okay hello everyone this is Melodye and I am here to give you the short version of the definition of life. All the pictures in this presentation come from our textbook and the textbook has some really nice pictures. So Biology is the study of life which means he probably should define it, which is why this section. and there are lots and lots of different forms for life that life takes and anything that involves life, life's interactions ,of individuals with each other and with their environment also counts as part of Biology. Okay, the first thing is our definition currently is that cells make up the basics of life. So every kind of living organism that we know of is based on cells. And here are some examples. There's a bacterium, little teeny tiny cell, here's a Protista, archaeans. okay they're all, these are pretty small and you notice that they have something in common and that is that there's an outer boundary and then there's a lot of stuff on the inside. So a lot of what we're gonna be doing this quarter is looking at the stuff inside a cell to see how a cell works. Also living things have to have DNA. This is a bit restrictive. That's one of the reasons viruses don't count as something living. They aren't made of cells and they don't all contain DNA. So DNA is a molecule that passes on genetic information for the next generation and it's got the information to make the proteins which make other things that the cell is going to need to do cell work. Okay, there are five characteristics that you should know something about anyway. Life is organized and you can see from this graphic from the book that atoms are organized. IF you've started chapter two you know the structure of an atom, and you put enough atoms together you get molecules and molecules together you get organelles. Okay, put a bunch of organelles together you can get a cell. Tissues are a bunch of cells together performing the same function, an organ is a structure that carries out a specific function for the organism. An organ system is several (Organ system) Organs working together. So here we've got leaf and branches different organs but they work together to support the organism. For us that would be something like the heart and lungs working together because you can't have one without the other got to have both so that would be an organ system and then the organism the entire living unit and then if you've got a bunch of the same kind of thing living together it's a (speech) it's a population sorry and if you look at a population and its environment and it's some other things living things around it it's a community and if you look at a community including its environment you've got an ecosystem and all the ecosystems in the world add up to the biosphere. One interesting property of organization is that it can lead to emergent properties. Emergent properties are things that you get that you don't expect so you put a bunch of nerve cells together and you get a brain, which has different components different functions than just individual nerves so you get behaviors and characteristics that are different from what you started with. One example would be if you take wooden planks. Those are individual building materials and you can put them together to build a house. So the house is more than just wooden planks it's the way they're organized and it gives protection from the environment and safety. Okay also life requires energy and on this planet our main source of energy is the Sun. Because plants, anything that does photosynthesis ,takes in light energy so they don't have to eat anything, but the consumers like us we get our energy from the plants and then there's a whole other set that decomposers that use the energy after we're done with it and then they go back to make soil which allows the producers to grow so we've got producers consumers and decomposers. Life is also requires homeostasis it means keeping the [internal] environment constant so homeostasis and this picture from the textbook is supposed to illustrate how this works. But the main function ,the main behavior that leads to homeostasis is there has to be a sensor and an effector. So when you're talking about heating and cooling a home the sensor is the thermostat, the effector is the furnace and when the room is too warm thermostat senses it which then shuts off the heater okay and if it shuts off long enough hopefully the room cools down but if it cools down too much the sensor, thermostat, senses that and turns the heater back on which heats up the room and keeps heating it until the sensor says okay high enough and it turns off the heater. So it's a feedback system that leads to homeostasis and homeostasis is not just for temperature although humans do have internal mechanisms for controlling body temperature. So this person in addition to being able to adjust metabolism to keep the internal temperature right also can adjust behavior to put on clothing to help keep them warm. And this person is adjusting their internal hydration. Their sensor said you're thirsty drink water so they're drinking water. (and) Everything fluctuates around some kind of setpoint. Okay life also requires growth. Organisms are produced so reproduction. Reproduction, it can be asexual, so like this plant right here it's a strawberry plant, produces little runners with new little plants growing up from them. This is asexual reproduction. Only one parent is involved and the offspring have that same genetic identity as the parent they're genetically identical. You can also have sexual reproduction where two parents provide some of the DNA to produce offspring, so the offspring are never genetically identical to the parent. And sexual reproduction is very good for a changing environment. Asexual reproduction is good for an environment that doesn't change at all. Short term, asexual reproduction is great but long term, environments just do not stay the same forever, so sexual reproduction is also a very handy strategy. (and) Also organisms grow so you start with a single cell and that grows to a multicellular organism which then grows up to the adult so even with asexual reproduction you've got the baby plants which will grow up to be as big as the adult plant and then the baby plants will send out their own runners to reproduce, these babies will grow up to also reproduce .and then the last thing is life evolves. So this little graphic here shows you've got a population of a bacterium and over time because of environmental factors and maybe errors in DNA replication you end up with a mutation and usually if there's no stress on the population that one mutation may stay there but it doesn't really change the makeup of the population. But if there's an environmental pressure, for example antibiotics and this little red one here has resistance to that antibiotic. Over time the antibiotics will kill off more of the green ones meaning the red ones can reproduce more and evolution occurs and you end up with a population that's got more of the antibiotic resistant bacteria present. Okay an example might be of a different kind of environmental pressure would be like these guys that pygmy seahorse it is a seahorse and it has the genetics that let it blend in with its coral habitat other seahorses don't look the same and so it would not do as well in this environment so at this environment around quarrel this little seahorse has a survival advantage it's less likely to be caught and eaten by some predator because it looks like a piece of coral. Okay and because more of them survive more of them are gonna pass on their genes so the majority of the, of these seahorses are gonna look like the coral that they're in the ones that blend better will do better and produce more offspring. Okay now, is it alive check those characteristics, see if its got cells, see if it's got DNA and you can make a determination about whether you see think something is alive or not. This is not the law this is the current definition and I certainly hope that in the future we will discover some forms of life that are not that don't quite fit our rules so we'll have to change our rules. I'm a unfortunate fan of Star Trek and I have hopes that someday we will find the silicon being that those in one of the original Star Trek episodes based on silicon rather than carbon but anyway that's just my personal prejudice