Course: BIS 105 Environmental Biology

Unit 2 Learning Module

Matter and Energy
Copyright
Adapted from CK-12 Foundation, Biology I Honors, Douglas Wilkin http://www.ck12.org/book/Biology-I---Honors-%2528CA-DTI3%2529/r2/.

Adapted from Editors, U. (2012, October 8). Sustainability: A Comprehensive Foundation. Retrieved from the Connexions Web site: http://cnx.org/content/col11325/1.40/

Adapted from OpenStax College. (2012, June 20). Entropy and the Second Law of Thermodynamics: Disorder and the Unavailability of Energy. Retrieved from the Connexions Web site: http://cnx.org/content/m42237/1.5/

Matter

Living things are made of matter. In fact, matter is the “stuff” of which all things are made. Anything that occupies space and has mass is known as matter. Matter, in turn, consists of chemical substances.

Elements

An element is a pure substance that cannot be broken down into different types of substances. Examples of elements include carbon, oxygen, hydrogen, and iron. Each element is made up of just one type of atom. An atom is the smallest particle of an element that still characterizes the element. At the center of an atom is a nucleus. The nucleus contains positively charged particles called protons and electrically neutral particles called neutrons. Surrounding the nucleus is a much larger electron cloud consisting of negatively charged electrons. An atom is electrically neutral if it has the same number of protons as electrons. Each element has atoms with a characteristic number of protons. For example, all carbon atoms have six protons, and all oxygen atoms have eight protons.

Chemical Compounds

A chemical compound is a new substance that forms when atoms of two or more elements react with one another. A chemical reaction is a process that changes some chemical substances into other chemical substances. A compound that results from a chemical reaction always has a unique and fixed chemical composition. The substances in the compound can be separated from one another only by another chemical reaction.

The atoms of a compound are held together by chemical bonds. There are different types of chemical bonds, and they vary in how strongly they hold together the atoms of a compound. Two of the strongest types of bonds are covalent and ionic bonds. An example of a chemical compound is water. A water molecule forms when oxygen (O) and hydrogen (H) atoms react and are held together by covalent bonds. Like other compounds, water always has the same chemical composition: a 2:1 ratio of hydrogen atoms to oxygen atoms. This is expressed in the chemical formula H_2O.

Compounds that contain the element carbon are called organic compounds. This is because they are found mainly in living organisms. Most organic compounds are held together by covalent bonds. An example of an organic compound is glucose (C_6H_12O_6). Glucose is a simple sugar that living cells use for energy. Compounds that do not contain carbon are called inorganic compounds. Water is an example of an inorganic compound.

Energy

Energy is a property of matter that is defined as the ability to do work. The concept of energy is useful for explaining and predicting most natural phenomena, and it is foundational for an understanding of biology. All living organisms need energy to grow and reproduce. However, energy can never be created or destroyed. It is always conserved. This is called the law of conservation of energy (or first law of thermodynamics). Therefore, organisms cannot create the energy they need. Instead, they must obtain energy from the environment. Organisms also cannot destroy or use up the energy they obtain. They can only change it from one form to another.

Although energy can be transformed from one form to another, the second law of thermodynamics describes the change will be from a more-ordered to a less-ordered state if there is no counteracting force. This means that systems tend to become more disordered over time. Scientists use the term entropy(represented by S in equations) to describe the amount of disorder in a system.

Some people misunderstand the second law of thermodynamics, stated in terms of entropy, to say that the process of the evolution of life violates this law. Over time, complex organisms evolved from much simpler ancestors, representing a large decrease in entropy of the Earth’s biosphere. It is a fact that living organisms have evolved to be highly structured, and much lower in entropy than the substances from which they grow. But it is always possible for the entropy of one part of the universe to decrease, provided the total change in entropy of the universe increases.

How is it possible for a system to decrease its entropy? Energy transfer is necessary. If I pick up marbles that are scattered about the room and put them into a cup, my work has decreased the entropy of that system. If I gather iron ore from the ground and convert it into steel and build a bridge, my work has decreased the entropy of that system. Energy coming from the Sun can decrease the entropy of local systems on Earth. But the overall entropy of the rest of the universe increases by a greater amount and the second law of thermodynamics is not violated.

Every time a plant stores some solar energy in the form of chemical potential energy, or an updraft of warm air lifts a soaring bird, the Earth can be viewed as a heat engine operating between a hot reservoir supplied by the Sun and a cold reservoir supplied by dark outer space—a heat engine of high complexity, causing local decreases in entropy as it uses part of the heat transfer from the Sun into deep space. There is a large total increase in entropy resulting from this massive heat transfer. A small part of this heat transfer is stored in structured systems on Earth, producing much smaller local decreases in entropy.

Forms of Energy

Energy can take several different forms. Common forms of energy include light, chemical, and heat energy. These forms of energy can be categorized as kinetic or potential energy.

Kinetic and Potential Energy

Energy constantly changes back and forth between kinetic and potential energy. Kinetic energy is the energy of movement. For example, a ball falling through the air has kinetic energy because it is moving. Potential energy is the energy stored in an object due to its position. A bouncing ball at the top of a bounce, just before it starts to fall, has potential energy. For that instant, the ball is not moving, but it has the potential to move because gravity is pulling on it. Once the ball starts to fall, the potential energy changes to kinetic energy. When the ball hits the ground, it gains potential energy from the impact. The potential energy changes to kinetic energy when the ball bounces back up into the air. As the ball gains height, it regains potential energy because of gravity. Chemical energy is potential energy that is held in the bonds between atoms. Changing the types of bonds between atoms can release energy or require energy.

How Organisms Change Energy

In organisms, energy is always changing from one form to another. For example, plants obtain light energy from sunlight and change it to chemical energy in food molecules. Chemical energy is energy stored in bonds between atoms within food molecules. When other organisms eat and digest the food, they break the chemical bonds and release the chemical energy. Organisms do not use energy very efficiently. As much as 90 percent of the energy they obtain from food is converted to heat energy that is given off to the environment.