5.1a The energy for life comes primarily from the Sun. Photosynthesis provides a vital

connection between the Sun and the energy needs of living systems.

5.1b Plant cells and some one-celled organisms contain chloroplasts, the site of photo-

synthesis. The process of photosynthesis uses solar energy to combine the inorganic

molecules carbon dioxide and water into energy-rich organic compounds (e.g., glucose)

and release oxygen to the environment.

5.1c In all organisms, organic compounds can be used to assemble other molecules

such as proteins, DNA, starch, and fats. The chemical energy stored in bonds can be

used as a source of energy for life processes.

5.1d In all organisms, the energy stored in organic molecules may be released during

cellular respiration. This energy is temporarily stored in ATP molecules. In many organisms, the process of cellular respiration is concluded in mitochondria, in which ATP is

produced more efficiently, oxygen is used, and carbon dioxide and water are released as


5.1e The energy from ATP is used by the organism to obtain, transform, and transport

materials, and to eliminate wastes.

5.1f Biochemical processes, both breakdown and synthesis, are made possible by a

large set of biological catalysts called enzymes. Enzymes can affect the rates of chemical

change. The rate at which enzymes work can be influenced by internal environmental

factors such as pH and temperature.

5.1g Enzymes and other molecules, such as hormones, receptor molecules, and antibodies, have specific shapes that influence both how they function and how they interact

with other molecules.