Hi. In this video, we're going to talk about development. How organisms start out is that single celled zygote and progress or develop to these complex multi cellular creatures that have specialized tissues, organs, bone structures, all these crazy functions. How does that happen? Well, it turns out that certain processes are fundamental to development across all organisms. Chief among these, of course, is cell division. How does a single cell turn into a multi cellular thing? Well, cell division, obviously right. And you guys might recall, from our discussion of cell division that might Assis is a highly regulated process. And right here we see a chart of the cell cycle or a figure of the cell cycle, and these black bars in it represent the various checkpoints in mitosis, the control mechanisms, the gates, if you will, that regulate the my tonic process. Now, in addition to these checkpoints, we also talked about social control, which is how cells neighbors can regulate their division. So in the course of development, the timing and location of cell division is incredibly tightly regulated as it's crucial for proper development. So these systems involved in this are chiefly these Might Todd IQ control mechanisms and also these social control mechanisms neighbors influencing each other to divide or to halt division. Now, in addition to cell division, cell differentiation is another crucial process. Cell differentiation is how one cell become, or one undifferentiated cell can become a specialized cell like a neuron, for example, the cells lining your stomach and the cells in your brain. Those neurons are very different looking cells, but they all come from the same place. And that is namely stem cells thes undifferentiated cells that, through differentiation give rise to specialize types of cells. And we call that process cell differentiation, and we call the ultimate end of it cell fate. It's the destiny of the cell. What will this sell become? That is the cell fate, right? Is this stem cell to become a neuron, or is it to become a cell of the intestine epithelial cell? Well, that's determined by its fate, and we'll talk more about how self fate is determined later on. Now, in plants, Uh, stem cells are actually located within the plant and remain there and continue to develop throughout the entire life of the plant, and we call these Mary stems, and actually plants have multiple mary stems. Basically anywhere you're going to get new growth. You have Mary stems. So to pretty obvious places are the roots right? The roots need to continue to grow, so you have root Mary stem Mary stems and also the shoot right plants continue to grow upward. They branch out, send out new leaves. You have thes, uh, shoot mayor stems, and we'll talk more about Mary stems when we cover plant development specifically now, animals also use stem cells. They use stem cells. Or I should say we use stem cells to repair our wounds, replace cells, and also to create the cells of the immune system which have to be developed in a very specialized fashion to match a specific immune function. So animals actually keep a supply of stem cells in their bodies. However, unlike plants, we don't have a carte blanche with our stem cells. We can't just continue to produce, you know, anything willy nilly. We use our stem cells for very specific things, and here in this figure, you can see an example of the fertilization event, which will lead to the formation of a zygote and how, over the course of development you will arise or you will give rise to specialize cells that will function in circulatory system or the nervous system like neurons were talking about, or the immune system as we were also talking about. All right, let's flip the page.