hey everybody it's mr smees and i'm here today to help you study for your ap environmental science unit exams final exam and the ap exam in may if you're ready to think like a mountain and write like a scholar let's get started first i want you to pause this video and hop down into the video description below so you can grab your free copy of the unit 1 ultimate review packet this packet has study guides that you can use to follow along with these videos it has practice questions it has two full length practice exams all with answer keys so you can make sure you're really thinking like a mountain and writing like a scholar as someone who's been teaching apes for years and scoring exams for the college board in may i can tell you that the number one thing that cost students college credit on this exam is frq writing it's just too difficult to go into that examine may without practicing so grab that ultimate review packet practice those frqs follow along with the study guide and check your work as you go with the answer keys in this video we'll review everything you need to know about unit 1 which is ecosystems now since you've already learned this info in class this is going to be a review if you need a deep dive into any of the topics in unit 1 you can find in-depth video reviews of all 11 topics over on my youtube channel go ahead and hop over there at any point in this video if you need a deep review of any of the topics we're covering so the first topic in unit one here is an introduction to ecosystems now in everyday life the word ecosystem habitat environment kind of all get used interchangeably but in apes we need to make sure we have clear definitions for each of those terms an ecosystem is the interaction of living and non-living things in a specific region whereas the word environment refers to the entire natural world so you can think of an ecosystem as a specific portion of the world's environment another term that gets misused a lot in apes is the term habitat a habitat just refers to the given environmental conditions that a certain species needs in order to survive so the arctic would be a great habitat for caribou but it wouldn't be such a great habitat for a copy bar beyond just the environmental conditions that a species needs in its habitat there's also the other organisms to consider organisms can have a whole host of different relationships with each other they may be competitors fighting over a shared resource with one another or they might be symbionts meaning they're living in close relationship with each other and here's the first big misconception i see apes students make every year and that's confusing symbiosis with mutualism symbiosis just refers to any organisms that live in close proximity to each other so when you go hiking and you forget to filter your drinking water and you develop a tapeworm or a parasite that's technically symbiosis that organism is living in very close proximity with you but it is absolutely not mutualism you are not benefiting from that tapeworm mutualism has to benefit both species great examples of mutualism would include bees and the plants that they pollinate and the coral reef which is made up of photosynthetic algae and little coral building animals called polyps so the key question in all species interactions is whether one both or neither species benefits from the relationship so pause the video now and try to fill out topic 1.1 in the ultimate review packet study guide so you can see if you really understand this topic if you struggle with that remember that you can hop over to my youtube channel and find an in-depth review of all of these species interactions in topic 1.1 on we go to topics 1.2 and 1.3 which are terrestrial and aquatic biomes now biome is just a region on earth that shares a consistent yearly average temperature and precipitation pattern so the tropical rainforest and the tundra are two great examples of very different biomes one of them is going to have both high annual average temperature and precipitation the other is going to have very low average annual temperature and precipitation the key thing to remember with biomes is that it all comes down to these average temperature and precipitation patterns so everything else in a biome is just a secondary characteristic that's determined by temperature and precipitation so we look at the tropical rainforest and we see this dense lush vegetation we see this rich animal biodiversity and we're tempted to think that it's a tropical rainforest because of those factors but we have to remember that high temperatures and high average annual precipitations are what result in all that plant biomass which results in all that animal diversity but what if the average annual temperature and precipitation patterns in a region change can the biomes shift can the trees of the tropical rainforest get up and just move somewhere else look the trees they're moving and the answer is yes if temperature and precipitation patterns are changed our biome locations can actually shift with those changes in fact we're currently seeing an expansion of the tropics away from the equator as global temperature rises if you want to see how well you're understanding biomes pause the video now go down to that table 1.2 in the ultimate review packet see if you can fill out that biome chart remember if you're struggling with any of the concepts in this video hop over to my youtube channel you'll find an in-depth review of every single topic covered on the exam well aquatic biomes are also influenced by temperature and precipitation there's three other factors we need to review about aquatic biomes that's salinity or saltiness level flow and depth the salinity level or the saltiness of an aquatic biome is incredibly important because the plants and animals that live there need to be adapted to the dehydrating effects of salt so trees like mangroves or other plants found in saltwater biomes will have adaptations such as thicker membranes or pores in their leaves that actually pump salt out now the flow of an aquatic biome is important as well not only does flow disrupt the surface which allows oxygen to diffuse into the water but it also carries sediments and with those sediments nutrients those nutrients are transported from one place to another and that's a huge factor that aquatic plants need in order to survive now let's take a look at a specific type of aquatic biome so we can see how these characteristics apply estuaries are a really unique and important category of aquatic biomes they're where the mouth of a river empties out into the ocean this gives them a really unique salinity level we often call these waters brackish because they're partially salt water partially fresh so the species that live there like mangroves or salt grasses have to be uniquely adapted to those salinity levels now because this is the mouth of a river emptying out to the ocean we have a huge amount of sediments and with those sediments nutrients that are transported along the river it's been picking up sediments all throughout its watershed and it's dumping those sediments into the estuary that makes it incredibly productive because the plants there have access to a huge amount of nutrients and that high plant biodiversity can support high animal biodiversity now there's only two things that you remember about biomes it should be that they're determined by average annual temperature and precipitation and that the organisms living in those biomes are uniquely adapted to those temperature and precipitation patterns as we move into topics 1.4 through 1.7 we have to remember one important rule that's the law of conservation of matter the law of conservation of matter is just a fancy way of saying that matter is never created or destroyed it's only changing forms in these next four topics we'll be focused on how carbon nitrogen phosphorus and water cycle throughout ecosystems before we do that we need to establish three common pieces of terminology that we're going to use in all of these cycles reservoirs are things that temporarily store matter sources are just processes that move matter between reservoirs and sinks are reservoirs that take in increasing amounts of matter over time because they take in more matter than they give off the first cycle that we'll look at today is the carbon cycle now there's two really important things to remember about the carbon cycle the first is that sources of carbon are returning carbon in the atmosphere and carbon sinks are taking carbon out of the atmosphere the second big thing to remember is that the amount of time carbon spends in its reservoirs varies a lot and that time is really important to global climate now we need to remember that the atmosphere is a critical carbon reservoir and that's because the amount of carbon the atmosphere stores at any given time determines earth's global climate the more carbon dioxide and methane that are added to the atmosphere the warmer earth becomes so as we look at the rest of the reservoirs and processes in the carbon cycle we want to be asking ourselves the question is carbon being taken out of the atmosphere or is carbon being put into the atmosphere photosynthesis is a really important step in the carbon cycle because it's the process of plants taking carbon out of the atmosphere and converting it into biological molecules like glucose or starch or other plant tissues if plants are really long-lived they can actually become carbon sinks so a sequoia or a redwood tree that lives for thousands of years takes in so much more carbon than it gives off lowering the levels of carbon dioxide in the atmosphere respiration on the other hand returns carbon dioxide to the atmosphere that's because organisms like plants and animals are breaking down glucose and exhaling or respiring that carbon dioxide out adding it back to the atmosphere but the most important carbon cycle step from a human standpoint is extraction and combustion so when we dig up fossil fuels and burn them for electricity we're returning carbon dioxide to the atmosphere that was out of circulation for millions and millions of years and this is why the rate of carbon cycling is so important even though respiration is also returning carbon dioxide to the atmosphere that carbon that organisms are exhaling was just taken out of the atmosphere by plants during photosynthesis think of respiration as spending a dollar that you just found on the ground whereas burning fossil fuels is like living on a credit card because you're putting way more carbon dioxide into the atmosphere than you're saving or taking out next we'll review the nitrogen cycle which just like the carbon cycle is the movement of nitrogen between reservoirs but with two big key differences the first key difference is that nitrogen is cycling far more quickly through its reservoirs than in the carbon cycle and the second key difference is that while the atmosphere is the major nitrogen reservoir that nitrogen in the atmosphere is in an unusable form for plants or animals it's biologically unavailable that's because the triple bond between these nitrogen atoms in its gas phase is just too strong to be broken apart by plants or animals and that's where nitrogen fixation comes in well it's not technically the first step because it's a cycle all the steps are happening at once it is the most critical step for life on earth and that's because it's the process of this unusable nitrogen n2 gas being converted into a usable form of nitrogen like ammonia or nitrate the main way that nitrogen is fixed in the natural world is by bacteria with specialized enzymes that can break apart these strong triple bonds and pair up those nitrogen atoms with hydrogens forming ammonia now this can be done by bacteria living freely in the soil or it can be done by symbiotic bacteria that live in the root nodules of plants called legumes we call these bacteria rhizobacteria because the greek word for root is rhizome now nitrogen can also be fixed by the extreme amount of energy given off by a lightning strike or fossil fuel combustion so in fact humans combusting fossil fuels is the way that we create synthetic nitrate-based fertilizers now there are more steps in the nitrogen cycle but nitrogen fixation is by far the most important step for you to understand for your exam remember it's so crucial because plants can't assimilate nitrogen or take it into their bodies if it's not in a solid fixed form like ammonia or nitrate so go ahead and pause the video now go down to section 1.5 in the ultimate review packet and see if you can fill out the rest of the steps in the nitrogen cycle now we'll take a look at the phosphorus cycle the big difference between the phosphorus cycle and the other three cycles we're talking about in this unit is that it doesn't have a gas phase this means that phosphorus is not moving around the atmosphere and as a result it's cycling much more slowly than the other three forms of matter now the major phosphorus reservoirs are rocks and sediments that contain phosphorus based minerals so unlike carbon and nitrogen which are bouncing all over the atmosphere as gas molecules phosphorus is just stuck in rocks and for phosphorus to be released from those rocks those rocks have to undergo weathering weathering is the breakdown of rocks by processes like the wind in the rain and the freezing and thawing of water these processes break the rocks down into smaller and smaller pieces which eventually releases some of the phosphate they store in the form of phosphate ions these phosphate ions are then carried away by runoff or by wind transporting sediments from one location to another and that's how phosphorus actually cycles between ecosystems now this process of phosphorus and sediments being carried from one place to another is called erosion now because these processes of weathering and erosion are so slow phosphorus is often a limiting nutrient in both aquatic and terrestrial ecosystems what this means is that plants have all the other nutrients they need to grow except for enough phosphorus and our final bio-geochemical cycle that we're studying here will be the water or the hydrologic cycle it's probably the cycle that's most familiar to us but there's one major thing we need to remember about it and that's that this process is actually driven by the energy from the sun so let's think about what this means for a second when water evaporates from a body of water like a lake or a river it's because the sun has given that water enough energy to actually convert it from a liquid into a gas phase when it rains it's because the moisture in the air has reached a condensation point based on the temperature of that layer of the atmosphere but you guessed it is based on the sun's energy other important water cycle steps we want to remember are infiltration which is the process of precipitation or surface water seeping into or sinking down through the layers of the soil into groundwater and transpiration which is the process of water leaving the stomata or the poor openings in leaves and entering the atmosphere as a gas phase now when it comes to water reservoirs the ocean is the major water reservoir on earth the problem is that that water is not usable for humans for things like drinking or for agriculture so other fresh water reservoirs like groundwater or polar ice caps or water that's stored in rivers and lakes is really critical for us to be able to use and unfortunately for us humans and other species that rely on fresh water the world's largest freshwater reservoirs are also the least accessible that's the ice stored at the north pole and the south pole and in the world's glaciers now that we've covered how matter cycles are ecosystems we'll wrap up unit one by taking a look at how energy cycles through ecosystems and it all starts with our mean green chlorophyll-filled machines the plants topic 1.8 covers primary productivity which is just a fancy name for the rate of photosynthesis in a given area now i'm going to say this again because it's the number one mistake ape students make in this part of unit one primary productivity is the rate not just the total amount of photosynthesis in a given area so it's the rate at which the producers or plants in the area are taking sunlight and converting that energy into glucose or other forms of organic matter it can be really helpful to think of primary productivity the way you think of a paycheck so when you apply for a job you want to know the amount of money you're going to make in dollars per hour or dollars per year primary productivity is the same way it's the production of energy over a certain amount of time now because we're not usually just interested in one individual plant we like to add in a unit of area as well so a great example of a way to measure primary productivity would be the amount of energy or kilocalories in a given area a meter squared over a given time period like a year also like human productivity plants don't get to keep all of that energy that they produce they have to use a lot of that energy that they harvest for processes like cellular respiration so we call this energy loss respiration loss think of this as the taxes that come out of your paycheck or the taxes a plant has to pay to upkeep its body build more cells do all of the things it takes to be a plant in fact we even use the same terms as we do for human paychecks to refer to plant productivity so gross primary productivity is the total amount of energy that plants produce but net primary productivity is the amount of energy that plants can actually store after they've given up what they need to for cellular respiration now we can actually calculate the gross primary productivity the net primary productivity or the respiration loss for a given ecosystem we just have to use this simple equation which is npp equals gpp minus rl or respiration loss so let's say we have a force ecosystem that we know has a gross primary productivity of 1000 kilocalories per meter squared per year it has a respiration loss of 250 kilocalories per meter squared per year we're just going to plug these numbers into our formula and subtract 250 from 1000 and that's going to give us a net primary productivity of 750 kilocalories per meter squared per year so pause the video now and see if you can work out the rest of the npp practice problems in the ultimate review packet remember the link is right down there in description not only we get practice problems for npp you get practice problems practice questions practice frqs for all nine units with answer keys so you can check your work as you go in topics 1.9 and 1.10 we'll take a look at how that energy that plants produce actually moves up through the food chain and we'll take a look at why most of that energy never actually makes it to the next step first we need to review what a trophic pyramid is it's just a way to represent the way that energy flows through an ecosystem from organism to organism at the base of all ecosystems you have the producers converting sunlight into organic forms of energy like glucose or starch or any other plant tissue that animals can eat then we have the primary consumers or the herbivores which are getting their energy by eating the plants then next you have the secondary consumers they are getting their energy by eating the primary consumers that ate the plants and finally we have tertiary consumers sometimes called apex predators that are preying on secondary and primary consumers for their energy source now the shape of the pyramid is key to understanding how energy flows through ecosystems the producers or the plants are at the base because they have access to the largest amount of energy they're producing energy directly from the sun they're not getting that energy from another organism the reason the pyramid gets narrower as we move up is that each level only receives 10 percent of the energy from the level below that's because the organisms at the level below use up a ton of that energy for cellular respiration from moving around so their body gives it off as heat or they just convert it into a form of biomass that's not digestible at the next level so those organisms at the next trophic level can't get any energy from it and this is the second law of thermodynamics in a nutshell each time energy is transferred from one trophic level to the next 90 percent of it is lost to the environment and only 10 percent of it makes it to the next trophic level in apes we call this the 10 rule this means that primary consumers only receive 10 of the energy from the producer level secondary consumers only receive one percent of the energy from the producer level and tertiary consumers or top predators only receive 0.1 of the energy from the producer level and that's why large predators like eagles and wolves require so much space in order for them to get the amount of energy they need there needs to be a thousand times as much plant biomass within that ecosystem for them and finally we'll wrap up unit 1 with topic 1.11 which is food webs and food chains now this is a really simple topic if you can keep one rule straight and that's that the arrows in a food web or a food chain show the movement of energy and matter so instead of looking at this food web diagram and thinking about what eats what we want to think about where energy and matter are moving so when this hawk eats the mouse the arrow represents that both matter and energy are transferred from the mouse to the hawk but we can trace this energy back even further than the mouse remember that the mouse had to eat this grass which had to take in that energy from the sun through the process of photosynthesis the grass also had to take in carbon dioxide from the atmosphere in order to produce that glucose that the mouse ate it's almost like the people at the college board put unit 1.11 last because it ties together all the concepts from earlier in unit 1 like the carbon cycle and the trophic levels the other thing we want to make sure that we understand about food webs is that the removal of one species can have a huge effect on the organisms in the rest of the food web especially on either side of it if this ecosystem loses its apex predator the hawk the populations of all its prey would increase so without the hawk preying on them the mouse and rabbit populations would increase which would likely lead to over grazing on the grass and less food for other herbivores the snake population would also increase which means it would decrease the populations of its prey the frog and the bird now the grasshopper population is increasing since its two main predators have declined and we call these powerful effects of predators in an ecosystem trophic cascades top predators like wolves and hawks often control the herbivore populations in their ecosystems which actually results in an increase at the producer level in those ecosystems in unit 2 we'll take a closer look at how wolves can actually reshape entire landscapes with this powerful trophic cascade effect and that ape scholars is unit one in the books i hope that your brain has assimilated some apes knowledge and incorporated into brain tissue in fact i hope your brain has actually become a sink for apes knowledge and if you don't get that one you probably want to review topic 1.4 remember if you haven't already gone down into the video description and grab your free copy of the unit 1 ultimate review packet do it seriously it will help you understand everything you need to know for unit one on the apes exam and if you want answers to the unwanted study guide as well as units two through nine practice up our cues full length multiple choice exams answer keys everything you need to be ready for the apes exam make sure to purchase the apes ultimate review packet we can be mutualistic symbionts you'll get everything you need to pass the apes exam in may to ace your class and i'll get the support from you to keep making awesome videos thanks for watching today ape scholars as always think like a mountain and write like a scholar