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
Atoms are in constant motion The rate at which atoms or molecules in a substance move determines its state
◦ Solid Molecules are tightly linked. Little energy ◦ Liquid Molecules are not as tightly linked Medium amount of energy
◦ 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
Living things undergo thousands of chemical reactions as part of the life process
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
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
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!
Most chemical reactions require energy to begin The amount of energy needed to start the reaction is called activation energy
Certain chemical substances (catalysts) reduce the amount of activation energy required Biological catalysts are called enzymes
Enzymes are an important class of catalysts in living organisms ◦ Mostly protein ◦ Thousands of different kinds ◦ Each specific for a different chemical reaction
Enzymes work on substances called substrates Substrates must fit into a place on an enzyme called the active site Enzymes are reusable!