Unit Overview pages The Life of a Cell The Chemistry of Life Atoms and Their Interactions Element: a substance that cant be broken down into simpler chemical substances. It is made of one type of atom. Section 6.1 Summary pages Elements Everything whether it is a rock, frog, or flower is made of substances called elements. Section 6.1 Summary pages Of the naturally occurring elements on Earth, only about 25 are essential to living organisms. Carbon, hydrogen, oxygen, and nitrogen make up more than 96 percent of the mass of a human body. Natural elements in living things Section 6.1 Summary pages Trace elements Trace elements such as iron and copper, play a vital role in maintaining healthy cells in all organisms. Plants obtain trace elements by absorbing them through their roots; animals get them from the foods they eat. Section 6.1 Summary pages Table 6.1 Some Elements That Make Up the Human Body ElementSymbol Percent By Mass in Human Body Element Symbol Percent By Mass in Human Body Molybdenum Oxygen Carbon Hydrogen Nitrogen Calcium Phosphorus Potassium Sulfur Sodium Chlorine Magnesium Selenium Iron Zinc Copper Iodine Manganese Boron Chromium Cobalt Fluorine O C H N Ca P K S Na Cl Mg Fe Zn Cu I Mn B Cr Mo Co Se F trace Atom: the smallest particle of an element that has the characteristics of that element. Section 6.1 Summary pages Atoms: The Building Blocks of Elements Atoms are the basic building blocks of all matter. All nuclei contain positively charged particles called protons (p + ) and particles with no charge, called neutrons (n 0 ). Nucleus: the center of an atom Section 6.1 Summary pages The structure of an atom Section 6.1 Summary pages The Structure of an atom Nucleus Electron energy levels The region of space surrounding the nucleus contains extremely small, negatively charged particles called electrons (e - ) This region of space is referred to as an electron cloud. Section 6.1 Summary pages The Structure of an atom Protons and neutrons are approximately the same size and mass, at around 1 AMU. Electrons are far smaller, and they are 11836 the size of protons and neutrons Because opposites attract, the negatively charged electrons are held in the electron cloud by the positively charged nucleus. Section 6.1 Summary pages Electron energy levels Electrons exist around the nucleus in regions known as energy levels. Nucleus 8 protons (p+) 8 neutrons (n 0 ) Oxygen atom Section 6.1 Summary pages Electron energy levels An atom of fluorine has nine electrons. How many electrons are in its second energy level? The first energy level can hold only two electrons. The second level can hold a maximum of eight electrons. The third level can hold up to 18 electrons. Section 6.1 Summary pages Electron energy levels Atoms contain equal numbers of electrons and protons; therefore, they have no net charge. If an atom of fluorine has nine electrons, how many protons are in an atom of fluorine? Section 6.1 Summary pages Atoms of the same element always have the same number of protons but may contain different numbers of neutrons. Isotopes of an Element Isotopes: atoms of the same element that have different numbers of neutrons Carbon-12, carbon-13 and carbon-14 are examples of isotopes. Section 6.1 Summary pages Compound: a substance that is composed of atoms of two or more different elements that are chemically combined. Compounds and Bonding Table salt (NaCl) is a compound composed of the elements sodium and chlorine. Chemical formula Section 6.1 Summary pages Atoms combine with other atoms only when the resulting compound is more stable than the individual atoms. How covalent bonds form For many elements, an atom becomes stable when its outermost energy level is full. Sharing electrons with other atoms is one way for elements to become stable. Section 6.1 Summary pages Two hydrogen atoms can combine with each other by sharing their electrons. How covalent bonds form Each atom becomes stable by sharing its electron with the other atom. Hydrogen molecule Section 6.1 Summary pages How covalent bonds form The attraction of the positively charged nuclei for the shared, negatively charged electrons holds the atoms together. Hydrogen molecule Section 6.1 Summary pages Covalent bond : an attractive force between two atoms that share electrons. How covalent bonds form Molecule : a group of atoms held together by covalent bonds. It has no overall charge. Water molecule Section 6.1 Summary pages An atom (or group of atoms) that gains or loses electrons has an electrical charge and is called an ion. Ion: a charged particle made of atoms. How ionic bonds form Ionic bond : attractive force between two ions of opposite charge Example: A chlorine atom becomes a chloride ion when it gains an electron. Section 6.1 Summary pages Chemical reactions occur when bonds are formed or broken, causing substances to recombine into different substances (ex. burning paper). Chemical Reactions Metabolism : all of the chemical reactions that occur within an organism Section 6.1 Summary pages In a chemical reaction, substances that undergo chemical reactions, are called reactants. Writing chemical equations Substances formed by chemical reactions, are called products. Section 6.1 Summary pages A molecule of table sugar can be represented by the formula: C 12 H 22 O 11. How many atoms are in a molecule of table sugar (sucrose)? Writing chemical equations The easiest way to understand chemical equations is to know that atoms are neither created nor destroyed in chemical reactions. They are simply rearranged. Mixture : a combination of substances in which the individual components retain their own properties. Section 6.1 Summary pages Mixtures and Solutions Neither component of the mixture changes. Section 6.1 Summary pages Solution : a mixture in which one or more substances (solutes) are distributed evenly in another substance (solvent). Mixtures and Solutions Sugar molecules in a powdered drink mix dissolve easily in water to form a solution. Section 6.1 Summary pages Chemical reactions can occur only when conditions are right. Acids and bases A reaction may depend on: - energy availability - temperature - concentration of a substance - pH of the surrounding environment Section 6.1 Summary pages pH : a measure of how acidic or basic a solution is. Acids and bases A scale with values ranging from below 0 to above 14 is used to measure pH. More acidic NeutralMore basic Section 6.1 Summary pages Substances with a pH below 7 are acidic. Acid : any substance that forms hydrogen ions (H + ) in water Acids and bases A solution is neutral if its pH equals seven. More acidic NeutralMore basic Section 6.1 Summary pages Substances with a pH above 7 are basic. Base : any substance that forms hydroxide ions (OH - ) in water. Acids and bases pH 11 Unit Overview pages The Life of a Cell The Chemistry of Life Water and Diffusion Summary Section 2 pages Water is perhaps the most important compound in living organisms. Water and Its Importance Water makes up 70 to 95 percent of most organisms. Summary Section 2 pages Water is Polar Sometimes, when atoms form covalent bonds they do not share the electrons equally. This is called a polar bond. Summary Section 2 pages Water is Polar Polar molecule : a molecule with an unequal distribution of charge; that is, each molecule has a positive end and a negative end. Water is an example of a polar molecule. Water can dissolve many ionic compounds, such as salt, and many other polar molecules, such as sugar. Summary Section 2 pages Water is Polar Water molecules also attract other water molecules. Weak hydrogen bonds are formed between positively charged hydrogen atoms and negatively charged oxygen atoms. Hydrogen atom Oxygen atom Summary Section 2 pages Water resists changes in temperature. Therefore, water requires more heat to increase its temperature than do most other common liquids. Water can move UP because of capillary action. Unique properties of water Summary Section 2 pages Unique properties of water Water is one of the few substances that expands when it freezes. Ice is less dense than liquid water so it floats as it forms in a body of water. Summary Section 2 pages Early observations: Bownian motion In 1827, Scottish scientist Robert Brown used a microscope to observe pollen grains suspended in water. He noticed that the grains moved constantly in little jerks, as if being struck by invisible objects. This motion is now called Brownian motion. Today we know that Brown was observing evidence of the random motion of atoms and molecules. Summary Section 2 pages The process of diffusion Diffusion : the net movement of particles from an area of higher concentration to an area of lower concentration. Diffusion results because of the random movement of particles (Brownian motion). Three key factorsconcentration, temperature, and pressureaffect the rate of diffusion. Summary Section 2 pages The results of diffusion When a cell is in dynamic equilibrium with its environment, materials move into and out of the cell at equal rates. As a result, there is no net change in concentration inside or outside the cell. Material moving out of cell equals material moving into cell Summary Section 2 pages Diffusion in living systems The difference in concentration of a substance across space is called a concentration gradient. Ions and molecules diffuse from an area of higher concentration to an area of lower concentration, moving with the gradient. Dynamic equilibrium occurs when there is no longer a concentration gradient. Summary Section 2 pages Diffusion in living systems Diffusion continues until there is no longer a concentration gradient and dynamic equilibrium has been reached. Unit Overview pages The Life of a Cell The Chemistry of Life Life Substances 6.3 Section Summary 6.3 pages Carbon compounds that come from living organisms are called organic compounds. A carbon atom has four electrons available for bonding in its outer energy level. In order to become stable, a carbon atom forms four covalent bonds that fill its outer energy level. The Role of Carbon in Organisms 6.3 Section Summary 6.3 pages The Role of Carbon in Organisms Two carbon atoms can form various types of covalent bondssingle, double or triple. Single Bond Double BondTriple Bond 6.3 Section Summary 6.3 pages Carbon compounds vary greatly in size. Molecular chains When carbon atoms bond to each other, they can form straight chains, branched chains, or rings. 6.3 Section Summary 6.3 pages Molecular chains Small molecules bond together to form large chains called polymers. Polymer : a large molecule formed when many smaller molecules bond together. Polymers usually form by covalent bonding. 6.3 Section Summary 6.3 pages Carbohydrate : a biomolecule composed of carbon, hydrogen, and oxygen with a ratio of about two hydrogen atoms and one oxygen atom for every carbon atom. The structure of carbohydrates 6.3 Section Summary 6.3 pages Glucose and fructose combine in a condensation reaction to form sucrose (table sugar) The structure of carbohydrates Monosaccharide : the simplest type of carbohydrate; a simple sugar (ie. glucose, fructose) 6.3 Section Summary 6.3 pages The largest carbohydrate molecules are polysaccharides, polymers composed of many monosaccharide subunits. (ie. potatoes, liver) The structure of carbohydrates Plant energy is stored in the form starch, animal energy is stored in the form of glycogen 6.3 Section Summary 6.3 pages Lipids : large biomolecules that are made mostly of carbon and hydrogen with a small amount of oxygen. (ie. fats, oils, waxes) The structure of lipids 6.3 Section Summary 6.3 pages The structure of lipids They are insoluble in water because their molecules are nonpolar and are not attracted by water molecules. 6.3 Section Summary 6.3 pages A fatty acid with single bonds is saturated; with double bonds is unsaturated The structure of lipids 6.3 Section Summary 6.3 pages Protein : a large, complex polymer composed of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur. The structure of proteins 6.3 Section Summary 6.3 pages The structure of proteins Amino acids : the basic building blocks of proteins There are about 20 common amino acids that can make literally thousands of proteins. 6.3 Section Summary 6.3 pages Peptide bonds : covalent bonds formed between amino acids. The structure of proteins 6.3 Section Summary 6.3 pages Proteins are the building blocks of many structural components of organisms. The structure of proteins 6.3 Section Summary 6.3 pages The structure of proteins Enzymes are important proteins found in living things. Enzyme : a protein that changes the rate of a chemical reaction. They speed the reactions in digestion of food. 6.3 Section Summary 6.3 pages Nucleic acid : a complex biomolecule that stores cellular information in the form of a code. The structure of nucleic acids Nucleotides : small subunits that make up nuclei acids 6.3 Section Summary 6.3 pages The structure of nucleic acids Nucleotides are arranged in three groupsa nitrogenous base, a simple sugar, and a phosphate group. Phosphate Sugar Nitrogenous base 6.3 Section Summary 6.3 pages DNA, which stands for deoxyribonucleic acid is a nucleic acid. The structure of nucleic acids Phosphate Sugar Nitrogenous base 6.3 Section Summary 6.3 pages The structure of nucleic acids The information coded in DNA contains the instructions used to form all of an organisms enzymes and structural proteins. Another important nucleic acid is RNA, which stands for ribonucleic acid. RNA is a nucleic acid that forms a copy of DNA for use in making proteins.