ENERGY AND LIVING THINGS Almost all of the energy in living systems needed for metabolism comes directly or indirectly from the sun. Metabolism involves either using energy to build molecules (photosynthesis) or breaking down molecules (cellular respiration) in which energy is stored.

Fig. 1 Flow of Energy

I. Building Molecules that Store Energy Photosynthesis – the process by which light energy is converted to chemical energy autotrophs – organisms that use energy from the sunlight to make organic compounds (ex: glucose – a carbohydrate) ex: plants, algae, prokaryotes

II. Breaking Down Food for Energy Cellular Respiration – the process by which cells produce chemical energy from carbohydrates; energy is released in food to make ATP, this ATP provides cells with the energy they need to carry out life functions heterotrophs – organisms that get energy from food instead of directly from sunlight ex: animals autotrophs – undergo cellular respiration to release ATP in the carbohydrates they produced

III. Energy Storing Molecule ATP – adenosine triphosphate a nucleotide with 2 extra energy-storing phosphate groups

The removal of a phosphate group from ATP releases energy producing ADP. ATP ADP + P + energy