 Something interesting happens at the cellular level. We can go in in two directions here Some organisms are what we call unicellular Organisms and then other organisms are multi cellular Organisms and hopefully you can see that we have to have two different Levels of life here because a unicellular organism is one that is its own unique Individual all by itself just just one cell like an amoeba or a paramecium or a bacterial cell Multi cellular organisms on the other hand have to have additional levels of organization Because they're composed of more than one cell If we're dealing with unicellular organisms the next level of organization is the population level if we're dealing with multi cellular organisms the next level of organization is the tissue level Now a tissue is Defined as two or more cells working together to perform a particular function and So you see we don't have tissues at the unicellular level because each individual cell is its own living entity So multi cellular organisms we go on to the tissue level of Organization unicellular organisms we go to the population level and we'll come back and talk about what a population is in just a few minutes And we'd like just mentioned four categories of Animal tissues so you can get some ideas to what we're talking about In animals you are an animal There are tissues called epithelial tissues and epithelial tissues line and cover but your body surfaces for example Your skin contains an epithelial tissue called stratified squamous epithelium muscle tissue for example in your in your body is a Particular type of tissue we call that skeletal muscle in your heart There's cardiac muscle in your stomach. They're smooth muscle other types of tissues include the nervous tissue Muscle tissue connective tissue is an important category of tissue and that includes things like bone so Plants have tissues too. I just wanted to mention a few of those and plants there are things like perincoma and Sclerencoma and calincoma and they all have very unusual sounding names So after the tissue level of organization We have the organ level of organization and Organs are composed of two or more tissues that work together to perform a particular function and Example of a very simple organ would be the conjunctiva the the membrane that lines your eye That conjunctiva is made of a type of epithelial tissue and a type of connective tissue and that by definition Is an organ or we could have complicated organs like the small intestine The small intestine is lined with something called simple column our epithelium and then there's some loose connective tissue And some smooth muscle So we have all sorts of different kinds of tissues and some organs some organs are much more simple so beyond the organ level of organization is We call the organ System level of organization complex complex animals may have many levels Many organ systems for example I typically recognize 11 organ systems in humans and those would include things like the Integumentary system, which is your skin and and hair and nails The skeletal system for example is is an organ system muscular system nervous system endocrine system lymphatic system, so there are many different types of organ systems within a human So we go from organ system To the organism level of organization And that's when we can come back and and pick up our unicellular organisms Unicellular organisms are organisms that are composed of just one cell Multicellular organisms on the other hand have Additional levels such as the tissue level the organ level and the organ system level Now an organism we could define it as just an individual living Entity an individual living creature one flathead catfish one blue and gold McCall one Gray wolf, so it's an individual living organism the next level of organism comes into place when we start thinking about all the Individuals of a particular species in a defined area So we might talk about all the white-tailed deer and pilot Mountain State Park or all of the Channel catfish and in Lake Norman or all of the White oak trees in a particular defined area So a population consists of all of the individuals of the same type in a defined area It's even more complicated the next level of organization is what we would call the community level of Organization in the community level of organization Includes all of the different kinds of living organisms in the same space So we could think about a freshwater farm pond for example could be a Community and all the living organisms all the different plants all the different bacteria all the different animals And fungi that live in that area make up what we refer to as the community So the next level of organization is what we refer to as as the ecosystem And of course an ecosystem could be something like a tropical rainforest or the the tundra or the savanna and Ecosystems and may encompass many communities and we also consider non-living Factors that are involved in ecosystems such as the amount of rainfall or sunlight or Temperature at average temperature of those kinds of things so ecosystems are Highly can be highly complex systems that may involve thousands and thousands and thousands of organisms and many populations of And many different communities So the final level of organization is the biosphere And the biosphere refers to that thin layer on earth as far down in the soil as we have to go to find the Deepest living organism and as far up in the atmosphere as we have to go to find the the highest living Organism with that thin layer on earth where life exists is is what we refer to as the biosphere And of course that's composed of many different kinds of ecosystems So levels of organization We've gone from the smallest to the largest. There are different kinds of people that study life at many different Levels for example, there are there are population ecologists that are interested in studying populations There are people that spend their entire life studying a particular organism Maybe someone is studying The a particular species of of scorpion and they spend their whole life studying that particular Animal there are people that study organ systems and that's all they do you think about your cardiologist and your gastroenterologist And whatnot there are people Medical doctors that specialize in organs and study tissues and certainly on the cellular level there are Psychologists that that study cells and organelles. So when my buddy asks, so you're a biologist What do you know about? it could run the entire gamut and It's certainly a diverse field to study