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Biology Chapter 2 Study Guide 21 The Nature of Matter Atoms Atoms are the basic unit of matter and come from the Greek word atomos which means unable to be cut Democritus asked himself If you take an object like a stick of chalk and break it in half are both halves still chalk and came up with a limit which was the smallest fragment the atom Atoms are small and when placed side by side 100 million atoms would make about the width of your finger The subatomic particles that make up atoms are protons neutrons and electrons Protons are positively charged neutrons have no charge and electrons have a negative charge The amount of protons in an atom equals the amount of electrons in an atom An electron s mass is 11840 of the mass of a proton Elements and Isotopes A chemical element is a pure substance that is made up of one type of atom Elements are represented by a symbol that has one or two letters in it on the periodic table The atomic number is the amount of protons the element has and the atomic mass is the mass of the protons added to the mass of the neutrons Isotopes are atoms of the same element but with a different amount of neutrons Ex carbon 12 carbon 13 carbon 14 All isotopes of an element have the same chemical properties because they have the same number of electrons Radioactive isotopes are when the nuclei are unstable and break down at a constant rate over time and can give off very dangerous radiation Geologists can analyze isotopes that can determine the ages of rocks and fossils and can treat cancer with the radiation from certain types of isotopes Chemical Compounds A chemical compound is a substance that is formed by the combination of two or more elements in definite proportions Scientists use chemical formulas to show the composition of compounds o Ex Table salt is NaCl which is a combination of sodium and chlorine Chemical Bonds Compounds are held together by chemical bonds The two main types of chemical bonds are ionic and covalent bonds An ionic bond forms when electrons are transferred from one atom to another An atom that loses electrons has a positive charge and vice versa Ions are positively and negatively charged atoms An ionic bond is the attraction between oppositely charged ions Biology Chapter 2 Study Guide o A covalent bond forms when atoms share their electrons o When atoms share two electrons it is a single covalent bond four electrons double and six electrons triple bond o When atoms join together by covalent bonds it is called a molecule Van der Waals Forces o The van der Waals forces are slight attractions that can develop between oppositely charged regions of nearby molecules when molecules are close together o The van der Waals forces are not as strong as ionic or covalent bonds but they can hold large molecules together o Ex When a gecko climbs up vertical surfaces they show that they have some sort of attraction to the surface which is called the van der Waals force 22 Properties of Water The Water Molecule o A molecule that has unevenly distributed charges is called a polar molecule because the molecule is like a magnet with poles o A water molecule is polar when there is an uneven distribution of electrons between the oxygen and hydrogen atoms where the negative pole is near the oxygen atom and the positive pole is near the hydrogen atom o Water molecules can attract to each other because of their partial positive and negative charges o Hydrogen bonds are not as strong as covalent or ionic bonds o A water molecule can be involved in as many as four hydrogen bonds at a time o Cohesion is an attraction between molecules of the SAME substance and explains why some insects and spiders can walk on the surface of water o Water is highly cohesive because of hydrogen bonding o Adhesion is an attraction between molecules of DIFFERENT substances o Capillary action is one of the forces that draw water out of the roots of a plant and up its stems and leaves Solutions and Suspensions o A mixture is something that is made of two or more elements or compounds that are physically mixed together o Solutions are a type of mixture that forms when ions gradually become dispersed in the water o The solute of a solution is the substance that is dissolved by the solvent o Suspensions are mixtures of water and nondissolved material Acids Bases and pH o The pH scale indicates the concentration of H ions in the solution and shows how acidic or basic a solution is o A pH of 7 tells that the solution is not acidic or basic but right in the middle Biology Chapter 2 Study Guide An acid is any compound that forms H ions in solutions and a base is a compound that produces OH ions in the solution Buffers are weak acids or bases that can react with strong acids or bases to prevent big sudden changes in pH 23 Carbon Compounds The Chemistry of Carbon There s a whole branch of chemistry just to study carbon compounds Carbon atoms have four valence electrons and each electron can join with an electron from another atom to form a covalent bond Carbon can bond with elements such as hydrogen oxygen phosphorus sulfur and nitrogen All living organisms have molecules that are made of carbon and other elements A carbon atom can bond to other carbon atoms which gives the carbon the ability to form unending chains Carbon carbon bonds can form single double or triple covalent bonds and chains of carbon atoms can form rings Macromolecules Some of the molecules in living cells are so large that they are called macromolecules giant molecules Macromolecules are made from thousands and thousands of smaller molecules Polymerization is a process that forms macromolecules Monomers are smaller units that when linked together form polymers Four groups of organic compounds found in living things are carbohydrates lipids nucleic acids and proteins These organic compounds are referred to as biomolecules Carbohydrates Carbohydrates are compounds made up of carbon hydrogen and oxygen atoms in a ratio of 121 and is usually the main source of energy for living things Plants and some animals use carbohydrates for structural purposes The breakdown of sugars glucose supplies energy and starches which are complex carbohydrates are stored in living things The monomers in starch polymers are sugar molecules Monosaccharides are single sugar molecules that include glucose and galactose which is a component of milk and fructose which is found in many fruits Polysaccharides are large macromolecules that are formed from monosaccharides and are used by animals to store excess sugar glycogenanimal starch The glycogen stored in your muscles supplies the energy for muscle contraction movement Plants use plant starch to store excess sugar as well They also make another kind of polysaccharide called cellulose which gives plants much of their strength and rigidity Biology Chapter 2 Study Guide o Cellulose is the major component of wood and paper Lipids o Lipids are a group of biological molecules that are usually not soluble in water and are made mostly from carbon and hydrogen atoms o Lipids include fats oils waxes and steroids o Lipids can be used to store energy and some are important parts of biological membranes and waterproof coverings o Lipids are formed when compounds called fatty acids are combined with a glycerol molecule o A lipid is saturated when the fatty acids contain the maximum number of hydrogen atoms and a lipid is unsaturated when there is at least one carbon carbon double bond in the fatty acid o Olive oil contains unsaturated fatty acids and tends to be liquid in room temperature o Corn oil sesame oil canola oil and peanut oil contain polyunsaturated lipids Nucleic Acids o Nucleic acids are macromolecules that contain hydrogen oxygen nitrogen carbon and phosphorus and are polymers that are formed from nucleotides o Nucleotides are individual monomers that consist of a 5 carbon sugar a phosphate group and a nitrogenous base o Nucleic acids store and transmit hereditarygenetic information o Ribonucleic acids RNA and deoxyribonucleic acids DNA are the two kinds of nucleic acids o RNA contains the sugar ribose and the DNA contains the sugar deoxynbose Proteins o Proteins are macromolecules that contain nitrogen carbon hydrogen and oxygen and are made up of amino acids Amino acids are made up of an amino group and a carboxyl group on different ends there are more than 20 different amino acids that are discovered o DNA stores instructions for arranging amino acids into different proteins o Proteins control the rate of reactions regulate cell processes form bones and muscles transport substances into and out of cells and help fight diseases in the body o Proteins have up to four levels of organization 1 sequence of amino acids in a protein chain 2 the amino acids can be twisted or folded in a chain 3 the chain can be folded 4 a complex structure is formed when 2 or more polypeptide chains interact 24 Chemical Reactions and Enzymes Chemical Reactions o A chemical reaction is a process that changes the properties or a set of chemicals and makes a new substance o Reactants are the elements or compounds that enter into a chemical Biology Chapter 2 Study Guide reac on o Products are the elements or compounds produced by a chemical reac on o Chemical reactions involve changes in the chemical bonds that join atoms in the compound o An example of a chemical reaction is the rusting of an old bike that has been sitting in the rain Energy in Reactions o Energy is released or absorbed whenever chemical bonds form or are broken o Chemical reactions that release energy often but not always occur spontaneously o Chemical reactions that absorb energy will not occur without a source of energy o Activation energy is the term that chemists use to refer to the energy that is needed to start a reaction Enzymes o A catalyst is a substance that speeds up chemical reactions by lowering the activation energy of that reaction o Enzymes are proteins that have the same function as a catalyst and speeds up the chemical reactions in cells o Enzymes are named after the type of reaction it catalyzes Enzyme Action o Reactants must collide with enough energy to break bonds and make new bonds for a chemical reaction to take place o Substrates are the reactants of enzyme catayzed reactions o The substrates bind to the active site of an enzyme and are bound together by intermolecular forces until the reaction is over o After the reaction is over the products are released and the enzyme goes to another substrate to start the process over again o Enzymes are affected by changes in the temperature o Enzymes that are produced by human cells work best at temperatures near 37 degrees Celsius o Cells have proteins that can turn enzymes on and of o Enzymes regulate chemical pathways make materials that the cell needs release energy and transfer information
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