2.  Energy ◦ The ability to do work or cause change ◦ Occurs in various forms ◦ Can be converted to another form ◦ Forms important to biological systems are chemical, thermal, electrical and mechanical energy ◦ Free energy is the energy in a system that is available for work

3.  Atoms are in constant motion  The rate at which atoms or molecules in a substance move determines its state

4. ◦ Solid  Molecules are tightly linked.  Little energy ◦ Liquid  Molecules are not as tightly linked  Medium amount of energy

5. ◦ Gas  Molecules have little or no attraction to each other  Fill the volume of the occupied container  Move most rapidly  To cause a substance to change state, thermal energy (heat) must be added to or removed from a substance

6.  Living things undergo thousands of chemical reactions as part of the life process

7.  Many are very complex involving multistep sequences called biochemical pathways  Chemical equations represent chemical reactions ◦ Reactants are shown on the left side of the equation ◦ Products are shown on the right side  A + B C + D

8.  Much of the energy organisms need is provided by sugar (food) ◦ Undergoes a series of chemical reactions in which energy is released (cell respiration)  The net release of free energy is called an exothermic reaction

9.  Reactions that involve a net absorption of free energy are called endothermic reactions  Photosynthesis is an example Mix Barium hydroxide and aluminum salt, and the products dissolve in water of hydration. This is VERY COLD!

10.  Most chemical reactions require energy to begin  The amount of energy needed to start the reaction is called activation energy

11.  Certain chemical substances (catalysts) reduce the amount of activation energy required  Biological catalysts are called enzymes

12.  Enzymes are an important class of catalysts in living organisms ◦ Mostly protein ◦ Thousands of different kinds ◦ Each specific for a different chemical reaction

13.  Enzymes work on substances called substrates  Substrates must fit into a place on an enzyme called the active site  Enzymes are reusable!