{"id":37,"date":"2018-06-28T17:59:50","date_gmt":"2018-06-28T17:59:50","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/suny-monroe-environmentalbiology\/chapter\/2-1-matter\/"},"modified":"2018-07-26T18:39:51","modified_gmt":"2018-07-26T18:39:51","slug":"2-1-matter","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-monroe-environmentalbiology\/chapter\/2-1-matter\/","title":{"raw":"2.1 Matter","rendered":"2.1 Matter"},"content":{"raw":"

Atoms, Molecules, Compounds<\/strong><\/h2>\r\n

At its most fundamental level, life is made of matter<\/strong>. Matter is something that occupies space and has mass. All matter is composed of elements<\/strong>, substances that cannot be broken down or transformed chemically into other substances. Each element is made of atoms, each with a constant number of protons and unique properties. A total of 118 elements have been defined; however, only 92 occur naturally and fewer than 30 are found in living cells. The remaining 26 elements are unstable and therefore do not exist for very long or are theoretical and have yet to be detected. Each element is designated by its chemical symbol (such as H, N, O, C, and Na), and possesses unique properties. These unique properties allow elements to combine and to bond with each other in specific ways.<\/p>\r\n

An atom<\/strong> is the smallest component of an element that retains all of the chemical properties of that element. For example, one hydrogen atom has all of the properties of the element hydrogen, such as it exists as a gas at room temperature and it bonds with oxygen to create a water molecule. Hydrogen atoms cannot be broken down into anything smaller while still retaining the properties of hydrogen. If a hydrogen atom were broken down into subatomic particles, it would no longer have the properties of hydrogen. At the most basic level, all organisms are made of a combination of elements. They contain atoms that combine together to form molecules. In multicellular organisms, such as animals, molecules can interact to form cells that combine to form tissues, which make up organs. These combinations continue until entire multicellular organisms are formed.<\/p>\r\nAll matter, whether it be a rock or an organism,\u00a0is made of atoms. Often, these atoms combine to form molecules<\/strong>. Molecule are chemicals made from two or more atoms bonded together. Some molecules are very simple, like O2, which is comprised of just two oxygen atoms. Some molecules used by organisms, such as DNA, are\u00a0made of many millions of atoms. All atoms contain protons, electrons, and neutrons\u00a0(Figure 1 below). The only exception is hydrogen (H),\u00a0which is made of one proton and one electron. A proton<\/strong> is a positively charged particle that resides in\u00a0the nucleus (the core of the atom) of an atom and has a mass of 1 and a charge of +1. An electron\u00a0<\/strong>is a\u00a0negatively charged particle that travels in the space around the nucleus. In other words, it resides outside\u00a0of the nucleus. It has a negligible mass and has a charge of \u20131.\u00a0Neutrons<\/strong>, like protons, reside in the nucleus of an atom. They have a mass of 1 and no charge. The\u00a0positive (protons) and negative (electrons) charges balance each other in a neutral atom, which has a net\u00a0zero charge.\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"500\"]\"\" Figure 1. Atoms are comprised\u00a0of protons and neutrons located within the nucleus, and electrons surrounding the nucleus. The nucleus of an atom should not be confused with the nucleus of a cell.[\/caption]\r\n

Each element contains a different number of protons and neutrons, giving it its own atomic number and mass number. The atomic number<\/strong> of an element is equal to the number of protons that element contains. The mass number<\/strong> is the number of protons plus the number of neutrons of that element. Therefore, it is possible to determine the number of neutrons by subtracting the atomic number from the mass number.<\/p>\r\n

Isotopes<\/strong> are different forms of the same element that have the same number of protons, but a different number of neutrons. Some elements, such as carbon, potassium, and uranium, have naturally occurring isotopes. Carbon-12, the most common isotope of carbon, contains six protons and six neutrons. Therefore, it has a mass number of 12 (six protons and six neutrons) and an atomic number of 6 (which makes it carbon). Carbon-14 contains six protons and eight neutrons. Therefore, it has a mass number of 14 (six protons and eight neutrons) and an atomic number of 6, meaning it is still the element carbon. These two alternate forms of carbon are isotopes. Some isotopes are unstable and will lose protons, other subatomic particles, or energy to form more stable elements. These are called radioactive isotopes<\/strong> or radioisotopes.<\/p>\r\n\r\n\r\n\r\n\r\n\r\n
EVOLUTION IN ACTION<\/strong><\/td>\r\n<\/tr>\r\n
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Carbon dating \u00a0<\/strong><\/p>\r\n

Carbon-14 (14C) is a naturally occurring radioisotope that is created in the atmosphere by\u00a0cosmic rays. This is a continuous process, so more\u00a014C is always being created. As a living\u00a0organism develops, the relative level of\u00a014C in its body is equal to the concentration of\u00a014C\u00a0in the atmosphere. When an organism dies, it is no longer ingesting\u00a014C, so the ratio will\u00a0decline.\u00a014C decays to\u00a014N by a process called beta decay; it gives off energy in this slow\u00a0process.\u00a0After approximately 5,730 years, only one-half of the starting concentration of\u00a014C will have\u00a0been converted to\u00a014N. The time it takes for half of the original concentration of an isotope\u00a0to decay to its more stable form is called its half-life.<\/p>\r\n

Because the half-life of\u00a014C is long, it is\u00a0used to age formerly living objects, such as fossils. Using the ratio of the\u00a014C concentration\u00a0found in an object to the amount of\u00a014C detected in the atmosphere, the amount of the\u00a0isotope that has not yet decayed can be determined. Based on this amount, the age of the\u00a0fossil can be calculated to about 50,000 years (Figure 2\u00a0below). Isotopes with longer half-lives,\u00a0such as potassium-40, are used to calculate the ages of older fossils. Through the use of\u00a0carbon dating, scientists can reconstruct the ecology and biogeography of organisms living\u00a0within the past 50,000 years.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"300\"]\"\" Figure 2. The age of remains that contain carbon and are less than about 50,000 years old, such as this pygmy mammoth, can be determined using carbon dating. (credit: Bill Faulkner\/ NPS)[\/caption]<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n

Chemical bonds<\/strong><\/h3>\r\n

How elements interact with one another depends on the number of electrons and how they are arranged. \u00a0When an atom does not contain equal numbers of protons and electrons it is called an ion<\/strong>. Because the number of electrons does not equal the number of protons, each ion has a net charge<\/strong>. For example, if sodium loses an electron, it now has 11 protons and only 10 electrons, leaving it with an overall charge of +1. Positive ions are formed by losing electrons and are called cations<\/strong>. Negative ions are formed by gaining electrons and are called anions<\/strong>. Elemental anionic names are changed to end in -ide. As an example, when chlorine becomes an ion it is referred to as chloride.<\/p>\r\n

Ionic and covalent bonds\u00a0<\/strong>are strong bonds formed between two atoms. \u00a0These bonds hold atoms together in a relatively stable state. Ionic bonds<\/strong> are formed between two oppositely charged ions (an anion and a cation). \u00a0Because positive\u00a0and negative charges attract, these ions are held together much like two oppositely charged magnets would stick together. \u00a0Covalent bonds<\/strong> form when electrons are shared between two atoms. \u00a0Each atom shares one of their electrons, which then orbits the nuclei of both atoms, holding the two atoms together. \u00a0Covalent bonds are the strongest and most common form of chemical bond in organisms. Unlike most ionic bonds, covalent bonds do not dissociate in water.<\/p>\r\n

Covalent bonds come in two varieties: polar and non-polar. A non-polar covalent bond<\/strong> occurs when electrons are shared equally between the two atoms. Polar covalent bonds<\/strong>\u00a0form when the electrons are shared unequally. Why does this occur? Each element has a known electronegativity<\/strong>: a measure of their affinity for electrons. Some elements, such as oxygen, are very electronegative because they strongly attract electrons from other atoms. Hydrogen, meanwhile, has low electronegativity and thus weakly attracts electrons, in comparison. \u00a0Polar covalent bonds form when the two atoms involved have significantly different electronegativities. \u00a0In biological systems, this occurs when oxygen bonds with hydrogen and when nitrogen (also quite electronegative) bonds with hydrogen.<\/p>\r\nWhen oxygen and hydrogen bond, for example, the shared electrons are pulled more strongly toward oxygen\u00a0and thus farther away from hydrogen's nucleus. Because the electrons move farther away from hydrogen, it becomes slightly positively charged (\u03b4+). The oxygen becomes slightly negatively charged as the electrons become closer to it (\u03b4\u2013). If two molecules with polar covalent bonds approach one another, they can interact due to the attraction of opposite electrical charges. \u00a0For example, the\u00a0slight positive charge of hydrogen in a water molecule can be attracted to the slight negative charge of oxygen in a different water molecule (Figure 3).\u00a0This interaction between two polar molecules is called a hydrogen bond<\/strong>. This type of bond is very common in organisms. Notably, hydrogen bonds give\u00a0water the unique properties that sustain life. If it were not for hydrogen bonding, water would be a gas\u00a0rather than a liquid at room temperature.\r\n

\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"368\"]\"Diagram Figure 3. Hydrogen bonds form between slightly positive (\u03b4+) and slightly negative (\u03b4\u2013) charges of polar covalent molecules, such as water.[\/caption]<\/figure>\r\n\r\n
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WATER IS CRUCIAL TO MAINTAINING LIFE<\/strong><\/p>\r\n<\/td>\r\n<\/tr>\r\n

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Do you ever wonder why scientists spend time looking for water on other planets? It is because water is\u00a0essential to life; even minute traces of it on another planet can indicate that life could or did exist on that\u00a0planet. Water is one of the more abundant molecules in living cells and the one most critical to life as we\u00a0know it. Approximately 60\u201370 percent of your body is made up of water. Without it, life simply would\u00a0not exist.<\/p>\r\n\r\n