Energy for Life

The Sun and Photosynthesis: How We Get Energy  All activities by living things require energy.  Consumers get their energy from the foods that they eat, but where do the producers get their energy?  Organisms can’t use light energy directly as a source of food.

 Photosynthesis convert light energy from the sun into chemical energy that is stored in sugar molecules.  This energy can be used by plants themselves or organisms that eat the plant.

 First, the plant must absorb light energy using chlorophyll, a green pigment that gives plants their color.  CO 2 and water is also absorbed.  Light energy breaks down the water into hydrogen and oxygen.  The hydrogen then combines with the CO 2 to form sugar molecules.

 The oxygen is released into the air.  The energy used to form the sugar is stored in chemical bonds.  When the bonds are broken, energy is release.  Energy is used to carry out the cells activities.

Energy is Released as Food is Broken Down  The major energy releasing process is cellular respiration.  During this process sugar is broken down and energy is released.  The chemical energy in food is also released by chemical reactions.

ATP, the Cell’s Currency for Energy Transfer  Cellular respiration converts the energy stored in complex molecules into chemical energy stored in ATP, adenosine triphosphate.  Each ATP molecule is made up of a sugar complex attached to three phosphates.  Energy is stored in ATP until it is released by reactions that remove one of the phosphates.

 Each ATP molecule releases energy whenever a phosphate is broken off or transferred to another molecule.  The molecule that remains has only two phosphate groups and is called ADP, adenosine diphosphate.