Energy and Living Things

1. Energy and Living Things Section 5-1

2. Energy Flows Between Organisms in Living Systems • Almost all energy in living systems needed for metabolism comes from the sun. • Energy from the sun enters living systems when plants, algae, and certain bacteria absorb sunlight. • Some of the energy from the sun is captured and used to make organic compounds. • Organic compounds store chemical energy and can serve as food for organisms.

3. Building Molecules that Store Chemical Energy • Metabolism involves either using energy to build molecules or breaking down molecules in which energy is stored. • Photosynthesis – process by which light energy is converted to chemical energy • Autotrophs – organisms that use energy from sunlight or inorganic substances to make organic compounds (food).

4. Building Molecules that Store Chemical Energy (con’t) • Most autotrophs are photosynthetic • Some autotrophs use chemical energy from inorganic substances to make organic compounds

5. Breaking Down Food for Energy • Chemical energy in organic compounds can be transferred to other organic compounds or to organisms that consume food. • Heterotrophs – organisms that must get energy from food instead of directly from sunlight or inorganic substances. Example: humans, animals – get energy from food through process of cellular respiration

6. Cellular Respiration • Metabolic process similar to burning fuel. • Releases much of the energy found in food to make ATP.

8. Cells transfer energy from food to ATP • Chemical energy that is stored in food molecules is released gradually in a series of enzyme-assisted chemical reactions. • When cells break down food molecules, some of the energy is released as heat. Much of the remaining energy is stored temporarily in molecules of ATP. • ATP – the energy currency inside cells. Delivers energy where needed.

9. Cells transfer energy from food to ATP (con’t) • The energy released from ATP can be used to power other chemical reactions. • Most chemical reactions require less energy than is released from ATP, so enough energy is released from ATP to drive most of a cell’s activities.

10. ATP Stores and Releases Energy • ATP is a nucleotide with two phosphate groups. • The phosphate groups store energy. • The “phosphate tail” of ATP is unstable because the phosphate groups are negatively charged and repel one another. The phosphate groups store energy like a spring that is compressed. The energy is released when the bonds that hold the phosphate groups together are broken.

12. Cells transfer energy from food to ATP (con’t) • Breaking the outer phosphate bond requires input of energy, but much more energy is released during the reaction. • ATP minus 1 phosphate (PO4) group is ADP • ATP → ADP + P + energy • The cell can readily use the energy released from this reaction.

13. Cells transfer energy from food to ATP (con’t) • The energy released from this reaction is used to power metabolism. • In some reactions, two phosphates are cleaved and AMP is made.