SCI 11 - MODULE 3 PDF

Module 3 ENERGY FLOW AND BIOGEOCHEMICAL CYCLES Nerissa Torreta 3.1 INTRODUCTION Module 1 showed you different perspectives about living systems. More than that, it underscored why the biological perspective is essential. In...

Module 3 ENERGY FLOW AND BIOGEOCHEMICAL CYCLES Nerissa Torreta 3.1 INTRODUCTION Module 1 showed you different perspectives about living systems. More than that, it underscored why the biological perspective is essential. In Module 2, the properties and principles of living systems were discussed and described as complex. Recall that it takes energy to make a living system more ordered. This module will focus on energy flow in living systems and how matter like elements or nutrients are used and reused. Think about this: where did the materials forming our body originate? It was recently made but was created so many years ago from dying stars when our planet evolved. Matter is recycled, and we shall review this as we discuss energy flows and biogeochemical cycles. 3.2 LEARNING OUTCOMES: At the end of the module, the student should be able to: 1) define energy, describe energy sources and discuss how energy is acquired; 2) examine an ecosystem, categorize the organisms present and generate a food web to illustrate energy flow; 3) compare and contrast energy flow and biogeochemical cycles; 4) present how anthropogenic processes alter biogeochemical cycles; and 5) discuss and assess the environmental implications of anthropogenic-induced alterations in biogeochemical cycles. 3.3 LEARNING ACTIVITIES 3.3.1 ENERGY FLOW Almost every process important to life (living systems) depends on a steady flow of energy. The flow of energy is the essence of life, specifically, of living systems. Energy is the ability to do work, and it is everywhere. What you need to do is to look for some motion, heat, and light. Let us see if you can identify its many different forms. By now, you have some excellent ideas of what energy is. You may best recall different forms of energy as MRS CHEN … Mechanical energy (kinetic energy) whose counterpart is potential energy (stored energy); Radiant energy (sun); Sound energy; Chemical energy; Heat energy; Electrical energy and Nuclear Energy. Energy can be possessed in two ways, either as kinetic or potential energy. 1 Energy may also be sourced from renewable or non-renewable sources. Can you give examples of this? Currently, non-renewable resources supply the bulk of our energy needs because technologies allow them to be harnessed on a large scale to meet consumer needs. Regardless of its source, the energy contained in the source is changed into a more useful form. Now that you know what energy is, let us consider how energy flows in living systems. The Laws of Thermodynamics are the basis of the flow of energy. The first law, the Law of Conservation of Energy, concerns the amount of energy in the universe. It states that the amount of energy in the universe is constant. It may be changed from one form to another but cannot be created or destroyed. Moreover, energy cannot be changed without some conversion into heat energy. The second law of Thermodynamics embodies this. It states that disorder (entropy) in the universe is increasing. As energy is used, more and more of it is converted into heat, the energy of random molecular motion. Thus, as energy is changed from one form to another, part of that energy assumes waste form (heat energy). Consequently, after transformation, the capacity of energy to do work is decreased. Thus, energy flows from higher to lower levels. The primary source of energy is the sun. How much of this is transformed into chemical energy? On average, only 2% of the total light striking a leaf surface is used to make food through photosynthesis, while most of it is transformed as heat. Yet, that small amount of radiant energy goes a long way in providing energy not only for the plants but also for other organisms! Study Figure 2.1 below to recall how energy flows at different levels in an ecosystem. Fig. 2.1 Flow of energy at different levels of ecosystem http://www.biologydiscussion.com/ecosystem/energy-flow-in-an- ecosystem-with-diagram/6740 2 How is the energy acquired? There are many ways by which energy is obtained. If we focus on living systems, energy is obtained by living things in three ways through photosynthesis, chemosynthesis, or eating/digesting other living or dead organisms by heterotrophs. Recall and review what you have learned in your high school Science. Remember photoautotrophs like algae, plants, and photosynthetic bacteria that harness radiant energy and convert it to chemical energy in the form of ATPs (adenosine triphosphates) to be used to synthesize complex organic molecules like glucose. Autotrophs are the foundation of every ecosystem on Earth. It may sound dramatic, but it's not an exaggeration! Autotrophs form the base of food chains and food webs, and the energy they capture from light or chemicals sustains all the other organisms in the community. Chemoautotrophs are organisms that create their organic food from inorganic chemicals like iron, nitrogen, sulfur, and magnesium and, in turn, supply energy to the rest of the ecosystem. Heterotrophs cannot capture light or chemical energy to make food and thus, mainly rely on autotrophs. By now, you are familiar with the concept of trophic levels. It is a feeding level, often represented in a food chain or food web. Primary producers constitute the bottom trophic level, followed by primary consumers (herbivores), secondary consumers, tertiary consumers, et cetera. Energy flows within these food chains, and as it moves up the trophic levels, some of it is dissipated as heat because organisms carry out metabolic processes. Only about 10% of net energy production at one trophic level is passed on to the next level because processes like respiration, growth, reproduction, et cetera reduce energy flow. Even the nutritional quality of the consumed material affects how efficiently energy flows. Consumers often convert high-quality food sources into new tissue more efficiently than low-quality food sources. The low energy transfer rate between trophic levels makes decomposers generally more important than producers in energy flow. Decomposers process large amounts of organic material and return nutrients to the ecosystem in inorganic form, which is then taken up again by primary producers. Ecological pyramids, also referred to as trophic pyramids, are graphical representations designed to show relationships between energy and trophic levels in an ecosystem. Often, the quantity of individuals, biomass, or energy at each given trophic level demonstrates these relationships. Thus, there are pyramids of biomass, energy, or numbers. Among these three types, the most useful is the pyramid of energy because it shows the relationship between energy and trophic level. 3 Study Figure 3.2 to review the concept of ecological pyramids. Fig. 3.2. An example of Pyramids of numbers, biomass, and energy. https://mrwallisscience.wikispaces.com/Class+notes Energy is passed from one organism to another through food webs and their constituent food chains. As energy passes from one trophic level to another, we need to address the important environmental consequence of increasing the concentration of persistent, toxic substances at each trophic level, from the primary producers to the different consumer levels. It is known as biological magnification or biomagnification. Many substances bioaccumulate, and notable among them is the pesticide dichlorodiphenyltrichloroethane (DDT), which have been shown to accumulate in eagles and raptors in the US, causing detrimental effects on their reproduction where they formed thin-shelled eggs that broke in their nests. Fortunately, the pesticide has been banned, and these bird populations have recovered. However, in many developing countries like the Philippines, the bioaccumulation of pesticides and other toxic substances continues to occur and needs to be addressed. In the Philippines, mussels have been reported to accumulate toxins from the dinoflagellates they have eaten, which in turn cause diseases or death to the humans who later eat these mussels. Energy flows in one direction through ecosystems, entering as sunlight (or inorganic molecules for chemoautotrophs) and leaving as heat during the many transfers between trophic levels. However, the matter that makes up living organisms is conserved and recycled. Like a wheel that has no beginning and no end, a cycle is a continual transformation process. The basic components of a cycle may be used over and over again in slightly different forms. But they always return to the original form to begin the cycle again. 4 3.3.2 BIOGEOCHEMICAL CYCLES Earth is a closed system for matter; thus, all elements needed for living systems came from what was present in the Earth's crust so many billion years ago. Matter is continually recycled on time scales which can vary from a few days to millions of years. Just imagine, what constitutes us have been present since early times. Elements are the critical components of life and must be available for biological processes. Many geological processes like weathering and erosion play a role in this recycling of materials. Because geology and chemistry have significant roles in studying these processes, recycling inorganic matter between living organisms and their environment is called a biogeochemical cycle. These cycles move chemicals through the biosphere, passing them through organisms and the biosphere's abiotic components like the atmosphere, marine, fresh waters, soils, and rocks. Biogeochemical cycles serve various functions at the ecosystem level and ensure the survival of various organisms, including us. These cycles are important because they: 1) enable the transformation of matter from one form to another, which enables the utilization of matter in a form specific for a particular organism; 2) enable the transfer of molecules from one locality to another; 3) facilitate the storage of elements; 4) assist in the functioning of ecosystems; 5) link living organisms with living organisms and living organisms with abiotic factors, and 6) regulate the flow of substances. Let's take a look at each of these and expound on why biogeochemical cycles are essential. Each living organism is a part of many different biogeochemical cycles. The details of these cycles may differ, but they follow similar patterns. Radiant energy powers process like photosynthesis and evaporation. It also drives the cycles that involve reservoirs where chemicals are stored or concentrated for long periods. These cycles function on both local and global levels, linking distant ecosystems. Earth has many biogeochemical cycles illustrating that our planet is a closed system. Elements are recycled and not replenished from outside sources. There are five most common elements associated with organic molecules that are vital components of life — hydrogen and oxygen (water), carbon, nitrogen, and phosphorus. These elements take various chemical forms and may exist for long periods in the atmosphere, land, water, or beneath the Earth's surface. It is essential to recognize that the cycling of these elements is interconnected. For instance, the leaching of nitrogen or phosphorus into bodies of water is affected by the hydrologic cycle. These elements cycle at different timescales and extent through the biosphere, from one organism to another, and between the biotic and abiotic worlds. 5 Human activities influence biogeochemical cycles. We hasten natural biogeochemical cycles when we cause disturbances, like when elements are mined when we continue to burn fossil fuels or clear areas of vegetation that store carbon. We have altered both nitrogen and phosphorus cycles when we overuse fertilizers because runoff carries the excess amounts into waterways. 3.4 CONCLUSION From this module, you should clearly understand the flow of energy in living systems through food chains and webs and how elements or nutrients are cycled through biogeochemical pathways. Energy flow and biogeochemical cycles are interrelated. There are many issues related to the topics discussed in this module, and to a certain extent, you have been asked to discuss them. More importantly, as you become aware of these issues, remember to do your little actions to alleviate these problems. After all, by taking all your small acts together, you are helping make Earth a better place to live. Multimedia resources: https://www.texasgateway.org/resource/food-chains-food-webs-and-energy-pyramids (with activities and videos) https://ocw.mit.edu/high-school/biology/exam-prep/ecology/communities ecosystems/biogeochemical-cycles-overview/ https://www.khanacademy.org/science/biology/ecology/biogeochemical cycles/v/biogeochemical-cycles References: Campbell, N.A., J.B. Reece, L.A. Urry, M.L. Cain, S.A. Wasswrman, P.V. Minorsky and R.B. Jackson. 2008. Biology 8th ed. California, USA: Pearson Benjamin Cummings. 1267p. Hairston, N.G., Jr. and NG. Hairston, Sr. 1993. Cause and Effect Relationships in Energy Flow, Trophic Structure and Interspecific Interactions. The American Naturalist 142(3): 379-411. Presson, J. and J. Jenner. 2008. Biology Dimensions of Life New York, USA: McGraw Hill Companies, Inc. 710p. 6 Raven, P.H., G.B. Johnson, J.B. Losos and S.R. Singer. 2005. Biology. New York, USA: McGraw Hill Companies, Inc. 1249p. Reece, J.B., L.A. Urry, M.L. Cain, S.A. Wasswrman, P.V. Minorsky and R.B. Jackson. 2011. Campbell Biology 9th ed. California, USA: Pearson Benjamin Cummings. 1309p. Solomon, E.P., L.R. Berg, D.W. Martin. 2008. Biology 8th ed. China: Thomson Brooks/Cole. 1234p. 7