Gro Torsethaugen, PhD Penn State Biology -­‐ BISC 003: Environmental Science There is a set of fundamental natural laws that explains the way the universe works. The universe is essentially made of matter and energy and the total amount of energy and matter in the universe is constant. Let's start with matter. A non-­‐technical definition of matter is "stuff”, something that takes up space and has mass. Matter exists in three different phases (solid, liquid, and gas). As you sit in your study area, you are surrounded by matter—the desk and the computer are solids, your favorite caffeinated beverage is a liquid that helps you through the little bit of chemistry and physics that will follow, and the oxygen is a gas that you breathe in to keep you going as your brain frantically burns sugar to help you process this information. Matter is that it does not appear out of nowhere. The total amount of matter in a closed system is fixed—matter cannot be created or destroyed. This is the law of conservation of matter. From a practical point of view, what does this mean? With the exception of meteors, satelites and spaceships, there is no significant input or output of matter or stuff to earth. Matter is constantly cycled between the living and nonliving environments. The carbon atoms in your body could have been part of the body of a dinosaur, a dandelion or William Shakespeare—it never disappeared when that organism died, it just changed form. With respect to matter, earth is a closed system—all the matter on and above the earth's surface © Penn State Biology -­‐ BISC 003: Environmental Science Gro Torsethaugen 2 has been on earth and will continue to be long after we are gone. Anything you have ever thrown away still exists— it may have decomposed or it may still be in the same form. Matter is made of different types of atoms (or elements) that are combined into molecules. All living organism are made of four major groups of macromolecules; proteins, carbohydrates, lipids and nucleic acids. All living organisms and macromolecules contain carbon atoms. Hydrogen, oxygen, nitrogen, phosphorus and sulfur are other abundant elements in living organisms. Let's start with matter. A non-­‐technical definition of matter is "stuff”, something that takes up space and has mass. Matter exists in three different phases (solid, liquid, and gas). As you sit in your study area, you are surrounded by matter—the desk and the computer are solids, your favorite caffeinated beverage is a liquid that helps you through the little bit of chemistry and physics that will follow, and the oxygen is a gas that you breathe in to keep you going as your brain frantically burns sugar to help you process this information. Matter is that it does not appear out of nowhere. The total amount of matter in a closed system is fixed—matter cannot be created or destroyed. This is the law of conservation of matter. From a practical point of view, what does this mean? With the exception of meteors, satelites and spaceships, there is no significant input or output of matter or stuff to earth. © Penn State Biology -­‐ BISC 003: Environmental Science Gro Torsethaugen 3 Matter is constantly cycled between the living and nonliving environments. The carbon atoms in your body could have been part of the body of a dinosaur, a dandelion or William Shakespeare—it never disappeared when that organism died, it just changed form. With respect to matter, earth is a closed system—all the matter on and above the earth's surface has been on earth and will continue to be long after we are gone. Anything you have ever thrown away still exists— it may have decomposed or it may still be in the same form. Matter is made of different types of atoms (or elements) that are combined into molecules. All living organism are made of four major groups of macromolecules; proteins, carbohydrates, lipids and nucleic acids. All living organisms and macromolecules contain carbon atoms. Hydrogen, oxygen, nitrogen, phosphorus and sulfur are other abundant elements in living organisms. It is not just matter that is conserved. Energy on a universal scale is conserved as well. Energy is the capacity to do work. Just like matter, energy cannot be created or destroyed. Energy is transformed from one form to another, but the total amount of energy does not change. This is the first law of thermodynamics. This may seem like a sweet deal, but there is a catch-­‐-­‐and that would be the second law of thermodynamics: when energy is converted from one form to another, some is always converted to low quality or a useless © Penn State Biology -­‐ BISC 003: Environmental Science Gro Torsethaugen 4 form of energy. Energy can be of high quality, which is energy capable of doing work, or low quality energy. Another way of stating the second law of thermodynamics is that entropy or disorder in the universe is always increasing. The second law suggests that you always "lose" high quality energy during an energy transfer. Entropy or the energy of disorder is very low quality energy that is not useful for doing work. When energy is transferred in biological, and most mechanical processes, this useless energy is in the form of heat. So how can life continue to exist in an ordered manner if the energy is degraded for every energy transfer? Ordered life on earth can exist because it is an open system with respect to energy. There is a constant input of radiant energy from the sun entering the earth's biosphere every day. For all practical purposes, the sun's energy supports all life on earth. To summarize: energy flows through the biosphere, earth is open system in regard to energy, and matter cycles within it, earth is a closed system in regard to matter. Ecology is the branch of biology that studies the interactions between living organisms (the biotic world) and their nonliving environment (the abiotic world). We just talked about how energy flow through the biosphere, but exactly how does that happen? Solar energy enters into living systems through autotrophs, self-­‐feeders or producers. An autotroph is an organism that can use an external non-­‐biological energy © Penn State Biology -­‐ BISC 003: Environmental Science Gro Torsethaugen 5 source (such as radiant or chemical energy) to take small simple molecules and build complex compounds, or in other words make their own food. Most producers or autotrophs are plants, algae or bacteria that use the process of photosynthesis to convert solar energy into chemical energy, more about that in a minute. Heterotrophs are organisms that are unable to make their own food and instead get their nutrients by consuming other organisms. There are several different categories of heterotrophs. Herbivores are plant eaters such as cows, caterpillars and rabbits. Carnivores are meat eaters such as cats, falcons and sharks. Omnivores eat both plants and animals, examples include raccoons, dogs and most humans. Scavengers feed on the recently dead, the turkey vulture is an example. And detritus feeders, such as earthworms feed on decay. In addition to consumers, there are heterotrophs that are classified as decomposers. These are the fungi and other soil microorganism that secrete enzymes into the surrounding environment to break down complex molecules. There is one final type of heterotroph; those that feed on living hosts. Pathogens and parasites are found in all the kingdoms of life—there are parasitic plants, animals and fungi as well as pathogenic bacteria. In general, parasites are multicellular organisms that feed on a living host, and pathogens are single celled organisms that cause disease. © Penn State Biology -­‐ BISC 003: Environmental Science Gro Torsethaugen 6 All living organisms are made of cells. Cells are very complex, but surprisingly similar from one organism to another. Organelles are small compartments inside the cells that have various jobs, just like organs perform various jobs within your body. Examples of these jobs are the metabolic processes of photosynthesis, which occur in chloroplasts and cellular respiration, which is happening in organelles called mitochondria. © Penn State Biology -­‐ BISC 003: Environmental Science Gro Torsethaugen 7 So photosynthesis is the process that occurs in organelles called chloroplasts, which are located within the cells of plants and other photosynthetic organisms Solar energy is captured and converted to chemical energy. This energy use carbon dioxide, a small simple molecule, to build sugar, a larger more complex molecule. Oxygen is a handy by-­‐product from this process; a gas that we all know is essential for life on earth. The overall equation for photosynthesis is CO2 + H2O → C6H1206 (glucose) + O2 Heterotrophs or consumers rely on the sugar that the autotrophs or producers make. The cellular process that breaks down sugar to extract energy is called cellular respiration. Cellular respiration occurs in organelles called mitochondria inside the cells of all eukaryotic organisms, plants included. Cellular respiration is the breakdown of glucose in a controlled series of steps such that the energy contained within the sugar molecule is converted to biologically useful energy, ATP molecules. The overall equation for cellular respiration is: C6H1206 (glucose) + O2 → CO2 + H2O © Penn State Biology -­‐ BISC 003: Environmental Science Gro Torsethaugen 8 If you look at the overall reaction of photosynthesis and cellular respiration you may notice that they appear to be a simple reverse of each other, the products of photosynthesis (glucose and oxygen) are the substrates in cellular respiration, and vice versa. Oxygen and glucose are produced in the chloroplast, these products are used in the mitochondria. Coming out of mitochondria are carbon dioxide and water that again are used as substrates in the chloroplast. Notice the difference in energy input and output though; solar energy is the energy input in photosynthesis, while ATP or biologically useful energy molecules is the energy output from the process of cellular respiration. So why do you have to learn this in an environmental science course? As we will get back to, these two metabolic processes are an essential part of the carbon cycle, and having a basic understanding of the carbon cycle is essential if you want to understand the various ways human activities are contributing to global climate change. So that was a little bit cell biology and biochemistry, let’s get back to ecology. So the producers, mostly plants in terrestrial ecosystems and algae or plankton in aquatic ecosystems, is the bottom of the food chain. Through the process of photosynthesis, they convert solar energy to chemical energy that is passed from organism to organism in food © Penn State Biology -­‐ BISC 003: Environmental Science Gro Torsethaugen 9 chains. Each step in the food chain is called a trophic level. Matter and energy is transferred from one trophic level to the next as one organism eats another. And as stated by the second law of thermodynamics, some energy is converted to useless energy, or heat, at every energy transfer or between each trophic level. So as we go up the food chain, less and less of the original useful energy remain. This means that each primary consumer have to eat many producers and each secondary consumer have to eat many primary consumers and so on. This is why you will always find more primary consumers than secondary consumers, at least in terms of biomass, in any ecosystem. © Penn State Biology -­‐ BISC 003: Environmental Science Gro Torsethaugen 10 In nature it is however more accurate to talk about food webs instead of food chains, as most species consume several different species and most species are consumed by several different species as illustrated in this food web from Chesapeake Bay. Only approximately 10% of the energy from one trophic level is transferred to the next trophic level in the food chain or web. The concept of food and energy pyramids is explained well on pages 42-­‐43 in your textbook. This is an important concept to consider in regard to the environmental impact of our food choices. Consider the amount of resources it takes to make 1 lb of corn compared to 1 lb of beef as an example. Keep in mind that most of our food comes from agriculture. As we will get back to, large amounts of resources, such as land, water, fertilizers, pesticides and energy are used to make our food. A large percentage of the cows we eat are raised on corn. So if we start with the energy stored in corn as 100%, how much of that energy does a herbivore get compared to a carnivore? If you eat the corn directly you are at the second trophic level in the food chain and you get approximately 10% of the original energy in the corn. If we on the other had feed that corn to the cow, and then you eat the cow you are at the third trophic level in the food chain and you only get 1% of the original energy, since 90% of the energy is lost at each level. That does not mean that there is less energy in meat. It means that a lot more © Penn State Biology -­‐ BISC 003: Environmental Science Gro Torsethaugen 11 energy and resources were used to produce your steak compared to that corn on the cob. So if you want to reduce your environmental impact, or in other words use less energy and resources, it is a good idea to eat less meat and more plant based foods. That does not mean that you need to become a vegetarian, just like you don’t have to completely give up driving a car to reduce the environmental impact of transportation. Simply eating less meat will make a difference. The term biogeochemical cycles is used to describe how the various elements cycle through the environment. Water is not an element, but an important molecule, and how this molecule cycle through the environment is called the water cycle or the hydrologic cycle. To learn why water is such an amazing molecule, make sure you read “Exploring Science, A Water planet” on page 34 in the textbook. Then there are the nutrient cycles; the carbon, nitrogen, phosphorus and sulfur cycles. I have included links to good tutorials for each of these cycles that you can use in addition to the information in the textbook when you prepare your response to this lesson’s discussion forum. The links to these tutorials can be found in video library and the lesson 2-­‐discussion forum. © Penn State Biology -­‐ BISC 003: Environmental Science Gro Torsethaugen 12 It is important to have a basic understanding of the biogeochemical cycles when studying environmental science because many environmental problems is a result of a disruption of one or more of the biogeochemical cycles. When describing a nutrient cycle include all the components, both biotic (or living organisms such as the producers, consumers and decomposers), and the abiotic (or non-­‐living components, such as soil, water and air.) Identify the processes by which these nutrients move through the ecosystem, such as photosynthesis, consumption, decomposition and so on. And keep these questions in mind while you study nutrient cycles: Why do living organisms need this nutrient? Which macromolecules contain this element? (figure 2.8) What does all nutrient cycles have in common? And what makes each nutrient cycle unique? And finally how is each nutrient cycle affected by human activities? •
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Water Cycle: http://bcs.whfreeman.com/thelifewire/content/chp58/5802001.html Carbon Cycle: http://bcs.whfreeman.com/thelifewire/content/chp58/5802002.html Nitrogen Cycle: http://bcs.whfreeman.com/thelifewire/content/chp58/5802004.html © Penn State Biology -­‐ BISC 003: Environmental Science Gro Torsethaugen 13 •
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Phosphorus Cycle: http://www.sumanasinc.com/webcontent/animations/content/phosphorouscycle.
html Sulfur Cycle: http://nortonbooks.com/college/biology/animations/ch37a02.htm So how do we affect the various biogeochemical cycles by our daily activities? By using resources and disposing of waste in various forms. And how do we use resources? The main ways we use resources are transportation, food, household operations (heating, cooling, lighting, washing, cooking etc) and personal items (clothes, electronics, toys and all of our other stuff). These activities contribute to environmental problems like air pollution, global climate change, water pollution, habitat alteration and species extinction. In this lesson’s discussion forum you will start to explore exactly how your own daily activities affect the various nutrient cycles and how they contribute to environmental problems. Keep in mind that each activity may affect more than one nutrient cycle, try to make as many connections as possible. Where does all the materials used to make an item come from? Which resources were used to produce and transport that item? And where will that item end up when you are done with it? © Penn State Biology -­‐ BISC 003: Environmental Science Gro Torsethaugen 14 As we will get back to in the human population lesson, the environmental impact of a society is a combination of the size of the population and the amount of resources used by the average person in that society. © Penn State Biology -­‐ BISC 003: Environmental Science Gro Torsethaugen 15