okay class if you want to go ahead and grab your notebooks out with something to write with we're going to start with a new topic today so go ahead and grab out your materials yes uh in the back question uh yeah Mr L why you such a nerd bro dang sick burn bro yo thanks thinking about that all day I mean you keep trying to teach us all this stuff but like why waste your energy you know like does it even [Music] matter when studying ecology and organisms at a macro level it is clear that no living thing goes without any interaction with their environment living things depend on each other and also on other non-living things scientists study these many interactions that occur between living and non-living things in an ecosystem which is a space defined by the interacting components an example of an ecosystem could be a forest which contains both living and non-living material in constant interaction by defining the specific space of an ecosystem an ecologist can determine the ways in which both energy and matter move either through it or within it as we will come to discuss throughout this video but there are two main categories of ecosystems that you need to know about before we move forward which are termed open and closed an open ecosystem describes a system where all resources can enter and exit including energy and matter and a closed ecosystem restricts the movement of matter but does not restrict the movement of energy so we could Define the forest near your neighborhood as an open ecosystem because energy and matter are free to move as organisms and abiotic factors move and the sealed mesocosm you have in your biology classroom as a closed ecosystem because no matter can move in or out but energy via sunlight and heat can the focus of this video is about how matter and energy are transferred in ecosystems and we are going to start with talking about energy for most ecosystems the influx of sunlight is the principle source of energy that keeps the ecosystem going the sun emits solar radiation that travels through space and and hits our planet and some organisms in these Sun exposed ecosystems can harness that energy and convert it into chemical energy that their cells can use we'll go through the details about this later but notice here that I said sunlight is the principal source of energy of most ecosystems and not all ecosystems there are some ecosystems on our planet that do not receive sunlight at all but still Thrive with different inputs of energy these are places like caves and the Deep parts of the ocean that sunlight can't reach again more on that later a simple diagram called a food chain is used to predict the movement of energy and biomass through an ecosystem it consists of organisms which can be Illustrated as a drawing or written out as a name and text and arrows which show the direction that energy is moving the idea behind a food chain is to show the feeding relationships between organisms which in turn will tell you how the energy is moving looking at this example we can see that we have four organisms which are grass a grasshopper a mouse and an owl if if we take a look at the feeding relationships between these organisms we can say that the owl will eat the mouse the mouse if it's a certain species like a northern grasshopper mouse will eat the grasshopper and the grasshopper will eat the grass so we know who is eating who let's draw arrows to depict how the energy is moving the grasshopper is eating the grass which means the energy within the grass is being transferred to the grasshopper so the arrow points to the right the Mouse eats the grasshopper so the mouse is gaining that energy that the grasshopper had stored in it tissues AKA it's biomass so the arrow points to the mouse who is gaining that energy and the owl eats the mouse and also gains energy in the same way so the arrow points to the owl this is how we put a food chain together knowing who eats who will show you the direction that the energy and biomass moves constructing a food chain is a great way to show the feeding relationships between specific organisms in an ecosystem but they do have a problem they are often Limited in scope because most ecosystems have more organism and more possible feeding relationships within them to be shown in one simple chain to get a more realistic view of the complex feeding relationships within ecosystems we can construct a food web a food web operates under the same basic principles of a food chain but ideally takes into account every organism and every feeding interaction we can see here that the hawk doesn't just consume the mouse for energy it consumes the rabbit and the snake as well and the mouse is eating both the grass and the wild flowers to gain energy this is more realistic as many organisms have more than one food source the arrows in the food web just like within a food chain show the transfer of energy that is stored within that specific part of biomass being consumed energy is stored within carbon compounds in the cells and tissues of organisms which we holistically refer to as biomass while an organism is alive it carries these carbon compounds within its cells using them for energy as necessary and gaining more through the consumption of other organisms but in our reality no organism lives forever everything eventually dies at some point and when that happens what happens to those carbon compounds it had stored in its biomass there is a special category of organisms that get energy from breaking down carbon compounds found within dead and decaying organic matter and they are called decomposers organisms like bacteria and fungi are decomposers that feed off of entire dead organisms like a deer that dies in the woods or parts of organisms like when leaves fall off trees and die or organic waste created from organisms like a pile of feces from a bear that poops in the forest because bears do poop in the woods right because everything eventually dies and is broken down by decomposers we can add decomposers to the ecosystem with arrows stemming from well everything this is showing the relationship between decomposers and energy we'll talk more about decomposers and their importance with matter later on in this section let's continue our conversation about chemical energy with talking about how organisms obtain chemical energy and what they use it for all organisms no matter how large or small need energy to build structures we see these at the cellular level in the form of macro molecules through processes like carbon fixation in which carbon is taken from an inorganic form and used to create an organic molecule and in anabolic reactions that put monomers together to form polymers every living thing needs this chemical energy so how do they get it well there are two distinct methods of obtaining chemical energy that we see in organisms on our planet they can either make the chemicals themselves or steal it from another organism that made it by eating it organisms that can make energy carrying organic molecules from inorganic substances are called autot TRS Auto meaning self and tro meaning food these organisms can create their own food those organic molecules for themselves a great example of this would be a plant a plant harnesses energy from the Sun and takes inorganic molecules from the environment to create sugar which is a food source that it later breaks down for energy we'll break down autotrophs more on the next slide there are two categories or types of autotrophs that we see in nature which are called photo autotrophs and chemo autotrophs in either type external energy must be used for these organisms to create their carbon compounds they need this external energy source to support an initial set of reduction reactions that use up energy photo autot tropes use light as their external energy source and undergo the process of photosynthesis this makes up the vast majority of autotrophs on the planet and include Plants algae and cyanobacteria hemo autot tropes do not use sunlight as an energy source and instead are able to harness the energy from inorganic chemical reactions within their environment certain procaryotes including bacteria can undergo this process a chemo autotrof example you need to know for the IB exam can be seen in the bacterium acido bacillus ferrooxidans this bacteria lives in extremely acidic conditions and is an iron oxidizing chemo autotop iron sulfide is a compound found within the sedimentary rocks of its environment when exposed to oxygen in the presence of water the iron sulfide produces iron ions sulfate ions and sulfuric acid the outer membrane of the Aero oxidans bacteria can oxidize the iron ions and take in their electrons which are accepted by electron carriers within their inner membrane these electrons provide energy that is used to create other energy carrying molecules like ATP and nadh which can be taken and used to create other carbon compounds like sugars that can be broken down later for more energy so again the key point to remember here is that photo autotrophs get their external energy from sunlight and chemo autotrophs get their external energy from chemicals within their environment so we know that autotrophs can make their own food but what about the rest of us after all we as humans can can't just stand out in the sun and use that energy to make food which don't get me wrong would be very cool instead of making our food we have to get it from consuming other organisms that already have it and by it here I'm referring to carbon compounds like sugars fats proteins and nucleic acids organisms that obtain their food this way are called heterotrofos heterotrophs have to consume other organisms and steal their compounds to break them down for energy and this truly is the process of stealing as no organism wants to be killed and eaten by another organism though some organisms create structures like fruits and budding vegetables that are designed for that purpose though removing them does not kill the organism let's take chicken muscle as an example when you're consuming chicken let's say a chicken leg you are eating the muscle that that chicken used to move its leg within that muscle tissue are nutrients that the chicken stored and used within its cells for that tissue to operate like fat and protein that chicken intended for those fats and proteins to be used for its leg to work but we instead kill the chicken and rip off its leg and eat its muscle to ingest those nutrients to use it for our body this is called assimilation when organisms absorb carbon compounds from other organisms and use them to build structures for their own body which can be summed up to the phrase you are what you eat but don't feel too bad because the chicken got those nutrients from a different plant that it consumed and so goes the circle of life heterotrophs are classified by the ways they digest food which can be done internally or externally consumers like us digest their food and break it down internally before it is absorbed into their cells and other organisms called sapres secrete enzymes onto their food to break it down externally and then absorb those products examples of sapres are bacteria and fungi which are decomposers in either case because the organic compounds that organisms consume are generally large polymers they need to be broken down into their smaller monomer forms via digestion before they can cross the threshold and enter the cells of the organism while autotrophs and heterotrophs obtain their food in different ways by either synthesizing it or stealing it they use their food for the same purpose to create cellular energy in the form of ATP both autotrophs and heterotrophs undergo the same process to generate ATP which is through cellular respiration the process of cell respiration is discussed in detail in other videos but for our purpose here you need to understand that both plants and animals have mitochondria and their cells which make this process happen so if they make their food or steal their food the carbon compounds that make up the food are oxidized and the energy stored in their bonds are used to create ATP which provides energy for each organism to perform essential functions and survive when we start to piece together feeding relationships in an ecosystem it is beneficial to classify organisms within levels based on what they eat we call these levels trophic levels and they describe the position an organism has within a food chain or food web if we take a look at the levels within this food chain at the base level we have the grass which is an autotrof and we call that the producer from there we have the grasshopper which consumes the producer so we name it the primary consumer the Mouse eats the grasshopper making it the secondary consumer and likewise the owl eats the mouse making it the tertiary cons consumer within a food chain the trophic levels are very cut and dry but they can get a bit complicated when looking at a food web for example what level would you classify the hawk as in this food web take a second and try to figure it out we need to consider all possible food chains connected to the hawk within this food web to understand its trophic level and we can see that the Hawk is eating the rabbit The Mouse and the snake from the perspective of eating the rabbit the hawk is a secondary consumer from the perspective of the mouse it is also a secondary consumer and from the perspective of the snake it is a tertiary consumer so our answer here would be that it is both a secondary and tertiary consumer when feeding relationships get complicated as seen within food webs like this organisms can occupy more than one trophic level because many organisms often have more than one food source all all of the energy moving within a food web can be complicated to keep track of to simplify and illustrate the amount of energy in each trophic level within an ecosystem ecologists create diagrams called Energy Pyramids these pyramids are constructed in a specific way with the lowest trophic level on the bottom aka the producers and the subsequent trophic levels stacked above in order from primary to secondary to tertiary consumer an energy pyramid should always be created with rectangles that represent the amount of energy in each level which results in the pyramid looking like steps and not like a large triangle the measurements for energy are usually calculated in kles per met squared per year so we can say here as an example that the producers in this ecosystem contain about 123,000 kles per me squ per year of energy the primary consumers contain around 12,400 K per me squ per year of energy the secondary consumers contain around 1,250 K per mqu per year of energy and the tertiary consumers contain about 1188 KJ per me squ per year of energy for the IB exam you need to know how to construct Energy Pyramids like this based on given data from specific ecosystems we will go over how to approach this type of data over the next few slides let's keep the numbers from the previous slide and talk more about energy pyramids you may have already noticed that from one level to the next like from The Producers to the primary consumers there is a large amount of energy being lost and this is probably one of the most important Concepts to understand about ecology and food webs is that from one trophic level to the next most of the energy around 90% of it is lost now there are two things we need to highlight here when referencing energy loss in an energy pyramid first when we are talking about energy we are talking about stored energy within chemical compounds that exist within the tissues of organisms this is the energy stored within that chicken leg we discussed earlier that you then obtain when you consume it second when we say that energy is lost it isn't lost in an absolute solute sense because we know that energy cannot be created or destroyed it can only be changed so when we say lost what we really mean is that the energy is in a state that organisms can no longer use like heat for example heat contains energy but we can't eat heat energy and use it to power our body so in that sense heat energy is lost to us but more on that on the next slide so when we look at an energy pyramid like this and say around 90% of the usable energy is lost between each trophic level and only around 10 % of the remaining energy is being transferred to the next trophic level why is this happening one reason is because the organisms are using up the energy to live via the process of cell respiration think about it the grass takes in energy from the Sun to create sugar molecules these sugar molecules contain energy stored that can be moved onto the next trophic level but did the plant make the sugar molecules for the grasshopper no it made them for itself the plant goes through cell respiration oxidizing those sugars to create cell cellular energy it needs to maintain its structures and live and because that energy is being used and oxidized it is no longer in a form that can be passed to the next level in addition to that not all organisms completely consume every part of their food think back to that chicken leg sure you eat the muscles but did you eat the bone and all of the tendons probably and hopefully not this leaves tissue unconsumed by a consumer and left for a decomposer which we can add in their energy here on the side of the pyramid they take the energy from any leftover tissue that is not consumed which again contributes to less energy being moved up to the primary secondary and tertiary levels continuing to talk about energy loss in ecosystems we mentioned on the last slide that organisms go through cell respiration to create chemical energy that they can use in their cells as the process of cell respiration occurs some of the chemical energy is converted into heat and you can recall that heat is a form of energy that organisms cannot use AKA it's lost we we know that all organisms go through cell respiration which is why heat is lost at every level of our energy pyramid contributing to only 10% of available energy being able to move up to the next trophic level you can feel the heat generated by Your Body by simply holding one hand closely over your opposite arm that heat is radiating off of your body and being lost to the environment in a form that we can no longer use the energy lost between each trophic level has a limiting effect on the size of food chains restricting how many organisms they can support because around only 10% of energy is transferred from one level to the next it has a compounding effect on organisms higher up in the food chain so if we were to look at the shark in this food chain the available energy it has to consume is 10% of 10% of 10% of 10% because there is less energy available at the top in general the size of the shark population will be limited there is not enough energy to support a population size of hundreds of billions of sharks but there is enough energy coming from the Sun to support a population of hundreds of billions of phytoplankton it is for this reason that food chains cannot be infinitely long and usually end with a fourth or fifth order [Music] consumer [Music]