Final answer:
An organism is a living thing composed of one or more cells. It shares common characteristics such as the need for energy, response to the environment, growth and reproduction, and maintaining a stable internal environment.
Step-by-step explanation:
An organism is a living thing, a biological entity that can be defined in space and time. It is composed of one or more cells, which are the basic building blocks of all organisms. Organisms share common characteristics such as the need for energy to carry out life processes, response to the environment, growth and reproduction, and the maintenance of a stable internal environment.