, they form a connected system - in this case, an organ system. Additional functions emerge from that cooperation, which one organ couldn’t complete on its own.
Life is full of these kinds of interlocking parts, like the whale’s nervous system, for example, which sends messages to the rest of her body to swim away towards that tasty swarm of krill, or to belt out a tune. Laughs You should collab with BTS - be pretty awesome.
Which reminds me of that first theme - form fits function. Throughout the levels of biological organization, the structure of a thing tends to enable the thing to do what it needs to do to survive. This match between form and function is explained by evolution - a process of gradual change in a population as they adapt to their environment over generations. Evolution explains life’s unity and diversity.