living organisms are incredibly ordered and contain what's known as a biological hierarchy of organization. And we've talked about this plenty in our previous bio courses. So we're just gonna do a quick review here and in our example of the biological levels of organization, noticed that on the far left we have larger and more complex organisms and structures, and as we move from the left towards the right, we get smaller and less complex organisms and structures. Now, starting over here on the far left, we have multi cellular organisms, which includes ourselves, obviously, and humans are composed of multiple organ systems where each organ system is a collection of individual organs that work together. Now the organs are made up of a bunch of tissues, and the tissues are a collection of the same types of cells. And we've learned that cells are made up of smaller components called organelles, and the organelles are made up of macro molecules where the term here macro means large. So these air large molecules and the macro molecules include proteins, carbohydrates, lipids and nucleic acids, and moving forward in our biochemistry course, we'll talk a lot more about the macro molecules and the organelles. Now the macro molecules are made up of smaller molecules, and the molecules are made up of individual atoms that are bound together chemically. And, uh, these include the atoms that we see on the periodic table. And the way that this hierarchy works is that the lower levels are used to build the immediate higher levels and notice that we have this big red box that is going around the macro molecules, molecules and atoms levels. And what this is referring to is what's known as the biochemical unity of life. And all that saying is that all living organisms have a resemblance, and you can see that when you compare these bacteria to May. No, I'm just kidding. The biochemical unity of life does say that there is a resemblance between all living things, but that resemblance is seen at the atomic and molecular levels of life. And there's a lot of evidence at the atomic and molecular levels that support what's known as a common universal ancestor. We're all life today, is theorized to have evolved from a single universal common ancestor, and hopefully these bacteria don't look like may. But at the biochemical and molecular levels. We have a great resemblance, and that's pretty fascinating. So that concludes our lesson on the characteristics of life, and I'll see you guys in our practice videos.