1. Cell Energy

2. From Sun to Cell Nearly all the energy that fuels life comes from the sun. The energy is captured by plants through photosynthesis. Photosynthesis is the process by which plants, algae, and some bacteria use sunlight, carbon dioxide, and water to make the sugar glucose. Plant cells absorb light energy with pigments. Chlorophyll, the main pigment used in photosynthesis, gives plants their green color.

3. From Sun to Cell, continued

4. Getting Energy from Food Cellular Respiration During cellular respiration, oxygen is used to break down food into carbon dioxide and water. This process releases energy.

5. Getting Energy from Food, continued In prokaryotes, respiration takes place in the cell membrane. In eukaryotes, most respiration occurs in the mitochondria. During cellular respiration, some of the energy is released in the form of heat. Some of the energy is also stored as ATP, which is the fuel for cellular activities.

6. Getting Energy from Food, continued Connection Between Photosynthesis and Respiration Each process makes the materials that are needed for the other process to occur. Fermentation When muscles can’t get the oxygen for cellular respiration, they use fermentation to get energy. Fermentation is the breakdown of food without the use of oxygen. Some bacteria and fungi, such as yeast, also use fermentation to get energy.