A biological organism is any living entity that exhibits the characteristics of life, such as growth, reproduction, and response to stimuli. Organisms can be unicellular, like bacteria, or multicellular, like plants and animals. They are made up of cells, which are the basic units of life, and they carry out various functions necessary for survival. Biological organisms interact with their environment and other organisms in complex ways. They obtain energy through processes like photosynthesis in plants or metabolism in animals. Each organism plays a role in its ecosystem, contributing to the balance of life on Earth.