Unit 2 – The Chemical Basis of Life

1. Unit 2 – The Chemical Basis of Life

2. I. Life requires about 25 Chemical Elements A. Elements 1. Matter – anything that occupies space and has mass 2. The various forms of matter are composed of one or more chemical elements a) Element- a pure substance that cannot be broken down into other substances by chemical means

3. 3. About 25 elements are essential to life. a) Oxygen (O), Carbon (C), Hydrogen (H), and Nitrogen (N) make up about 96% of the living matter in your body. b) Calcium (Ca), Phosphorus (P), Potassium (K), Sulfur (S), and a few other elements account for most of the remaining 4%.

4. c) Trace elements are elements that make up less than 0.01% of your body mass, but are critical to your health 1) Example: Iron (Fe); essential for carrying oxygen in your blood

6. B. Compounds 1. A compound is a substance containing two or more elements that are chemically combined in a fixed ratio. a) Example: water (H2O) 2. A compound’s properties may differ greatly from those of its component elements. a) Example:Salt (NaCl)

7. II. Chemical properties are based on the structure of atoms A. Atoms 1. An atom is the smallest possible particle of an element a) comes from the Greek word atomos meaning “indivisible”

8. 2. Structure of the atom a) Proton- a subatomic particle with a positive charge (+); found in the nucleus b) Electron- a subatomic particle with a negative charge (-); found outside the nucleus in energy levels c) Neutron- a subatomic particle that is neutral (no charge); found in the nucleus d) Nucleus- the center of the atom containing protons and neutrons

9. Neutrons Color Purple Electrons (E-) Color Red E- E- E- Protons + Color Green N P+ P+ P+ Nucleus N N N N E- P+ P+ N E- Energy Level – Color Blue

10. 3. Atomic Number- the number of protons in an atom’s nucleus; also the number of electrons a) Left alone, an atom tends to hold as many electrons as protons b) The number of electrons is NOT constant like the number of protons 1) The number of electrons determines how the atom interacts with other atoms 2) The number of protons determines the atom’s properties 4. Atomic Mass- the number of protons plus the number of neutrons

11. B. Isotopes 1. Isotopes of an element have the same number of protons in their atoms but different numbers of neutrons. a) Example:

12. C. Electrons and Reactivity 1. An atom’s electrons determine how it reacts with other atoms. a) Electrons differ in the amount of energy they have and how tightly they are held by the protons in the nucleus.

13. b) Electrons in the highest energy level of an atom determine how that atom reacts. 1) The first or lowest energy level (nearest the nucleus) can hold two electrons. 2) Every energy level after the first can hold up to 8 electrons.

15. III. Chemical bonds join atoms to one another A. Ionic Bonds 1. An ionic bond occurs when an atom transfers an electron to another atom a) Example:

16. 2. Ions- atoms (or groups of atoms) that have become electrically charged as a result of gaining or losing electrons

17. B. Covalent Bonds 1. A covalent bond forms when two atoms share electrons 2. The number of bonds an atom can form usually equals the number of additional electrons that will fill its highest energy level a) Example:

18. 3. Molecules- two or more atoms held together by covalent bonds a) chemical formula- tells you the number and types of atoms in a molecule b) structural formula- indicates how atoms in a molecule are linked by bonds c) space-filling model- a drawing that depicts a 3-D model of a molecule

20. C. Chemical Reactions 1. A chemical reaction is the breaking of old bonds and the formation of new bonds that result in new substances a) Example:

21. b) Reactants- the starting materials for a chemical reaction c) Products- the ending materials in a chemical reaction FYI… 2. Exothermic reactions- chemical reactions that release energy 3. Endothermic reactions- chemical reactions that absorb energy

22. IV. Life depends on the unique properties of water A. The structure of water 1. Water is made up of 2 hydrogen atoms and one oxygen atom a) Oxygen pulls electrons much more strongly than does hydrogen. This unequal pull results in the shared electrons spending more of their time with the oxygen atom (creates a V shape).

23. b) The oxygen end has a slight negative charge, while the hydrogen atoms are slightly positive. This is called a polar molecule.

24. 2. Hydrogen bond- a bond created by the weak attraction of a slightly positive hydrogen atom to a slightly negative portion of another molecule.

25. B. Water’s Life-Supporting Properties 1. Cohesion and Adhesion a) Cohesion – the tendency of molecules of the same kind to stick to one another 1) Example: beads of water on the outside of a glass

26. b) Adhesion- the attraction between unlike molecules 1) Example: Figure 4-13Cohesion and adhesion contribute to the rise of water molecules within a tree's water transport system. The dotted lines in the diagram indicate hydrogen bonds.

27. 3. Low Density of Ice a) Density is the amount of matter in a given volume. b) The solid state is more dense than the liquid state. c) This is important to living things because if ice didn’t float, bodies of water would freeze from bottom to top, trapping the fish and other organisms in a shrinking layer of water without access to nutrients.

28. Figure 4-15Ice floats because its molecules are less densely packed than those in liquid water.

29. C. Water’s ability to Dissolve other substances a) Solution- a uniform mixture of two or more substances 1) Solvent- the substance that dissolves the other substance 2) Solute- the substance that is dissolved

30. b) Aqueous solution- a solution in which water is the solvent 1) Water is the main solvent in all cells, blood, and plant sap Figure 4-16Sodium chloride dissolves as Na+ and Cl- ions become attracted to water molecules and break away from the surface of the solid.

31. D. Acids, Bases, and pH 1. Acid- A compound that donates H+ ions to a solution 2. Base- A compound that removes H+ ions from an aqueous solution 3. pH scale-describes how acidic or basic a solution is

32. a) pH scale ranges from 0 to 14, with 0 being the most acidic and 14 being the most basic. b) Pure water and aqueous solutions that have equal amounts of H+ and OH- ions are said to be neutral (pH of 7).

34. 4. Buffers- substances that cause a solution to resist changes in pH; works by accepting H+ ions when their levels rise and donating H+ ions when their levels fall

35. V. Carbon is the main ingredient of Organic molecules A. Carbon Skeletons and Functional Groups 1. Carbon has 4 electrons in its highest energy level, which means they can form up to 4 bonds with other atoms.

36. 2. Most carbon-based molecules are organic molecules; non-carbon-based molecules are classified as inorganic molecules.

37. 3. Carbon can also bond with atoms of other elements a) Hydrocarbons- organic molecules that are composed of only carbon and hydrogen

38. 4. Functional group- a group of atoms within a molecule that interacts in predictable ways with other molecules a) Hydrophilic- molecules that attract water molecules (hydroxyl groups)

39. B. Monomers and Polymers 1. Monomers – small molecular unit that is the building block of a larger molecule 2. Polymers- long chains of small molecular units (monomers) a) Every living cell has thousands of different kinds of polymers and yet all of these polymers are built from a collection of fewer than 50 kinds of monomers.

40. C. Building and Breaking Polymers 1. Each time a monomer is added to a chain, a water molecule is released; this is called dehydration synthesis. 2. Cells break bonds between monomers by adding water to them; this is called hydrolysis reaction.

41. Figure 5-4In the dehydration reaction, two monomers bond to each other, making a polymer chain longer. The hydroxyl group of one monomer reacts with a hydrogen atom from the other monomer. The reactions involved ultimately release a water molecule.

42. Figure 5-5In the hydrolysis reaction, the addition of a water molecule breaks the polymer chain.

43. VI. Carbohydrates provide fuel and building material A. Sugars 1. Carbohydrate- an organic compound made up of sugar molecules a) contains the elements carbon, hydrogen, and oxygen in the ratio of 1 carbon: 2 hydrogen: 1 oxygen b) the carbon skeletons of carbohydrates have a ring shape

44. 2. Monosaccharides- simple sugars that contain just one sugar unit a) Examples: glucose, fructose, and galactose b) Sugar molecules, particularly glucose, are the main fuel supply for cellular work

45. Figure 5-6The complete structural diagram of the monosaccharide glucose (left) shows all its atoms. The simplified representation (right) shows just the core ring formed by some of the carbon and oxygen atoms. Ring shapes are common in sugar molecules found in nature.

46. 3. Disaccharides- consists of 2 monosaccharides (double sugar) a) the most common disaccharide is sucrose; consists of a glucose molecule linked to a fructose molecule 1) major carbohydrate in plant sap

47. Figure 5-7Sucrose is a disaccharide (double sugar) consisting of two monosaccharides linked together.

48. B. Polysaccharides 1. Polysaccharides are long polymer chains made up of simple sugar monomers a) Starch is a polysaccharide found in plant cells 1) Examples: potatoes, rice, and corn are all rich in starch

49. b) Animal cells store excess sugar in the form of glycogen; this is stored as granules in liver and muscle cells. c) Cellulose serves as a building material in plants; they protect cells and stiffen the plant. 1) Most animals cannot digest cellulose because they lack the molecule necessary to break the bonds between the glucose monomers in cellulose.

50. 2) Cellulose is referred to as fiber and serves to keep the digestive system healthy. d) Almost all carbohydrates are hydrophilic; this is due to the many hydroxyl groups in their sugar units. Therefore, monosaccharides and disaccharides dissolve readily in water.