APES Chapter 2 Environmental systems

Introduction: Mono Lake

Mono Lake is a terminal lake which collects many salt and minerals while passing through mountains and desert soil. It has a higher salt concentration than the ocean, and with evaporation leaving the salt and minerals behind, large structures have formed as a result. As more evaporation has occurred the salt concentration has risen to a level at which many species cannot survive in, besides the Mono brine shrimp, larvae of the alkali fly, and microscopic algae. In the early 1900's, an aqueduct was built to provide water to communities in Los Angeles. This caused a ripple effect of changes for this system. Water was taking from Owen Lake which neighbored Mono. Owens Lake dried up, leaving a barren area with exposed soil, increasing the amount of dust storms in the area. The dust contained arsenic which is harmful to human life. The redirecting of water escalated, increasing evaporation, and leaving Mono Lake with double the salt concentration as before, and killing all life in it. Today through pushing and urging of litigation, the lake has refilled and the species are now thriving. Mono Lake is a prime example of an interconnected activities which form an environmental systems. The human activities created a ripple effect, changing factors throughout the whole system.

Environmental Systems 2.1

Environmental systems are interconnected. They involve life interacting with abiotic factors. These systems are composed of matter, and have energy transferred throughout. They have inputs and outputs. Earth itself is an environmental system. It receives energy from the sun and transfers it to life on Earth. A smaller system includes Mono Lake, where the algae survives in the water, and when eaten by shrimp, transfers energy, and again when eaten by birds. Each factor is interconnected. If all the algae died off, the shrimp would subsequently, and the birds would migrate elsewhere with a more generous food supply. Mono Lake and Earth are both systems which differ greatly in size, from a cell to an ocean. While Earth itself is an environmental system, it is also composed of many smaller ones. In relation to Mono Lake, the consumption of energy between algae, shrimp, and birds, is a system within the entire lake, which is a system of water flow and salt deposits.

2.2 Components and States of Matter


Matter is defined as anything that that occupies space and has mass. The mass is the amount of matter an object contains. Mass is a measurement. Matter is composed of basic building blocks called atoms, which are the smallest particle which still holds the chemical properties of an element. Atoms make up elements, and elements can be found in three states of matter, solid, liquid, and gas. When a particle contains one more than one atom, it is defined as a molecule. Molecules which contain more than one element are defined as compounds.

Chemical Bonds

Molecules and compounds require a chemical bond to join atoms. They join together through 3 different types of bonds including covalent, iconic, and hydrogen. When atoms share electrons they have a covalent bond. A water molecule is held together by a covalent bond. When atoms transfer electrons, they have an ionic bond. When this bond occurs one atom will become negatively charged due to a loss, and one will become positively charged due to a gain of electrons. The difference in their charges causes them to attract towards each other forming an ionic bond. Ionic bonds can include NaCl (salt), and because this bond is less strong than a covalent bond, it is more easily dissolvable. The weakest bond of all three is a hydrogen bond. When a hydrogen atom is bonded with an atom through a covalent bond, is bonded to another molecule. In this instance, when different elements form covalent bonds, the electrons may be shared unequally.

H20 is bonded with a hydrogen bond. Two hydrogen atoms shares share their 2 (4 total) electrons with oxygen, making them positively charged but oxygen negatively with 4 remaining unshared electrons. This causes one side to have a more positive charge and one side more negative. When this occurs, it's called a polar molecule. The result of this is shown above, where the more negatively charged O atom is attracted to the positively charged H atom.

Properties of Water

The weak bond in water molecules makes it ideal for supporting life. It has unique properties such as surface tension, capillary action, boiling, freezing, and the ability to be used as a solvent. Cohesion and adhesion are possible due to hydrogen bonding. Water molecules have the ability to 'stick' to themselves and other substances. Surface tension is essential for the pace of evaporation and, even broader, life on Earth. Surface tension wouldn't exist without cohesion, and without surface tension, water would not be able to form droplets. This includes rain droplets to morning dew. Without this attraction, water would evaporate in a matter of milliseconds. There would be no time for absorption or collection.

Capillary action occurs when the attraction of adhesion is greater than cohesion. This allows water to be absorbed and transferred. Capillary action allows water to be distributed by vessels throughout trees, which is essential to life on Earth.

Water's freezing point is 32 degrees fahrenheit and it's boiling point is 212 degrees fahrenheit, and between these two temperatures, is liquid. Life on Earth requires water for many processes, and for most, requires water to be in a liquid state of matter. Most water on Earth is liquid, and because water is joined by hydrogen bonds, it requires a lot of energy to change the temperature of it, let alone the state of matter it's in. This resistance to temperature changes prevents extreme shifts in temperature on Earth. In addition, as water changes states it's density changes as well. As it freezes, the molecules expand, making it less dense. This allows ice to float, and regulates the temperatures in lakes or ponds so life can still live under the surface.

Water is an ideal molecule for a solvent because it is polar. Polar molecules are able to bond easily with other polar molecules. This ability for substances to easily dissolve in water allows many living organisms to store various types and quantities of molecules in their cells.

Organic Molecules

All macromolecules which are most essential to life (carbohydrates, proteins, nucleic acids, and lipids) are organic compounds. Organic compounds are compounds that are bonded by either carbon-carbon or carbon-hydrogen bonds. Any compound composed of carbon, hydrogen, and oxygen are carbohydrates. A common carbohydrate is glucose (C6H12O6). Glucose is a simple sugar which allows for a quick release of energy. Plants receive their energy from starch, which is a chain of covalently bonded glucose molecules. Not only do plants receive energy from glucose, but the animals that eat plants do as well. They obtain the energy from the cellulose in plants, which is another chain of glucose molecules. Proteins are composed of amino acids. Amino acids are chains of organic molecules containing nitrogen. Protein provides structure, stores energy, allows for internal transportation, and defends against foreign substances. Proteins also make up enzymes which control the speed of chemical reactions. Another type of organic compounds is nucleic acids, which are found in all living cells. When nucleic acids form long chains, they form DNA, which is the genetic materiel containing the code for reproducing and is needed for an organism to pass to its offspring. Proteins are synthesized by the translation of DNA by RNA. The last organic compound is lipids. These do not mix with water and include fats, waxes, and steroids. They make up a significant portion of the membranes surrounding cells.

2.2 Energy and Thermodynamics


Energy is the ability to do work or transfer heat. Power is the rate at which work is done. Every system on Earth absorbs and transfers energy. Energy is measured in joules. Energy can take many forms and be converted between them. These forms can include potential, kinetic, light, chemical, and sound. Potential energy is energy that has been stored but not yet released. When the potential is released it becomes kinetic energy, which is the energy of motion. When potential energy is stored, it is stored in chemical bonds known as chemical energy.


Energy is not created or destroyed, only transferred from one form to another. This is the first law of thermodynamics. For example, a car uses gasoline (chemical energy) and transfers it to kinetic energy which moves the car.

The second law of thermodynamics states that when energy is transformed, it contains the same amount of energy, but a lesser power. In relation to the car example, not all the energy from the gasoline is kinetic. Energy is wasted on friction from the engine, tires of the road, and brakes.

2.4 Ecological System's Conversion of Energy

Living organisms are constantly converting energy. Plants absorb energy from the sun, and convert it to sugar (glucose), which is consumed by animals as energy. In this instance, the sun providing heat to the plant is the input. Plants depend on that input to produce energy. The amount of energy within an ecosystem greatly influences it's sustainability. A system with a large amount of energy will often be able to support more life. For example, an orange grove requires a lard amount of sunlight to be able to have enough energy transferred to create an orange.

2.5 Inputs and Outputs in Systems

Earth is composed of many ecological systems, most of which are open. This means the system may give or receive matter and energy with other systems. Earth itself is partially an open system, receiving energy from the sun. Solar energy is the input and heat energy is the output. In regards to matter, Earth is a closed system, not giving or receiving matter from other systems. When a system has an equal number of inputs to outputs, it is defined as a steady state. In steady states, the system does not change over time. Most ecological systems are in this state due to their ability to respond to altercations in the inputs or outputs. These responses are called feedback loops. A positive feedback loop occurs when a system responds to a change and as a result, returns to its original state. In a negative feedback loop, a system's response amplifies the change. For example, in a positive feedback loop, melting ice decreases the amount of light reflected from albedo, and exposes more of the Earth's surface, warming the Earth and melting more ice. An example for a negative feedback loop is a rise in temperate increasing evaporations rates, increasing the amount of light reflected by clouds, which decreases the temperate.

When the rate of an input changes, it affects factors throughout the entire system. For example, if less sun is reflected from Earth and more is absorbed, Earths temperature rises. If the temperature rises, more water evaporates, then more clouds are formed, and more rainfall.

2.6 Changes Over Time and Space

Many environmental systems contain geographic variation due to different conditions. For example, in Texas a sycamore tree can thrive near a river valley due to the warm temperature and water supply, however in the mountains a pine tree would thrive due to their tolerance to low temperatures and little water. Another example of how a system can change over time includes the Sahara Desert. Thousands of years ago it supported life and agriculture. As Earth's position altered, it decreased the amount of monsoons in South Africa, creating the Sahara Desert. By studying these changes and variations of systems allows scientists to predict and anticipate future changes in our environment.


Friedland, Andrew, and Rick Relyea. "Chapter 2" Environmental Science for AP. 2nd ed. W.H. Freeman, 2015. 31-56. Print.

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