I. Characteristics of Living Organisms A. Living things share the following characteristics: 1. Living things are made up of units called cells. a. Remember that cells are like little packages of chemical reactions. b. Life processes only occur as a result of chemical reactions in cells (life is chemistry) 2. Living things reproduce. 3. Living things are based on a universal genetic code. (Contain DNA)

4. Living things grow and develop. 5. Living things obtain and use materials and energy. (Eat or Photosynthesize) 6. Living things respond to their environment. 7. Living things maintain a stable internal environment. (Maintain Homeostasis) a. Homeo=Same Stasis= Status 8. Taken as a group, living things change over time. (Evolve)

B. Levels of organization Atoms  Molecules  Macromolecules  Cells  Tissues  Organs  Organ Systems  Organism Remember----Life depends on chemistry. Remember----Life depends on chemistry.

II. The Chemistry of Life A. Atoms –“smallest” part of matter 1. Made of *Protons (+) *Neutrons (no charge) *Electrons (-) *Electrons (-)

2. A chemical element is a pure substance that consists entirely of one type of atom a. Example: a. Example: all atoms with 6 protons are called carbon all atoms with 6 protons are called carbon all atoms with 79 protons are called gold all atoms with 79 protons are called gold

Common elements found in living organisms: Common elements found in living organisms:HydrogenOxygenNitrogenCarbon

3. Atoms of the same element that differ in the number of neutrons they contain are known as isotopes. are known as isotopes. Ex. Carbon can have 6 neutrons (Carbon 12) Carbon can have 7 neutrons (Carbon 13) Carbon can have 7 neutrons (Carbon 13)

4. A chemical compound is a substance formed by the chemical combination of two or more elements a. The atoms in compounds are held together by chemical bonds. b. Bond formation involves the electrons that surround each atomic nucleus.

B. Three types of chemical bonds 1. An ionic bond is formed when one or more electrons are transferred from one atom to another.

a. An atom that loses electrons has a positive charge. (Sodium ion = Na+) An atom that gains electrons has a negative charge. (Chlorine ion = Cl-) An atom that gains electrons has a negative charge. (Chlorine ion = Cl-) b. These positively and negatively charged atoms are known as ions.

2. A covalent bond forms when electrons are shared between atoms. a.The structure that results when atoms are joined together by covalent bonds is called a molecule.

3. Hydrogen Bond --more to come