Which process involves the breakdown of complex organic molecules into simpler ones to 

The correct answer is Respiration.

Key Points

• Respiration is the process by which cells break down complex organic molecules such as glucose into simpler molecules like carbon dioxide and water.
• This process releases energy, which is used by the cells to perform various functions essential for life.
• Respiration occurs in the mitochondria of eukaryotic cells.
• There are two main types of respiration: aerobic respiration, which requires oxygen, and anaerobic respiration, which does not.
• The energy released during respiration is stored in the form of ATP (adenosine triphosphate), which cells use for various activities.

Additional Information

• Excretion is the process of removing waste products from the body, not breaking down molecules.
• Transpiration is the process of water movement through plants and its evaporation from aerial parts, especially from the leaves.
• Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesize foods with the help of chlorophyll.