2. 2.4 Energy Conversions 1 Energy conversions are described by principles called the laws of thermodynamics. Energy Flow 2.4 Energy Conversions The first law of thermodynamics states that energy cannot be created or destroyed, but it can change form. On a broader scale, the first law is called the law of conservation of energy and it states that the total energy of the universe is constant.

3. 2.4 Energy Conversions 2 The first law of thermodynamics means that organisms cannot create their own energy, but must obtain it from an outside source. 2.4 Energy Conversions (cont.) Energy Flow An important difference between living and nonliving systems is the ability of living systems to conserve and use some of the energy released in chemical reactions.

4. 2.5 Energy and Entropy 1 The second law of thermodynamics states that systems tend to change in a way that increases the disorder, or entropy, of the system plus its surroundings. 2.5 Energy and Entropy Because energy tends to spread out into the surroundings, the free energy in a system is slightly less after each energy conversion than before. The world becomes increasingly disordered as free energy is released. Energy Flow

5. 2.5 Energy and Entropy 2 Organisms must be well organized to remain alive and to grow. Energy is the key to maintaining organization in all living systems. In ecosystems, light or chemical energy flows from the environment (the Sun or inorganic chemicals) to producers to consumers to decomposers. 2.5 Energy and Entropy (cont.) Energy Flow

6. 2.5 Energy and Entropy 3 As energy flows through food webs, it eventually escapes in the form of heat energy, resulting in a one-way flow of energy. Living systems overcome the tendency toward entropy by constantly obtaining energy from their surroundings. Organisms stay organized and can function and grow only as the entropy of their surroundings increases. 2.5 Energy and Entropy (cont.) Energy Flow

7. 2.5 Energy and Entropy 4 Energy flow in an ecosystem

8. End of Section 2