Energy and Living Things Section 5-1

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.

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).

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

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

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

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.

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.

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.

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.

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.