Final answer:
An organ is formed when groups of tissues collaborate to perform a specific function. These tissues are made up of similar cells, which, when combined into organs, form organ systems, eventually constituting an organism.
Step-by-step explanation:
An organ is formed when groups of tissue work together to perform a specific function. In multicellular organisms, cells of a similar type form tissues, such as muscle or nervous tissue. These tissues unite to create an organ, such as the heart or brain, which is a critical component of an organ system like the circulatory or nervous system. When multiple organ systems work in harmony, they constitute an organism, a complete living entity.
Understanding how cells are structured and function is fundamental to comprehend how tissues operate, which in turn is essential for knowing how organs perform. Organs are not only anatomically distinct but also carry out one or more specific physiological functions by combining different types of tissues.