ENV 11 CHAPTER 10 QUIZLET (Systems and Cycles: Are We Harming Earth's Life Support System?)

Ocean acidification

The ongoing decrease in the pH of Earth's oceans caused by the absorption of carbon dioxide (CO2) from the atmosphere. About one-third of the CO2 emissions from humans since the 18th century have been absorbed into the ocean (and if not for this, the atmospheric concentration of CO2 would be even higher than it is now). When CO2 is dissolved in water, it forms carbonic acid (H2CO3). As the water becomes more acidic, it becomes more difficult for marine organisms to build and maintain their skeletons and shells, significantly altering marine ecosystems. Of course, the other side effect is climate change.

Flows

The mechanisms and rates by which stock in a system changes over time. There is an inflow from the faucet and there is an outflow through the drain. We have designed this aspect of our plumbing system to be very easy to understand and operate. We manipulate the faucet and drain to regulate the amount of water in the tub. If you want the amount of water in the tub to increase, make sure the inflow outpaces the outflow. You can do this by plugging the drain (outflow) and turning on the faucet (inflow). If you want the amount of water in the tub to decrease, make sure the outflow outpaces the inflow: open the drain and turn off the faucet. If you want to keep the water level constant for your bath, you can either keep the drain plugged and turn off the faucet or you can keep the faucet running at a rate that matches the outflow through the drain—either way, the inflow equals the outflow and the stock of water remains constant.

Balancing feedback

In a system, a type of feedback that counteracts the direction in which a particular stock is changing. This is called__________, or a negative feedback loop because it works against the direction in which the stock is changing. If the stock is falling, it will work to increase it. If the stock is rising, it would cause the stock to fall. When a musician's amplifier is screeching from the reinforcing feedback loop described earlier, an adjustment is made to break this cycle; that adjustment is a ____________________ as it reduces the level of a rising stock of "loudness." You operate _________ feedback mechanisms in your everyday life. If you get uncomfortable when a room is too cold because the stock of heat is falling, you might adjust a thermostat to increase the stock of heat. If you notice that the stock of money in your bank account is falling, you might reduce your spending and/or increase the hours you are working. In either case, you are operating a _______________ mechanism to counteract the direction of change of the stock. For example, thermostats in home heating and cooling systems act as ______________ feedback to maintain the desired temperature.

Nitrogen conversion process

1) Lightning strikes trigger reactions that produce, or "fix," nitrate ions from N2 molecules in the air. These fall to Earth in precipitation. 2) Bacteria nodules often found in legumes such as these runner beans fix nitrogen from the atmosphere to produce ammonia, a chemical that can be used by plants. 3) Bacterial and fungal decomposers break down nitrogen compounds in animal waste and dead plant and animal matter. 4) Under the right conditions—often, wet and muddy conditions in agricultural areas—nitrogen in the soil can be transformed by bacteria back to N2 and released into the air.

Diazotrophs

A bacterium with an enzyme that uses free nitrogen from the air along with hydrogen to produce ammonia. Bacteria known as ____________ possess an enzyme that uses free nitrogen from the air along with hydrogen to produce ammonia. This normally happens as part of mutualistic relationships with other organisms. For example, the Rhizobium genus of bacteria are ___________ that live in the roots of plants in the legume family, such as peanuts, lentils, beans, and alfalfa. They fix nitrogen, providing ammonia needed by their host plants while utilizing sugars and the root structure provided by the plant.

Feedback

A loop in a system that responds to and produces changes in levels of stocks that either amplify or counter a change. Musicians who use amplifiers and microphones encounter this when their microphones pick up sound from the amplifiers and run that sound back through the amplifiers, increasing the stock of "loudness" unless adjustments are made to the sound system. The loud screech of ________________ at a concert is a reinforcing ______________ loop in which the sound produced by the musician is amplified, and then picked up by a microphone and amplified again (and again).

Reinforcing loop

A loop that responds to the direction of change in the stock by enhancing that same direction of change. A __________________ in Biosphere 2 related to low air concentrations of O2 affected the capacity of the scientists there to do the work required for survival, such as growing and preparing food. As their productivity slipped, they were less able to nourish themselves, which further diminished their capacity to do work, causing productivity to slip even more. This sort of feedback goes by many other names as well, including positive feedback, runaway or snowballing loops, and vicious or virtuous circles (depending on whether it results in detrimental or beneficial outcomes). The important thing to remember is that it pushes the stock to change in the direction in which it is already heading. If the stock is falling, this phenomena would cause the stock to fall further. If the stock is rising, a reinforcing loop would cause the stock to rise further. Rapid growth of a population exemplifies the latter sort of _____________, e.g., rabbits were introduced in Australia and gradually took over the landscape because of the lack of predators. A similar loop happened with mealybugs, which had no predators in Biosphere 2. As their population increased, they produced more eggs, and their stock soon rose to such an extent that they covered the trunks, branches, and leaves of the trees in Biosphere 2. For example, the rapid growth of mealybug populations over time in Biosphere 2 is an example of a ________________. The thicker arrow for births relative to deaths represents how the birthrate was outpacing the death rate.

Methanogens

A methane-producing microorganism that thrives in oxygen-poor environments. _______________ cannot function in the presence of oxygen and instead live in anoxic (oxygen-free) environments. In these environments, they consume and convert (process) carbon compounds anaerobically (without oxygen), expelling CH4 as a by-product. Where are these methanogens living? While some are in extreme environments such as hot springs and hydrothermal vents in the ocean, many are in places much more familiar to us. _________________ live in and play a key role in the function of animal digestive tracts, including those of humans. Cattle have multi-compartment stomachs that host large quantities of ______________, which they use to digest cellulose from plants. The cattle then release CH4 from their guts through belching, flatulence, and defecation. Termites also host _________________ in their guts to aid the digestion of plant fibers. Warm moist environments such as wetlands host large quantities of _______________, as do anoxic underground environments where these microorganisms play a role in decomposing biomass. Carbon also moves from the biosphere to the atmosphere in CH4 emissions from wildfires because of the incomplete combustion of trees and other biomass.

Biogeochemical cycle

A path that shows how matter on Earth flows through different parts of the environment. The "bio" in the term indicates that the element passes through living things. And the "geo" in the term indicates that the element also spends time in some of Earth's nonliving planetary components such as rocks, water, and/or the atmosphere. Another way to think about this is matter may spend time in any of Earth's four "spheres": lithosphere (rigid mechanical properties. On Earth), biosphere (the zone of all life on earth, compairsing of ecosystems), hydrosphere (combined mass of water found on earth), or atmosphere (combination of gases that envelop Earth in four main layers). Each sphere is a temporary storage compartment for a share of a particular element's overall stock on Earth. And we can look for paths by which the element flows into and out of each storage compartment.

Sink

A place where matter accumulates and is held for a long period of time. We call a place where matter accumulates and is held for a long period of time a ________, and most of the oxygen contained in the lithosphere stays in that _________ for a very long time; the residence time of oxygen in the lithosphere is about 500 million years. Oxygen is also a major component of water (H2O), composing 89% of the hydrosphere by mass both as a component of H2O and as O2 dissolved in water. Thus, the hydrosphere is a tremendous sink of oxygen.

Ammonification

A process where bacteria and fungi break down nitrogen compounds in animal waste products and in dead plant and animal matter and release ammonia. A variety of organisms make nitrogen available in soils and oceans in other ways. Some bacteria and fungi break down nitrogen compounds in animal waste products and in dead plant and animal matter and release ammonia in the process. This is called _____________.

Nitrogen fixation

A process where free nitrogen—inert nitrogen gas (N2)—in the air is converted to soluble ammonium (NH4+) and nitrate (NO3−) ions that plants, algae, and bacteria can take in and use. Nitrogen fixation occurs primarily in two ways. One way is very dramatic: through the power of lightning. The high energy of lightning triggers a series of reactions that result in nitrate ions falling to Earth's surface in precipitation. Observations by NASA satellites show that lightning strikes about 40 times each second on Earth—almost 3.5 million strikes per day—delivering about 13,000 tons of nitrate a day. While that may seem like a lot, it accounts for less than 10% of nitrogen fixation on Earth. Most nitrogen fixation takes place in the biosphere.

Eutrophication

A process where marine and freshwater environments are enriched with nutrients, such as phosphorus or nitrogen from agricultural runoff or other sources, causing rapid growth, death, and decomposition of algae and phytoplankton. The decomposition process consumes and depletes oxygen levels in the water. This process starts when freshwater environments are enriched with phosphorus from agricultural runoff or other sources, and phytoplankton and algae grow and reproduce rapidly in a reinforcing loop that can double the population every 24 hours. When the population density of the phytoplankton and algae exceeds the carrying capacity of the area, they die off rapidly, creating deposits of decaying matter that settles in the water. This causes explosive growth of decomposing bacteria that consume oxygen as part of their respiration processes. The depletion of dissolved oxygen suffocates other organisms that cannot move out of the area.

Nitrification

A process where microorganisms convert ammonia to nitrogen compounds. Most of the ammonia from this process then undergoes _________________ as ammonia-oxidizing microorganisms convert ammonia to nitrogen compounds. When these compounds then dissolve in soil water, plants can take up the nitrogen through their roots. So, like the phosphorus cycle, there is a loop within the biosphere that is circulating nitrogen between plants and animals at the surface and microbes in the soil.

Denitrification

A process where microorganisms use nitrogen compounds for respiration and create N2 gas, returning it to the atmosphere. __________________ occurs when still other types of microorganisms underground or underwater use nitrogen compounds for respiration and convert them back into N2 gas, returning it to the atmosphere. While we have focused on the relatively rapid cycling of nitrogen between the atmosphere and the biosphere, on longer timescales nitrogen is incorporated into the lithosphere. Nitrogen moves into the lithosphere as sedimentary rocks form and is released millions of years later when these rocks slowly weather.

Models

A simplified concept or representation of a complex process that is designed to help understand interactions among different factors. Scientists often use these to focus on the way certain aspects of a system function and interact. These can take many forms, ranging from mathematical equations and computer simulations to simple diagrams.

Stock

A supply of something that we want to observe and measure over time. Inflows increase the ____________ and outflows decrease the ______________.

Open system

A system that is affected by outside influences. In terms of energy flow, Earth is an ____________—powered almost entirely by the rays of the Sun.

Closed system

A system that is self-contained, neither receiving inputs nor sending outputs beyond the system's borders. Earth is largely a ____________ in regard to matter. Aside from a relatively tiny amount of space debris that enters Earth by collisions with meteorites and comets, matter on Earth is used and re-used in different places, for different purposes, and in different states.

Macronutrients

An element or key elements, which organisms use in large amounts, such as phosphorus, oxygen, nitrogen, and carbon.

Emergent properties

An outcome arising from the function of the system as a whole. In terms of the respiratory system, a system is much more than a collection of parts such as the diaphragm, bronchi, and alveoli. The function of the system depends on the concerted actions of the parts. When you remove a part, you alter the function of the system because that part is interconnected with others. For example, if you eliminate the diaphragm, your body could not create the negative pressure that draws O2 into the body from the atmosphere. The remaining emergent property of the system—providing oxygen to the body—would be disrupted. In another part of the system, if the alveoli were not able to facilitate the exchange of O2 into your blood, cells throughout your body would be deprived of this vital gas and cease to function. Once again, the system as a whole would fail. Finally, consider also how the respiratory system is linked to other systems. Your circulatory system—heart, blood vessels, and blood—transports the O2 and CO2. Your nervous system uses receptors in your brain stem that detect CO2 levels in your blood to regulate your breathing to maintain proper levels of O2.

Systems

Collections of components interacting with each other to produce outcomes that each component could not achieve on its own. In 1985, construction began on Biosphere 2, a sealed steel, concrete, and glass structure covering more than 3 acres in the Arizona desert. Its builders attempted to create a self-sustaining habitat for humans by mimicking Earth features such as rain forests, rivers, and oceans in miniature and providing areas suitable for agricultural production (it was named Biosphere 2 because the builders considered Earth to be "Biosphere 1"). In 1991, eight people who called themselves "Biospherians" sealed themselves in Biosphere 2 for 2 years to see if it could sustain human survival. They survived, but not without serious challenges and significant help from the outside. For example, Biosphere 2 failed to adequately provide oxygen (O2), our most essential resource. Though Biosphere 2 was designed with lush communities of plants to provide O2 for the humans to breathe, after several months the air in Biosphere 2 had lost about 7 tons of O2, dropping from 21% O2 to just 14%. The problems of Biosphere 2 illustrate the complex workings of our planet. Earth is more than just a collection of resources: it is a multitude of interconnections and nested ___________. _________________ can also be human creations. For example, plumbing operates as a system, as does the electrical grid and many of the other facilities operating within the cities and towns where we live. We have less tangible cultural, economic, social, and political systems too. So, systems can involve a very broad array of objects and concepts.