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Current time:0:00Total duration:9:47

Video transcript

for the last 38 episodes of crash course biology we've talked about how to make an organism and you know what I've learned and those 38 weeks putting a living thing together is hard there are molecules that make up organelles that run cells which come together to form tissues which make up organs that make up systems and knowing this stuff is incredibly important because it shows us the ground rules for being a living thing on this particular planet anyway but still there's so much more to biology than that I mean understanding how an organism goes about its internal business is great but it doesn't tell us much about its place in our world for that we need ecology the study of the rules of engagement for all of us earthlings psychology seeks to explain why the world looks and acts the way that it does why the South Pole looks different from the Congo and why there are mosquitoes all over the place while black rhinos are practically extinct the short answer to this question is because the world is crammed with things both animate and not that have been interacting with each other all the time every day since life on this planet began even shorter answer is that all life and all of these things interacting with each other depend on just two things try to guess what they are in the meantime get ready because crash course biology is taking its final voyage outside the body and into the entire world anyway you could think of all living things great white sharks pond scum potato plants as molecules that react with each other each one of us organisms is pretty piddling in the scheme of things just like a single oxygen molecule which we need to make ATP to fuel our bodies but it can't get much done by itself but if you get a million oxygen molecules together with some other types of molecules suddenly they're unleashing a google jillion megawatts of ATP power to animate the bag of meat that is you the same principle applies to organisms as you put individual organisms together they can interact with each other in their environments to create something larger than the sum of its parts and just as every organism has a hierarchy of biological systems from molecules to organelles to cells to tissues to organs so too does earth have tiers of ecological order like what a bunch of members of the species are together in a certain area and they interact pretty often you've got a population population ecologists study why populations grow or shrink over time depending on where they are when two or more populations of different species live together we call that a community you can think of an ecological community as mr. Rogers neighborhood but with the people in the neighborhood eating each other sometimes because that's what species do when they live together they interact sometimes that means predation sometimes cooperation and sometimes competition for resources like food and water and living space so a community ecologist studies how the interactions between community members and their environment affect how many of each species there are within a community another level up from communities are ecosystems which are made up of groups of organisms in a specific area and the nonliving parts of their environment like soil and water and air if you take a bunch of living things and plop them down in one place that has a specific mix of climate and soil chemistry and topography that's going to make up one kind of ecosystem but you put them down in a completely different place and they're got at work in completely different ways to form a completely different ecosystem ecosystem ecology specifically explores how energy and materials flow through an ecosystem and how the physical environment impacts the stuff living there now a lot of people get ecosystems confused with the next step up which is biomes a biome however is where organisms have evolved similar techniques to adapt to a general set of conditions for example a grassland is a kind of biome there are scores of different grassland ecosystems all over the globe but the organisms in each one have made similar evolutionary concessions to all the conditions the grasslands share like your hot summers and your cold winters in not too much rain but more rain than you'd find in a desert biome other biomes include tropical rainforests Tundra deserts and oceans the only level above the biome is the biosphere which includes the atmosphere and the whole earth and everything that gets used by anything that's alive so why do all of these many levels of ecological activity look the way that they do like why do some organisms like to live in one place but not another and what makes Earth's various populations communities ecosystems and biomes different from each other well factors that determine what a place is going to look like fall into two different categories biotic or living and abiotic not living biotic factors include stuff like predators as well as animals or plants to provide either competition or some benefit like food or shelter abiotic factors on the other hand include temperature moisture sunlight elevation elements that have nothing to do with organisms in the ecosystem but which influence them just as much as other living things do now from these two categories the most influential factors are the ones that living things are most particular about that is the things that they need most but only at certain levels and these preferences all come down to chemistry for example almost all chemical reactions that happen inside living things are governed by enzymes so the catalysts for pretty much all the action going on inside view and these enzymes are most effective within a set of temperatures chemical reactions within the body slow way down when it's really cold and very high temperatures change the shape of enzymes making them less effective so temperature is one of the major factors that determines why animals live in certain places if you look at the places on the earth with the most biodiversity or different kinds of living things you'll find that it's in the places where the temperatures within the ideal range for enzyme function what else well everybody's got to eat at least if you're an animal or a fungus or some other kind of heterotrophs so you'd think that food will also be way up on the list but actually it's plants and other autotrophs like cyanobacteria and protists that are the base of nearly every food chain and they have to be fed to so again it comes down to chemistry the key ingredient plants need for photosynthesis is water which is also what we need to burn ATP maintain homeostasis in our bodies and all that jazz so the quest for food ultimately comes down to a need for water so yes prized water and temperature are the two things that are going to sum care about the most ergo there would be colleges focus on when determining why certain organisms hang out in one place over another together these two factors define every biome on the planet for instance a saguaro cactus has evolved to live in the Sonoran Desert of North America which is super hot and gets very little precipitation so the Sonoran Desert is full of animals and plants that can just like the Saguaro take the heat and also the extreme face crumbling dryness but if you put these animals in the Amazon rainforest even though it's hot enough for them it's just too wet so yeah the things that live in a vial are ultimately determined by how much water is there in the temperature and in turn these inhabitants determine how the biome looks called its physiognomies so now we are going to take a look at all the different types of biomes out there there are the places on the planet that get lots and lots of rain around 300 centimeters a year and are pretty warm around 25 to 30 degrees C on average which is speed aware and weather as far as I'm concerned these biomes are the tropical rainforests which generally hug the equator and have unbelievably high biodiversity because everybody is wanting to get a piece of that sweet tropical action and then on the complete opposite side of that scale we have the tundra most of which is above the Arctic Circle in Antarctica or way up at the top of some mountains Condren gets little precipitation and some well below zero temperatures and what lives there not much a couple of mosses and liverworts maybe a few species of grasses some birds and a handful of mammals the same goes for the desert biome where there's very little rainfall and very high temperatures like the tundra without much water they can't be very many large plants and where there aren't a lot of plants there aren't a lot of other organisms even when temperatures are close to what makes living things happiest between these three extremes we've got biomes that require more or less water combined with high ashore lowest temperatures these are your moderate or temperate biomes and they include temperate grasslands like you find in the North American Prairie or temperate deciduous forests found over much of Europe and North America and Tyga's are coniferous forests found across Canada much of northern Russia and Scandinavia so of all these biomes in the middle experience pretty moderate temperatures most the time the availability of water must be what makes them different from each other some of these biomes have a lot of trees and as we know trees need a lot of water so if you find yourself in a temperate forest it's pretty safe bet that that particular ecosystem gets a fair amount of precipitation and if the Carboniferous Flores taught us anything it's that having a bunch of trees around changes the landscape the climate and even the geology of the biome if you don't have a lot of trees in a biome it means you probably don't get enough rainfall for their liking and without trees more sunlight reaches the ground and gets to grasses and other small plants leading them more of a temperate grassland ecosystem and where you get grass you get animals like bison and pronghorn and other ungulates whose digestive systems are big fermentation vats that process cellulose all day long and then when you got ungulates you also get predators all these animals are way different than what you'd find in a temperate forest so biomes are different because the plants are different because the rainfall and temperatures are different but of course there are also biomes entirely under water we can't forget that the surface of the planet is 3/4 water and since water availability isn't an issue in the ocean marine biomes differ in things like temperature pressure oxygen content how much light is available and stuff like that so thanks to the science of ecology we know that the way the world works can be explained mostly by temperature in water but this is just the beginning my friends yes the end of biology 101 maybe and we'll always have that time that we spent learning and loving won't we but there's so much more to find out together how des living things affect the climate the chemical makeup of the atmosphere even the geology of our planet how do they affect each other and maybe more importantly how are we humans affecting all of these things and what can we do differently to ensure that we all get to keep existing join me as we get to know our planet on a whole new level starting next week
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