All animal and plant cells contain organelles, "little organs," which regulate specific functions within the cell. Two types of organelles, mitochondria and chloroplasts, are energy-related; they supply molecules of adenosine triphosphate (ATP), which power the processes of life and growth. Although both animal and plant cells contain mitochondria, only plant cells also contain chloroplasts, which regulate the processes of photosynthesis.
The cells which make up all living organisms fall into two categories: simple prokaryotic cells which lack a membrane-bound nucleus and the more complex eukaryotic type, which contains a nucleus that holds all components needed for the workings of the cell and the organism. Animal and plant cells are eukaryotic, carrying the organelles which perform functions such as synthesizing protein and processing ATP for energy.
Eukaryotic Cells and Energy
Adenosine triphosphate (ATP) is a high-energy molecule contained in the nucleus of eukaryotic cells. This molecule provides all energy needed for various physiological processes, and is renewed through oxidation, so a cell always contains a supply of ATP to fuel the energy demands of the organism. While both plant and animal cells utilize ATP for energy, plants also contain chloroplasts, a type of specialized organelle for producing energy through photosynthesis.
Mitochondria and Energy
Mitochondria, an organelle found in both plant and animal cells, contains protein-rich components called cristae, which produce ATP. ATP is converted to adenosine diphosphate (ADP), a process which releases energy. Through the action of food energy stored in the mitochondria, ADP is converted back to ATP and the cycle continues.
Chloroplasts and Energy Production
In addition to mitochondria, plants have another source of ATP in chloroplasts, which synthesize solar energy through the action of chlorophyll. This process produces glucose, an essential energy source. Because chloroplasts provide an additional source of ATP through photosynthesis, a plant's reserves of ATP produced by the mitochondria are not depleted by producing glucose.