 Greetings. My name is Jerome Bernardino, and I will be tackling the dynamics and interactions of living systems with their environments. Just to give you a mental roadmap of the flow of topics, I would like to show you this brief outline of the discussion. As you can see, there are only three major salient topics that we're going to tackle, and all of these topics are mainly streamlined on the dynamics and interactions of living systems with their environment. So, first, we're going to take a look at the concept of the energy. And afterwards, we're going to tackle the concept of biogeochemical cycles. And finally, we're going to talk about the dynamics in populations, particularly the regulatory mechanisms. Based on this outline, the following objectives should be met by the end of the discussion. First is for you to describe and differentiate between the cycling of energy and matter in a given system. The second one is for you to demonstrate a clear understanding of systems and their regulations with respect to energy and biogeochemical cycles. And the last objective, which also happens to be the most important of all, is for you to gain a deeper sense of appreciation for the interactions of energy and matter with the dynamics of living systems. Let me begin with the discussion by showing you this introductory figure. Well, you must examine this figure by heart for everything that will transpire in this presentation will revolve around the concept depicted by this figure. In essence, this figure is one that depicts a living system wherein there are interactions between the different components involved. Essentially, there are only two of these components, namely energy and matter. The point that I would like to emphasize at this moment is the fact that in order for a system to be classified as a living system, it needs to be described as both an open system and a closed system. By definition, an open system is a system wherein energy is cycled and transferred within that given system to another system. In other words, energy is not compartmentalized in a given living system. This is what is meant by the open nature or property of a living system. In order for you to understand this statement, let us define what energy is in the first place. By definition, energy is defined as the capacity to do work. And in order for work to be done, there has to be an input and that input should be in the form of energy. This definition will only make sense if we know what is being pertained to by the term work. And so work, on the other hand, is defined as the displacement of a body against an opposing force. And if we're going to take notice of this definition, we can deduce that in order for work to proceed, a displacement or a movement within a system needs to take place. Hence, in a more technical sense, work is defined as the product of force and the distance displaced, meaning to say there should always be an input of force and this force alone should be the ultimate reason behind the displacement of that particular object. However, in our discussion of energy and work, we should only be limited to the concept of biology. And so in biology, work describes any displacement against a force that a living thing encounter or generate. Well, to understand this statement, allow me to give one concrete example of a biological phenomenon wherein work is done. One biological phenomenon wherein work is done is the process of osmosis, which is basically the movement of water molecules across a semi-permeable membrane down the concentration gradient. Well, in other words, it is the movement of water molecules down the concentration gradient or from a region of higher concentration to a region of lower concentration. Simply put, this displacement of water molecules to the other side of a membrane is an exemplification of work at play. In addition to that, you must take note that the process of work is facilitated by energy. Now, why am I saying these things? My point here is, this energy that is fueled or that fuels the work to be done in a given living system is not compartmentalized to that system alone. In other words, energy can and must be passed and transformed from one form in one system to another system. In order for that system to facilitate work and therefore essentially serve their purpose in the entire ecosystem. There is one figure that may help us understand this statement and that figure is this. This figure shows an energy pyramid in a given ecosystem. Well, basically, in a given ecosystem, several types of pyramids can be generated. In particular, there are three of these pyramids. The first one is the energy pyramid. The second one is the pyramid of numbers and the final one is the pyramid of biomass. But what I would like to emphasize at this moment is the fact that among these three types of pyramids, the energy pyramid is the only one that should be upright in form. In other words, both the biomass pyramid and the pyramid of numbers can be inverted in form. However, the energy pyramid should always appear to be upright. The main reason behind this lies in this particular figure alone. As you can see, beginning from the primary producers occupying the base of the pyramid, the percentage of energy decreases following the hierarchy of the trophic levels. For example, the percentage of energy contained within primary producers is 100%. This amount was then decreased to 10% in the primary consumers, which is the next trophic level. Again, that amount was further decreased to 1% in the secondary consumers and so on and so forth. As you may have noticed, there is a pattern with regards to this reduction of the percentage of energy across the trophic levels. We call this pattern the 10% rule. By definition, the 10% rule explains that only 10% of the energy is transferred from one trophic level to the next trophic level and this rule essentially underlies the open property of living systems. In addition to that, you must take note that the remaining 90% of the energy was not transferred to the next trophic level. At this point, you might be wondering what happened to this huge amount of energy that is not transferred to the next trophic level and there are two possible explanations behind this. The first one can be explained by the second law of thermodynamics, which states that the entropy of a given system always increases. In particular, the transfer of energy to another system always and will always entail the release of heat and this release of heat will correspond to the increase in entropy. In other words, some of the 90% of energy are released as heat to the environment. The second reason is this. A huge chunk of the energy that is not transferred to another system was used or utilized by the system to fuel its processes such as metabolism, for example. In order for you to understand this statement, I would like you to show this particular figure. This figure shows the correlation between the two types of metabolism in an individual. These two types of metabolism are number one, the anabolism and number two, catabolism. By definition, anabolism pertains to a building up procedure, meaning to say complex polymers are synthesized out of the simpler monomeric subunits. A classic example of an anabolic process is the process of photosynthesis. Well, the second type of metabolism is catabolism. By definition, catabolism pertains to the breaking down procedure, meaning to say a complex polymer is broken down into its monomeric subunits and a classic example of a catabolic process is the process of aerobic respiration. The point that I would like to highlight at this moment is the fact that a huge chunk of the 90% of energy that is not transferred is utilized by the organism. For instance, light energy coming from the sun that is utilized by plants enables the anabolic process of converting carbon dioxide and water to twice phosphate, which is a form of carbohydrate. And so, meaning to say, by virtue of the open property of living systems, light energy was converted from chemical energy, or it was converted to chemical energy rather in the form of carbohydrates. And so, these carbohydrate molecules will in turn entail and contain energy. However, you have to take note that plants will only pass 10% of the energy entailed by this carbohydrate molecules to the next trophic level. In retrospect, you must take note that organisms take in nutrients that contain energy and this energy is usually in the form of chemical energy. And so, these nutrients are then catabolized, meaning to say they are broken down into their usable forms of energy, which is the ATP. And eventually, these usable forms of ATP will then be utilized to build macromolecules or polymers necessary for organismal growth, metabolism, and reproduction. As a final point, you must bear in mind of the fact that these usable forms of energy that were essentially utilized by the system correspond to the majority of the 90% of energy that was not transferred to another system. At this point, it is now high time that we take a look back at this figure in order for us to transition to the next topic. I mentioned a while ago that in order for a given system to be classified as a living one, it has to be described as both an open system and a closed system. We are now through with the discussion of a system being an open one. Let me now proceed to taking a look at the system as a closed system. By definition, a closed system is one in which matter is cycled within a given system, meaning to say matter is compartmentalized in a closed system and not the energy. And so in order for living systems to do this, they must have a process in which the physical and the chemical components cycle within the system. We call this process the biochemical cycle. As the name suggests, a biochemical cycle is a series of interrelated events that cycle biological, geological and chemical components in an ecosystem. By definition, biogeochemical cycles are cycles that entail movement of chemicals from biotech, meaning to say from the organisms that utilize them to the biotic components. In other words, to the immediate environments we're in, these chemicals are to be deposited and vice versa. You must take note that essentially what are being cycled here are chemical elements. And so, since it is a cycle, these elements are used repeatedly in different forms, but they must return to their original form. And in addition to that, this cycle of elements presents a number of importances to the ecosystem, but we will only delimit the discussion to only three importances of these cycles. And so, the first importance is this. The biogeochemical cycles allow the transformation of matter to different forms that are useful for a particular organism. This particular importance is very significant because there is an involvement of the biological key players, which are the organisms themselves. Simply put, the organisms are involved primarily because they are the ones that assimilate or process these elements into other forms. The second importance is this, which has something to do with the interconnections within the ecosystem. Well, you know very well that these interconnections or interactions are vital to every given system. In effect, biochemical cycles or the biogeochemical cycles provide a linkage between the living organisms with their co-living organisms and these living organisms with their abiotic factors. In this way, the elements was transformed or are transformed rather from one form to another via these interactions. Finally, the last importance has something to do with the composition of the abiotic components of the ecosystem. Thus, this last importance of biogeochemical cycles is the enabling of the movement of elements from one locality to another. Eventually, whenever these elements move from one locality to another, they become part of the localities serving a particular purpose. Now, all of these three take part in establishing the dynamics in certain types of systems. And one of these systems is the population. And so, with these in mind, let me now proceed to the final topic in my presentation, which is all about the dynamics in population, particularly the regulatory mechanisms. Whenever we speak of the dynamics in populations, we simply refer to changes that take place in these populations. One encompassing concept may help us understand this concept and it is this one, the ecosystem feedback. In simplicity, the ecosystem feedbacks underlie the fact that the change in one part of a living system allows for changes in another system. In other words, the ecosystem feedback is a counter-bouncing effect that helps regulate the overall state of the ecosystem. And you must take note that this regulation can be of two forms, namely the negative feedback mechanism and the positive feedback mechanism. The difference between these two forms of regulation can be seen in the succeeding figures. These figures show the difference between the negative and the positive feedback mechanisms. The figure on top signifies the negative feedback mechanism, while the figure below represents the positive feedback mechanism. In both of these two forms of regulation, an input, process, output, and feedback take part in the regulation of the overall state of the ecosystem. However, the only difference between the two is this. The negative feedback mechanism negates the effect of the stimulus or the input, while the positive feedback mechanism further reinforces or enhances the effect of the stimulus or input. In order for you to understand and appreciate what I am saying, I would like you to bear notice of the concrete examples that I am going to provide. And these examples are the regulatory mechanisms wherein the negative and the positive feedback mechanisms are at play. To be specific, these regulatory mechanisms are the population regulatory mechanisms. This graph shows the dynamic relationship between the population sizes of the prey and the population sizes of the predators through time. And by merely looking at the graph, we may be able to conclude that the population size of the prey is highly influenced by the population size of the predator. Specifically, whenever the population size of the predator skyrockets, the population size of the prey in turn will take a nose dive, and this makes sense. But what I would like to emphasize at this point is the fact that this particular example of population regulation is a form of negative feedback mechanism wherein the population size of the predator serves as the stimulus or input that negates the population size of the prey. In addition to this, you must take note that the negative feedback mechanism serves as a source of stability for the entire population. This is not self-explanatory. Allow me to help and guide you in understanding this statement. The negative feedback mechanism serves as a source of stability simply because it maintains the population size of prey at a certain acceptable level or range that the environment can sustain. In ecology, there is one particular term that designates this maximum number of individuals in a population that the environment can sustain indefinitely. This term is what we call the carrying capacity, and so in reiteration, the negative feedback mechanism serves as a source of stability because it is able to sustain the carrying capacity of the environment. This figure, on the other hand, shows the dynamic relationship between grasses and shrubs through an ecological event known as succession. This evolutionary event lays the groundwork for exemplifying and showing a positive feedback mechanism. Initially, grasses predominate in this area because their roots penetrate the topmost layer of the soil. On the other hand, shrubs are initially outnumbered by grasses simply because their roots penetrate deeper into the soil, and so in effect, the roots of shrubs intercept minimal amounts of rainfall while the roots of grasses receive huge amounts of rainfall or water. Because of these, grasses outnumber shrubs in the initial stages of succession. However, a tipping point will be reached such that shrubs will set in motion a cascade of ecological changes that will lead to their fast rate of growth. This tipping point marks the onset of positive feedback mechanism wherein the shrubs will continue to grow larger than the grasses, eventually leading to the depletion of sunlight in grasses. Whenever this is the case, we can therefore conclude that the positive feedback mechanism serves as a source of instability. The reason behind this will also lie in the concept of carrying capacity yet again. Well, to be specific, in the example I presented, whenever the shrubs continue to grow indefinitely, in other words, whenever they exhibit positive feedback mechanism, the carrying capacity will be reached. In turn, whenever the carrying capacity is switched or exited or surpassed, there will be forces of changes that can drive the entire system beyond the normal operating parameters, eventually disrupting the populations. Given these concepts, we can now draw inferences based on this presentation. In conclusion, the dynamics and relationships of living systems with their environments, such as the regulation of the population level, are highly influenced by the interplay between energy and matter. Thus, the concepts of energy and biogeochemical cycles are indispensable tools that may help us understand the dynamics of living systems.