Photosynthesis and cellular respiration are important biological processes. Photosynthesis occurs in leaves and involves using energy from sunlight, carbon dioxide, and water to produce oxygen and energy-rich glucose. It has two stages - the light-dependent reaction converts light to chemical energy, while the light-independent reaction uses this energy to produce glucose. Cellular respiration uses glucose and oxygen to produce energy, carbon dioxide, and water. It occurs in the mitochondria and provides energy for cells. Both processes are essential for energy flow in ecosystems.