Which of the following is an example of an organ?

The heart is an example of an organ because it is a specialized structure made up of different types of tissues that work together to perform specific functions in the body. In the case of the heart, its primary role is to pump blood throughout the circulatory system, supplying oxygen and nutrients to tissues and removing waste products. An organ is defined as a collection of tissues that work together to carry out a specific task, and the heart fits this definition perfectly, comprising cardiac muscle, connective tissues, and nerve tissues.

In contrast, ribosomes, the nucleus, and mitochondria are all examples of organelles, which are substructures within a cell that perform specific functions. Ribosomes play a critical role in protein synthesis, the nucleus houses genetic material, and mitochondria are known as the powerhouses of the cell, generating energy. While these organelles are essential for cellular function, they do not function independently at the level of an organ in the organism's structure.